Nutrition

Nutritional requirements increase significantly and play a pivotal role in the cow’s energy status and health at the time of birth and in the early weeks of lactation when milk production is reaching its peak.

The transition from the dry period to lactation is one of the most stressful parts of a dairy cow’s life. Physiological and hormonal changes accelerate during the eighth month of gestation as the milk secretion glands enlarge in the udder and the cow prepares to give birth. Nutritional requirements increase significantly and play a pivotal role in the cow’s energy status and health at the time of birth and in the early weeks of lactation when milk production is reaching its peak.

Managing calcium metabolism and reducing the prevalence of hypocalcemia (milk fever) in transition cows continues to challenge even the best dairy farmers and managers. Calcium is a macromineral necessary for bone formation and muscle function. Cows that are hypocalcemic for extended periods of time have poorly functioning rumens that lead to other metabolic problems including ketosis, displaced abomasums, laminitis, retained placentas, metritis, and mastitis. Research has shown that cows with even subclinical levels of milk fever are likely to produce several hundred pounds less milk over the course of lactation.

During the dry period, calcium requirements are minimal and these mechanisms for replenishing plasma calcium are relatively inactive and are slow to start up again at the time of calving. The beginning of lactation, however, places a sudden and large demand on the calcium supplies and the mechanisms that keep it in balance in the dairy cow. A cow producing 22 pounds of colostrum will lose 23 grams of calcium in a single milking. This is about nine times as much calcium as is present in the entire plasma calcium pool of the cow. Calcium lost from the plasma pool must be replaced through increased calcium absorption in the intestine and calcium resorption from the bones.

Cows normally do a good job of keeping calcium balanced through a complex interaction of vitamin D and parathyroid hormone — except at the time of calving. Because the replenishing mechanisms needed to metabolize calcium are slow to respond at the time of calving, nearly all cows experience some degree of hypocalcemia during the first days after calving. Intravenous calcium treatments have been the treatment of choice for decades to help the cow along while intestinal and bone mechanisms have time to adapt.

In the 1980s dairy researchers began to recognize that macrominerals and their ions play a critical role in cellular metabolism. We know that at the time of freshening it’s necessary for calcium to be pulled from the bones because dietary calcium and the mechanisms required to metabolize it from the diet are not operating at full capacity. For this to occur the cow’s system must be slightly acidified — which involves a negative ionic charge referred to as anionic — to draw out the positively charged cationic calcium ions and get them into the bloodstream.

All ions have a negative or positive charge. To understand the anionic-cationic dynamic, think about the poles of a magnet. One pole is positive and the other is negative. Like poles repel each other and opposite poles attract each other. The same type of thing happens with ions in the bloodstream. In the case of the positively charged calcium ions, there needs to be a negatively charged environment to pull them out of the bones and get them into the bloodstream. If the bloodstream is overloaded with other positive ions — remember, like charges repel each other — the calcium ions can’t get to the bloodstream because they are held back. This is often the case in a close-up cow’s diet and the troublemakers are most often sodium and potassium ions, which also have powerful cationic charges.

When balancing diets for dry cows that are close to calving we need to get the system slightly acidified for approximately two to three weeks prior to calving. This acidification requires knowing the values of the two cations, potassium and sodium, and the two anions, sulfur, and chloride, for the entire ration. Therefore, an analysis of all the feedstuffs in a close-up diet is required. The determination of whether a diet is anionic or cationic is calculated using a formula that measures the acid/base balance in the feed.

The cation-anion balance is most often known as the dietary cation-anion difference or DCAD. The DCAD formula will result in a positive or negative value when the cations are added together and subtracted from the sum of the anions. A positive value indicates that the diet is alkaline (more cations) or, if negative, acidic (more anions). A properly formulated anionic diet will result in a negative value typically around –5 to –10. (There are variations of this formula in use that incorporate other dietary minerals including phosphorus, calcium and magnesium, all of which have small additional impacts on the resulting calculations.)

The importance of having accurate values for the four main minerals in the dry cow diet cannot be overstated. Particularly in forages, mineral values vary considerably. Grass and legume forages are notoriously high and variable in potassium, which is the primary cation affecting DCAD, resulting in a positive value. Chloride and sulfate salts added to a dry cow/close-up diet are the means by which a positive DCAD becomes a negative DCAD.

All milk cow diets are positive DCAD diets due to the high levels of potassium in forages. When formulating close-up diets, look for low potassium forages. The higher the potassium in the diet, the more chloride or sulfate that must be added and there will come a point where the ration becomes unpalatable to the cow and too expensive to be practical.

Monitoring whether an anionic diet is being accomplished requires testing the pH level of the urine of these cows. A pH of 7 indicates neutrality; < 7 = acidic and > 7 = alkaline. The normal urine pH of a milk cow is around 8. So any pH value approaching 7 indicates that there is some acidification going on. The target for urine pH in anionic diets should be about 6.5–6.0. However, a close-up diet with a pH in the low 7 range will still have some minimal anionic affect.

Transition dry cow and close-up diets that incorporate anionic salts have been shown to reduce the propensity for milk fever and improve calcium metabolism at the time of calving. Those cows are less likely to experience other metabolic problems that often rob them of high milk peaks and overall production during their lactation.

What makes a rumen healthy are the billions of microbes – bacteria, protozoa, fungi, and yeasts – whose job it is to ferment the feedstuffs that a cow consumes in her diet. Collectively, we call them “bugs.”

Feeding a dairy cow is first about maintaining a healthy rumen. If the rumen isn’t working efficiently, the cow will neither be feeling her best or able to produce the milk we expect from her. What makes a rumen healthy are the billions of microbes – bacteria, protozoa, fungi and yeasts – whose job it is to ferment the feedstuffs that a cow consumes in her diet. Collectively, we call them “bugs.” The rumen bugs also have their own life cycle and nutritional requirements. As they expire they become a major source of the cow’s metabolizable protein.

The ruminant species that includes not only dairy cows, but goats, sheep, deer, moose, llamas and alpacas, has been created for the purpose of using, for much of their diet, plant material that monogastric species such as swine and poultry as well as humans cannot digest. The rumen is nature’s wonderful way of allowing ruminants to use forages that are high in cellulose such as pasture grasses, corn stalks and even weeds that can be converted into food and fiber. It’s the way undomesticated animals like deer, elk, moose and bison can survive in the wild. It’s the way exotic beasts of burden like camels, alpacas and llamas can survive in harsh environments. This all happens because of a process called fermentation and it’s the bugs in the rumen that make it happen.

Fermentation is the bioconversion of complex carbohydrates into smaller molecular units. Fermentation also occurs during the baking of bread and the brewing of beer. The end products of rumen fermentation are called volatile fatty acids (VFA), which are absorbed in the cow’s small intestine and are converted to glucose in the liver. The rumen can ferment fibrous cellulose as well as nonfiber carbohydrates (NFC) such as grains and other commodity byproducts.

For modern dairy cows, the rumen must function continuously and consistently around the clock for them to produce the many gallons of milk they do. Any disruption in feed supply or a drastic change in diet will disrupt the work of the rumen bugs. When reduced in number for any reason, cow health and milk production suffers.

Excessive levels of the nonfiber carbohydrates (NFC), while having the ability to increase metabolizable energy in a cow’s diet, can disrupt the delicate pH balance in the rumen, which affects the bugs’ ability to ferment feed at their optimal ability. The nonfiber carbs such as starch and sugars are more easily broken apart by the bugs and when there’s excessive amounts of those carbs being fermented, more acid is produced than can leave the rumen, and the rumen environment becomes increasingly more acidic. The bugs can’t function as well as the acidity increases and other microbes take over, which create an even more potent acid – lactic acid. It’s the accumulation of lactic acid that causes rumen acidosis.

Read more: Rumen Protected Fats in Dairy

Proper balancing of feed rations is necessary for creating and supporting a healthy microbial population in the rumen. Keeping the pH level in a rumen between 6.0 and 6.5 is the generally accepted range to support good fermentation in the rumen. Diets excessively high in NFC will produce acids that will drive pH below 6.0, which creates a hostile and even toxic environment for the fiber-digesting bacteria. Continued low rumen pH levels will eventually result in clinical acidosis for the cow and a rapid decline in milk components, milk production and health.

The challenge for ruminant scientists and dairy farmers is to feed those carbohydrates that are soluble and quickly fermented while providing adequate fiber to keep rumen microbes in the rumen long enough to accomplish fermentation. In the modern dairy industry acute and subacute rumen acidosis are second only to mastitis as the most prevalent metabolic diseases in dairy cows. It’s generally believed today that most commercial dairy farms in the U.S. – and especially those on diets containing high levels of corn – experience some level of acidosis in their cows.

Complex carbohydrates such as cellulose, which are most abundant in forages, are the key to keeping a rumen happy, healthy and balanced. It’s recommended that the level of forage in dairy cow diets does not drop below 30 percent of total dry matter consumed. In an effort to balance carbohydrate fractions and avoiding an acidotic rumen, nutritionists suggest keeping nonfiber carbohydrates balanced between 32 percent and 38 percent of dry matter intakes when feeding higher levels of grains like corn and barley or byproducts such as wheat midds, hominy and distillers grains. When rations contain high quality hay, haylage, brown mid-rib corn or sugar beet or citrus pulp, and the effective fiber is adequate, the level of NFC can be increased to 38 percent to 42 percent of total dry matter intake.

The high producing cows in any dairy herd require much higher levels of fermentation in the rumen to meet energy needs and microbial efficiencies to sustain their milk production. Any large variation in rumen pH throughout the day will have the greatest impact on the fresh cows.

The economics of dairy farming have necessitated the increase of milk production per cow for many dairy farmers to remain afloat financially. To get more milk out of a cow means increasing her plane of nutrition and making sure that microbial fermentation is optimal throughout the day. The greater the number of microbes in a rumen, the more fermentation that can be accomplished. The more microbes working in the rumen also means more microbial protein that will be available for proper amino acid nutrition. The more nutrients a cow can absorb every day, the more milk she can produce.

Read more: Optimizing the Rumen

Various health challenges may occur in animals and humans when high enough levels of mycotoxins are ingested through contaminated foods.

Mycotoxins are toxic chemicals produced by fungi. Various health challenges may occur in animals and humans when high enough levels of mycotoxins are ingested through contaminated foods. Both ruminant and non-ruminant species are at risk for mycotoxicosis – the illnesses that develop as a result of ingesting mycotoxins.

The presence of mycotoxins indicates that there has been fungal contamination in feedstuffs. There are many dozens of mycotoxins that have been identified but only a handful – those that are most common in animal feedstuffs – have been studied to a large enough extent to know how they affect animal and or human health. Mycotoxins are usually present only in microscopic amounts, being measured in parts-per-million (ppm) and parts-per-billion (ppb).

It’s important to understand that although mycotoxins are produced by fungi, not all fungi produce mycotoxins. Mold, also a member of the fungus family, tends to get the most blame for mycotoxins in animal feeds. Fungi and molds usually grow in warm, moist and humid conditions. The exact circumstances or growing conditions in which fungi produce mycotoxins is not well understood.

Mycotoxins have been around since the beginning of time. However, they began to be identified as problems in the 1960s. Prior to the emergence of globalized agriculture, issues with mycotoxins were most likely isolated and limited to short time periods and small geographic regions. A crop or a storage facility, for instance, may have developed mycotoxins for a season but would disappear as crops were rotated and storage facilities were emptied and cleaned. As commercial farming incorporates more monoculture and agriculture becomes more globalized, the prevalence of mycotoxins in the food supply has increased.

Modern animal agriculture uses grains and grain byproducts as a primary food source. Dairy cows are routinely fed diets consisting of corn, barley and wheat-based ingredients. Due to the abundance of carbohydrates, all grains are susceptible to mold growth and the production of mycotoxins when conditions are favorable. Mycotoxicosis and other metabolic challenges occur when diets contain grains and byproducts that are heavily contaminated with mycotoxins.

Feeds contaminated with mycotoxins can cause a variety of illnesses in dairy cows and young stock that may result in poor milk production, poor growth rates, poor fertility or abortions and lead to death when organs such as the liver or kidneys are seriously affected. In all cases, depending on the type and severity of mycotoxin contamination, the animal’s defense mechanisms and immune system will fight to mitigate the problems caused by mycotoxicosis.

Mycotoxins are highly resistant to degradation or destruction during processing or storage. Mycotoxins can also develop during storage even when none was present during growth. Despite processing and heat, corn byproducts such as distillers grains (DDG) and corn gluten will also remain contaminated with mycotoxins if the original corn grain was contaminated. Adverse storage conditions with high heat and humidity have been known to produce mycotoxins, as fungi are produced during storage.

Corn – including corn silage – is the most widely grown crop in the U.S. and is a primary feedstuff in dairy cow diets. Corn is highly susceptible to mold growth as it grows. Mold grows on the ears, on the leaves and on the stalks and remains there during harvest, transportation and storage. However, depending on the moisture, humidity and temperature during all stages of growth, corn may or may not develop mycotoxins in any given season.

The mycotoxins, deoxynivalenol (also known as DON or vomitoxin), fumonisin and zearalenone all come from a fungal species called fusarium and are known to be problematic for dairy cows as well as monogastric species. Mycotoxicosis in farm animals is often difficult to diagnose and treat effectively. There are great differences in the susceptibility of mycotoxicosis in animals, depending on species, age and sex. Mycotoxins have an immunosuppressive effect, although the exact target within the immune system may differ. Many are also cytotoxic meaning they can do direct damage to the gut, skin or lungs. Presence of multiple mycotoxins may be synergistic, increasing the susceptibility of the exposed animal to other infectious diseases.

Feedstuffs such as DDG or corn gluten have long been used for protein and energy supplementation in dairy cow diets. Hominy, another corn byproduct, is often used to supplement diets that are low in energy. All of these products have proven nutritional value but can still be problematic if contaminated with mycotoxins. Mycotoxin contamination in corn is nearly unavoidable and it’s difficult to find a crop of corn that does not contain a mycotoxin. In the U.S., the mycotoxin, aflatoxin, is the only mycotoxin that is regulated by the U.S. Food and Drug Administration. Aflatoxin B1 has been identified as a potent natural carcinogen and is routinely monitored in grains and is commonly found in peanuts as well as cottonseed, a product used by the dairy industry. Aflatoxins appear to be more prevalent in feeds that have been grown or stored in hot, moist and humid conditions.

Feed manufacturers and other feed handlers are required to regularly test for aflatoxins to ensure that levels do not exceed legal limits. Other common mycotoxins such as DON should also be tested on a regular basis because they pose significant health problems for all species (see table). Dairy farmers who suspect they may have mycotoxin issues in their herd should verify with their feed supplier that the feeds they bring in are regularly tested and those tests are well below dangerous levels. Once again, it is nearly impossible to find feeds that do not have at least some minute level of mycotoxins in them.

Mycotoxins in dairy feeds do not just affect corn. Other grains such as wheat, rye and barley also are susceptible to mold growth. Each of these grains can support mold growth when growing conditions are optimal. Although fungicides may be effective in decreasing fungal growth in plants, a more environmentally friendly way to limit fungi is through crop rotation and avoiding monoculture farming.

In the case of DDG or wheat byproducts such as mill run, it’s difficult to identify mycotoxin contamination with a visual examination. Laboratory testing is the most effective way to determine if plants are contaminated and what types of mycotoxins are present. Most forage testing labs offer mycotoxin testing for a number of the most commonly found mycotoxins. The key to avoiding mycotoxin contamination is to purchase feeds from reputable suppliers that test for mycotoxins on a regular basis.

There are now a number of different mycotoxin absorbents or binders available. Some are clay based (for example, aluminum silicate) and others are carbohydrate based (for example, oligosaccharides). All of these products form chemical bonds with various mycotoxins, rendering them ineffective in the animal gut. Depending on the level of contamination, problems may still persist even if binders are included in the diet. Research is ongoing to find binders that bind with specific mycotoxins. One type of binder may be more effective on certain types of toxins whereas another binder may be more effective on other toxins. In today’s dairy diets it’s always prudent and precautionary to keep a binder in the diet year-round. Check with your feed supplier or an animal nutritionist for more information.

Unfortunately for animal agriculture, mycotoxins are a growing concern as agriculture becomes more globalized and feeds are being imported and exported more frequently around the world. Knowing the geographic origin and the growing conditions of feeds and byproducts and testing of feeds is the best way to avoid mycotoxin contamination in animal feeds.

Read more: Mycotoxins and Binders

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Nutrition for dairy cows is being fine-tuned daily – the result of an increasing need for improved feeding efficiencies as milk prices remain low and other production costs increase. There’s also the growing pressure of environmental regulations focusing on nutrient management coming from a dairy’s waste stream.

As dairy farmers seek to increase milk production per cow, the diets they feed their cows must be formulated to deliver just the right amount of nutrition without over-feeding or wasting nutrients. Feeding cows is the largest expense on dairy farms and every feedstuff offered in the diet must be evaluated for the energy, protein, vitamins and minerals it contains to satisfy milk production in mature cows or growth rates in young stock.

Formulating dairy diets was once a fairly straightforward procedure as only a handful of nutritional constraints such as crude protein, crude fiber and ash were quantifiable. The complex inner workings of the rumen were poorly understood as were the requirements for protein and energy. In less than a century, though, dairy scientists and ruminant biologists have unlocked many of the secrets of a cow’s digestive system along with the metabolic requirements for macro and micro nutrients.

Today, the term “crude protein” is no longer relevant in formulating milk cow diets. It’s now recognized that cows do not have protein requirements, per se, but requirements for specific amino acids that are contained within the proteins.

A similar development has occurred for crude fiber. Fiber is now partitioned into various fractions with differing rates of digestibility in the rumen, depending on their molecular construction. Rumen microbes use certain forms of nitrogen – again coming from different amino acids as well as nonprotein sources – whereas other amino acids are necessary for metabolic needs and milk composition. Some recent research has shown there are multiple pools of fermentation in the digestion process that affect what kinds of protein and fiber are used in the diet.

Various universities, agricultural institutions, research facilities and private companies have spent millions of dollars to understand the rumen digestive process, developing products that improve rumen health, microbial population and optimizing the fermentation process to cash in on the billion-dollar dairy feed industry to make the modern dairy cow more productive.

Historically, the dairy industry has embraced and implemented new technologies that have the potential to improve milk production per cow or overall farm gross revenue – even while profitability per cow decreases. Unfortunately for dairy farmers worldwide, the implementation of new and advanced nutrition technologies, while making dairy farming increasingly more efficient and environmentally sustainable, has served to make milk and feed prices volatile and profit margins smaller, resulting in the pursuit of even higher production efficiencies.

None of this would be possible if not for the use of computers and the ability to process data quickly. Computer software has been specifically designed to formulate diets from an array of constraints and pricing points designed to model rumen function and predict milk production scenarios for a combination of feedstuffs and environmental conditions such as weather and housing. Today, dairy farmers rely on nutrition software that can quickly predict milk production through “least cost” optimization programs that use linear programming algorithms.

Ration balancing programs allow dairy farms to formulate in a matter of minutes various diets for different levels of milk production within the herd showing potential revenue and income-over-feed cost margins. Herds can be grouped into as many production groups as there’s room for, as well as formulating diets for dry cow, transition cows and heifers. The age of computers doesn’t stop with ration modeling. In the milking parlor, computers can measure milk flow in real time. A cow wearing a transponder can walk into a robotic milking unit and be fed a precise amount of feed for the milk she’s producing while the robot’s computer analyzes the milk for quality and components.

With feed costs making up more than 50 percent of many dairy farms’ expenses, monitoring daily feed usage and inventories is critical to dairy profitability. Feed wagons and trucks with vertical and horizontal mixers have scales that interface with computers that keep track of feed usage, making sure cows are getting the diet the nutritionist says they should and feed isn’t being wasted and nutrients are being over- or underfed.

The particle separator box developed by Penn State University is a handy tool that should be used frequently to evaluate particle length of the mixes being fed to the cows. The particle separator gives a very accurate portrayal of how well the total mixed ration is being undermixed, overmixed or mixed correctly. Even if the feeder on the dairy is mixing ingredients correctly, mixing time may be reducing forage length, which can have a detrimental effect on rumen function if particle length is too short.

Since forage is the foundation of all dairy cow diets, high forage quality is critical to maximize milk production. In the last two decades, forage testing laboratories have provided more services to analyze fiber fractions and digestibilities, enabling dairy farmers and nutritionists to make informed decisions about the forage they produce or purchase elsewhere. More recently, labs have begun offering assays of starch digestibility as well, since university research has determined there are multiple pools of starch digestion in the rumen as well as fiber digestion.

Between improved mixing and feeding equipment technology, competent ruminant nutritionists, computerized ration formulation and diet modeling, along with the services from private and commercial laboratories that provide extensive information on feed quality, today’s commercial dairy farmers should never wonder how to maximize or improve milk production.

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The trace minerals that receive the most attention are copper, zinc, manganese, selenium, cobalt, and iodine. Deficiencies in trace minerals can impact growth, health and reproduction.

Cattle of all kinds – dairy and beef – as well as other ruminant species such as goats and sheep, have a host of metabolic functions that require trace minerals. Many are required for the immune system to function properly, some are required for the proper function of enzymes, while others are critical to proper cellular function and protein synthesis. Particularly for lactating cows with high milk production or close-up cows during the transition period, deficiencies in trace minerals can impact growth, health and reproduction.

The trace minerals that receive the most attention are copper, zinc, manganese, selenium, cobalt and iodine. Although the subject of trace minerals has received extensive study for many years and many of the functions of trace minerals are well documented, there are still many aspects of trace minerals that are poorly understood, such as the symbiotic relationships that they have with one another as well as with macro minerals such as calcium and potassium. For many years, the inorganic forms of trace minerals – those bound to sulfates and chlorides – have been fed to production and companion animals. Recently, researchers have found ways to combine trace minerals to organic molecules such as amino acids. These organic trace minerals are purported to be more bioavailable than inorganic forms.

The most active area of trace mineral research with animals involves their influence on the immune system. Trace minerals are crucial for the development of an adequate immune response in cattle, especially in stressed animals. Zinc, manganese, copper and selenium are important for optimal immune function and growth in cattle, particularly when stress levels are high. Zinc plays a crucial role in stabilizing cell membranes against reactive oxygen species (ROS) that cause inflammation and signal neutrophils (white blood cells) to fight against inflammation. Zinc also contributes to the structure and function of more than 2,500 enzyme systems involved in metabolism.

Selenium helps in preventing cellular damage by inactivating ROS. Cattle with deficiencies in zinc and selenium have shown depressed white blood cell activity during inflammation. Copper also plays a role in the neutralization of inflammation, contributing to the process of destroying invading organisms that destroy cells. Less is known about the role of manganese in supporting the immune system but has been identified as necessary for synthesis of cholesterol, estrogen, progesterone and testosterone.

Trace minerals are fundamental in the structure and function of several proteins that participate in processes involved in cellular expansion as well as energy production and DNA replication. Zinc and copper play central roles in how oxygen is transferred in the bloodstream. A host of enzymes are involved with energy transfer between cells. Cobalt is needed for synthesis of vitamin B12, which is a necessary part of energy metabolism along with red blood cell formation.

Balancing dairy diets for proper levels of trace minerals can be challenging due to large fluctuations of mineral content of feeds. Some trace minerals have a relatively large margin between amounts needed to meet requirements and maximum tolerable level. Copper and selenium, on the other hand, have small margins between meeting requirements and toxicity levels. Other trace minerals such as molybdenum will be antagonistic to copper, competing directly with copper and reducing its absorption. In addition, it’s recognized that some forms of inorganic trace minerals are not absorbed in the cow and are excreted through manure and urine, releasing these unneeded elements into the environment where they have no use.

Trace minerals fed in excess of requirements may not only impede absorption of other trace minerals, but they can also be toxic. However, due to the expense of trace minerals, over-feeding in cattle diets is seldom a problem. Care must be taken even when recommended levels are being added to diets because problems may occur if the water source on a dairy has a high level of a particular mineral, which again may cause toxicity or be antagonistic to other minerals. Copper, sulfur and molybdenum, due to their atomic similarities, can impede each other’s absorption. In regions of the country where molybdenum levels are known to be elevated, copper and sulfur must be increased. Copper can also be impeded in the presence of too much iron. Selenium and sulfur can also be antagonistic to each other. Care must be taken when there are known deficiencies in soils or excessive levels of a particular mineral in water.

Trace minerals complexed with amino acids or proteins have arrived in recent years to improve their bioavailability and reduce potential for environmental pollution. Zinc complexed with the amino acid, methionine, for instance, has proven to be highly effective in providing highly bioavailable levels of zinc. A number of trace minerals are now available from commercial sources that manufacture organically complexed trace mineral products. Copper, zinc, cobalt, manganese and selenium can be purchased in complexed forms.

Research has confirmed that organically complexed trace minerals are less affected by antagonistic trace minerals. The difference in absorption and bioavailability between an inorganic form of a trace mineral compared with an organic complex is minimal when presence of other antagonist minerals is low. However, when presence of antagonists is high, organic complexes appear to have an advantage in being more highly bioavailable.

It’s widely accepted that organic complexes of trace minerals are more absorbable than their inorganic cousins – sulfates, oxides and chlorides. This makes it possible to use less trace minerals in a cow’s diet to accomplish the same effect. Due to the high cost of many inorganic trace minerals, it’s recommended that dairy diets contain a combination of inorganic and organic trace mineral sources.

By feeding a combination of organic and inorganic trace minerals nutritionist and dairy farmers will be able to meet the trace mineral requirements of their cattle when dietary levels of antagonist are high as well as when the animal is stressed. Trace mineral levels in animal waste will be reduced, risk of mineral toxicity will be reduced and animal health, growth and milk production will be improved.

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Animal agriculture in general and ruminants in particular are considered to be a key contributor to excessive greenhouse gas (GHG) accumulation.

Photo: aurielaki/istock

Environmental concerns over increasing levels of methane emissions into the atmosphere constitute much of the discussion on climate change. Animal agriculture in general and ruminants in particular are considered to be a key contributor to excessive greenhouse gas (GHG) accumulation. The U.S. dairy industry must address the issue of methane coming from cows and heifers.

Total U.S. GHG emissions were reportedly 6,870 million metric tons (MMT) of carbon dioxide (CO2) equivalent in 2014. (This calculation includes methane CH4 and nitrous oxide at an equal value of heat-absorbing capacity as CO2. Methane is over 20 times more potent as a GHG in part due to its ability to retain heat compared with CO2. A small amount of methane represents a large amount of CO2 equivalent.) Methane emissions from U.S. dairy cattle were reportedly 41.9 MMT of CO2 equivalents in 2014 – or 5.7 percent of total methane emissions.

The U.S. dairy industry contributes a small percentage of the total GHG. Livestock worldwide, however – which are largely dairy and beef cattle – are considered to contribute closer to 20 percent of total GHG due to poorer nutrition management and higher percentages of grazing. Clearly, U.S. dairy cows are not the most guilty party when it comes to GHG. However, the U.S. dairy industry has committed to decreasing methane emissions by 25 percent by the year 2020.

How to lower enteric methane

A paper presented at the 2016 Cornell Nutrition Conference by Dr. Larry Chase outlines a number of nutrition and herd management options that have the potential to lower enteric methane in the dairy industry:

• Increase productivity and feeding efficiency, which results in more milk per cow and the need for fewer cows to produce a set quantity of milk.
• Improve forage quality, which will result in lower NDF levels in diets. Certain types of grasses produce higher levels of methane based upon carbon structure in those grasses.
• Consider corn silage with higher digestibility has been shown to lower enteric methane.
• Process grains to improve starch digestibility in the rumen
• Feed ionophores to improve the energy status of cows and heifers and reduce methane production from rumen microbes.
• Rumen inert fats may improve energy status requiring less fermentation in the rumen.
• Rumen modifiers may offer the opportunity to alter the rumen microbial population.
• Implement herd grouping and ration formulation strategies to improve efficiency of nutrient use.
• Decrease the age at first calving for replacement heifers, which would lower total animal numbers in dairy herds.
• Implement feeding management practices that improve consistency and minimize variability.
• Provide facilities and herd management systems that improve cow comfort and reduce stress.
• Improve herd health and reproductive performance.

The average Holstein dairy cow is reported to release ¾ to over 1 pound (373 to 509 grams) of enteric methane per day depending upon the level of milk production. Enteric methane is the methane produced in the digestive tract of cows and is released into the atmosphere by flatulence from the colon or belching from the rumen. Methane production is highly correlated to feed intakes, and since lactating dairy cows consume large amounts of feed with the goal of producing milk, milk production accounts for over 50 percent of the methane emissions from dairy farms. Therefore, the primary area of focus for reducing methane in the dairy industry centers on lactating dairy cow diets and nutrition.

Ruminant nutritionists have a tricky situation with regards to lowering enteric methane. Decreasing enteric methane requires altering the rumen microflora, which could have a deleterious effect on cow health and milk production. Methane is a naturally occurring biological byproduct of fermentation in the rumen and intestines. Chart 1 shows that as milk production increases, total grams of enteric methane produced climbs with it. This is directly a result of a cow consuming more feed to produce the milk. Certainly cows that produce more milk will produce more enteric methane. Chart 2, however, shows that as milk production increases, grams of methane produced per pound of milk decreases. This indicates that as a cow’s milk production increases, less methane is produced in the rumen.

This efficiency is not fully understood but can be partly explained by the fact that lactating diets formulated for higher levels of milk production usually contain more grains and commodity byproducts, which are known to produce less methane than high-forage diets. High forage diets create more enteric methane. Research supports the conclusion that feed rations higher in NDF tend to increase methane emissions, while higher starch rations tend to decrease methane emissions.

An area of dairy management that should be aggressively addressed for dairy farm productivity and profitability as well as assisting in the reduction of methane production is that of improving conception rates and lowering average days-in-milk in herds. Cows with shorter, more productive lactations will improve overall milk production on dairy farms, reducing the need for high inventories of heifers, the second largest source of methane on the dairy. Although it’s impossible to completely eliminate enteric methane emissions coming from dairy cows, dairy farms that focus on both feeding and reproductive efficiencies automatically reduce methane production that will lower the carbon footprint from the dairy industry.

According to Dr. Chase, research shows that a 2,000-pound increase in milk production during a cow’s lactation results in a 1 percent decrease in the carbon footprint on a dairy farm. A herd with average annual milk production of 20,000 pounds that incorporates summer grazing had a carbon footprint similar to a confinement herd producing 26,000 pounds of milk or more. Ironically, an all-grass herd producing 16,000 pounds of milk had a carbon footprint similar to the summer grazing and confinement herds described already. This research contradicts the current sentiment favoring pasture grazing systems for dairy cows as being advantageous to environmental sustainability and a more eco-friendly means of producing dairy products. This objective approach of evaluation should be used more frequently by the industry to examine alternative farm management strategies that will result in a more proactive approach to reducing methane emissions from the dairy industry.

Read more: Executing the Perfect Manure Management Plan

A general rule of thumb is that a well-managed pasture should be able to produce an average of about one ton of dry matter per acre throughout the growing season.

Pastures provide forage, which is the foundation of dairy cow diets. The higher the quality of any forage – essentially meaning the more it can be fermented and converted into energy in the rumen – the greater the value of the pasture and its contribution to a dairy’s profitability. At the heart of extracting the most from pasturing dairy cows is the dairy farmer’s ability to optimize forage quality during a growing season while not over-grazing and damaging pastures.

In most parts of the country, pasturing cows is seasonally limited – cows can’t be run out on pasture all year long. Even with managed intensive grazing, dairy farms must still bring cows into a confined environment for part of the year to keep them fed, healthy and productive. Winter snow covers the ground in many regions, making grazing impossible. Where snow is not an issue, growth of grass still comes to a near standstill due to cold weather and shortened daylight hours, which is absolutely crucial to photosynthesis and plant growth.

Like any living organism, a plant’s singular biological purpose is to reproduce and propagate. Perennial pasture grasses and legumes have a growth cycle with the most nutritional herbage – high in protein and low in fiber – being produced at the beginning of a season. As forages grow and mature, their nutritional value declines as they lignify and flower or go to seed. In doing so, they spoil the party for livestock nutrition.

Milk production for dairy cows is primarily a function of feed intake, forage quality and balanced nutrition. Two significant challenges for any dairy that grazes a herd is keeping the quality of the forage from degrading to a point where it’s no longer nutritional enough to produce a desired level of milk and also knowing how much dry matter and nutrition is coming from the pastures on any given day throughout the grazing season.

For many dairy farmers, having milk cows that spend a good deal of their lives grazing on well-managed and productive pastures is an environmentally friendly and profitable way to dairy. In regions with good soils and dependable water, high quality pastures allow dairy farmers to optimize feed tonnage and forage quality. Well-managed intensive grazing of dairy herds can result in improved milk-revenue-over-feed-cost margins.

It should be understood that cows consuming pastures should be receiving adequate nutrition that will support a desired level of milk production. While it’s tempting during times of low milk prices to reduce purchased feed costs, the grass that is taking the place of the grains must be highly digestible. Many pastures, due to previous poor management, do not have the ability to provide a consistent supply of high quality forage week in, week out over the summer months. Cows should not be put on pastures with a goal of easing life for the dairy farmer.

Dairy farmers must look at pasture grass the same way as for hay or haylage. Just as the quality of hay and haylage varies with maturity, pasture grass will be at its nutritional best in the early vegetative stage. Farmers must develop an expert eye as they watch the length of grass on any given day. They also must know what types of grass varieties are in the pastures. Grasses are not the same. They grow at different rates and have different nutritional values at different stages of growth. The most productive pastures will have a diversified variety of grasses and legumes that will be at different stages of growth throughout the season rather than all grass coming to maturity at the same time.

Even small changes in nutrient content of pasture grasses will have a profound effect on milk production since so much of the diet is coming from this single feed source. Imagine that you would replace half of your grain concentrate with forage. You may save a dollar per cow per day on grain costs but what will happen to milk production? Make money or lose money? You can quickly see that the quality of the forage will have a profound impact on net income when switching to a pasture program.

Cows are big animals that consume between 30 and 50 pounds of dry matter each day depending on if they’re dry or lactating. Lush pasture grasses are 80 percent to 85 percent water. For a cow to consume 40 pounds of dry matter in a day she must eat about 200 pounds of grass. Dairy farmers and nutritionists must be able to calculate how many cows can be grazed on a given amount of acreage before grass runs out.

A general rule of thumb is that a well-managed pasture should be able to produce an average of about one ton of dry matter per acre throughout the growing season. The cow mentioned already who is consuming 40 pounds of dry matter per day will consume over 1,200 pounds of dry matter in a month – well within the expected 2,000 pounds that the acre can produce. Therefore, generally, farmers who are contemplating grazing a herd of milk cows should plan on having a minimum of an acre of pasture per cow.

This is fine as long as the pastures hold up. As long as there’s enough rainfall to keep the grasses growing, a pasture can support a herd of cows for many weeks. When the season gets warmer and rainfall slows down, cows can quickly over-graze a pasture. Dairy farmers must learn how to manage the pastures based on weather and how the grass is holding up. Over-grazing pastures will stress the root systems, impacting their ability to remain healthy. Weeds can quickly invade a pasture that is stressed.

Pastures vary from farm to farm and region to region. One style of grazing may work better on one farm than on another. It must be approached on a farm-by-farm basis. The decision to pasture cows should be heavily based on the realistic economics of income-over-feed-cost that the dairy will realize from pasturing cows.

The most limiting nutrient for dairy cows is energy. Balancing and feeding diets that can keep the rumen at a consistent level of energy production – especially for high milk producers – can be a challenge. No matter if rations are being fed to the fresh cow, the transition cow, cows in late lactation or heifers, all energy created by rumen microbes must have sufficient amounts of carbohydrates included in the diet. To make energy metabolism even more complicated, the weather, hot and cold, can raise energy requirements for cows and heifers dramatically.

Ruminant nutrition requires that rumens have substantial levels of forage to remain healthy and productive. Forages, however, are the least digestible of the feedstuffs we feed our cows. The cellulose in forages is seldom completely fermented by rumen microbes. The fermentation process produces the precursors to glucose synthesis, which is the primary source of energy in cows. When glucose synthesis is reduced, so is the cow’s overall metabolism, limiting growth in the case of young calves or milk production in older cows. The introduction of feedstuffs such as grains or other commodity byproducts into diets provide starches and sugars that are more easily fermented by rumen microbes than cellulosic fiber from forages.

For cows in late lactation, producing lower levels of milk, or heifers and dry cows, diets heavy on forages with less starch and sugar tend to provide adequate energy levels for maintenance, growth and production. However, for cows with increased milk yields, the need to raise energy intakes to support the additional production requires higher feed intakes or greater energy density in the diet. As is often the case, forages that must be included in the diet will prevent energy density from being increased. An effective solution to increasing energy density in ruminant diets is to add fat to the rations.

Unlike in the stomachs of monogastrics where fat is converted to glucose, rumen microbes do only a minimal job of fermenting fat molecules. In the rumen, free fatty acids undergo a biological process called biohydrogenation, which results in all fats becoming saturated while still in the rumen and not converting them to volatile fatty acids. Saturated fats are less digestible in the small intestine. Even if polyunsaturated or monounsaturated fats are fed to cows, much of it is converted to saturated fats before leaving the rumen.

In addition, moderate amounts of any fat will coat fiber particles to the extent that rumen microbes cannot ferment the fiber. Once fiber fermentation is compromised, energy synthesis is reduced as well as butterfat production. Even though, in theory, fats are the most energy-dense of all feeds, for them to provide metabolizable energy, they must be fed in a form that bypasses the rumen and proceeds directly to the small intestine.

Breaking down rumen bypass fats

Rumen-protected (or rumen bypass) fats are commercially manufactured fat products of varying fat content and fatty-acid profiles that allow increased energy densities in all ruminant diets. RP fats enable nutritionists to increase energy density in dairy cow diets without having to add more starch or sugar. Adding a starch source to raise energy intakes often requires several pounds of grain, which may result in acidosis. RP fats replace the need for excessive levels of grains and commodity byproducts.

Rumen-protected fats offer the option to dairy farmers of adding extra energy to a diet to compensate for low energy corn silages or other roughage. Adding a pound of RP fat to a dairy cow diet will provide enough energy to support an extra half-gallon of milk per day. In the case of heifers or dry cows, RP fat will enable cows to maintain body condition during excessively cold periods where more energy is needed for maintenance. RP fats should be regarded as a tool with which to adjust energy density in diets depending on the other feedstuffs that are available for rations. In many cases, it may not be necessary to add RP fats in diets all year long – instead add fats only when conditions require the addition of a more energy dense diet to compensate for feedstuff quality or adverse weather conditions that cause cows to require more energy.

The commercially available rumen-protected fat products on the market today are primarily combinations of various unsaturated fatty acids that have various coatings on them to prevent rumen microbes from converting them to saturated fats. Research has shown that mono- and polyunsaturated fats are more bioavailable once absorbed through the small intestine. Unsaturated fats increase milk production and feed efficiency in high producing dairy cows. Feeding rumen-protected fats is also appropriate for dry cows, heifer and calves in excessively hot or cold weather conditions that increase maintenance requirements.

Along with improving the immediate energy status and alleviating negative energy status during early lactation, the RP fats have also been found to improve reproductive function in early lactation. Several polyunsaturated fats are instrumental in ovary health and follicular development. Even if cows may not need additional dietary energy for body condition or milk production, feeding a properly formulated RP to dry cows has been shown to improve conception rates.

In dairy herds that are managed with more than one production group, addition of RP fats in the early lactation or high production groups will give the greatest benefits in production and feed conversion efficiency. Depending on the energy value of feedstuffs, lower producing groups may or may not benefit from adding RP fats to the diet.

The two most commonly used RP fat products today are: 1) fats that are combined with calcium to form a calcium salt that remains inert in the rumen and 2) fats that are coated with a polymer coating that resists rumen degradation. Both technologies enable the fat to bypass the rumen and are absorbed in the small intestine where the various fatty acids are metabolized. RP fat manufacturers each have their own recipe of various fatty acids in the products. Dairy producers and nutritionists should study the research and product claims of the various products on the market and choose the product that will give the most desired result. In some cases fat combinations will favor milk production while others will favor milk component or improving body condition. RP products are expensive but their efficacy is usually worth the investment.

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Protein nutrition and amino acid metabolism will continue to be an area of intense focus in the fine-tuning of dairy cow diets.

Figuring out protein nutrition in ruminants can be tricky. The protein fed in the diets of dairy cows and other ruminants is not directly absorbed and metabolized like it is in monogastrics such as pigs and chickens. The protein – more specifically, the nitrogen and amino acids in the protein – fed to ruminants is first used to feed the microbes in the rumen. About 50 percent of the protein that a cow metabolizes comes from the dead rumen microbes that have finished their fermentation obligations and go on to be absorbed in the small intestine. This microbial protein is considered to be the best protein in terms of quality and amino acid profile.

If not complicated enough, the other half of the protein that a cow needs does indeed come from the feedstuffs in the diet. However, the nutritional value and efficacy of that protein in those feeds is highly dependent upon the amino acid (AA) profiles in those feedstuffs and how well those AA survive the journey through the rumen and make it to the small intestine for absorption. Rumen microbes get first dibs on protein from feedstuffs, break them apart, take what they want and leave the rest. The resulting profile of AA coming from feedstuffs absorbed in the small intestine can often be deficient in essential AA.

Years ago, most dairy farms had small herds and the cows derived most of their nutrition from forages – either hay or pasture. High grain and commodity byproducts were not in common use and balancing rations was in its infancy. It was understood that immature forages had more protein and was preferable over mature forages. An understanding of how much and how rapidly protein degraded in the rumen wasn’t fully understood until the 1960s.

There has been a paradigm shift in how we view protein in dairy cow diets. We no longer can speak of crude protein (CP) levels in a ration because CP is merely a measure of nitrogen content and not of specific AA. Neither do the concepts of rumen degradable protein (RDP) and rumen undegradable protein (RUP) fully address the complexity of balancing amino acids. Many feedstuffs and byproducts do not have the proper profile of essential AA required by high-producing cows.

Much of the research into establishing AA requirements has focused on the AA profiles in cow’s milk and body tissue and comparing it with the AA profile of microbial protein in the rumen. The more microbial protein that can be developed in a rumen, the better the protein status of a cow will be, lowering the need for protein byproducts that offer questionable levels of rumen bypass amino acids.

Delivering accurate and consistent levels of metabolizable AA by way of feedstuffs has been a challenge due to the variation of amounts and bioavailability in feedstuffs. Diets that consist of high percentages of corn and corn byproducts are recognized to be deficient in lysine. Diets that consist of high percentages of a single feedstuff can be highly deficient in many of the essential AA. Diets should be formulated to include a variety of feedstuffs in order to avoid limiting one or more of the essential amino acids.

Rumen-protected methionine has been available for many years and has a credible track record for good results and return-on-investment in increasing milk protein levels in milk. Rumen-protected lysine has been available for a shorter period of time and, though the initial results are encouraging, more time is needed to evaluate its efficacy. A number of rumen-protected methionine and lysine products are on the market today.

The dairy industry once again finds itself in a situation of low milk prices and milk-over-feed margins. Dairy farmers continue to seek ways to lower feed costs without losing milk production or lower milk components. The dairy industry struggles to do its best in the prevailing economic environment, competing for scarcer resources along with having to address the issue of nutrient (nitrogen) management and economic stewardship. A complete understanding of AA metabolism and requirements in the dairy cow has been at the center of the quest to improve feeding efficiencies and reduce environmental nitrogen pollution.

Too much protein in a dairy cow diet costs money. Not feeding enough protein or the correct type of protein in a dairy cow diet costs money, too. Improving our knowledge of protein nutrition in dairy cows will accomplish at least three things:

• The intrinsic and virtuous goals of more completely understanding the biology of cows’ metabolisms so that we can improve the value of the milk produced along with feeding efficiencies – and ultimately the profitability – of our cows and our dairy businesses. Decreasing the cost of protein nutrition in dairy diets will mean money in the pockets of dairy farmers.
• Environmental concerns and costs associated with nutrient management and nitrogen pollution. Improving protein efficiency in dairy cows means reducing nitrogen being released into waterways, aquifers and the atmosphere.
• Incorporation of rumen-protected technology for amino acids will reduce the need for the use of animal-sourced byproducts as a protein source.

Balancing for amino acids in dairy cow diets is complex and will not produce desired results if other areas of dairy management are not up to par. Addressing critical management items such as days-in-milk, cow comfort, feedbunk management, vitamins, minerals and water quality as well as dry matter intakes, moisture levels of silages, and feeding high quality forages will more than likely increase milk production per cow long before addressing specific amino acid needs. Holstein herds that can’t manage a 60-pound milk average have other things to fix first.

Most dairy farms continue to find it necessary to improve feeding efficiencies and increase the value of the milk produced by increasing milk components to stay in business. Protein nutrition and amino acid metabolism will continue to be an area of intense focus in the fine-tuning of dairy cow diets.

Read more: Optimizing the Rumen

Achieving the optimal balance of protein to carbohydrates in the rumen will make the rumen more efficient in growing microbes and produce the most power.

Recent years have not been kind to dairy farmers as milk prices have once again sunk to unmanageable lows and the cost of purchased feeds shows little sign of dropping. Feeding cows during this economic downturn remain challenging for most dairy farms. There’s just no easy way to keep throwing money at the herd when the feed bill continuously consumes a larger portion of a dwindling milk check.

The national Milk-Feed Price Ratio, monitored by the University of Wisconsin, has dropped below 2.0 for April and May of 2016, verifying that there isn’t a lot of money left after paying the feed bill on the average dairy farm. This metric measures the average monthly milk price received around the nation and compares it to the cost of a theoretical 16 percent crude protein diet fed to milk cows. The ratio aids in evaluating if a dairy farmer can “afford to produce milk” depending on what the milk price may be relative to the feed cost. The conventional thought has been that when the ratio is 3 to 1 or greater, dairy farming tends to be profitable.

During the past 10 years, this ratio, calculated monthly, has made it to 3 to 1 only a few times, with most ratios remaining in the lower 2 to 1 range. The ratio dropped to its lowest point of 1.3 to 1 during mid-2012 when feed prices were exceptionally high. During 2014, despite record high milk prices, the ratio made it only as high as 2.96. As low milk prices continue during 2016, challenges to feeding dairy herds remain.

Every dairy farmer must decide how to feed cows and what level of milk to support when times are trying. To cut costs, diets are often reformulated with less expensive, less nutritious feedstuffs. This is one option. However, the single driver when altering diets to compensate for feed costs should be to ensure the rumen remains healthy. When rumen activity, fermentation and microbial growth are compromised, cows will quickly diminish in productivity – often resulting in even greater loss of net revenue.

The rumen can be likened to a large container that houses a continuous fermentation process. Microbes – mostly bacteria – in the rumen do the fermenting. However, these microbes also need nutrients to live and multiply. Their life cycle occurs while they digest forages and other carbohydrates. In recent years ruminant nutritional research has focused heavily on digestion and passage rates of various carbohydrates and matching them with a protein that provides adequate levels of nitrogen at the most opportune time. This is done to keep a large, healthy microbial population in the rumen.

Think of an efficient rumen as a smoothly running automobile engine: For it to run efficiently and develop the greatest amount of horsepower, the gasoline and air mixture must be correct. If there is too much gasoline for the amount of air available, the engine will run too rich and may flood out. If there is too much air for the amount of fuel available, the engine will be starved for gasoline, run too lean and not be able to deliver the desired power. Achieving the optimal balance of protein to carbohydrates in the rumen will make the rumen more efficient in growing microbes and will produce the most power.

In a cow’s diet, carbohydrates are the primary source of energy and proteins are primarily a nitrogen source for rumen microbes. When microbes ferment carbohydrates in the rumen they produce volatile fatty acids (VFA). VFA provide up to 80 percent of a cow’s energy needs. Slowing down fermentation reduces VFA production and energy available to the cow. At the same time, microbes must use nitrogen coming from peptides and other nitrogen sources from the dietary protein in the feedstuffs. The larger and more robust the microbial population in the rumen is, the more metabolizable protein available for digestion in the small intestine.

The challenge in trying to achieve this optimum protein and carbohydrate balance is that often there is either too much rapidly degradable carbohydrates relative to the available rumen degradable protein or too much rumen degradable protein for the microbes to utilize.

Carbohydrates and proteins are degraded at different rates in the rumen. The challenge in attaining an efficiently operating rumen that will optimize microbial growth is to match up the faster digesting carbohydrates with more rumen soluble proteins and, at the same time, keep enough nitrogen available to ferment the more complex, slower digesting carbohydrates such as hay. Excessive protein in the ration may lead to an over-production of ammonia, which is a potentially toxic situation. Excessive levels of highly fermentable carbohydrates in the ration can result in an acidotic rumen. Both situations represent lost opportunity to the dairy farmer.

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