Farming Magazine - February, 2014

COLUMNS

Dairy Nutrition: Energy for the Cold

By John Hibma


Photo by Scott Bauer/ars.usda.gov.

I'm getting too old for the cold.

It's the beginning of December as I write this, and we've already had some ice on the ponds here in Connecticut, with nighttime temps getting down into the single digits. I never knew what "wind chill" was until I moved to the East Coast. A big snowstorm crossed the country a couple of days before Thanksgiving; fortunately, it lost most of its punch somewhere in Pennsylvania. And don't get me started about the freezing rain that I woke up to a couple of mornings later.

It takes a whole lot more energy to tolerate the colder weather. My fuel oil bill reminds me of that every winter. Even though our farm animals have thicker coats of hair and metabolisms that do a better job of keeping them warm, it really doesn't take significantly lower temperatures to impact milk production and growth rates in our cows and calves.

Cows are in a thermoneutral zone (TNZ) from about 40 to 65 degrees Fahrenheit. That's the temperature range at which their bodies don't have to expend extra energy trying to cool down or stay warm. Even though the rumen is a natural heater with the fermentation process going on, once ambient temps drop below 32 degrees Fahrenheit, extra energy is required to keep cows warm.

Unless that extra energy is provided for in the diet, cows will start to draw on their body fat reserves to stay warm. It doesn't take long before a cow loses body condition when dietary energy is declining. Once a cow's body condition gets down around 2.5, milk production begins to suffer as well, as she attempts to channel more energy into trying to keep weight on.

Cows naturally try to compensate for colder temperatures by increasing feed intake. Given the opportunity, cows will eat more when it's cold. Grains and commodity byproducts offer more energy per pound than forages. In fact, when temperatures become extremely cold, forages alone will not supply enough calories to keep cows warm.

As milk production increases at the beginning of a lactation, say when fresh cows are making over 100 pounds of milk per day, those dietary energy requirements increase significantly, especially when temps drop below freezing.

A typical feed ration that has been balanced in the fall of the year when daytime temperatures are in the mid-60s calls for a cow to consume about 46 to 48 pounds of dry matter to support 70 pounds of milk production. Then, in January and February, when the daytime temperature doesn't climb above 20 and nights are well below freezing, that same cow must eat another 4 pounds of dry matter to compensate for her increased energy needs. The most efficient way to get those extra calories into your cows is with feedstuffs that are calorie-dense. A surefire product that will deliver calories to cold cows is the rumen-protected fats that are available from your feed suppliers. However, those products are not inexpensive, and you must use them judiciously.

You also shouldn't take a current feed mix and increase the amounts without re-evaluating the entire diet. Since vitamins and minerals are formulated to the correct levels with a specific inclusion rate of a grain mix, increasing grain mixes will only overfeed those expensive ingredients.

Reformulating your dairy cow diets is usually the most cost-effective means of getting more energy into your cows during the winter. In this current economic climate, every dairy farmer should be formulating cow and heifer diets with the aid of computerized ration evaluators that incorporate least-cost optimizers. Nutrition modeling software does an amazingly accurate job of formulating rations that meet nutritional needs for a wide range of temperature and humidity combinations.

Neonatal calves are especially susceptible to the cold. Calves are born with very little extra body fat to keep them warm when nutritional calories are deficient. With little body fat to draw on, the cold weather will quickly slow the growth rate of young calves and lower their immune function, making them more susceptible to getting sick.

The TNZ for calves is at a higher temperature range than for cows. Their TNZ ranges between 50 and 75 degrees Fahrenheit. In other words, cold conditions will bother calves more quickly. A good rule of thumb for compensating for cold and increasing dietary energy for calves under 1 month of age is: for every drop of 1 degree Fahrenheit in ambient temperature below the TNZ, maintenance energy (ME) increases by 1 percentage point. For example: At 25 degrees Fahrenheit in a calf hutch or calf barn, the ME requirement increases by 25 percent. If the temperature falls to 0 degrees Fahrenheit, you need to increase ME in the diet by 50 percent. In many parts of the country where winter temperatures remain below freezing for days or weeks at a time, milk solids requirements (fat and protein) must be doubled in order to maintain health and growth rates.

Calf raising trials have shown that calves receiving about 2.5 megacalories (Mcal) of energy per day gained about 0.4 pound per day when the environmental ambient temperature was 50 degrees Fahrenheit. The ME requirement was about 1.9 Mcal, with the remainder of the calories being used for weight gain. When the ambient temperature dropped to 25 degrees Fahrenheit, nearly all of the 2.5 Mcal coming from the diet was needed for maintenance requirements, leaving none for weight gain. With an ambient temperature drop from 50 to 25 degrees Fahrenheit, the energy needed for gain increased about tenfold.

Energy requirements for dairy cows, heifers and calves increase significantly during cold weather. Proactively avoiding losses in milk production and weight is generally less expensive than losing the milk revenue that can't be recovered and having to wait for calves to catch up on their weight. Just as we must turn up the thermostat in our homes to keep warmer during the winter - burning more wood, oil or gas - we also have to increase the calories consumed by our animals to keep them at the peak of their production and growth when the weather turns cold.

The author is a dairy nutritional consultant and works for Central Connecticut Cooperative Farmers Association in Manchester, Conn.