Dairy farmers are often focused on herd genetics. Each has its own priority criteria, such as milk output, milk components, good legs and hocks, size and build, grazing ability, somatic cell score, fertility or calving ease. Depending on the farm’s management system, different traits may be valued more or less than others. Thus the genetic merit of traits will differ, depending on farm goals and management practices.
“For conventional dairy, farmers are looking at fertility and longevity, as well as somatic cell score,” said Bradley Heins, associate professor, Organic Dairy Management, West Central Research and Outreach Center, University of Minnesota. Heins’ area of expertise is animal genetics in conventional and grazing dairy herds.
“A grazing dairy looks at the same traits of fertility, longevity and somatic cell score. However, they also add in smaller body size and may look at other minor traits such as A2 or kappa casein,” he said. “Smaller cows tend to have less health problems, and have [a] longer productive life. Larger cows tend not to do well in grazing situations with all of the walking. Most graziers prefer to handle smaller cows because of management and they possibly may consume less feed and be more feed efficient.”
The cow’s phenotype, or outward expression of genes, is dependent not only on its raw genetic material but also on the environment in which it is raised, which can influence overall performance positively or negatively. Knowing what factors play a role in maximizing herd performance – no matter the genetics – can increase dairy profitability. This combination of genetics and environmental influence has economic implications on every dairy.
Milk production of dairy cows has increased substantially in recent decades. Some of the change is due to improved facilities and management, leading to better cow comfort and health. Artificial insemination (AI), coupled with the ability to determine the genetic makeup of sires and the likely expression of selected genetic traits in the next generations, has also contributed to high production cows.
Various traits have differences in heritability. Heritability measures the probability that a given trait is passed on through the genes, from one generation to its offspring. Heritability varies from trait to trait, and heritability of traits can vary between breeds. The heritability of some traits is linked.
Heritability is a tool used to determine how closely an animal’s phenotype – or performance – is actually due to genetic merit, and how much is influenced by nongenetic factors. Heritability of 0.40 is considered high, indicating that the expression of the trait is likely to be passed along via the genes and that 40 percent of the differences seen in the trait between animals is due to genetics. The remaining 60 percent of the difference is due to environment and management factors. Low heritability, of 0.15 or less, indicates that the trait in question is not very likely to be passed to its offspring.
As per the Virginia Cooperative Extension publication, “Using Heritability for Genetic Improvement:”
Specifically, heritability is the percentage of all differences between animals that is caused by gene effects that transfer from generation to generation. The percentage that remains is not caused by transmissible genetic effects. Often, environmental effects are an important part of the remainder.
The percentage of protein and fat in milk tend to be the two most heritable traits, along with animal stature. Others, such as rate of mastitis or ketosis, daughter fertility or longevity are of low heritability, and thus the environment plays a significant role in their expression. But even low heritability traits can be selected for over time, and consistent selection of those traits of importance to the dairy will slowly increase their presence in the phenotype of the herd.
Performance records are kept on sires by each breed organization. Sire summaries combine several dozen traits, analyzed from an AI bull and its multiple offspring, and determine the likelihood that those traits, alone and in combination, will be passed onto its progeny. Producers using AI have an extensive record of sire genetics to use for breeding purposes. This information allows for selection of the traits deemed most important to herd performance.
But not all dairy farmers use AI. Many dairy farmers use natural service breeding and primarily rely on phenotype observations to select traits and improve their herds.
“Only about 50 percent of dairymen use AI,” Heins said. “In the grazing world, it is much lower. I am not all that in favor of breeding naturally, but I would watch for temperament of the bull, body size (smaller is better) and calving ease.”
Not just milk
Daughter calving ease, service sire calving ease, daughter fertility, udder characteristics or body condition score are just a few of the many traits that can be of importance in a dairy herd. Indicators of health status, reproductive capabilities and longevity are generally not as heritable as milk output. As farmers began to select for traits using genotype, milk output was often targeted due to immediate economic benefits. But selecting for high milk production often comes at a cost.
“There is an antagonistic relationship between milk and fertility. By selecting for increased milk production, we are selecting for reduced fertility in cows,” Heins said. “There is also a thought that if we select for larger cow body size, we will get more production. This is actually not true.”
High milk cows tend to have reduced fertility and an increase in health concerns. These lead to a shorter productive life and can negate the benefit of more milk, Heins said, referring to a University of Minnesota study. This study, spanning 40 years, showed a longer lifespan for medium-framed cows, as well as the same milk production as larger-framed cows.
As cows become increasingly inbred, the negative results of trait selection – such as for high milk – can cause complications. For Holsteins, reproductive issues have become more common and problematic. Holstein genetic selection has led to larger cow size, environmental issues related to cow comfort, as cows outgrow stall size and barns become crowded, which detracts from any inherent genetic potential of the selected traits.
Peter Mapstone, Pastureland Dairy, Manlius, New York, inherited a high-production Holstein herd. Finding himself with a major labor shortage soon after taking over the dairy, he began immediately grazing these confinement cows. Realizing that pure Holsteins were no match for grass-based dairying, he crossed with Jerseys with good results on the first-generation cows, an effect known as hybrid vigor. He’s bred in other genetics since then, and began crossing back to Holstein. Jersey genetics will again be bred into the herd, for a new generation of primarily Holstein-Jersey crosses.
Speaking at the Northeast Organic Farming Association of New York’s (NOFA-NY) annual Dairy and Field Crop Conference in 2016, Mapstone said that selecting for the high production of that purebred Holstein herd wasn’t the most profitable approach to dairy farming. Ketosis issues, the cost of feeding a high-grain diet and injuries to the cows negated the benefit of more milk per cow output.
“Dairy farmers tend not to think over the lifetime of the cow. They try to get as much milk out of the cows today. Selecting for improved fertility and health of cows will actually be more profitable in the long run than selection for milk,” Heins said. “A farmer should select for net merit (NM$), an index that combines production, fertility, productive life, functional type and calving ability. This is probably the most appropriate index to improve profit of dairy farms.”
The NM$ is computed by the U.S. Department of Agriculture and reflects relevant economic factors affecting dairy profitability. The index assists dairy farmers in weighing economically important traits when selecting herd genetics. Traits can be used to select for income or to reduce expenses. More information on using the index, as well as on other indicators that can be used to enhance herd performance, can be found here by searching “genetic improvement programs.”
No matter how great your herd genetics, and how well-suited for your farm they may be, environmental factors have a major impact on any inherent genetic potential. If your cows aren’t comfortable and healthy, their genetic potential is compromised. A cow’s genetic potential for performance is also compromised by herd management practices.
Uncomfortable, stressed cows – due to overcrowding, stall size, improper diet or too little time for resting and rumination – are not performing optimally, no matter their genetics. Stressors such as these require the cow to focus on survival and not on maximizing normal functioning, such as milk output and reproduction.
Spending energy to compensate for environmental concerns, such as inadequate ventilation and heat or cold stress, means that cows don’t have the energy to perform their best, either. Immune system challenges due to poor nutrition, injury or respiratory and mastitis concerns, all of which can be caused by facility design and or management practices, take away from performance, no matter how optimized the genetic merit of the herd.
Dr. Jen Burton, also speaking at the NOFA-NY conference, explained that immunity and reproductive ability are heritable traits, and both require great energy from the cow. If an immune response is needed, the cow will have to switch off the reproductive response. Keeping cows comfortable and healthy means less immune response and more reproduction capability.
Health concerns limit lifetime milk. And it isn’t just lactating cows that suffer from poor health or nutrition impacts. Heifer nutrition deficits will impact that cow’s production during first lactation, if not longer. Calves and heifers that have experienced immune challenges such as respiratory disease will never live up to their ultimate genetic potential.
“Cow comfort can make a huge impact on reducing profit and milk production, as well as increasing the likelihood of health problems, culling and or mortality,” Heins said. “Nutrition can limit high milk output. If cows are not fed properly and to their requirements, we can see losses in milk.”
Heat stress in dry cows can cause lifetime drops in milk production for both the dry cows and their calves. Calves born to mothers experiencing heat stress in the last two months of gestation see their lifetime milk production decrease significantly, with heat stress having “major effects on the calf,” and a lifetime impact of 10 pounds per day of decreased milk output, said Dr. Albert De Vries, Department of Animal Sciences, University of Florida. In the Northeast, over 100 pounds of milk per cow are lost each year due to “milk not being made if dry cows are not cooled. It is basically profitable to cool dry cows anywhere except Alaska.”
Competition for resources such as lying time in stalls or access to feed occurs with overstocking. In the Northeast, dairy overstocking is commonplace. Overstocking stresses the cows beyond whatever environmental stress response they would have had if the barn was not crowded, and amplifies it.
Getting more milk in the bulk tank doesn’t necessarily require the best high-production genetics, or adding cows and overcrowding facilities. Changes in management can increase milk output without making genetic changes. And management changes can happen now with the cows you have. Optimizing cow comfort and welfare through facility design and animal management, selecting traits – high and low heritability – that match the needs of your dairy farming practices, and remembering that lifetime profitability has to do with more than high milk output, can bring about the best results for your dairy’s profitability now and in the future.
“I think that dairy producers and industry people focus too much on milk production,” Heins said. “Yes, milk production pays the bills, but there are other benefits that are hard to measure on dairies. If dairymen actually tracked costs for health treatments, fertility and other things related to cow health, they may find that selection for milk production may not be what it is all cracked up to be.”