Long-term trends suggest the dairy industry has a mixed record when it comes to maintaining the health of our cows. On the one hand, we have seen a substantial decline in somatic cell counts. Improved management, a shift of cows to drier climates and aggressive culling of problem cows thanks to replacement heifer availability and high beef prices deserve much of the credit for this favorable udder health trend.
Not to be overlooked is the contribution of breeders that have selected aggressively for improved udder conformation and lower somatic cell scores.
There are also some trends and metrics that are more problematic. On-farm mortality rates for mature cows more than doubled from 1980 to 2000 for both Holsteins and Jerseys, and this was before downer-cow legislation was enacted that caused a further rise in on-farm mortality.
The good news is: Mortality rates appear to have leveled off since that time. We don’t have good, long-term estimates of lameness incidence, but many studies suggest that lameness rates are currently very high.
What producers can do today
Maintaining a healthy herd of cows is advantageous from both an economic and cow-welfare perspective. Fortunately, there is a range of traits available to dairy producers to help them improve the health of their herd through genetic selection.
The single-best tool producers have to select for healthier cows is predicted transmitting ability (PTA) for productive life. Productive life PTA is expressed as the number of months the daughters of a bull will survive in the lactating herd beyond the average cow.
Cow longevity is influenced by a variety of factors, including their fertility and milk production levels, but it is also heavily influenced by the health of a cow. Traits such as mastitis, metabolic problems like ketosis and uterine infections have all been favorably associated with productive life evaluations.
Selecting bulls with high productive life PTA is particularly important for herds that struggle with high mortality. The results from one of our evaluations suggested that one of every four cows that died on-farm could be eliminated by selecting sires with high productive life.
A second opportunity to help reduce disease incidence through genetic selection is less intuitive than selecting for productive life. Producers can select for lower dairy form. Dairy form is a measure of whether cows are angular and thin (high dairy form) or rounded and able to maintain body condition throughout lactation (low dairy form).
We have long selected for cows to be angular and thin because such cows were perceived as higher-producing and more efficient. However, research is clear that this is the opposite of what we should have been doing from a cow-health perspective, and there are many sires with high-producing daughters that are also able to maintain body condition.
Selecting against dairy form is counterintuitive for many, but low-dairy form bulls generally have healthier daughters. Similarly, many producers have selected for larger cows, but genetic research suggests that smaller cows could be healthier.
The other fitness traits available to producers include somatic cell score (SCS), daughter pregnancy rate (DPR), calving ease and stillbirth evaluations. All of these traits are effective in helping develop a healthier herd of cows.
Keep in mind, lower values are preferred for calving ease and stillbirth evaluations. DPR reflects the fertility of a bull’s daughters. Cows that are fertile experience fewer of the metabolic problems that plague infertile cows with extended lactations when they calve the following lactation.
One last option available to dairy producers is crossbreeding. The hybrid-vigor boost we receive when crossbreeding results in a reduction of most health problems. Crossbreeding might be the fastest route to a healthier herd, but there are many considerations that need to b e made before such a decision is made.
One area where we have few tools to help us from a genetic selection standpoint is foot health and lameness. Many producers emphasize foot and leg conformation traits, such as foot angle, in an attempt to reduce lameness incidence. Unfortunately, such traits have a weak genetic relationship to foot health and producers are unlikely to improve their herd’s foot health by considering such traits.
What the future might hold
Additional tools may be available to producers in the not-too-distant future to help select for healthier cows. Dairy producers record a lot of health data into farm management software. That data can be used to generate genetic evaluations for specific health events.
Such data is usually not uniformly recorded across farms and takes a lot of work to standardize, but sires with healthier daughters can be identified with that type of farm data.
There are concerns over who would have access to a farm’s cow health data that must be addressed, but our national genetic evaluations are shifting from the USDA to a private organization (the Council on Dairy Cattle breeding), which may help to reduce those concerns.
New technology innovations may also open the door to new genetic selection opportunities. Newer milk-testing equipment can evaluate milk samples for ketone bodies and specific fatty acids. We may be able to use such data to generate genetic evaluations for ketosis resistance, for example.
Activity monitors, rumination collars, bodyweight scales and other innovations all have potential to help us develop genetic evaluations for cow health events.
Healthy and productive
Dairy producers have proven it is possible to have healthy cows that produce a lot of milk through selection for healthier udders. There is an opportunity to extend our selection for healthier cows by emphasizing traits such as productive life and through the development of new traits from data recorded on-farm.
Genetic selection efforts cannot produce healthier cows overnight, but they are a critical part of the long-term strategy to develop cows that can withstand the rigors of high milk production. PD
Chad Dechow
Assistant Professor of Dairy Genetics
Penn State University
