Protecting fertility in the summer heat By Jaclyn Krymowski for American Dairymen Magazine
n the midst of summer, heat abatement is a commonplace battle for most dairymen. The stress of excessive heat is an obvious concern for the animals’ welfare and efficient milk production. But the shadow of its impact reaches as far as reproduction. An understanding of how the rising mercury interacts with a cow’s reproductive physiology is necessary to prevent major fertility and heat detection losses. A cause for concern
Heat stress hurts reproduction in two different ways. It impairs fertility (in both cows and bulls) and decreases the heat detection rate. For example, a 1986 study on a dairy in Florida found that only 18-24% of heats were detected in the hotter months compared to 45-56% of detections in the cooler seasons. Decreased physical activity due to discomfort is a big contributor to this kind of change. “High producing dairy cows produce a lot of internal heat simply as a byproduct of the increased metabolism associated with this very high level of milk production,” said Paul Fricke, a dairy reproductive specialist at the University of Wisconsin
in an extension podcast. To regulate their body temperatures, they must lose some of their heat via dissipation into the outside environment. When outside temperatures increase it becomes more difficult to naturally dissipate that heat. Cattle compromise for this through increased respiration by panting. “…the duration and the intensity of estrus expression is dramatically decreased, so if becomes harder and harder to see cows in estrus,” said Fricke. The other issue is decreased fertility. The first few days following ovulation the embryo is highly sensitive to the cow’s body temperatures. An animal that is heat stressed will have a negative impact on an embryo
at such a vulnerable stage. “There’s a class of proteins called heat shock proteins that can actually prevent the problems,” said Fricke. “But because in this early state of development, these proteins aren’t able to be synthesized. (Therefore) This early embryo is highly susceptible to the elevated maternal body temperature. So, what we see is a decreased conception rate which is associated essentially with early pregnancy loss.” Dr. Vicki Lauer, professional services veterinarian for Animart, added heat stress can last as long as 40-50 days after exposure to high temperatures. She noted breeding bulls will also suffer decreased performance resulting from less activity and poor sperm production. Some studies show it can take 6-12 weeks for a bull to completely recover lost sperm production due to heat stress.
What can be done?
There are lots of tools which can effectively combat heat. That said, * Continued on page 24