Protecting fertility in the Summer heat
Published on Tue, 07/10/2018 - 2:17pm
Protecting fertility in the Summer heat
By Jaclyn Krymowski
In 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, there’s no single thing that can be done and be expected to resolve all issues. Heat abatement only works when there are multiple strategies at work. The basics that should be permanently in place on every farm include sprinklers, misters, and fans. For cattle on pastures or dry lots, these may not always be readily in place. Adequate shade, especially along the feedbunk is absolutely necessary in these cases.
Even the best heat abatement measures in place are not enough to return fertility and heat detection to normal. Another Florida study found that a herd utilizing different cooling system still saw significantly decreased pregnancy rates in the summer. Timed A.I. programs can be very helpful because they eliminate the need to rely on heat detection. When it comes to fertility losses, embryo transfer is an expensive, but effective, option. Fricke explained this works because only the earliest stages is an embryo is susceptible to the mother’s heat stress. An embryo placed into a donor cow is mature enough to withstand her heat fluctuations. In herds battling heat stress, embryo transfer can potentially double fertility, said Fricke.
Because embryo transfer is an expensive option, the individual situation must be evaluated to determine if it will be the profitable choice. Some factors include the cost of the embryo and transfer procedure and the degree to which herd fertility has been lost due to heat stress. A fact sheet by Professor P.J. Hansen of the University of Florida titled “Impact of Heat Stress on Female Fertility” gave a scenario based on a 2012 study in the Journal of Dairy Science to illustrate profitability. “As an example, consider the case where pregnancy rate in the summer is 15% to A.I. using conventional semen and 25% using embryo transfer with sexed semen. In this scenario, embryo transfer would be profitable. It would cost $1,157 to produce a female pregnancy using timed A.I., $1,042 to produce an embryo using an oocyte harvested by ultrasound, and $820 to produce an embryo using an oocyte recovered from a slaughterhouse ovary.”