Understanding early embryonic loss in beef cows
On average, fertilization is achieved 90-95 percent of the time when a cow is bred through natural service or artificial insemination (AI). However, roughly only 60 percent of the cows remain pregnant from that same single service.
These are numbers that Research Scientist Tom Geary, Ph.D. of USDA-Agriculture Research Service, Fort Keogh in Miles City, MT, has been studying. Embryonic mortality is something that is affecting the beef industry both on the seedstock and commercial levels.
“Embryonic mortality is a likely culprit anytime there is a major shift in calving distribution,” Geary said.
Most of the embryonic loss occurs before day 20 and doesn’t disrupt a cow’s estrous cycle. Embryonic mortality occurs roughly 25 percent of the time when maternal recognition of pregnancy fails.
“It is easy to detect embryonic loss from day 28-45 but those aren’t the ones that are causing the problems for producers,” Geary said.
What can be gained by more cows and heifers conceiving at the first breeding and maintaining a pregnancy?
“Calving seasons would be shorter—it’s important to tighten those down,” stated Geary. A shorter calving season increases profitability by enabling producers to manage cattle better according to their environment.
He also points out that seedstock bulls born early in the calving season are more likely to make the cut for the bull sale.
“Right now I’m not sure if some producers realize the amount of embryonic mortality that is happening,” Geary said.
Geary estimates that the cost of embryonic failure to the beef and dairy industries with today’s prices could easily be $2 billion annually in lost productivity.
Progress in finding out when and why a pregnancy is failing during the first few weeks after fertilization is difficult without earlier pregnancy diagnosis. Now, with very extensive tests and detailed blood sampling, pregnancy can be detected as early as day 17-18.
Generally, day 28 after breeding is the earliest pregnancy can be determined with ultrasound or blood tests.
Collaborative research with colleague Mike Mac- Neil and Dr. Mike Smith at the University of Missouri has identified the factors that are most important for maintaining a pregnancy when timed AI is used.
An increased level of estradiol in a cow’s blood at the time of breeding is the single most important variable that affects fertility.
Estradiol is the predominate estrogen produced when the cow is in estrus (heat) and ovulates, so with natural service, this is not a limitation.
Other factors that affect fertility are progesterone levels on day seven after breeding, progesterone before breeding and the ovulatory follicle size.
Although informative, it is key to keep in mind that these factors are not mutually exclusive as these are all factors that exist together during fertilization and early embryonic life.
“As a whole that only accounts for a small percentage of the variation in pregnancy success,” Geary said.
These findings support the role of progesterone from CIDRs because of the increased synchrony that is gained in a timed AI situation. Use of a CIDR also improves a producer’s ability to induce estrous cycles among anestrous cows.
“Tight synchrony is obviously the key, along with the appropriate timing of AI related to peak estrus,” Geary said.
Management practices to limit reproductive losses
Limiting handling stress is one step cattlemen can take to decrease negative effects to reproduction.
“Try to decrease handling stress for heifers especially,” said Geary.
Heifers react differently to stress than do cows, particularly handling stress.
Cows are more conditioned and maybe not stressed out as much because the situation is not new to them.
“It all depends on what the animal perceives as stress,” Geary said.
The best time to move or transport cattle is right after breeding (within 24 hours). The critical window to maintain a low-stress environment is from day 12-15 after AI.
With all this said, Geary understands that producers sometimes have to move animals at inopportune times and oftentimes have been doing it for years. Embryonic mortality is nothing new, so producers who need to do this have learned to accept a certain level of viable pregnancies.
Geary pointed out an example of another stress factor that is out of ranchers’ control. He mentioned how the reintroduction of wolves in the Western states could be having an effect on cattle reproduction, specifically pregnancy rates.
Dr. Reinaldo Cooke and colleagues at Oregon State University have conducted research on the stress effects of wolves by introducing cattle to the sounds and smells of wolves and visual stimuli of dogs. The study showed a link between the predator influence and stress. Elk have also been shown to have lower pregnancy rates in areas where wolves exist and some of this is suspected to be due to stress.
Researchers from South Dakota State University, University of Wyoming and University of Minnesota found that post-AI nutrition has an effect on pregnancy rates. Specifically, a decrease in plane of nutrition resulting in loss of body weight can decrease pregnancy rates among heifers.
Geary says that during periods of drought it is important to supplement appropriately to maintain nutrition.
He also urges producers to keep good records during synchronization and breeding. The information can help identify any causes of decreased fertility in their herds if the problem arises.
The other side of the equation
Male fertility may account for pregnancy failures, as well. A Fort Keogh field trial suggested that 10 percent of the time fertilization is achieved by less than optimal sperm which could result in loss of pregnancy.
Science is beginning to uncover the role of the male in fertility. In the future, there may be a test that can help characterize a bull’s fertility. Breeding soundness exams could incorporate a simple test that detects bio-markers that are associated with lower fertility, for example, the amount of marginal sperm within a semen sample.
“Pay attention to bull fertility and the role it could play in pregnancy,” Geary said.
Each bull is expected to contribute to the production of 20-30 calves, so the fertility of each bull is at least 20 times more important than a single cow’s fertility.
Science is getting better at measuring embryonic mortality and Geary wishes he could identify all the factors that pertain to pregnancy in cows.
He and his colleagues are looking for the additional mechanisms involved in embryonic mortality. After they are recognized, researchers can go back in a whole herd perspective and figure out what goes on in order to increase fertility. — Rebecca Mettler [This article was originally written for American Red Angus Magazine, republished here with permission.]