From time to time, you hear through the grapevine that someone’s herd had an unusually high number of open cows at fall preg check time. That is when you wipe your brow and say “glad that didn’t happen to my herd”! In some cases, the poor reproductive response is isolated to a particular pasture, bull or age/management group and the origin of the problem may be easier to find. If not, the search for an answer will take longer and will be helped by accurate and complete records, and sometimes diagnostic testing. What follows highlights some of the starting points for troubleshooting.
Information on when cows did get pregnant during the breeding season can be very informative. This requires that pregnancy diagnosis occur early enough that pregnancies can be reasonably staged. The tools and experience of your veterinarian will determine when pregnancies are beyond a point where age can be determined accurately (generally best if longest pregnancy is under 100-120 days of age). If 60% or more of the cows are pregnant during the first three weeks of the breeding season, it is a reasonable assumption that a majority of cows were cycling at the start of the breeding season and that bulls were fertile at this point.
If detail on timing of pregnancy is not available, written records of cowherd body condition at the start of calving and breeding can inform the possible roll of nutrition on cyclicity. If open cows have low body condition at pregnancy check, review the nutrition program, weaning time and genetic potential for milk production and their match for the environment. Bull body condition and information on bull breeding soundness exams would indicate if the bull(s) were considered potentially satisfactory breeders at the start of the season. Was the bull to cow ratio appropriate for the age of bull(s) and pasture conditions and what if any breeding activity was observed?
Unfortunately, bull fertility is not a static trait. Think back through the breeding season about the incidence of footrot, pinkeye or evidence of neighbor’s bull(s)/cow(s) in the pasture. A bull could be temporarily infertile due to illness or injury and fine by the time the open cows are identified. Nevertheless, retesting bulls may be justified and screening for problems such as Trichomoniasis can occur at the same time.
A review of routine vaccinations, actual products and timing of administration to both males and females will likely be part of your veterinarian review. If any cattle were purchased, biosecurity practices and disease testing prior to introducing them to the main herd should be considered. Similar information from neighbors with fenceline contact may need to be explored as well.
While there can be a number of infectious causes of pregnancy loss, a few are much more likely to cause losses relatively early in gestation that would be noted at a routine pregnancy check around weaning time. Those would include Trichomoniasis, Camplyobacteriosis, Neosporosis, and Leptospirosis. Your veterinarian will know about the incidence of these problems in area herds and can tap into resources of the K-State Veterinary Diagnostic lab or similar as these possibilities are evaluated.
Various stressors such as a nutritional change, predators or extreme heat can cause early embryonic loss or reduced conception rates. Because animals are adaptable and vary in their tolerance to stress, it may be very difficult to assign one of these stressors as a cause of embryonic loss with complete certainty. While it may seem to the owner that everything is the same year to year, small annual changes such as increasing mature cow size, may show no negative impact until some other stressor comes into play to push the system past a tipping point.
Less than adequate nutrition is the most common cause of reduced pregnancy rates in cowherds. Good records documenting cow body condition at key times (especially pre-calving), vaccination and semen testing records will help narrow the focus when attempting to find the reason for a low pregnancy rate. It may take reviewing the list of possibilities many times before an answer becomes apparent. Producers that identify a poor reproductive response in the fall have more options, with potentially better economic outcomes, than those that wait until calving to see what happens. Happy preg checking.