By Sandy Johnson, extension beef specialist, Colby and Gregg Hanzlicek, DVM, Veterinary Diagnostic Lab
When the number of cows pregnant is far below expectations, poor reproductive performance by both cows and bulls must be considered. Keep in mind that in some cases multiple issues may contribute. This article will focus on the female and highlight questions that are typically asked when troubleshooting low pregnancy rates.
The most common reason for poor pregnancy outcomes is related to nutrition. Heifers may not have achieved sufficient growth in time for breeding and cows may not have the needed energy reserves to resume normal cycles and rebreed. A number of disease issues can occur that impact pregnancy rate and the nutrient status of the female will impact her ability to withstand the challenge or develop immunity in response to vaccination.
Did females achieve an appropriate weight and body condition by the time of calving? Bred heifers should reach 85% of mature weight by first calving in a body condition of 5.5 to 6. For raised replacements, weight of mature cows should be known. In other cases, estimates should be realistic. Replacement heifers should be weighed and body condition scored periodically to monitor progress towards weight and condition targets.
Mature cows need to gain about 150 pounds in weight of the fetus and fluids before calving and should be in a body condition score of 5 at calving. Adequate body condition at calving is considered paramount to successful re-breeding. Given the quality of typical feed resources and the level of milk production in the US cow herd, meeting total energy demand for milk production with enough left over to increase body condition is extremely challenging. A positive energy balance is needed to end postpartum anestrus. If the environment is such that the cows lose condition after calving, they must have enough condition so they can lose some weight and still cycle and rebreed in a timely fashion.
This emphasizes the importance of monitoring body condition year-round to avoid the need to add body condition when nutrient demands are high and considerable high energy supplementation is needed to improve cow condition. Too often this gap is not filled and low pregnancy rates result. In extreme cases, calving time brings weak calves, poor colostrum and low milk production. A number of resources are available to learn how to body condition score and track changes through the year. See…Guide to Body Condition Scoring in Cows and Bulls, Body Condition Score Card, Body Condition Scoring Record Book. Extended and unexpectantly harsh winter weather conditions can catch producers with a bigger energy drain than normal feedstuffs can address. Failure to make adequate adjustments will show up in reduced pregnancy rates and in extreme cases, mortalities.
Were feedstuffs analyzed for nutrient content and rations balanced accordingly? Maintaining necessary body condition requires accurate information on the quality of feedstuffs so any deficiencies can be met. The use of “book values” to balance rations has been the cause of more than one instance of poor pregnancy performance.
Do you know how much cows weigh and use this to determine stocking rates and feed delivered? Weight of the animal is a major determinant of how much an animal eats. Pastures should be stocked by weight rather than number. Historical stocking rates may not reflect current mature cow size. If actual weights are not available, weight of cull animals adjusting for condition can help with estimates.
When was the poor reproductive performance noted? Often both late term abortions and weak calves are observed in the same herd simultaneously if vitamin or trace mineral imbalances are a factor. Vitamin and mineral imbalances may contribute to lowered reproductive performance, however, overall protein and energy status are more likely to explain a large number of open females. A large number of cows cycling late in the breeding season or after the end of the breeding season often point to a disease issue such as Trichomonas.
Were more open females observed in any particular age or management group? Because they are still growing and experience more calving difficulty, young cows often represent the largest share of opens. Females that are still growing have different nutrient demands than mature cows and because of size may not be able to get their share of supplied nutrients if managed as a group.
Did 2-years olds calve in advance of the mature cows? Young cows need more time to resume normal estrus cycles following calving. Breeding heifers 2 to 3 weeks ahead of mature cows helps keep young cows on schedule. There may be exceptions to this recommendation if the genetics are well suited to the environment and stressors such as calving difficulty are absent.
Did open 2-year olds calve early or late in relationship to contemporaries? Heifers that conceive in the first 2 cycles of their first breeding season are in the best position to rebreed in a timely manner in subsequent seasons and remain in the herd longer.
What biosecurity practices are in place? Quarantine all purchases and don’t buy used cows less than 120 days pregnant to avoid Trichomonas. If a neighboring herd has no biosecurity (trades cows) some type of set back fence may be needed to prevent close contact.
Are females vaccinated appropriately for your location and disease challenges? Typically, annual vaccinations should include IBR, BVD, Campylobacter (Vibro) and Lepto. Consult with your local veterinarian on use of killed and modified-live vaccines and timing to avoid causing abortions.
Was the breeding season length appropriate? -In a well-managed herd, a 60-day breeding season should allow a pregnancy rate of 90% or greater. If something unexpected happens to reduce the number of cows pregnant in the first cycle of a shorter breeding season, the risk for a poor pregnancy outcome is greater than with a longer breeding season when there is more time for those cows to conceive. Ways to maintain a relatively shorter calving season and minimize risk of a poor pregnancy outcome include an early pregnancy check (30-45 days into the season) with the potential to extend the breeding season or leaving bulls out longer and pregnancy checking early enough to stage pregnancies. Consideration could be given to retaining some late bred females if the early response was poor. The down side of the early pregnancy diagnosis is the need to reconfirm pregnancy because of the normal attrition at that stage. The goal should be a tight calving season and optimizing returns from opens or late bred cows that don’t fit the production system.
Shortening a very long breeding season (>100 days) with a number of gradual steps can result in higher pregnancy rates than previously experienced with extended breeding periods. If cows have poor body condition at calving, and nutrition is of marginal quality or quantity post calving, a short breeding season will typically be disappointing. Mature cows in good body condition take 45 – 55 days to resume normal cycles after calving, young and thin cows often take twice this amount of time. This information combined with what we know about early embryonic loss can be used to project when and how many cows will become pregnant in the subsequent season. Some producers elect to use a very short breeding season to select heifer replacements. If doing so, be realistic about how many are cycling before the start of the breeding season and will get pregnant the first cycle. If you want to give most heifers a second chance to conceive, recognize that return heats from a synchronized estrus will come over an 8 to 10-day period or more.
Was the bull:female ratio appropriate for the situation? – For bulls under 24 months of age, the general rule of thumb is one cow per month of age of the bull. Mature bulls can be placed with 25 – 30 cows depending on pasture size. This ratio can become functionally altered if a bull gets sick or injured. If the “right” bull is injured, there may be very little impact, but disastrous if the “wrong” bull is injured. A literature summary of bull:female ratios used after ovulation was synchronized and all cows were fixed-time inseminated on the first day of the breeding season found similar season long pregnancy rates for ratios of 1:25-30 or 1:40-50 (assume 50% pregnant to AI and 50% of cows remain for natural service). Those inexperienced with AI or reason to fear a poor AI response may want to take a more conservative approach. Studies of use of natural service with estrus synchronization have shown normal bull to cow ratios (1:25-30, not extensive pasture size) can be used successfully with mature bulls. This supports the idea that return heats after successful synchronization and AI do not require additional bull coverage. However, in both cases, activity should be monitored closely in case of bull injury. Too many bulls may be counterproductive in the case of inexperienced yearling bulls covering a synchronized estrus or cycle after a synchronized estrus.
Were there any weaknesses in an estrus synchronization and AI program? The goal of an AI program is to get lots of cows pregnant on the first day of the breeding season to the desired genetics. There are many details that must be in place for a successful AI program and the results will be no better than the weakest of these. See the publication Tips for a Successful Estrus Synchronization and AI Program and other materials at www.beefrepro.org. When the AI program has a poor response, it will have trickle down impacts on the natural service season. At minimum it delays rebreeding. If the estrous response of the females is low, expect a poorer outcome and adjust the number of natural service sires or length of breeding season. Several good options are available to synchronize estrus and ovulation and are identified in resources provided by the Beef Reproduction Task Force at beefrepro.org. Numerous failures in synchronization protocols come from being fooled into using something not on this list or attempts to modify protocols without fully understanding the physiology.
Reproduction drives profitability in cow/calf enterprises. The use of this guide should help troubleshoot and avoid common problems with low pregnancy rates.
Thank you for this article. It is very helpful and thorough.