With spring calving in full swing, it is a good time to start thinking about if your cows are prepared for breeding season. Making sure your cows are in a good body condition score prior to calving is one of the most important steps to ensuring your cows stay on track to rebreed whether you plan to turn bulls out, synchronize, AI, or a combination. If you plan to utilize synchronization to tighten your breeding season, there are a few things you should consider.

Good Year-Round Nutrition and Adequate Body Condition Score (BCS)
One of the biggest impacts on rebreeding success is BCS at the time of calving. Traditionally, it is recommended that cows should be at a BCS of 5 (1^st calf heifers should be at a BCS of 6) at calving for optimal reproductive performance. While postpartum interval has been shown to shorten with increasing BCS, it is not economical to feed beef females to a BCS of 7 prior to calving. A review of multiple studies evaluating BCS on postpartum interval found that a cow in a BCS of 5 or 6 can return to cyclicity 10 – 18 days sooner than a cow in a BCS of 4 and 29 – 37 days sooner than a BCS of 3. However, in some cases, cows can be capable of rebreeding at a BCS lower than 5 due to individual variation. This can largely be attributed to the direction of weight gain or loss after calving. Studies have found that thin cows, that are on an increasing plane of nutrition and gaining weight, can have equivalent pregnancy rates as cows in moderate condition that are maintaining their body weight. However, thin cows that are determined to be losing condition can have a reduction in pregnancy rates up to 30%. It can be difficult to improve body condition on thin cows after calving because their nutrient requirements are the highest that they’ll be all year. Sorting cows into groups by BCS 90 days prior the calving season can help provide extra supplementation as well as utilizing estrus synchronization protocols to help thin cows return to estrus. More information can be found on this topic in “Body Condition Score and Getting Thin Cows to Rebreed.”

Good Record Keeping
Anyone who has used an estrus synchronization protocol knows that timing is critical and keeping track of dates of injections can be the difference between success or a lot of wasted money. Even if the weather is not ideal, giving injections or breeding on time is key. Synchronization protocols are very time sensitive and may be less effective or fail if not followed correctly. UNL has many resources listed on the Beef Reproduction website such as the “Estrus Synchronization Planner” that has been developed and maintained by Iowa State University to help plan and schedule protocols as well as UNL’s own “Breeding Cost Cow-Q-Later” to help make financial decisions on the most economical protocol for your herd.

Bull Management
As with most segments of the cattle industry, implementing health programs is key to maximizing animal performance. It is important to note that when utilizing an estrus synchronization program with natural service, the breeding pressure on the bull increases. A low performing bull that has been sneaking by can cause a synchronization protocol to fall apart. It is important to have annual breeding soundness exams performed on bulls 60 days prior to the breeding season to ensure that they are at peak performance. Unfortunately, breeding soundness exams do not evaluate libido so utilizing a bull with proven breeding drive is wise when synchronizing cows as they will have more ground to cover in a shorter amount of time. Evaluating bull BCS 90 days prior to the breeding season is also recommended as bulls are expected to lose between 100-200 lb during the breeding season which could be equivalent to 1-2 BCS. If utilizing AI make sure that semen is collected or purchased from a Certified Semen Services lab.

Skilled  Labor
Variation in pregnancy rates between AI technicians can be up to 20% or more according to a review by Kansas State University. Keeping records on individual technicians can help you identify problems. Heat detection also requires a skilled eye and having experienced and reliable labor identifying females in estrus can determine the success of synchronization with AI. Heat detection is simply observing for changes in behavior such as cows/heifers standing to be mounted by a bull or another female. However, knowledge of secondary signs of standing estrus such as mounting other females, clear mucus discharge, or swollen vulva are important in identifying females approaching standing estrus. Checking for heat 30 minutes, twice a day is considered a minimum for Bos taurus cattle. Increasing the frequency of heat detection may help identify less expressive females. The use of heat detection aids such as tail chalking or heat-mount patches are also useful tools which will aid in estrus detection.

Calving Distribution
Multiple studies have shown that cows calving in the first 21 days of the calving season are more likely to respond to synchronization and AI. Although some synchronization protocols help induce estrus and ovulation in non-cycling cows, cows that calved at less than 20 days just before the breeding season will not respond to synchronization. While CIDRs are labeled for use at a minimum of 20 days post-partum, uterine involution (recovery from calving) takes approximately 30 days so synchronization response earlier than that may be low. However, utilizing CIDRs on your late calving cows may help them catch up. Annual synchronization programs help gradually increase the proportion of cows that calve in the first 30 days of calving and eventually increase pregnancy rates to AI. For a first time synchronization, consider starting with heifers and early calving cows. A good protocol to begin implementing estrus synchronization is the one shot prostaglandin with natural service to start tightening your herds breeding season.

Other Considerations
Other factors that may impact the success of an estrus synchronization program are cow age (first calf heifers tend to take approximately 20 days longer than mature cows to resume estrus), good low-stress facilities, effective vaccine and health program (some combinations of synchronization protocols with routine vaccination has shown to reduce pregnancy rates), utilizing the correct protocol (some protocols are recommended for heifers vs mature cows) and, of course, attention to detail. Visit the Beef Reproduction Task Force website for more information.

Interviews with the authors of BeefWatch newsletter articles become available throughout the month of publication and are accessible at https://go.unl.edu/podcast.