For the cow/calf producer, getting cows bred in a timely manner is critical for financial viability of the enterprise. For this reason, breeding season must be more than just turning the bull out with the cows, crossing your fingers and hoping for high conception rates. I recently came across a good article by Les Anderson, Beef Extension Specialist at the University of Kentucky about management practices and decisions that determine a successful breeding season. Here are excerpts from that article:
Reproductive management begins with evaluation and management of BCS. Body condition score is a numerical estimation of the amount of fat on the cow’s body. Body condition score ranges from 1-9; 1 is emaciated while 9 is extremely obese. (An OSU Extension fact sheet illustrating BCS is available on-line at: http://ohioline.osu.edu/factsheet/anr-54) A change in a single BCS (i.e. 4-5) is usually associated with about a 75-pound change in body weight. Evaluation of BCS prior to calving and from calving to breeding is important to ensure reproductive success.
Rebreeding performance of cows is greatly influenced by BCS at calving. Cows that are thin (BCS < 5) at calving take longer to resume estrous cycles and therefore are delayed in their ability to rebreed. Research has clearly demonstrated that as precalving BCS decreases, the number of days from one calving to the next (calving interval) increases in beef cows. Females with a precalving BCS of less than 5 tend to have production cycles greater than 1 year. Thin cows need a longer breeding season, which results in more open cows in the fall. They may also result in lighter calves to sell the next year because the calves from these thin cows will be born later in the calving season.
Management of BCS after calving also impacts rebreeding efficiency. Maintenance requirements for energy and protein increase 25-30% for most beef cows after calving. Rebreeding efficiency is enhanced in cows that calved thin if their energy intake is increased. Although the best management plan is to calve cows in a BCS of 5+, increasing the energy to cows that are thin at calving can boost reproductive performance.
Dystocia (calving problems) can severely delay the onset of estrus after calving. Research shows that for every hour a female is in stage 2 active labor there is a four-day delay in the resumption of estrous cycles after calving. Early intervention helps; 16% more cows conceived when cows were assisted within 90 minutes of the start of calving. The best method is to reduce the incidence of dystocia via selection but early calving assistance will increase the opportunity of cows to rebreed.
One often overlooked management tool that can improve reproductive performance is breeding soundness exams in bulls. Producers need to think of breeding soundness exams as breeding season insurance. These exams are a low-cost method of insuring that your bull is not infertile. Bulls should be examined for breeding soundness about 30 days before they are turned out.
Lastly, producers need to develop a plan to enhance the rebreeding potential of their first-calf heifers and late-calving cows. Young cows and late-calving cows have one characteristic in common that will greatly impact their reproductive success; anestrus. After each calving, cows undergo a period of time when they do not come into estrus. This anestrus period can be as short as 17 days but can also last as long as 150 days depending upon a number of factors. Typically, mature cows in good BCS will be anestrus for 45-90 days (avg about 60-70 days) while first-calf heifers will be anestrous for 75-120 days. Cattlemen can reduce the anestrous period by fence-line exposure to a mature bull or by treating the cows with progesterone for 7 days prior to bull exposure. Sources of progesterone include the feed additive melengestrol acetate (MGA) or an EAZI-Breed CIDRÒ insert (Zoetis Animal Health). Both sources have been shown to induce estrus in anestrous cows and exposure of anestrous cows to progesterone for 7 days before bull exposure will not reduce fertility. Pregnancy rates will actually be increased in these females because inducing estrus will increase the number of opportunities these cows have to conceive in the breeding season.