Body-condition score at calving is the single most important trait determining when a cow resumes heat cycles and, therefore, when she is likely to re-conceive for the next calf crop, says Oklahoma State University Extension specialist Glenn Selk, PhD. However, he points out it also is very important to avoid condition loss between calving and the breeding season to maintain excellent rebreeding performance.
Selk cites a two-year OSU study comparing groups of cows that either maintained or lost body condition between calving and the start of the breeding season. Researchers allotted 75 cows in year one and 70 cows in year two into two groups. One group, intended to lose body condition, received 2 pounds of cottonseed meal from calving, beginning February 11, until mid April. The other group, targeted to maintain condition, received 5 pounds of cottonseed meal daily. All cows had free choice access to grass hay during February and March, and both groups calved in similar body condition.
Cows were exposed to fertile bulls for 90 days both years starting May 1, with pregnancy rate determined 70 days after the breeding season. Cows that were fed to maintain body condition from calving until the beginning of the breeding season averaged 94 percent pregnant, while pregnancy rates among those that lost nearly a full condition score were 73 percent. Body condition maintained throughout the winter until calving time must be continued until rebreeding to accomplish high rebreeding rates, Selk says.