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. However, it is also very important to avoid condition loss between calving and the breeding season to maintain excellent rebreeding performance.
Figure. 1. Winter weight and body condition change and rebreeding percentage for cows allowed to maintain or lose condition after calving (Wettemann, et al., 1987 JAS, Suppl. 1:63).
A two-year Oklahoma State University study (Figure 1) shows the impact of losing body condition in the period from calving to the start of the breeding season. Seventy-five cows in year 1 and seventy cows in year two were randomly allotted to receive either 2 pounds (LOSE) of cottonseed meal from calving (beginning February 11) until mid April or 5 pounds (MAINTAIN) of cottonseed meal daily. All cows had free choice access to grass hay during February and March. Cows were exposed to fertile bulls for 90 days each year starting May 1. Pregnancy rate was determined at 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% pregnant, while those that calved in similar body condition but lost nearly a full condition score were 73% rebred. The body condition that was maintained throughout the winter until calving time must be maintained until rebreeding to accomplish high rebreeding rates.
Glenn Selk, Oklahoma State University Emeritus Extension Animal Scientist