Even with the best of intentions situations exist where the calving season gets to be longer than ever intended. Conditions that result in poorer body condition at calving and breeding can lead to delayed return to estrus and a long calving season the following year. The calving seasons could get long rather abruptly due to disease outbreak or bull infertility or gradually get longer and longer over several years. Sometimes heifer development or young cow nutrition shortfalls create the problem.
Whatever the cause, long calving seasons reduce weaning weights and increase variation in those weights. To determine the best route back to a tighter calving season, it helps to review the influence of days postpartum and body condition on when cows might be expected to begin cycling again after calving.
In a 60-day breeding season, a cow that was bred on the last day of this year’s breeding season will only be 22 days postpartum at the start of the next year’s breeding season. In contrast, a cow bred on the first day of this year’s breeding season will be 82 days postpartum at the start of next year’s breeding season.
Data from over 3000 Kansas cows (Figure 1), predicts that approximately 70% of cows that are 81 to 90 days postpartum would be cycling at the beginning of the breeding season and less than 10% would be cycling when less than 30 days postpartum. If a 90-day breeding season is allowed, then the last cow to be bred is just one week from calving at the start of next year’s breeding season. If she is in good condition this cow may have one and possibly two opportunities to conceive before the end of a 90- day breeding season.
Source: www.cattlenetwork.com
