Breeding Season Length Versus Calving Percentage in Beef Cattle Herds

Long breeding seasons result in long calving seasons. This results in calvings distributed through a range of environmental and nutritional conditions and a disparity in calf maturity at any planned weaning time. It also results in cows entering their period of maximal nutritional requirements over the same range of environmental conditions. Attempts to increase cow and calf productivity often include focusing the calving season on a "best" time of year by shortening the associated breeding season. In general, any beef production system which allows the periodic collection of all animals in the herd for examination, vaccination, and culling will utilize a limited breeding season in one form or another. The advantages of a limited breeding season, be it 1 or 6 mo, go far beyond the focusing of the calving season on the optimum environment. Limited breeding seasons allow, 1) defined annual check points for productivity and profitability, 2) annual herd health procedures at specific points in the growth and reproductive processes; 3) rational culling procedures based on reproductive success; and 4) assessment of replacement needs for herd improvement and maintenance of herd size. Short breeding seasons of only 40 to 45 d have been used successfully on a number of farms. However, many producers recognize, based on their experience, that herd calving rate may be unacceptably low when such a curtailed breeding season is used in their environment and with the resources at their disposal. This discussion will address the relationship between breeding season length and calving rate based on three of the most influential reproductive parameters, conception rate per estrus exposed, gestation length, and duration of postpartum anestrus.