Reproductive Efficiency in Beef Cattle

Nutritional and Medical Considerations

Abstract

Cow-calf efficiency can be defined both in terns of biological efficiency and economic efficiency. Measures of biological efficiency include pregnancy rate, percentage calf crop weaned and calf weight weaned per cow exposed. Economic efficiency may be measured by net return per cow/calf unit or net return to the beef cattle enterprise. Biological and economic efficiency are often closely related, but in some situations only a limited relationship exists. For example, if biological efficiency defined as calf weight weaned divided by cow exposed is high, economic efficiency may or may not be high, depending on cow costs and the price of calves. Economic efficiency is of most importance to producers and is dependent on: 1) percent calf crop weaned, 2) weaning weight, 3) sale price of calves, and 4) annual cow costs (Ritchie, 1984). Maximizing production may not always be consistent with maximizing net profits over the long term. Identifying optimum levels of production ( those consistent with maximum continuing net profit) should be the goal. The optimum levels for reproductive measures such as pregnancy rate and percentage calf crop weaned are in fact high and quite close to maximum in most cases. Focusing on high reproductive efficiency at minimal cost is essential in moving cow-calf producers closer to optimum levels of production.

Where do reductions in reproductive efficiency occur? Bellows (1984) summarized losses in potentially weanable calves and reported that most losses occur either because cows fail to become pregnant or lose calves at or near calving. Nutrition is a major factor contributing to these losses. The purpose of this paper is to discuss factors, primarily nutritional, contributing to these losses.