As we approach and enter the calving season, many of us should be concerned with the body condition (BCS) of our heifers and young cows. Research has demonstrated that mature cows with a BCS of 4 or less at calving require 80 days to resume cycling after calving, whereas cows with a BCS of 5 or 6 at calving require 55 days to resume cycling (Houghton, 1990). First calf heifers likely require an additional 0.5 to 1 BCS at calving to achieve the same results. One misperception preventing producers from improving BCS is that a modest increase in nutrition will increase calving difficulty. Remembering the difference between a modest increase and an overabundance of protein and/or energy is important.

A modest increase in energy will lead to a rise in BCS without affecting calving ease. Research conducted by L.R. Corah (1975) revealed that a 35% increase in energy in the last 100 days before calving resulted in a 4 lb increase in calf birth weight with no difference in calving difficulty. Similarly, Bellows and Short (1978) demonstrated that a 90% increase in total digestible nutrient for 100 days prior to calving only increased birth weight by 4 lb. Even this tremendous increase in energy resulted in a negligible (4%) increase in calving difficulty.

However, pregnancy rates during the subsequent breeding season were improved by 15% or more in each study.

Improving the protein status of pregnant females can also improve BCS. A study by R.V. Anthony (1986) fed diets that provided 80% or 140% of crude protein requirements (a 60% increase). The greater crude protein diet increased BCS from 5.4 to 6.1. Yet, calf birth weight only increased by 2 lb, and there was no difference in calving difficulty.

One of the clearest representations of the effect of BCS on birth weight and calving difficulty is a series of experiments conducted by Wettemann and others in 1986. These researchers fed heifers to achieve a BCS of 4, 5, or 6 at calving. Each successive increase in BCS increased calf birth weights a modest 2-3 lb. More importantly, calving difficulty was not affected by BCS. However, each increase in BCS resulted in at least a 10% improvement in pregnancy rate in the following breeding season. Clearly, improving pre-calving BCS is integral to rebreeding success.

Additional benefits of improving nutrition prior to calving include improved colostrum quality, increased calf survivability, increased weaning weight, improved steer calf quality grade, and improved heifer calf reproductive performance. The benefits of improved nutrition are too important to ignore. Research has proven a modest increase in nutrition does not increase calving difficulty. It is also important to note that virtually all research indicates mature cows are even less susceptible to nutritionally-induced calving difficulty. Consult with your nutritionist to develop a program to improve your reproductive efficiency and cowherd performance.