Several studies at the Gudmunsen Sandhills Laboratory in Nebraska looked at the value of protein supplement for wintering spring-calving cows. One study was conducted with cows grazing winter range and a second study was conducted with cows grazing either winter range or corn stalks. In each study, half the cows were fed the equivalent of 1 lb./head/day of protein supplement (either 42% or 28% CP, depending on the study) three times per week from December 1 through February 28 while the other half were not fed any supplement. In both studies, cow weight and body condition at calving were greater for cows fed supplement but breeding rates were not different between the two groups. Steer calves from the supplemented cows had greater pre-weaning gains and weaning weights than those from un-supplemented cows. Economic returns from protein supplementation differed between studies. In one study, protein supplementation improved returns from steer calves because of an increased number of live calves at weaning, while in the second study, returns on steers were only increased when steers were retained to slaughter with steers from supplemented cows having greater carcass value.
Performance of heifer calves was also evaluated. In one study, heifers born from cows receiving winter supplement had greater pre-breeding body weights, higher pregnancy percentages, and more of them calved in the first 21-days of the calving season than those born from cows that were not fed the supplement. This did not hold true in a second study, even though heifers from cows receiving winter protein supplement tended to be slightly younger at puberty.
These studies suggest that winter protein supplement may have a greater effect on subsequent calf performance than it might have directly on reproductive performance of the cows fed supplement. It is important to note that body condition scores of all cows in these studies was greater than 4.5 and reproductive performance might still be affected if condition dropped much lower than this. A consistent economic value of providing winter protein supplement to cows was recognized if steer calves were retained through slaughter.