A recent Oklahoma State University (OSU) trial with stockpiled hay contained a surprise. As discussed in an earlier column, warm-season grasses (not including fescue) should be supplemented with protein when grazed during the winter.
Working with Bermudagrass, this is exactly what the OSU researchers found. Cows grazing the stockpiled Bermudagrass from December 1 through January 22 lost 83.8 lbs. Cows supplemented with 2 lbs./day of a 25% crude protein supplement lost less than 20 lbs. (19.6 lbs.).
Although 83.8 lbs. is less than 10% of a cow's weight, it is important to realize that the weight loss occurred in only 49 days. In others words, the cows were losing 1.7 lbs./day. This was a university trial and the cows were taken off the experiment before any serious problems occurred.
In a real-life situation, however, if the cows had been left on the stockpiled grass unsupplemented until calving, the consequences could have resulted in "weak calf syndrome."
The surprise in this trial was that the crude protein content of the stockpiled Bermudagrass during the winter was not that much lower than during the fall. For example, the average crude protein during November was about 8.7%, whereas during December it was 7.7% and January 8.2%.
The researchers postulate that while the crude proteins appear similar, the digestibilities may have fallen significantly (due to winter vernalization). Although the actual digestibilities were not analyzed, that is a plausible explanation.
It's plausible because, without a doubt, the response to the supplementation was coming from protein. Proof is seen in the fact that during November there was very little response to supplementation.
Unsupplemented cows were gaining 1.3 lbs./day, whereas supplemented cows were gaining only about 0.2 lbs. more per day. As soon as cold weather hit, the change in bodyweight between supplemented and unsupplemented cows increased sixfold (see Table 1).
Results Don't Apply To Fescue Once again, I want to point out that results of this trial only apply to warm-season grasses, and would not be applicable to fescue, crested wheatgrass, Russian rye or other winter cereal pastures and/or cool-season forages.