Abstract
Cows in early lactation may respond favorably to as high as 17% dietary protein, but to routinely feed over 15% often is uneconomical. The needs of cows for protein during the last 3 or 4 months of lactation appear to be as low as 12%. The method of feeding NPN to dairy cows in partially satisfying dietary protein requirements is important. Incorporation of urea into concentrate feeds consumed at infrequent intervals has resulted in depressed milk yields in some studies. Incorporation of urea or ammonia into corn silage in other studies has resulted in milk yields as high as those obtained with controls fed natural protein diets. Ammoniated silage having more insoluble nitrogen than silage containing urea has slightly superior feeding value. Incorporation of urea into alfalfa pellets or into gelatinized grains are two methods for improving its value as a feed ingredient for dairy cows. Data were presented on two groups of experimental cows with similar lactation records (34 kg/cow/day) as supportive evidence to the proposition that high-producing dairy cows benefit from NPN additions to rations containing natural protein in excess of 11 to 12%. One group of cows receiving a 14% natural protein diet maintained this high productivity while consuming slightly less total feed than a second group which received a NPN-silage diet, but efficiency of conversion of feed dry matter to milk was the same for both groups. The NPN-silage diet contained 11.8% natural protein and 2.2% protein equivalent from urea. Further data are presented as supportive evidence to the above proposition in which milk production decreased in a reversal trial when urea was removed from alfalfa meal before pelleting the supplement part of a diet containing 11.6% natural protein. This trial was of limited scope involving four cows in 28-day feeding periods. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.