Urea as a partial protein substitute in the feeding of dairy cattle

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Abstract
Urea was fed to 7 lactating cows in an amt. equivalent to 33% of the N of the production ration or 25% of the total N intake. Periods on the urea diet were compared with periods in which urea was replaced by the N equivalent of blood meal and with periods in which neither urea nor blood meal was fed. The milk yields of 5 cows were maintained on the urea diet; with the 2 other cows the lactation curves were difficult to interpret. The composition of the milk was not adversely affected by urea feeding. Changes in body wts. were small but were somewhat better maintained on urea than on blood meal. Urinary and fecal N were estimated in all exptl. periods. The dietary urea was not completely retained, an average of 25% (range 12%-47%) passing through the animals unutilised. This apparent wastage of urea was much reduced when urea feeding was preceded by a N-deficient diet. Though increasing the urinary volume, urea feeding did not result in any harmful diuresis. The concs. of urea in the blood and milk were similar and never exceeded 28 mg./100 ml.