The Utilization of Urea by Dairy Cattle

The value of urea in the ration of lactating dairy cattle has been reported by various workers (1,7,14,15,19).These reports show that the urea can be used effectively as a partial source of nitrogen and can replace at least partially the high protein supplements in the concentrate mixtures.No data were found in the literature concerning the supplementation of the ration of dairy cows with DL-methionine when urea was included in the ration.However, Bailey and Ross (2) found that cattle apparently can use inorganic sulphates and that methionine had no apparent advantage over Na~SO4 when used in the ration.Other workers (10, 11) reported improved urea utilization when methionine was added to the ration of sheep.When an alfalfa hay ration of dairy cows was supplemented with 20 and 40 g. of L-cystine no benefit was observed (8).Similar results (18) were obtained with L-cystine when fed to sheep. EXPERIMENTAL PROCEDUREThe data reported here covered three experiments conducted during the barn feeding periocl over a 3-yr.span.The experiments are designated as trials 1, 2 and 3 in the order in which they were completed.Twelve cows were used in each of the trials and divided into three groups of four cows each according to the experimental design outlined by Cochran et al. (4).Every cow was On each of the experimental rations used in a trial.An adjustment period of 10 days was followed by three 20-day experimental periods with a 5-day change-over period between the second and third experimental periods.The cows were weighed at the beginning and end of each period on 3 consecutive days.Roughage consumption for each cow was held to a constant amount.Daily milk production weights were recorded on each cow and 1-day composite milk samples were taken at 10-day intervals to determine the butterfat content of the milk.The levels of feeding were determined according to Morrison's (13) minimum standards for maintenance and milk production.The concentrate allowances were adjusted at the beginning of each experimental period on the basis of milk production and body weights during the adjustment and change-over periods, as recommended by Lucas (12).Digestion trials were conducted during the last week of each experimental period according to the procedure outlined by Eheart et al. (5).During trial 1, three different cows were used for each digestion trial, while during trials 2 and 3, the same three cows were used for each digestion trial.