Abstract
Six pairs of Holstein cows were selected on the basis of lactation number, previous lactation yield and calving date. Beginning two months prior to calving, all cows were fed increasing amounts of urea as a constituent of a concentrate mixture. On the eighth day of lactation, the concentrate fed to one member of each pair was changed to a mixture in which an equivalent quantity of nitrogen was provided as soya bean meal; the other cows continued to receive the urea mixture. Roughages fed were those which were available at the time (tropical grasses, grass silage and sugar-cane tops) and were estimated to be sufficient for maintenance and production of about 3 kg of milk. For milk produced in excess of 3 kg the concentrate mixtures were fed at the rate of 1 kg for each 2 kg of milk. Urea replaced about 75 per cent of the nitrogen (which was provided by soya bean in the second ration) in the concentrate or about 50 per cent of the total dietary nitrogen consumption. Locally produced dried sweet potato chips and cane molasses (with some imported maize) comprised the concentrate energy feeds. Although total milk yield was significantly depressed, there were no significant treatment differences in average milk produced or in the average decrease in yield between the 4th and 32nd weeks of lactation, as a result of substituting urea for soya bean meal. A real difference in favour of soya bean meal was 0·9 kg of milk per day, representing a treatment difference of about eight per cent. The results are encouraging for the use of urea to replace up to 50 per cent of the total dietary nitrogen intake.
