Sixty Israeli-Friesian cows were allocated, after calving, to five treatment groups of 12 cows per group according to the concentration and source of crude protein (CP) in the concentrate. Three groups received all their protein from plant sources: a basal control group (BP) was given concentrate containing 92 g CP per kg dry matter (DM), a medium-protein group (MP) was given a diet with soya-bean meal (SBM) added to give a CP concentration of 143 g/kg DM, and a high-protein group (HP) was given a diet with SBM added to give a concentration of 180 g/kg DM. Two groups were given the basal concentrate supplemented with urea (MU) or urea phosphate (MUP) up to approximately the same CP level as the MP group. The only roughage used was vetch-oats hay at a level of 350 g/kg total DM intake. The cows were given the experimental diets ad libitum throughout lactation.
No difference was found between treatments in DM intake (kg/day), mean milk and fat-corrected milk (FCM; 40 g fat per kg) yields (kg/day), milk protein concentration, days from calving to conception or services per conception, during the entire lactation period. However, FCM yields during 60 days after calving were significantly higher for cows given the CP-supplemented diets than for the BP group. The FCM yield of the cows given the HP concentrate was higher than for those given the other concentrate mixtures only during the first 15 days after calving. Milk fat concentration was higher in cows given the BP and HP concentrates than in those given the MP ration, but only a trend in this respect was observed when part of the plant protein was replaced by urea or urea phosphate.
The rate of body-weight loss after calving tended to increase with increase in amount of plant protein in the diet but was highest for the cows given the diets supplemented with non-protein nitrogen. Later in lactation, the body-weights of cows given the MP, HP and MUP diets increased immediately after they reached their lowest weight whilst cows given the BP and MU diets started gaining weight 165 and 120 days after calving, respectively.
Rumen ammonia-N and blood urea-N concentrations (mg/1) for treatments BP, MP, HP, MU and MUP were: 56 and 101; 120 and 226; 143 and 269; 191 and 227; and 179 and 212, respectively. The relationship between rumen ammonia concentrations, blood urea concentrations and CP utilization for the different treatments is discussed. Supplying urea as urea phosphate tended to improve performance by an increase in annual milk and milk protein yields as well as in live-weight gain.