A COMPARISON OF UREA AND ALFALFA CUBES AS A SOURCE OF PROTEIN ENSILED WITH CORN SILAGE
Sixteen Holstein cows in mid-lactation were randomly assigned for a 35-day period to either corn silage supplemented with urea (4.95 kg/tonne) or corn silage supplemented with alfalfa cubes (90 kg/tonne) at ensiling time. These treatments were then reversed during a 7-day changeover period and the trial continued for a further 35 days. The silages were fed ad libitum and grain was fed in the parlor at the rate of 1.0 kg/4.0 kg milk yield. The protein and acid detergent fiber contents of the urea–corn silage were 11.6 and 25.3%, while those of alfalfa–corn silage were 11.1 and 28.6%. Cows offered the urea–corn silage consumed less forage dry matter expressed as percent of body weight, 2.04 vs. 2.11 and produced less milk, 26.08 vs. 26.86 kg/day (P < 0.05). During the feeding of the alfalfa cube–corn silage, cows gained an average of 4.09 kg/35 days, but lost 3.68 kg/35 days when urea–corn silage was fed (P < 0.05). There was no effect of form of nitrogen supplementation on milk composition or rumen volatile fatty acids, but blood urea nitrogen and plasma glucose were significantly higher (P < 0.05) and plasma calcium lower for cows fed urea–corn silage than for those fed alfalfa cube–corn silage. Apparent dry matter and protein digestibilities were higher for the urea–corn silage than for cows fed alfalfa cube–corn silage but digestibility of acid detergent fiber fraction was greater for cows fed alfalfa cube–corn silage.