The effect of two methods of feeding the concentrate supplement to dairy cows of high genetic merit

Two experiments were carried out with Holstein Friesian early lactation cow s of high genetic merit to evaluate the effects on intake and milk producti on when the animals were offered a concentrate supplement either within a c omplete diet (CD) or separately from grass silage (separate feeding, SF) th rough a computerized out-of-parlour feeder system. This system offered the daily allowance of concentrates in four x 6 h time windows and the cows cou ld choose to have several accesses to concentrate within each time window. In experiment 1 12 first lactation COWS were used in a two-treatment change -over design with 10-week periods, while in experiment 2 48 animals (28 in lactation 1 and 20 in lactation 2 or over) were used in a continuous design with an average of 80 days on experiment. In both experiments the diets on the CD treatment were offered ad libitum with a concentrate proportion of 0.61 in total dry-matter (DM) intake while on the SF treatment grass silage was offered ad libitum and the allowance of concentrate was made equal to the mean concentrate intake of the CD treatment during the previous week. A ll the animals in experiment 2 were turned out to pasture on 5 April for 12 0 days to examine the residual treatment effects. Twelve mid to late lactat ion cows and eight rumen-fistulated beef steers were also used to evaluate the effects of the two feeding methods on nutrient utilization and rumen fe rmentation, respectively. In the latter two trials, the concentrate on the SF treatment was also offered four times daily but in a conventional trough -feeding arrangement. In experiment 1 both silage and total DM intakes were similar between the t wo treatments. However, in experiment 2 silage DM intake was significantly increased (P < 0.001) and total DM intake tended to be higher. (P > 0.05) w ith the SF treatment. Feeding the complete diet tended to increase milk yie ld in both experiments (P = 0.057 in experiment 1), but significantly reduc ed both the concentration and yield of fat in experiment 2 (P < 0.05). Ther e were no significant treatment effects on the concentration of protein in either experiment, nevertheless in experiment 1 the yield of protein Teas s ignificantly increased (P < 0.05) with the CD treatment. When the animals i n experiment 2 were turned out to pasture, there were no significant residu al effects of the indoor feeding treatment on milk production, or yield of fat or protein. However, the concentrations of fat and protein in milk, obt ained during the first 60 days on pasture, were significantly higher for th e cows offered the concentrate separate from silage during the indoor feedi ng treatment. The nutrient utilization and rumen fermentation trials indica ted no significant difference between the CD and SF treatments in either wh ole tract apparent digestibility of nutrients (DM, organic matter, energy o r nitrogen (N)) or rumen fermentation characteristics (pH, ammonia-N concen tration, total volatile fatty acids (VFAs), or molar proportion of each ind ividual VFA in the rumen liquor). It is concluded that feeding the concentr ate within a complete diet rather than separately from the silage had no si gnificant effects on total DM intake, milk production, nutrient digestion o r rumen fermentation.