THE EFFECT OF DIET IN WINTER ON THE BODY-COMPOSITION OF YOUNG STEERS AND SUBSEQUENT PERFORMANCE DURING THE GRAZING SEASON

Friesian steer calm born in August were reared from 3 to 7 months of age on silage alone (S) or on silage and concentrates to supply metabolizable energy (ME) in the proportion of 0.5: 0.5 (55) or 0.1 : 0.9 (19). The mixed diets were either offered to appetite (55A and 19A) or restricted to provide the same energy intake as the S group (55R and 19R). The cattle were then grazed for a 6-month period as a single group. During the winter the S, 55R and 19R groups had similar live-weight gains. Despite having the highest nitrogen intakes the S group deposited less protein, but more fat than the other two groups. There were no significant differences within A or R groups, but the A groups had higher live weights, empty-body weights and carcass weights than the R groups and had more fat and less protein per kg empty body weight at turn-out to grazing. Compensatory growth was exhibited by the S, 55R and 19R groups during the grazing season. It arose because of differences in intake and not because of differences in the energy content of the gain. Intake was inversely related to the level of fat per kg empty body weight at the start of grazing. There was no evidence that the nature of the diet in winter had an effect on subsequent herbage intake. It was concluded that diet per se in winter had no residual effect on intake at grazing, but that it did have direct and residual effects on the relative deposition of fat and protein which could lead to an association between the level of fat in the empty body and intake. Inefficient use of nitrogen from silages with moderate fermentation characteristics was also demonstrated.