a1 Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 2QS
An experiment was conducted to measure the response of spring-born suckled calves to supplementary feeding when they grazed, with their dams, on swards of different heights in the autumn. Two swards were maintained at mean heights of either 5·8 cm or 9·0 cm, and calves were offered 0, 0·76 or 1 -51 kg organic matter (OM) per day of a commercially available supplement for a period of 60 days until weaning. Supplement intakes by the calves grazing the taller sward increased throughout the 60-day period, but did not exceed 0·75 kg OM per day. There was no response in terms of calf live-weight gain to the provision of supplement on the sward maintained at 9·0 cm. On the shorter sward, intake of supplement increased at a greater rate and reached 0·75 kg OM within 3 weeks. Maximum intake by those calves offered 1·51 kg supplement OM per day was 1·25 kg OM per day. The provision of supplementary feeding when mean sward height was 5·8 cm resulted in a significant increase in calf live-weight gain (P < 0·05), although supplementary feeding did not fully compensate for the reduction in milk and herbage intakes because of partial substitution of supplement for herbage. During the winter after weaning the calves that had previously grazed the shorter sward showed increased live-weight gain compared with those that had previously grazed the taller sward but prior supplementary feeding was without significant effect in this group.
(Received June 27 1991)
(Accepted August 23 1991)