The significance of differences in levels of feeding, before and after calving, on milk yield under intensive grazing

Abstract

The effects of varying the plane of nutrition immediately before and after calving on milk yield, milk composition, live-weight change, and feed intake were examined. In each of two years, individual members of 30 sets of identical twins were fed either to gain approximately 0.7 kg live weight daily, or to maintain live weight during the last 4 weeks of pregnancy. After calving, one half of the cows on each treatment was grazed at a medium (4.1 cows/ha) or a heavy (4.9 cows/ha) stocking rate. At the end of the first 8 weeks of lactation, butterfat yields were 21% and 15% higher in successive years for cows which gained weight than for those which merely maintained weight in the last month of pregnancy. Differences in fat yields associated with intensity of grazing after calving were significant in the second trial only. There were significant differences in milk composition associated with pre-calving feeding, but no significant interactions between pre- and post-calving treatments for milk yield or milk composition. Group dry matter intakes before calving were assessed by cutting, weighing, and drying representative samples of pasture before and after grazing, and by eye appraisal. The correlation coefficient between these methods was 0.82. Intakes before calving were compared with calculated requirements of cows in late pregnancy and with estimates previously published. Ways to use data from the present experiments for improving winter feeding of dairy cattle and rationalising grazing management programmes are outlined.