Liveweight changes of steers, ewes and lambs in relation to height of green annual pasture

Abstract

Relationships were examined for weight (liveweight) changes of yearling steers and autumn lambing ewes and their lambs against height (median height) of green annual pasture. The sheep and steers grazed separately at five rates of stocking and together in seven ratios at one equivalent rate of stocking. Some aspects were examined in July in each of three years and others in winter and spring of one year. The lambs responded to an increase in pasture height up to at least 120 mm. The response was the same for the lambs 6 and 11 weeks old. The ewes lost weight about six weeks after lambing where the pasture was less than about 38 mm high and later responded to pasture height according to their earlier weight loss. The steers at the heavier rates of stocking lost weight on pasture below about 12 mm high, reached maximum rate of gain when it was about 120 to 140 mm, then gained weight at a slower rate on even taller pasture. The steers at the lightest rates of stocking did not respond to pasture height, although it was initially only 18 to 60 mm. The rate of weight gain of the lambs and steers in July increased in successive years on pasture of the same height. The year effect could have been partly due to differences in pasture density (lambs) and clover percentage (steers). At a given pasture height, the lambs generally grew faster with mixed than with separate stocking, but steer growth was the same for both methods of stocking.