Responses to supplements by weaned lambs when grazing mature pasture or eating hay cut from the same pasture

Abstract

Weaned cross-bred lambs either grazed mature pasture or were confined to yards where they were offered material cut from ungrazed areas of the same pasture. A 1:2 mixture (on an air-dry basis) of sunflower meal and oat grain was offered for 81 days at 0, 200, 400 or 600 g/head or ad libitum. Individual estimates of intake of pasture and supplement by grazing sheep at four levels of supplementation were made on four adjacent plots.Weight gain increased from -30 to 178 g/day in the grazing animals as supplement intake increased up to 1030 g D.M./day and from -25 to 142 g/day in the yarded animals as supplement intake increased to 1076 g D.M./day. Growth of greasy wool increased from 4-5 to 11-7 g/day for grazing animals and from 4-5 to 10-2 g/day for those kept in yards.At levels of supplement intake below 400 g D.M./day, the intake of grazed pasture increased by up to 58% compared with unsupplemented animals. However, when the intake of supplement was increased to about 650 g D.M./day, pasture intake fell, with an estimated substitution rate of 1 -1 g D.M. pasture per g D.M. supplement. At all levels of supplementation, the intake of hay by the yarded lambs was less than half the intake of herbage in the field. However, at levels of supplement intake between 300 and 500 g D.M./ day, the substitution rate was similar to that measured in the grazing animals, suggesting that this is an attribute of roughage quality, rather than differential eating behaviour between grazing and yarded animals.The wastage, w (g D.M./day), of supplement was linearly related to the amount offered, s (g D.M./day), by the equation w = 0263s -38-8; R 2 = 089 Variability in supplement intake between individual grazing lambs was not affected by the level of supplementation but the coefficient of variation of supplement intake was considerably greater than that of the intake of unsupplemented pasture. Variability in the intake of pasture increased with the level of supplementation but variability in the total intake of food was similar at each level of supplement, indicating some degree of individual compensation in the intake of the two components. INTRODUCTIONgrazing animals than in the intake of those in yards. However, the results did not indicate whether the In an examination of the possible role of supple-higher level of substitution resulted from the poorer ments for weaned lambs over the summer, Freer et quality of the roughage available to the grazing al. (1985) found that when a mixture of sunflower lambs or from a possible inhibition of their grazing meal and oat grain was offered to lambs eating hay activity due to supplementation. in yards, their weight continued to increase at the The experiments reported here attempted to same rate up to high levels (1 kg/day) of supple-resolve this question by comparing the responses to mentation. However, when the same mixture was supplementation of weaned lambs that were grazing offered to lambs grazing mature pasture, the rate of mature pasture with those of lambs that received response was...

Evaluation of a remote drafting system for regulating sheep access to supplement

“…Substitution rates usually increase as the nutritive value and leaf content of forage improves and the ability of grazing sheep to select a better-quality diet than pen-fed sheep may have led to a greater substitution rate of lupins for forage under the grazing conditions than under the pen conditions. Similarly, Freer et al (1988) concluded that the higher substitution rate exhibited by grazing than by yarded lambs at moderate to high levels of supplementation (Freer et al 1985) was a result of the higher quality of the roughage consumed by grazing animals rather than differences in eating behaviour between grazing and yarded animals. However, the plateau in growth rate response in the present experiment at the relatively low level of 72.5 g/wether.day was unexpected, given that the growth rate response to lupins access in the pen experiments did not appear to have plateaued at 127 and 155 g/wether.day (Experiments 1 and 2, respectively).…”

Nutrient Requirements of Domesticated Ruminants

“…Recent advances in the use of alkane markers for the estimation of the separate intakes of herbage and supplements by grazing animals (Mayes and Dove 2000) provide promise of a wider range of information in the future. If the supplement can rectify defi ciencies in the herbage of nutrients such as nitrogen or sulfur, which are restricting the activity of the microbial population in the rumen (see Chapter 3), then the intake of herbage may increase and the substitution rate will be negative (Freer et al 1988). The results of fi eld experiments reviewed by Allden (1981) show wide variability in the responses of grazing animals, but the model being described here allows these supplements to increase herbage intake up to the point where the calculated intake of RDP is no longer defi cient.…”