On 6 Taranaki hill country farms, the effect of herbage mass and composition on the growth of lambs from birth to weaning was studied. On each farm 2 representative paddocks were selected and set-stocked with ewes from before lambing to weaning. Ewes and lambs were weighed at docking (early October), mid-November and at weaning in mid-December. Pastures were assessed fortnightly for herbage mass and composition. From docking to mid-November, no association between herbage mass and live-weight gain was found. The only factor influencing live-weight gain of ewes and lambs over this period was the percentage of green leaf material in the pasture. However, the live-weight gains of ewes and lambs from mid-November to weaning were negatively correlated with total herbage mass at lambing. Also over this period, live-weight gains of ewes were positively correlated with percentage of green, and negatively correlated with the percentage of stem, in pasture. With increasing levels of herbage mass at lambing there was associated decline in the percentage of green and increase in the percentage of stem in pastures over the mid-November to weaning period. Despite a large variation in stocking (11 to 26 su/ha) no relationship between stocking rate and live-weight gain of ewes or lambs was found. However, the total live-weight of lambs weaned/ha was correlated with stocking rate. The relationships established between pasture parameters and animal performance and between live weight of lambs weaned/ha and stocking rate indicate that higher spring stocking rates in Taranaki hill country than are presently adopted may decrease herbage mass at lambing thereby increasing the proportion of green herbage which will improve lamb growth and overall production/ha.
Proceedings of the New Zealand Society of Animal Production, Volume 46, , 125-128, 1986
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