Retention of energy and nitrogen by young sheep on different feeding patterns

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Abstract
In each of two experiments the comparative slaughter technique was used to compare the retention of energy by young Border Leicester × Merino wethers when the same total amount of food was offered according to two different feeding regimens. These were designed to simulate, in pens with a diet of pelleted lucerne, feeding patterns typical of continuous and intensive rotational grazing.In the first experiment ten 9-month-old sheep that were offered the same amount of food daily (mean intake 367 g digestible organic matter) during each of 14 weeks made mean daily gains of 39 g live weight, 6·3 g body fat and 0·59 MJ (140 kcal) energy compared with a gain of 30 g live weight, a loss of 1·4 g body fat and a gain of 0·28 MJ (67 kcal) energy by a similar group that ate the same total quantity of food but in amounts that ranged, during each week, from 1·8 to 0·1 times the daily intake of the other group. This cyclic feeding pattern caused a small decrease in the digestibility of dietary organic matter.In the second experiment two similar feeding patterns were compared with ten pairs of 3-month-old sheep eating twice as much food each week as in the first experiment. One member of each pair was, in each of 13 weeks, offered food ad lib. for 3 days and then amounts falling to 20% of voluntary intake on the seventh day; the other one ate the same amount of food each week but in seven almost equal feeds. The latter sheep gained, on average, 132 g live weight daily and retained 58 g body fat and 2·96 MJ (707 kcal) energy compared with 124 g live weight, 49 g body fat and 2·61 MJ (624 kcal) energy by the sheep on the cyclic feeding pattern. In neither experiment was wool growth affected by feeding pattern.The greater effect of the cyclic feeding pattern in reducing the efficiency of energy retention in the first experiment is attributed to the higher number of days each week during which these animals were estimated to be in negative energy balance. These results suggest that adverse nutritional effects of a fluctuating feeding pattern in rotational grazing are likely to be most important where sheep are being rationed near their maintenance level and only small where food is ample.