Milk and herbage intake of suckled and artificially reared lambs at pasture as influenced by lactation pattern

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Abstract
East Friesland × Blackface (EFX) ewes with sustained lactation (S) and pure Scottish Blackface (BF) ewes with normal lactation (N) were mated to Suffolk rams. Twenty pairs of twin lambs born to the EFX ewes were used in the experiment. One lamb of each pair was re-allocated as a single lamb to either an EFX or a BF ewe (ER) and the second lamb was artificially reared (AR). At pasture the AR lambs were fed four times daily at levels corresponding to the milk intake of the ER lambs, which was measured weekly. Herbage intake was measured only in wether lambs.The intake of milk and herbage between weeks 3 and 12 was lower in the AR groups than in the corresponding ER groups but the differences were not significant.Total metabolizable energy intake as milk in the ER-S group from weeks 3 to 12 was significantly higher than that in the ER-N group (668 v. 450 MJ). Corresponding intakes in the AR-S and AR-N groups were 613 and 416 MJ. Herbage intake over the same period was 187 and 238 MJ for ER-S and ER-N, and 137 and 219 MJ for AR-S and AR-N. Total intake from milk plus herbage was significantly higher in the S group (855 and 750 MJ, respectively, for ER and AR lambs) than in the N group (688 and 634 MJ).There were negative correlations of herbage intake with milk intake (–0·533) and with live-weight gain (–0·094), and positive relationships between live-weight gain and milk intake (r = +0·832), and between live-weight gain and total intake (r = +0·900). Differences in milk intake resulted in significant differences in live weight at 12 weeks (respectively, 34·6 and 29·7 kg for ER-S and ER-N; 32·3 and 29·1 kg for AR-S and AR-N).It is concluded that lambs reared artificially at pasture may be used to investigate the relationship between milk and herbage intake. It was suggested that if milk does not meet the requirements of voluntary intake or growth potential, herbage intake may be increased to fill the deficit but this does not compensate fully for a lower milk supply.

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