Supplementation of grazing suckling lambs with concentrate. The interaction between the level of supplementation and the herbage allowance, and the effect on the level of parasitism

Abstract

In order to determine the effects of concentrate supplementation of grazing suckling lambs, lambs supplemented ad libitum with high-moisture whole maize grain (C) were compared to unsupplemented lambs (NC), during two successive years. Thirty-six Ile de France ewes suckling twin lambs were used in these two experiments ; they were grazed rotationnally around paddocks of natural pastures, with a stocking rate of 12 ewes/ha. Lambs were 7 weeks old when turned out to grass and 16 weeks old at the end of the grazing period. They were further fattened indoors and, after slaughter, carcass quality was assessed. The effect of supplementation on lamb growth rate at pasture and on carcass quality varied between experiment 1 and 2. The hypothesis was that these results may have been due to differences in herbage allowances. A third experiment was therefore carried out : 24 ewes suckling twin lambs were allocated 8 weeks after lambing between four grazing treatments : two levels of herbage allowance x two levels of supplementation. Daily herbage organic matter (OM) allowances were 57,0 (H) and 38,5 (B) g OM.kg LW^-1. Lambs were either supplemented ad libitum (C) or unsupplemented (NC). The sward consisted of tall fescue and was grazed rotationnally. At the low allowance level, supplementation increased lamb growth rate (287 g.d^-1 vs 226 g.d^-1), whereas it had no effect at the high level (277 g.d^-1 vs 276 g.d^-1). Therefore, supplementation increased lamb growth rate only when herbage allowance was low. It also reduced parasitism, even when herbage allowance was high. It also improved the firmness of subcutaneous fat, when it led to a reduction of the duration of fattening indoors after weaning.

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