Effects of willow (Salix) supplementation for 31 and 63Â d on the reproductive performance of ewes grazing low quality drought pasture during mating

A grazing experiment, conducted for 63 d from 12 January 2003, in the late summer/autumn of 2003, at Massey University's Riverside Farm, near Masterton (New Zealand), evaluated the length of feeding necessary (0, 31 and 63 d) to achieve reproduction responses from supplementation with willow tree trimmings in ewes grazing dry summer pastures of low nutritive value during mating. A rotational grazing system with 300 mixed age Romney ewes (54.3 ± 0.56 kg) was used, with 100 ewes per treatment (control, short supplementation and long supplementation). All ewes were offered 0.70 kg dry matter (DM)/d of low quality pasture, containing 78% dead matter, with pre- and post-grazing pasture masses of 1261 and 821 kg DM/ha, respectively. The effect of short (31 d) and long (63 d) willow supplementation (1.4 kg fresh/ewe/d) on live weight (LW) and body condition score (BCS) change, reproductive rate at pregnancy scanning, lambing, docking and weaning, and wool production was measured. Pasture consumed was typical of drought pasture, very high in neutral detergent fibre (NDF; 603 g/kg), low in organic matter digestibility (49%; OMD), and contained substantial concentrations of the anti-nutritional fungal metabolites zearalenone (Z) and trichothecenes. The willow diet selected was a superior feed to the drought pasture diet selected, with a higher N content, OMD and ME and it contained substantial concentrations of the secondary compounds condensed tannin (CT), salicin and other phenolic glycosides. Willow supplementation for 63 d (long treatment) reduced ewe LW loss (−96 g/d versus −147 g/d; P < 0.05) and loss in BCS (−0.79 versus −1.09; P < 0.05), compared to unsupplemented ewes, but these differences disappeared in the post-treatment period. There were no treatment effects on reproductive rate at scanning and lambing, probably due to the toxic concentrations of Z in the pasture consumed by ewes during mating (1.5 mg/kg DM). However, the long treatment weaned 13% more lambs than control ewes, due to a 9% unit reduction in post-natal lamb mortality from 17.1 to 8.4% (P < 0.05). There were no treatment effects on wool production and staple length, only a small treatment effect on the LW of male lambs at birth and no effect on lamb weaning weight. Overall results from 3 years of experimentation showed that supplementing ewes grazing drought pasture during mating with poplar and willow tree fodder consistently reduced LW loss and loss in BCS and substantially increased ultrasound scanning and lambing percentages, provided that the pasture or tree material was not contaminated with fungi that produce oestrogenic mycotoxins. When adjusted to equal birth rank, supplementation with tree fodder during mating also reduced post-natal lamb mortality in all 3 years, with overall means of 17.8 and 11.7% for the control and tree supplemented groups, respectively.