Reproductive performance from feeding tree fodder to ewes grazing drought pasture during mating

Abstract

Grazing experiments were conducted in late summer/autumn of 2001 and 2002, at Massey University's Riverside Farm, Masterton, to determine the effects of poplar and willow supplementation during drought on ewe reproductive rate, when grazing low quality drought pasture. Ewes (55-57 kg live weight) grazed drought pasture in a rotational grazing system, with pre- and post-grazing pasture masses of 1040- 940 and 530-550 kg dry matter (DM)/ha. In 2001, poplar trimmings were offered at the rate of 1.50 and 0.75 kg/ewe/day (fresh), to the high and low treatment groups, respectively (n=100 ewes/group). In 2002, 1.40 kg/head/day (fresh) willow and poplar trimmings were offered to the willow or poplar treatment groups (n=95 ewes/group). The poplar trimmings offered to ewes in the 2002 experiment were severely contaminated by poplar leaf rust. Poplar and willow consumed was higher in mean nitrogen content and organic matter digestibility, and lower in average neutral detergent fibre content, than the low quality drought pasture consumed by the control ewes. Control ewes lost live weight (82 and 104 g/day) during the mating periods in both experiments. Supplementation with poplar and willow slightly reduced live weight loss and loss of body condition, however these differences disappeared in the post-treatment period. Reproductive rate was low in the control groups of ewes (121 & 131 lambs born/ 100 ewes mated). In the 2001 experiment, poplar supplementation increased ewe reproductive rate by 20% units (p<0.05) and 34% units (p<0.001) for the low and high treatment groups, respectively, as compared to the control group. In the 2002 experiment, willow supplementation increased reproductive rate by 15% units (p=0.01) compared to the control group, with the advantage increasing to 21% units (p<0.05) at docking. Poplar supplementation had no effect on reproductive rate in the 2002 experiment. Increases in reproductive rate in supplemented ewes were mainly due to increases in the number of multiple-births. It was concluded that poplar and willow trimmings are beneficial supplements for increasing the reproductive rate of ewes grazing drought pasture during the premating and mating periods, providing the tree fodder is not contaminated with rust. Poplar and willow supplementation increased intakes of DM, metabolisable energy (ME) and crude protein, and increased protein intake as a proportion of ME intake during the mating period in the 2001 experiment. All of these factors could be involved in explaining the increased reproductive performance of poplar and willow-supplemented ewes. Keywords: Drought feeding; Poplar (Populus sp.) supplementation; Reproduction; Willow (Salix sp.) supplementation