Effects of pasture allowance in winter on liveweight, wool growth, and wool characteristics of Romney ewes

Abstract

In each of two years, pasture allowances of 0.7, 1.2, 1.7, or 2.2 kg dry matter (DM)/ewe per day were offered to groups of Romney ewes for 6 weeks in June — July. The ewes were then run together until weaning in December. In Year 1 there were 70 2-year-old ewes per group; mean initial liveweight was 47 (SE 0.25) kg. In Year 2 each group comprised 25 2-year-old ewes with a mean initial liveweight of 48 (SE 0.49) kg and 25 6-year-old ewes with a mean initial liveweight of 57 kg. For liveweight change (g/day), the inverse linear relationship with pasture allowance (kg DM/ewe per day) for ewes with one lamb in utero was: [liveweight change = 136 (SE 4.4) — (132 (SE 5.0) allowance)]. On average, the pasture allowance that resulted in zero liveweight change was predicted to be 1.0 kg DM/ewe per day. With a pregrazing pasture mass of c. 2000 kg DM/ha, zero liveweight change was associated with a residual pasture mass of 760 kg DM/ha, a utilisation of 66%, and an apparent intake of 0.59 kg DM/ewe per day. For ewes with zero, one and two lambs in utero, zero liveweight change was predicted to occur on pasture allowances of 1.3, 1.0, and 0.8 kg DM/ewe per day, respectively. However, a similar allowance (c. 1.3 kg DM/ewe per day) would maintain body weight (conceptus free) for ewes in all three categories. Pasture allowance in June-July affected liveweight in August by up to 3.4 kg but this effect had largely disappeared by December. Pasture allowance did not affect lamb birth weight. Wool growth, fibre diameter, and staple length growth rate during the period of differential feeding in June — July, and subsequently in July-August, increased significantly with increasing pasture allowance in June-July. The maximum effect of pasture allowance on clean wool production between June and December was 0.12 kg. The relative effect of pasture allowance on staple strength was similar to that on wool growth in July-August. Fibre growth was continuous through the winter, reaching a minimum in July-August, about 6 weeks before the start of lambing. In June-July (mid pregnancy) pregnant ewes grew 0.8 g (18%) less wool per day than non-pregnant ewes; in July-August (late pregnancy) ewes with one lamb in utero grew 0.7 g (21%) less wool per day than non-pregnant ewes and 0.4 g (17%) more wool per day than ewes with twins. There was no significant interaction between number of lambs in utero and pasture allowance.

Keywords:

• pasture allowance
• sheep
• ewes
• pregnancy
• winter
• liveweight change
• birth weight
• wool growth
• fibre diameter
• staple length growth
• staple strength