Effect of sward height during late pregnancy on intake and performance of continuously stocked June- and August-lambing ewes

Abstract

Herbage organic matter intake (OMI), grazing behaviour and ewe and lamb production were measured during the last 4 weeks of pregnancy in 2-year-old and mixed-age Border LeicesterxRomney ewes due to lamb in June (winter) or August (spring). The intake of herbage (averaged across lambing date groups) was 1.4¦0.1, 1.71¦0.1, 1.7¦0.1 and 1.9 9¦0.1 kg OM ewe-1 day-1 (mean ¦ s.e.m., P < 0.01) for ewes continuously stocked on 10-year-old ryegrass (L. perenne) and white clover (T. repens) pastures maintained at sward surface heights (SSH) of 2.0, 4.0, 6.0 and 8.0 cm respectively. Ewes that were in a good body condition score achieved their required daily intake of energy at a SSH of 2.0 cm. Relative to ewes on the 8.0 cm SSH treatment, those on the 2.0, 4.0 and 6.0 cm SSH treatments attempted to increase intake by increasing grazing duration rather than biting rate. Ewe liveweight, condition score, midside wool growth rate and mean fibre diameter were not affected by sward surface height in either lambing group. There was no within season effect of SSH on lamb birthweight, but lambs born in June were lighter than lambs born in August (4.4k0.2 v. 5.3¦0.2 kg, P < 0.001). This trial has shown that, at the same SSH, June-lambing pregnant ewes achieve a similar daily herbage intake to that of August-lambing ewes. A target SSH of 2.0 cm during the last month of pregnancy was shown to be appropriate for both August- and June-lambing ewes in good condition. However, for August-lambing ewes in poor condition, a SSH of 2.0 cm at this stage of pregnancy would be detrimental to overall production, particularly in terms of ewe liveweight loss.