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.

Pasture management to minimise the detrimental effects of pre‐lamb shearing

“…Shearing treatment had no effect on mean fibre diameter, a result that agrees with Dabiri et al (1995a). The negligible effect of sward surface height during the three weeks after pre-lamb shearing on wool growth rate or fibre diameter is consistent with the results of Morris et al (1993).…”

“…Herbage samples were washed to remove soil contamination, dried at 100°C to a constant weight, and then weighed to determine dry weight. Samples of herbage for pasture composition (the proportions by dry weight of grasses, clover, weeds and dead material) were hand-plucked adjacent to the quadrat, bulked, and sub-sampled to about 2.5 g for the measurement of pasture composition (Morris et al 1993).…”

“…Wool growth rate (WGR) was measured as the clean weight of midside wool grown per unit skin area per unit time (Morris et al 1993). The wool samples that had been used for measuring wool growth were also used to estimate mean fibre diameter (MFD) using the airflow technique (Ross 1958).…”

“…First, there was the energy cost of additional fetal growth (as reflected in lamb birthweights), particularly in ewes shorn with the standard comb. Second, in order to attain their physiological limit to feed intake, ewes on the 3 and 5 cm swards would have had to spend a longer time, and expend more energy, grazing (Coop & Drew 1963;Morris et al 1993). Shorn ewes on the lower SSH would, therefore, have had to spend more time exposed to cold compared with those on the 7 cm sward which would have been able to seek shelter for a greater part of the day.…”

“…The fact that shearing treatment increases feed intake in non-pregnant and lactating ewes, but not in late pregnant ewes, suggests that this difference is accounted for by the different physiological states of the ewes. In late pregnancy, ewes cannot readily increase their feed intake and in some instances, especially with twin-bearing ewes, feed intake may even decline (Owen & Ingleton 1963;Morris et al 1993), despite their energy requirements for pregnancy increasing (Rattray 1986). If late pregnant ewes cannot take advantage of increased SSH by increasing feed intakes then greater sward surface heights would be expected to be of little benefit in ameliorating the effects of cold exposure.…”