The performance of housed ewes, shorn at various stages during pregnancy and offered silages ad libitum made from grass harvested at two contrasting stages of growth, was studied. The mean increase in silage dry matter (DM) intake due to shearing (0-11 kg/day; P > 0-05) was small in comparison with that resulting from offered earlier-cut silage (0-27 kg/day; P < 0-001). The mean increase in twin lamb birth weight from ewes shorn at least 6 weeks before lambing was almost 1 kg per lamb (P < 0-01) with no significant effect on ewe live-weight change. Greatest increase in lamb birth weight (1-11 kg; P < 0-01) was produced by shearing several times during pregnancy, with least response (0-23 kg; P < 0-05) from shearing once only, 4 weeks before lambing. The effect of silage quality on lamb birth weight was not significant, despite the large difference in DM intake of the two silages. This difference in intake was reflected by ewe live-weight change over pregnancy with those ewes offered early-cut silage gaining 5-57 kg while those offered late-cut silage lost 4-53 kg (P < 0-001). There was a marked fall in respiration rate and rectal temperature after each shearing and, compared with shorn ewes, unshorn ewes had a mean gestation length which was 2-04 days shorter (P < 0-01). In terms of lamb growth rates, ewe milk yields and milk composition, the performance on all treatments after turn-out to pasture was satisfactory and no significant carry-over effect of treatments applied during pregnancy were observed during the first 5 weeks of lactation.
The response of finishing Blackface lambs (mean initial live weight 29·6 kg) to shearing and level of concentrate supplementation on a silage-based diet was examined in two experiments. Silage intake decreased as concentrate level increased at mean rate of 0·13 and 0·26 g silage dry matter (DM) per g concentrate DM, in experiments 1 and 2 respectively, with no significant differences between unshorn and shorn lambs. Lambs gained 36, 97, 135, 193 and 224 g/day (s.e. 9·1; P < 0·001) in experiment 1 and 97,133,170,185 and 222 g/day (s.e. 9·9; P < 0·001) in experiment 2 when 0, 200, 400, 600 g/day and concentrate ad libitum were offered respectively. Shearing increased silage DM intake from a mean of 0·50 to 0·56 kg/day (s.e. 0·016; P < 0·05) in experiment 1, and from 0·80 to 0·90 kg/day (s.e. 0·013; P < 0·001) in experiment 2. There was no interaction between shearing and the level of concentrate offered. Despite higher DM intakes by shorn lambs, their live-weight gains were lower than those of unshorn lambs. Gains of unshorn and shorn lambs averaged 153 and 120 g/day (s.e. 5·8; P < 0·001) in experiment 1 and 162 and 161 g/day (s.e. 5·7; P > 0·05) in experiment 2 respectively. This appears to have resulted because shorn lambs could not fully compensate for their increased energy requirements after shearing, by increasing their DM intake. Shearing did not significantly influence carcass characteristics.It was calculated that with lambs gaining 150 g/day, concentrate requirement was increased from 286 to 335 g/day and total DM intake from 965 to 1107 g/day as a result of shearing.
Winter clipping of breeding ewes has given variable increases in lamb birth weight associated mainly with increased ewe voluntary food intake (Rutter, Laird and Broadbent, 1972; Vipond, King, Inglis and Hunter, 1987). The requirement for energy is greatest during the last six weeks of pregnancy but increasing uterine occupation of rumen volume may limit the ewe's ability to increase intake after clipping in late pregnancy. The additional influence of forage quality on intake after clipping is not clear. The present experiment was designed to study the independent and interacting effects of clipping regime and silage quality on lambing performance.Sixty Greyface ewes of uniform age were individually penned 14 weeks before lambing. Precision chop silage offered ad libitum was either early cut [188.3 g dry matter (DM)/kg, 155.7 g crude protein (CP)/kg DM, 740 g digestible organic matter (DOM)/kg DM] or late cut (184.5 g DM/kg, 100.9 g CP/kg DM, 689 g DOM/kg DM). For all treatments concentrate feeding was introduced 7 weeks before lambing, on an increasing scale to provide a total of 21 kg/ewe. Silage type was factorially arranged with 6 clipping regimes.
It has been clearly established that shearing ewes during pregnancy increases lamb birthweight (Austin and Young, 1971; Rutter, Laird and Broadbent, 1971; Black and Chestnutt, 1990). Fewer studies have examined the response of fattening lambs to shearing although both Salman and Owen (1981) and Marai, Nowar and Bahgat (1987) noted a significant increase in growth rate. This was accompanied by an increase in voluntary food intake and consequently little change in the food conversion efficiency.The objective of these experiments was to study the influence of shearing on voluntary food intake and growth rate of fattening lambs offered various levels of concentrate feeding plus ad libitum forage.
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