Relationships between energy intake, nutritional state and lamb birth weight in Greyface ewes

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Abstract
Summary: Individual feed intakes of housed mature Greyface (Border Leicester × Scottish Blackface) ewes were adjusted weekly to maintain plasma 3-hydroxybutyrate concentrations during the final 6 weeks of pregnancy at the following values: treatment 1 (adequately nourished; 17 ewes) less than 0·7 mmol/1; treatment 2 (moderately undernourished; 15 ewes) at about 1·1 mmol/1; treatment 3 (severely undernourished; 15 ewes) at about 1·6 mmol/1.The mean energy intakes (MJ metabolizable energy (ME)/day) required to maintain the prescribed nutritional states in single- and twin-bearing ewes were: treatment 1, 14·3 and 16·3; treatment 2, 10·6 and 11·6; treatment 3, 8·1 and 10·0 respectively.The moderate degree of undernourishment had no significant effect on the birth weight of single lambs, but reduced the birth weight of twins by 8·2%, while the more severe undernourishment reduced the birth weights of singles and twins by 21·5 and 25·8% respectively.Foetal energy requirements, estimated by regression analysis, appeared to decrease from more than 2 MJ ME/kg/24 h at 35 days prepartum to 1·54 MJ ME/kg/24 h in the week before parturition.The amounts of energy required to sustain the nutritional states of treatments 1–3 in non-pregnant ewes were calculated to be 348, 271 and 231 kJ ME/kg0.75/24 h, compared with a maintenance requirement, determined in this experiment, of 344 kJ ME/kg0.75/24h.It is concluded that in individually fed ewes a nutritional state characterized by plasma 3-hydroxybutyrate concentrations of 1·1 mmol/1 would constitute an acceptable compromise between an uneconomically high energy input and an excessive reduction in lamb birth weight.