The effect of environmental temperature during pregnancy on thermoregulation in the newborn lamb

Abstract

Twenty-four pregnant Scottish Blackface ewes were divided into three temperature-treatment groups 14 days before expected lambing: closely shorn and kept at 6°C (cold treatment, CD); in full fleece at 26°C (warm treatment, WM); and in full fleece at 6°C (controls, CL). Food allocation and intakes were similar for each group. Their lambs were tested for cold-induced summit metabolic rate capability (SMR) on the day of birth at a mean age of 12 h using water immersion to provide cooling. On the following day, the calorigenic response to subcutaneous injections of noradrenaline (NA) was measured to assess non-shivering thermogenesis capability. The ewes were blood-sampled during pregnancy and the lambs before and after the SMR test.In the ewes, .blood glucose and free fatty acid levels were higher during cold treatment, but not significantly so. Blood glucose was lower in lambs from CD ewes (CD lambs) before SMR tests; other differences were not significant.During the cold test, SMR was highest in CD lambs, but not significantly so. Rectal temperature declined least during test in the CD lambs (P < 0-05).The peak metabolic response (PMR) following NA injection was about 1-5 times greater in CD lambs than in the CL and WM lambs (P < 0-05). The mean elevation of PMR over thermoneutral metabolic rate was respectively: 2-8, 1-8 and 1-7 times in the CD, CL and WM lambs (P < 0-05), and this elevation was sustained for longer in the CD lambs (P < 0-01). Thus, the total metabolic response to NA was markedly greater in CD lambs.It was concluded that cold exposure during late pregnancy favoured the deposition of (or checked the normal decline in) foetal brown adipose tissue, so raising the neonatal capacity for non-shivering thermogenesis.

Metabolic rate responses to cold and to exogenous noradrenaline in newborn Scottish Blackface lambs genetically selected for high or low resistance to cold

“…rate) and by noradrenaline injection (increased by 2-4 times resting rate). The size of the cold-induced elevation in metabolic rate was very similar to that (3-5 times basal rate) reported by Alexander and Williams (1968) in Merino lambs and by Stott and Slee (1985) using Scottish Blackfaces as in the present experiment. However, our noradrenaline-induced peak metabolism was proportionately 0-66 of the cold-induced peak metabolism compared with only 0-31 found by Alexander and Williams.…”

“…Thus, administration of a standard dose of noradrenaline should induce a thermogenic response from which differences in BAT-dependent NST capability can be measured. An infusion technique was used by Stott and Slee (1985) to measure variations in neonatal NST induced by physiological treatments during pregnancy. However, Slee,69 Simpson and Wilson (1987) showed that subcutaneous injection was the best method for large-scale experiments.…”

Adipose Tissue Development During Early Postnatal Life in Ewe-Reared Lambs

“…It is known that the rate of loss of UCP can be delayed by hand-rearing at a cool ambient temperature (Darby, Clarke, Lomax & Symonds, 1996), but the exact time course of postnatal changes in adipose tissue development or the extent to which they may be linked to changes in body temperature remains to be established. The loss of BAT characteristics reflects the decreased requirements for non-shivering thermogenesis as a result of enhanced insulation via wool growth (Stott & Slee, 1985) and increased adipose tissue deposition (Darby et al 1996) in conjunction with improved thermal efficiency (Symonds, Bryant, Clarke, Darby & Lomax, 1992). This also coincides with the age at which plasma insulin-like growth-factor-I (IGF-1) concentrations increase rapidly depending on the level of food intake , although it has yet to be determined if this could be related to altered adipose tissue deposition as has been suggested in pigs (Brameld, Atkinson, Saunders, Pell, Buttery & Gilmour, 1996a).…”

Genetic selection for cold resistance in Scottish Blackface lambs

“…Improved ewe nutrition in late pregnancy can reduce perinatal lamb mortality (Khalaf, Doxey, Baxter, Black, Fitzsimons and Ferguson, 1979a and b). Cold exposure of the ewe during pregnancy may also improve the subsequent cold resistance of the newborn lamb (Stott and Slee, 1985). These methods may however be impractical or uneconomic for the sheep farmer.…”