Every year many thousands of newborn lambs die of cold exposure. This thesis is concerned with some of the physiological and genetic factors involved in the resistance of neonatal lambs of ten different breeds to hypothermia with particular reference to their heat production capabilities. The project was a development-of preliminary work carried out at the Animal Breeding Research Organisation, Edinburgh during the year immediately preceding this study. An attempt was made to reproduce in the laboratory, a standard cold stress comparable to that experienced by the newborn lamb born into cold, wet and windy conditions. A suitable test was evolved using water as the cooling medium to reduce body temperature and measuring heat production (in the form of oxygen consumption) using an indirect open-circuit calorimeter. 265 lambs of ten different breeds were tested. Significant breed differences were found for resistance to body cooling and base metabolic rate. Peak metabolic rate was significantly affected by weight. The results of the experimentation (1976-1979) give an insight and k4o into the variation existing, both within and between breeds, jit the traits likely to be useful in the selection of individuals and breeds most suited to survive severe environmental conditions during the neonatal period. An attempt was made to separate the effects of factors such as weight, skin thickness, age, sex and litter size. In particular, observations during cooling tests indicate the possible importance of tissue insulation, recorded in the form of skin thickness, in aiding the neonate to maintain body temperature in a cooling environment where fleece insulation is low. It was thought that the insulative properties of the birthcoat were unlikely to be expressed under waterbath conditions and no significant effects of birthcoat were found despite there being significant breed variation in this trait. To demonstrate birthcoat effects a wind tunnel procedure was used with artificial wind and rain providing a cold stress. Use of this equipment allowed separation of the effects of birthcoat extremes within the Welsh Mountain breed. The effect of fasting lambs from birth (4hrs) and pre-partum cold exposure of the dam were investigated for effects on the newborn's metabolic response to cold and cold resistance capabilities in the Scottish Blackface breed. The fasted lambs showed enhanced cold resistance possibly as a result of fat metabolism being initiated prior to the applied cold stress. Cold exposure of pre-partum ewes increased gestation length and the birth weight of their lambs. Base metabolic rate was lower for fasted lambs and peak metabolic rate enhanced in lambs from cold stressed ewes. The contribution of non-shivering thermogenesis was investigated and emphasis placed on fat metabolism in early post natal life when brown adipose tissue may be particularly relevant in cold thermogenesis. Metabolic responses to injected noradrenaline were investigated and a comparison made between maximum metabolic response to cold and catecholamine stimulation in the Cheviot breed. Some methods of rewarming were also studied with passive techniques showing possible field application. The possibilities for selection of more cold resistant types of sheep are discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:280599 |
| Date | January 1982 |
| Creators | Samson, D. E. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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