Twenty-four Southdown and 24 Welsh Mountain year-old female sheep, half on high-plane and half on low-plane nutrition, were shorn and given two acute cold exposures in climate chambers. For 2 weeks before and 2 weeks between exposures the sheep were kept in a subcritical (+ 8°C) or a thermoneutral (+30°C) environment. Before the temperature treatment each sheep received an injection of Brucella abortus vaccine. Blood samples were taken during exposure to + 8°C and + 30°C and during the acute cold exposures for estimation of free fatty acid (FFA), protein-bound iodine (PBI), glucose, acetone, serum protein and antibody levels. FFA and glucose levels alone were measured in 32 similarly treated Scottish Blackface sheep.
1. Low plane sheep had higher PBI levels at all temperatures, and higher glucose levels during acute cold exposure than high plane sheep. Otherwise most major effects were attributable to ambient temperature.
2. At +8°C the PBI, FFA, glucose, serum protein and acetone levels were higher than at + 30°C.
3. Blackface sheep had lower FFA and glucose levels than Southdown and Welsh sheep at both temperatures.
4. During acute cold exposure, PBI, acetone and FFA levels increased further. PBI levels were highest in sheep previously at + 30°C, and acetone highest in sheep previously at + 8°C. Very high FFA levels were recorded, especially in sheep not previously cold-acclimatized.
5. Glucose levels increased initially, but fell towards the end of acute exposure, suggesting that relatively less carbohydrate and more fat was utilized for energy metabolism during this period.
6. Serum protein levels fell during acute exposure, possibly because protein catabolism increased. The proportions of albumin and γ-globulin increased and decreased respectively.
7. No effects of temperature on antibody levels were detected.