Five ewes, with a wool depth of approximately 5 mm, were placed in a neutral (20 + 2°C) environmental temperature on day 139 of pregnancy, and five similar ewes were placed in a cold (0±2°C) temperature. They remained in these environments until their lambs were 8 days old. Samples of udder secretions, when present, and right-atrial blood were taken from the ewes at 12-h intervals.
Milk from ewes in the neutral environment had a high fat concentration for a brief period after parturition, before the full development of lactose secretion occurred.
In ewes exposed to the cold environment, plasma cortisol concentration was increased during the 2 days before parturition. Cold exposure had no effect on the onset of milk lactose secretion but increased the concentration of fatty acids in milk during the period −0·5 to +4·5 days relative to parturition.