Metabolic adaptation during lactation in winter-shorn sheep

Abstract

SUMMARYThe effects of winter shearing, 8 weeks before lambing, on ewe and lamb live weight changes over the first 30 days of lactation were studied in Reading between February and March 1984. Differences in ewe body condition score (BCS) and plasma concentrations of glucose, nonesterified fatty acids (NEFA), 3-hydroxybutyrate, growth hormone (GH), insulin, cortisol and thyroxine between shorn and unshorn groups of ewes were measured over the same period.Lambs from shorn ewes grew, on average, 20% faster than those from unshorn controls even though both groups of lambs were of similar mean birth weight. There was no difference in maternal feed intake between shorn and unshorn groups, and ewe live weight and BCS decreased between the day of lambing and day 30 of lactation in all ewes. Plasma samples taken at hourly intervals for 24 h on days 12 and 27 of lactation demonstrated that shorn ewes had significantly lower plasma concentrations of insulin than unshorn controls; on day 27 of lactation, higher circulating concentrations of GH were recorded in the shorn group. There were no differences in the plasma concentrations of glucose, NEFA, cortisol or thyroxine between the two groups of ewes. It is concluded that metabolic adaptation by shorn ewes to the cold environment of a British winter during early lactation results in endocrine changes in ewes which are likely to increase the partition of nutrients towards milk production. This results in a higher lamb growth rate than in lambs reared by unshorn controls.