PATTERN OF MILK-PRODUCTION OF EAST FRIESLAND AND SCOTTISH BLACKFACE EWES AND ASSOCIATED BLOOD METABOLITE AND HORMONE PROFILES

Patterns of milk production and circulating blood metabolite and hormone concentrations were determined throughout a 14-week lactation in groups of 10 twin-rearing East Friesland (EF) and Scottish Blackface (SBF) ewes. All ewes were offered, ad libitum, a pelleted diet throughout the experiment and milk yields were measured weekly. Pooled blood samples (six samples, 20-min intervals), collected before feeding, on 1 day of each week, were assayed for plasma glucose, non-esterified fatty acids, 3-hydroxybutyrate (3-OHB), albumin, total protein, insulin, growth hormone (GH), cortisol, prolactin, thyroxine (T4), and triiodothyronine (T3). At weeks 2, 4, 10, and 14, samples were collected at 20-min intervals for 8 h and assayed individually for plasma insulin, GH, cortisol, and prolactin. Mean daily intakes and milk yields of ewes were similar in the two breeds. Mean pre-feeding concentrations of most blood metabolites during the experiment were also similar in ewes of the two breeds but SBF ewes had higher plasma concentrations of 3-OHB (0.67 v. 0.43 mmol/l; P < 0.01) and total protein (73.2 v. 66.4 g/l; P < 0.001). SBF ewes had higher overall mean concentrations of insulin (9.53 v. 4.36 mU/l; P < 0.001), cortisol (7.59 v. 5.73-mu-g/l; P < 0.05), prolactin (457.1 v. 316.1-mu-g/l; P < 0.05), and T3 (1.32 v. 1.12-mu-g/l; P < 0.001). GH and T4 profiles were similar in the two breeds. Following the daily introduction of fresh food, there were significant increases in concentration of insulin (P < 0.001) and cortisol (P < 0.01) while there was a decrease in mean concentrations of GH (P < 0.001) and prolactin (P < 0.01). There were significant interactions between breed and feeding effects on insulin, GH, cortisol and prolactin concentrations. Patterns of milk production in ewes of these breeds were associated with changes in insulin:GH ratios both before and after feeding which may be of a causal nature.