CHANGES OF BLOOD METABOLITES AND HORMONES IN BREEDING CALVES ASSOCIATED WITH WEANING

Changes of blood metabolites and hormones were studied in female breed ing calves before, during and after weaning from 4 to 18 weeks of age. Calves were initially fed increasing amounts of whole milk (up to 7 k g/day in week 8 of life). Milk intake was then gradually decreased up to the age of 16 weeks, when calves were completely weaned and only fe d hay and concentrates. Average daily gain was 0.85 kg. Postprandial c oncentrations of glucose, insulin, insulin-like growth factor-I and 3. 5.3'-triiodothyronine concentrations gradually decreased (P < 0.05) wi th age, while those of beta-hydroxybutyrate, protein, albumin, haemogl obin and iron increased (P < 0.05). Concentrations of cholesterol tran siently increased, whereas those of urea reversibly decreased. Non-est erified fatty acids, triglycerides and growth hormone did not consiste ntly change during the duration of the study. In conclusion, changes o f glucose, beta-hydroxybutyrate, haemoglobin, iron, insulin, insulin-l ike growth factor-I and 3.5.3'-triiodothyronine mere markedly differen t from those usually seen in veal calves of the same age.