Changes of blood metabolites and hormones in breeding calves associated with weaning.

Changes of blood metabolites and hormones were studied in female breeding 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 kg/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 fed hay and concentrates. Average daily gain was 0.85 kg. Postprandial concentrations of glucose, insulin, insulin-like growth factor-I and 3.5.3'-triiodothyronine concentrations gradually decreased (P < 0.05) with age, while those of beta-hydroxybutyrate, protein, albumin, haemoglobin and iron increased (P < 0.05). Concentrations of cholesterol transiently increased, whereas those of urea reversibly decreased. Non-esterified fatty acids, triglycerides and growth hormone did not consistently change during the duration of the study. In conclusion, changes of glucose, beta-hydroxybutyrate, haemoglobin, iron, insulin, insulin-like growth factor-I and 3.5.3'-triiodothyronine were markedly different from those usually seen in veal calves of the same age.