Eighty-four foals of different breeds (Thoroughbred, Standardbred, German Warmblood), aged 5-6 months, were used in a study to evaluate the effects of weaning, sex, breed on haematological, metabolic and hormonal parameters. The values of leukocytes, neutrophils, red blood cells, haemoglobin, packed cell volume, platelets, activity of g-GT and concentrations of cholesterol, cortisol and thyroxin rose on day 1 after weaning, while the percentages of eosinophils, lymphocytes and serum concentration of triglycerides decreased one day following weaning. These parameters returned to pre-weaning values on day 14 post-weaning except serum cholesterol, which fell to a significantly lower level on day 14 post-weaning than pre-weaning value. Serum alkaline phosphatase declined markedly on day 14 post-weaning. The most pronounced rise was observed for cortisol (51%) and thyroxin (40%) values. Females presented higher mean corpuscular haemoglobin concentration and cortisol concentration than males (P<0.05). German Warmblood foals presented a less-altered picture following weaning as compared with Thoroughbreds and Standardbreds. It is concluded that foals respond immediately to weaning, which may lead to suppression of the activities of bone cells i.e., osteoblasts. In addition, serum concentrations of cortisol and thyroxin influence one another in weanling foals. The Thoroughbred foals appear to be the most sensitive to weaning.

Key words: Foals, Haematology, Hormones, Metabolites, Weaning