Diurnal Changes in Cortisol Level, Neutrophil Number and Lyzozyme Activity in Foals during the First 13 Weeks of Life and in their Lactating Mothers

Abstract

In the blood of 11 foals and their lactating mothers (Standardbred) diurnal changes in the cortisol level, neutrophil number and lysozyme activity were studied during the first 13 weeks of life. The investigations began when a foal reached 7 days of age and were repeated every two weeks till 13 weeks of age. Blood samples were taken from the jugular vein every 4 hours for one day. Experiments were repeated in two following years. In the first year 6 mares and 6 foals born by these mares were examined, and in the second year--5 of the mares from the first year and the 5 new foals borne by them. All horses were kept and fed under the same conditions. Diurnal rhythm in neutrophil number and lysozyme activity was found neither in foals nor in mares. In the cortisol level a diurnal rhythm was found as early as in the first week of life of a foal as well as in the first week of lactation in mares. The mean diurnal values of cortisol level and lysozyme activity in foal blood were lower by 58% and 22%, respectively, in comparison with mares.