Effect of isolation of lambs on serum cortisol concentration

Abstract

To study the effect of isolation of lambs on serum cortisol concentration, 2 pairs of twin lambs were weaned at 90 days of age, and isolated by dividing the paddock with a wire screen at 97 days of age. In addition, at 100, 130 and 160 days of age, they were visually isolated from each other with a solid plywood fence. Blood samples for cortisol analysis were collected from jugular vein at 30 minutes before and after each of the occasion. Results were as follows : 1) The weaning or at physical isolation has no significant effect (P > 0.05) on the serum cortisol concentration with a tendency of an increased level of concentration after weaning and the isolation. It is, therefore, assumed that taking ewes out of the flock or setting up of wire fence may not cause an appreciable stress on weaned lambs. 2) At 100 days of age, the visual isolation caused a significant increase in serum cortisol concentration at 30 min. after the isolation (P < 0.05). The cortisol level then returned to the previous level at 30 min. after the visual isolation was released by removing the plywood fence. 3) At 130 and 160 days of age, however, the visual isolation produced no appreciable change in the serum cortisol concentration of lambs. It is speculated that no response may be caused by the experience at 100 days of age and the sensory input other than the sight. It is not possible, however, to show clear evidence in the present study.