Correlation between peripheral melatonin and general immune status of domestic goat, Capra hircus: A seasonal and sex dependent variation

Caprine immune system has largely been neglected by ruminant researchers despite of its high economic importance in bioindustry. We made an attempt to note the annual/seasonal and gender dependent variation in immune status of the domestic goat, Capra hircus, Jamunapari breed and correlated with the concentration of peripheral gonadal hormones (testosterone, 17 -estradiol) and melatonin. Based on the data of general immune parameters such as total leukocyte count (TLC) and percent lymphocyte count (%LC) along with blastogenic response of splenocytes in terms of percent stimulation ratio (%SR), we found an annual variation in immune status of male, female and castrated male goats in a gender dependent manner. Female goats showed higher immune parameters than that of castrated as well as intact male goats. Testosterone in intact male goats was high throughout the year, which might be responsible for low immune status. However, in castrated male goats, plasma testosterone was undetectable and presented an immune status equivalent to that of female goats. We observed a high immune status during the winter season in all the groups of goats, which might be due to high circulatory concentration and longer duration of melatonin induced by short days. Being released by circulating lymphocytes, the concentration of interleukin-2 (IL-2) in blood plasma, showed an annual and seasonal variation being higher in female than castrated and intact male goats throughout the year, having a similar trend in plasma melatonin concentration. The higher immune status in female goats during the winter months might have helped them to overcome the winter bound stress, i.e. low temperature. Therefore, we may propose that testosterone acts as an immunosupressor while melatonin as an immunostimulator for goats as it showed a positive correlation with immune parameters noted.