The effects of bovine somatotropin on milk production, nutrient digestibility and plasma leptin of lactating goat during early lactating period

This study was designed to investigate the effect of bovine somatotropin on milk production, nutrient digestibility and plasma leptin of crossbred lactating goat during early lactating period and further that somatrotopin could influence feed intake during early lactation directly or indirectly via plasma leptin. The experiment was performed using ten crossbred lactating goats. One week after parturition, animals were randomly divided into two groups (n=5). Recombinant bovine somatotropin (rbST) or vehicle was injected at day 7th and 22nd after parturition to each group of animals. rbST increased plasma glucose, IGF-I concentration within 24 hours after supplementation. Within 48 hours after rbST supplementation, plasma leptin concentrations from the treatment group was higher than those from control group. In addition, rbST supplementation decreased dry matter intake while increased milk yield and water intake. Body weight of animals from each group was not different. Supplementation with rbST significantly decreased dry matter intake per body weight and then increased feed efficiency. Milk composition was not different between each treatment. Similarly, the nutrients digestibility, nitrogen retention and urinary allantoin concentration were not affected by rbST supplementation. The present experiment suggested that rbST supplementation could improve lactation performance of crossbred dairy goat during early lactating period. However, rbST supplementation during this period decreased feed intake and this behavioral effect was apparently caused by the direct mechanism of an increment of plasma leptin concentration.