Somatotropin supplementation decreases feed intake in crossbred dairy goats during the early phase of lactation

Abstract

Recombinant bovine somatotropin (rbST) has been shown to increase milk yield in dairy goats, especially during late lactation. The galactopoietic effect of rbST appears to derive mainly from the partitioning of nutrients to the mammary gland. Previously, this effect has been shown to coincide with an increase in feed intake. To test whether rbST has concomitantly an effect on milk yield and feed intake during the early lactation period, ten crossbred dairy goats during the peri-parturition period were selected and divided into two groups of five animals each. Two consecutive injections of sesame oil or rbST were performed at day 7 and 22 post-parturition (PP-7 and PP-22). Dry matter intake (DMI), water intake (WI) and milk yield of the individual animals were measured throughout the experiment. Blood was collected daily from day 6 post-parturition (PP-6) and throughout the first rbST injection period. Milk yield from the rbST supplemented group was slightly higher than the control group during the second rbST supplementation. Supplementation with rbST decreased significantly DMI per body weight. DMI digestibility from the second rbST injection did not differ between the treatments. The concentration of plasma IGF-1, insulin and glucose increased within 24 h after rbST injection. Importantly, plasma leptin also increased after rbST supplementation and this preceded the feed intake effect of rbST supplementation. The present results suggest that rbST induces a decrease in feed intake in dairy goats during early lactation, which relates to increase in the concentration of plasma leptin and in combination with galactopoietic effects of rbST, IGF-1 and insulin.