The effect of exogenously administered recombinant bovine somatotropin on intestinal phytase activity and in vivo phytate hydrolysis in hybrid striped bass Morone chrysops x M-saxatilis

It has been recently demonstrated that hybrid striped bass Morone chrysops x M. saxatilis exhibit intestinal phytase activity, an enzyme capable of liberating inorganic orthophosphate from the phytate molecule, thereby making phytate phosphorus ( PP) available for absorption and utilization by the fish. However, it was also determined that hybrid bass were able to digest only 1-2% of dietary PP. Therefore, an experiment was conducted to determine if exogenously administered recombinant bovine somatotropin (rbST) would increase intestinal phytase activity in hybrid striped bass to a level that would improve PP availability. The results indicate that exogenous rbST treatment, administered either through intraperitoneal injection or orally, does increase intestinal brush border membrane protein concentration. While injection with rbST led to significant increases in both specific brush border membrane and total intestinal phytase activity, oral rbST administration did not cause similar increases. Total P and PP digestibility were not influenced by rbST administration. While treatment with rbST does have the potential to enhance intestinal phytase activity in hybrid striped bass, it does not appear to increase PP digestibility. This observation limits the hormone's utility as an effective technique for improving PP bioavailability to this species.