ABOMASAL NITROGEN FLOW AFFECTS THE RELATIONSHIP BETWEEN DIETARY NITROGEN AND INSULIN-LIKE GROWTH-FACTOR-I IN GROWING LAMBS

Twelve abomasally cannulated wether lambs were fed isocaloric diets co ntaining 9, 12 or 15% crude protein to determine insulin-like growth f actor-I (IGF-I) responses to altered abomasal nitrogen flow and nitrog en status. Lambs were offered 1100 g/d of their respective diets. Volu ntary feed consumption was not affected by nitrogen intake. Ruminal an d total tract digestibilities of dry matter, organic matter and nitrog en increased linearly (P < 0.05) with increased dietary nitrogen. Abom asal flows of total, bacterial and rumen escape nitrogen increased (li near, P < 0.01), whereas dry matter and organic matter flows decreased (linear, P < 0.01). Total amino acid flow was greater (linear, P < 0. 01) in lambs fed additional nitrogen due to increased (linear, P < 0.0 1) flows of essential and nonessential amino acids. Nitrogen retention and blood urea nitrogen increased linearly (P < 0.01). Serum IGF-I co ncentrations and relative hybridization intensity of hepatic IGF-I mRN A increased (linear, P < 0.05) as lambs consumed more nitrogen. Serum IGF-I and hepatic IGF-I mRNA were correlated positively (P < 0.05) wit h nitrogen intake and abomasal flows of nitrogen and various amino aci ds. These data provide evidence of a relationship between abomasal ami no acid flow, as influenced by nitrogen intake, and hepatic gene expre ssion and serum concentrations of IGF-I in growing lambs.