Protein synthesis in splanchnic tissues of sheep offered two levels of intake

Protein synthesis rates were measured in liver and gastrointestinal tract (GIT) sections of fattening sheep offered lucerne (Medicago sativa) pellets at either 1.25 or 2 times energy maintenance. The measurement technique involved a large dose of [1-13C]valine over 60 min. Animals on the higher intake had a larger mass of liver protein (143 v. 100 g, P = 0.02), similar fractional synthesis rates (ks; 22.5 v. 22.1%/d, not significant) and greater absolute amounts of protein synthesis (32 v. 23 g/d; P = 0.016) compared with those on the smaller amount of ration. The ks values and RNA: protein in the GIT sections also tended to increase with food intake. Estimated total GIT protein synthesis was approximately three-fold that in liver and probably constituted 25-35% of whole body synthesis. All splanchnic tissues measured had lower translational efficiencies (g protein synthesized/d per g total RNA) than reported for milk-fed and newly-weaned lambs and this may relate to the decline in the rate of protein deposition as lambs progress to the fattening condition.