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

Abstract

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 [l- 13 C]valine over 60 min. Animals on the higher intake had a larger mass of liver protein (143 ν. 100 g, P = 0.02), similar fractional synthesis rates ( k s ; 22.5 ν. 22.1%/d, not significant) and greater absolute amounts of protein synthesis (32 ν. 23 g/d; P = 0.016) compared with those on the smaller amount of ration. The k s 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.