Body composition and growth hormone profiles in first-cross progeny of genetically Lean and Fat sheep

Coopworth sheep selected for and against live weight-adjusted ultrasonic ba ckfat were crossed to produce Lean x Fat genotype animals (F1). Fl rams wer e run with contemporaries from the parental lines to characterise their phe notype relative to the Lean and Fat lines (n = 13, 11 and 10 for Lean, Fat and Fl lines, respectively). Body composition was measured using Computed T omography at nine months of age. Significant genotype differences in live a nd carcass weight were found, with F1 rams significantly heavier than Fat l ine rams, but not different from Lean line rams. After adjusting for live w eight differences, Lean and Fl rams had significantly higher weights of mus cle, visceral organs and bone, and significantly lower weights of internal fat than Fat line rams. Fat line and Fl rams had a significantly greater we ight of subcutaneous fat than Lean line rams. Fl rams were intermediate, an d significantly different from Lean and Fat lines for weight of intermuscul ar fat. The three lines were also blood sampled every ten minutes for six h ours on 25 May to measure growth hormone (GH) concentration. GH secretory p atterns were described using mean and basal concentrations, peak frequency and amplitude. Fl rams had significantly more GH peaks than Fat line animal s (4.80 and 2.87 peaks/6 hours, respectively), but were not significantly d ifferent from Lean line rams (4.93 peaks/6 hours). No other GH secretion pa rameter was significantly different between genotypes (P>0.05).