Thirty-two Border Leicester ♂ × Scottish Blackface ♀ wether lambs aged about 5 months, were divided on the basis of live weight such that group G1 contained the 16 lightest lambs and group G2 the 16 heaviest lambs. Lambs in group G1 were subdivided equally at random to be either sham-implanted controls (group C1) or to be implanted with 35 mg trenbolone acetate (TBA) + 5 mg oestradiol-17β (OE) (group T1) at 24 kg initial live weight. Lambs in group G2 were also subdivided into two groups (C2 and T2) and similarly treated approximately 1 month later at 37 kg initial live weight. Animals were offered ad libitum, a diet containing an estimated 12·5 MJ metabolizable energy and 140 g crude protein per kg dry matter. The experimental treatments lasted for 60 days.
Samples of pre-heparin plasma were analysed for free fatty acid (FFA) and triglycerides (TG). Post-heparin plasma was analysed for lipoprotein lipase (LPL) activity. Samples of subcutaneous (SCAT), perinephric (PNAT), mesenteric (MAT) and intermuscular (IMAT) adipose tissue, liver and muscle, taken immediately post mortem, were analysed for total lipid concentration and fatty acid composition. Comparisons were made for the main effects of hormonal treatment and live weight.
Plasma FFA concentrations in heavier lambs (group G2) were significantly higher than in group G1 from week 1 pre-implantation to week 3 post implantation. Compared with group G1, animals in group G2 had significantly higher plasma TG concentrations at weeks 1, 2, 5 and 8 when data was analysed using pre-implantation values as covariates. The lipid concentration was lower in group G1 than in group G2. In group G1 compared with group G2 there were greater proportions of C12:0 and C18:2 in SCAT and C16:1 in PNAT and lesser proportions of C18:0 in SCAT and PNAT.
Significant effects due to hormonal treatment were recorded for plasma TG at weeks 1, 5, 6, 7 and 8 mainly due to increases in group T1 compared with group C1. Hormonal treatment increased the proportions of C12:0, C15:0, C16:1 and C18:1 in SCAT and C16:1 and C18:1 in IMAT; reduced the proportions of C16:0 and C18:0 in SCAT and C18:0 in MAT and IMAT and reduced the ratio of saturated to unsaturated fatty acids in SCAT and IMAT and to a lesser extent in MAT.