Fatty acid profiles, lipogenesis, and lipolysis in lipid depots in finishing pigs treated with recombinant porcine somatotropin

Thirty-two pigs (average weight, 74 kg) were used to determine the effects of recombinant porcine somatotropin (rpST) and dietary CP concentration on carcass and noncarcass tissues. Pigs were injected intramuscularly with either rpST (50 microns g center dot kg BW to the -1 center dot d to the -1; n = 16) or vehicle (n = 16) at 0900 for 24 d. Half the treated and control pigs were given ad libitum access to either a 14 or 20% CP corn-soybean meal diet. The left side of the carcass was physically dissected into separable skin, soft tissues, and bone. Tissue samples were obtained for enzyme assays, proximate analysis, and fatty acid profiles. Proximate analysis (fat, water, protein) of adipose tissue (AT) samples indicated that rpST decreased the percentage of ether extractable lipid (P < .01) and increased the percentage of protein and water (P < 0.5, P < .01) in intermuscular (IM), subcutaneous (SC), and intrafascicular (IF) AT depots and slightly altered fatty acid profiles of longissimus muscle IF and SC AT. Fatty acid synthesis and malic enzyme activity were decreased by rpST (P < .01), suggesting that lipogenesis was decreased; however, lipolysis was unaffected. Pigs fed the high-CP diet (20%) had decreased AT malic enzyme activity (P < .05) and fatty acid synthesis (P < .05). Additionally, pigs fed the high-CP diet had greater kidney weights (P < .01). Heart, liver, and kidney weights were heavier (P < .01) in pigs treated with rpST, whereas skin and total bone weight were unaffected. Neither weights nor lengths of four individual long bones were affected by dietary protein concentration or administration of rpST.