Abstract
Abstract. Research was conducted to determine if directing expression of insulin-like growth factor I (IGF1) specifically to striated muscle would enhance lean muscle growth in swine. At 120 kg BW, 25 transgenic (T) and 26 control (C) pigs were sacrificed to evaluate carcass composition. T-pigs had lower percentages of fat and higher percentages of lean tissues than C-pigs for the overall carcass and each carcass region (P ≤ 0.002 for each). Expression of the IGF1 transgene did not alter the percentages of the three fiber types in the five skeletal muscles, however, fiber areas of longissimus dorsi muscle (LM) and serratus ventralis were larger (P ≤ 0.031) in T- than in C-pigs. In Tpigs the relative abundance of IGF1 mRNA in gastrocnemius, gluteus medius, LM, and the average for all five skeletal muscles (ASM) was positively (P ≤ 0.011) correlated with percentage of carcass lean (r = +0.597 to 0.804), whereas the relative abundance of IGF1 mRNA in the LM and the ASM was negatively (P ≤ 0.047) correlated with average backfat (r = −0.546 and −0.488, respectively). Based on these results we conclude that expression of IGF1 specifically in skeletal muscle had a positive effect on carcass composition of swine.
Highlights
Growth is primarily regulated by growth hormone (GH), many of its effects are mediated by insulin-like growth factor-I (IGF1), a single-chain mitogenic polypeptide
In the transgenic pigs the percentage of lean tissue in each of the four primary regions of the carcass and the loin eye area were all significantly elevated in contrast to significant reductions in average backfat and P2 backfat depth and percentages of carcass fat estimated by dual energy x-ray absorptiometry (DXA) in comparison to sibling controls
In the IGF1 transgenic pigs, circulating concentrations of IGF1 were only elevated by 19% in gilts and 11% in boars and plasma pGH concentrations were unaltered in comparison to sibling controls (PURSEL et al, 2004)
Summary
Growth is primarily regulated by growth hormone (GH), many of its effects are mediated by insulin-like growth factor-I (IGF1), a single-chain mitogenic polypeptide. Lack of growth enhancement in these studies may be the unintended consequence of elevated plasma IGF1 inducing negative feedback of IGF1 on the hypothalamus, which would depress GH secretion from the pituitary (KLINDT et al, 1998). To avoid the consequences that might ensue from depressed GH secretion, Coleman et al (1995) constructed a skeletal α-actin-hIGF1 transgene to direct IGF1 expression in striated muscle of transgenic mice. Their objective was to direct sufficient expression of IGF1 in muscle to act as a paracrine agent without altering plasma IGF1 concentration sufficiently to depress GH synthesis and secretion. The purpose of the present paper is to further elucidate the impact of IGF1 expression on the carcass characteristics and muscle fiber morphology of the progeny from six transgenic founder swine
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