Abstract

CHEATHAM, R.C. et al. Effects of implant programs on performance, carcass characteristics, and lipogenic gene expression in Holstein steers. S. Afr. j. anim. sci. [online]. 2008, vol.38, n.3, pp.238-246. ISSN 2221-4062.

Nineteen Holstein steers were randomly assigned to one of four treatments; no implant (CON); 36 mg zeranol (Ralgro) on d 0 and 20 mg estradiol benzoate plus 200 mg progesterone (Synovex S) on d 84 and 169 (RSS); Ralgro on d 0, Synovex S on d 84, and 28 mg estradiol benzoate plus 200 mg trenbolone acetate (Synovex-Plus) on d 168 (RSP); or Ralgro on d 0, and Synovex-Plus on d 84 and 168 (RPP). Subcutaneous adipose biopsies were collected before implanting (d -14) and on d 97, 182 and at slaughter for measurement of mRNA concentrations of fatty acid synthetase (FAS) and acetyl CoA carboxylase (ACC). Implanted steers had greater average daily gain, dry matter intake, final body weight, hot carcass weight and longissimus muscle area than controls. No differences were observed in feed conversion ratio (FCR), dressing percentage, 12^th rib backfat, kidney pelvic and heart fat, marbling score, yield grade or Warner-Bratzler shear force values. Treatment did not affect serum metabolite concentration. Real Time PCR analysis of subcutaneous adipose mRNA concentrations indicated implants decreased ACC and FAS expression on d 97. ACC expression was increased significantly for RPP compared to RSP on d 182 and increased for the average of RSP and RPP compared to RSS on d 259, whereas FAS expression was not affected on d 182 or 259. Results suggest that lipogenic gene expression is affected by anabolic implants, particularly early in the feeding period and may partially explain how implants affect carcass characteristics, albeit a limited number of steers were used.

Keywords : Acetyl-CoA corboxylase; fatty acid synthetase; gene expression; Holstein steers.

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