Decreased growth in Angus steers with a short TG-microsatellite allele in the P1 promoter of the growth hormone receptor gene

A polymorphic TG-repeat microsatellite is located 90 base pairs upstream fr om a major transcription start site in the bovine growth hormone receptor g ene. A shorter allele with 11 consecutive TG is common in Bos indicus cattl e, whereas longer 16- to 20-TG-repeat alleles predominate in Bos taurus bre eds. The purpose of this study was to compare growth and carcass traits bet ween Angus steers that had two of the longer growth hormone receptor allele s with their half-siblings that had one short allele and one of the longer alleles. We genotyped 64 Angus sires with respect to the poly-TG microsatel lite and identified six bulls that were heterozygous in that they had one s hort 11-TG allele and one of the longer alleles. We then grouped 125 steer progeny of these six heterozygous bulls according to their genotypes: only the longer 16- to 20-TG-repeat alleles were found in 73 steer progeny (long /long homozygotes), whereas a short 11-TG allele was paired with one of the longer alleles in 52 progeny (short/long heterozygotes). Contrasts for the long/long homozygotes vs the short/long heterozygotes were significant for weaning weight (17 +/- 4 kg; P < .001) and carcass weight (14 +/- 5 kg; P < .01). Approaching significance (P = .03) was the contrast for USDA marbli ng score (-.3 +/- .2). No significant differences (P > .05) were detected f or contrasts in birth weight (.3 +/- .6 kg), longissimus muscle area (-.2 /- 1 cm(2)), or carcass fat depth (-.01 +/- .07 cm). This polymorphism has potential for use in DNA marker-assisted selection programs.