Effects of growth rate during the early fattening period on growth, carcass characteristics and circulating hormones in the different growth hormone genotypes of Japanese black steers

Abstract

ABSTRACT One of the bovine growth hormone (GH) genetic variants is a substitution of leucine (Leu) to valine (Val) at amino acid position 127 of the protein. The GH genotypes of 14 Japanese black steers used in the present study were Leu/Leu (A, n = 7) and Val/Val (B, n = 7). The steers in each genotype group were divided into two groups based on intended growth rate (high, 1.0 kg/day; low, 0.6 kg/day) during 10–17 months of age. The overall mean concentration of plasma GH was higher ( P < 0.05) in the A group than in the B group. The serum concentration of insulin‐like growth factor‐I was higher ( P < 0.05) in the B group than in the A group. The carcass weight of the A group was greater ( P < 0.01) than that of the B group. However, there was no significant difference in carcass weights between the 1.0 kg/day and 0.6 kg/day groups ( P > 0.05). The rib thickness of the 1.0 kg/day group was greater ( P < 0.05) than that of the 0.6 kg/day group. The crude fat content of longissimus muscle was greater ( P < 0.05) for the 0.6 kg/day group compared with the 1.0 kg/day group.