Effects of Restricted Concentrate Feeding during the Early Growing Phase on Growth Performance, Carcass Characteristics and the Somatotropic Axis in Holstein Steers

Abstract

Effects of nutritional restriction during the early growing phase on growth performance, carcass traits and the state of the somatotropic axis were investigated in 12 Holstein steers. During a rearing period (5 to 8 months old), 6 steers were given ad libitum access to a concentrate and a grass hay (ADLIB). The 6 other steers had their concentrate intake restricted at a rate of 1.5% of body weight (REST). Then, the steers of both groups were fattened with ad libitum access to another concentrate and the hay until slaughter (18 months old). The average daily gain for REST steers decreased (P<0.01) in the rearing period compared with ADLIB steers, whereas the difference tended to be reversed (P=0.10) in the fattening period. Feed conversion during fattening phase was improved (P<0.01) by the early nutritional restriction. Finishing weight, carcass weight, carcass grading factors and intramuscular lipid content were similar for both groups, but a trend for a higher (P=0.09) dressing percentage in the REST group was observed. Fat proportion in the 7th rib portionwas decreased (P<0.05) and the lean proportion tended to be increased (P=0.06) by restricted feeding. Restricted concentrate feeding decreased (P<0.05) plasma insulin-like growth factor I (IGF-I) at the end of the rearing period. The growth hormone (GH) secretory response to thyrotropin releasing hormone challenge and cellular density of pituitary GH cells, however, were unaffected by treatments. The results suggest that early nutritional restriction affect finishing carcass composition and the modulation of the developmental changes in plasma IGF-I may be involved in the process.