The effects of genotype and post-weaning nutrition on compensatory growth in cattle reared as singles or twins

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Abstract
Thirty-five Charolais × Blue-Grey and Charolais × (Hereford × Friesian) weaned suckled calves which had been reared as either singles or twins and 19 single-reared Luing and Charolais × Luing weaned suckled calves were given silagead libitumsupplemented with either 0·75 or 2·5 kg rolled barley per day during the post-weaning winter. During summer the cattle continuously grazed perennial ryegrass swards. The high level of barley supplementation increased winter live-weight gain by 0·25 kg/day (P< 0·001). During summer the cattle from the low level of feeding gained weight at 0·09 kg/day (P< 0·05) faster than those from the high level of feeding. However, by the end of the summer grazing period the cattle on the low level of feeding were proportionately only 0·97 the weight of the animals on the high level of feeding.During winter the performance of all genotypes was similar, but at pasture the Luing cattle gained less weight (P< 0·01) than the single-reared Charolais-cross genotypes.Twin-reared cattle took 55 days longer to reach slaughter condition, but produced carcasses of equal weight and fatness to those from single-reared cattle.The twin-reared cattle on the high level of feeding and the single-reared cattle on the low level of feeding attained a similar weight, body condition and ultrasonic backfat at turn-out. Thereafter, their herbage intakes and live-weight gains were identical suggesting that previous level of feeding per se is unimportant in determining an animal's subsequent intake and performance. Rather it is the body composition at a given age, irrespective of the pathway followed to attain that composition, that determines performance thereafter. It is also suggested that the inability of cattle to compensate for a reduction in level of nutrition during the first 3 to 4 months of life is due to the lack of potential for fat deposition, and there is thus limited opportunity for nutritional manipulation of body composition at that age.