The performance and body composition of young pigs following a period of growth retardation by food restriction

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Abstract
Pigs were fed either ad libitum or given 300 g/day of the same food (digestible energy 15·4M)/kg; crude protein 208 g/kg fresh food) from 6 to 12 kg live weight (LW). Four pigs were killed at 6 kg LWand eight (equal numbers from the two sexes) from each treatment at 12 kg LW. Eight pigs (three males and five females; AL) were continued on ad libitum feeding to 24 kg LW when they were killed. Ten (four males and six females; R) of the pigs which had been restricted to 12 kg LW, were fed ad libitum to 24 kg LW, when they were killed. The entire empty bodies of the pigs killed were chemically analysed and the weights of organs determined. The empty body was considered as three fractions: the entire skin, including the subcutaneous fat (SK); the internal organs and the empty gastrointestinal tract (INT) and the remainder (CARC). The distributions of the chemical components between these three fractions were determined.The R pigs took 19 days longer and 2·6 kg more food to go from 6 to 12 kg LW. At 12 kg LWthey had less gut fill, lighter organs concerned with food processing and less lipid, more protein and heavier CARC weights than the AL pigs. The R pigs took 5·5 days less and 2·4 kg less food to go from 12 to 24 kg than the AL pigs. At 24 kg LW they had more gut fill, similar weights of the organs concerned with food processing, and slightly less lipid and protein. Over the 12 to 24 kg weight interval the R pigs gained lipid and protein at faster rates than the AL pigs. None of the increase in protein growth rate was in the CARC fraction.It is concluded that pigs given a low intake of food adjust their organ weights to be sufficient to process the allowance. On being given ad libitum food they rapidly increase the weights of their organs to process the increased rate of intake, and increase their gut fill. These effects are seen as a short lived, greatly increased rate of LW gain. During rehabilitation lipid stores return to their normal level but carcass protein does not show an increased rate of growth.

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