Factors affecting voluntary feed intake in pigs. 3. The effect of a period of feed restriction, nutrient density of the diet and sex on intake, performance and carcass characteristics

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Abstract
1. Over the weight range 23–50 kg live weight, pigs were fed either ad libitum or to a restricted scale. From 59 to 91 kg live weight, eight pairs of barrows and eight pairs of gilts were fed on each of two diets varying in nutrient density. The effects of feed restriction, nutrient density of the diet and sex on voluntary feed intake, performance and carcass characteristics were studied.2. Pigs which had been restricted grew more slowly and contained less fat and more lean at 50 kg live weight.3. When restricted pigs were offered feed ad libitum from 59 to 91 kg live weight they ate more and had higher daily intakes of digestible energy than pigs liberally fed in early life.4. There was evidence of compensatory growth in pigs which had received the restricted diet, but there was no significant difference in feed utilization between restricted and ad libitum pigs. It was concluded that the compensatory growth was largely the result of increased appetite.5. Pigs finally fed on a low energy diet, in comparison with those on a high energy diet, ate more feed but less digestible energy indicating that appetite was physically limited. Efficiency of conversion of digestible energy to live weight was similar on both treatments. A higher proportion of acetic acid was produced in the caecum of pigs fed the low energy diet. Pigs receiving the low energy diet had lower killing-out percentages not entirely caused by differences in the weight of the gut and its contents. The carcasses of pigs on the low energy diet were leaner than those on the high energy diet.6. Barrows consumed more digestible energy per day than gilts, required more feed and digestible energy per unit live-weight gain, had lower killing-out percentages, shorter carcasses, larger backfat measurements and smaller eye-muscle areas as estimated by A × B measurements. Barrow carcasses contained less dissected lean and more fat than gilts' carcasses.7. The results are discussed in relation to other work and it is concluded that voluntary feed intake is influenced by the nutrient density of the diet and the level of energy requirement of the pig, which may be affected by previous nutritional history.