Some effects of dietary crude fibre on live-weight gains and carcass conformation of pigs

Abstract

1. The results of six trials have been examined in which pigs received rations with contrasting levels of crude fibre. The contents of crude fibre ranged from 3½ to 11½% and were related to a variety of basal diets.2. The main object of the trials was to study the effect of increased levels of dietary crude fibre on carcass conformation, under conditions where there was no disparity in rate of live -weight gain between the pigs receiving the higher and the lower level of fibre. Thus pigs on the high-fibre diets received extra food in order to equalize the intake of digestible nutrients.3. The results indicate that a rise in the level of dietary crude fibre was accompanied by a fall in the killing-out percentage, and hence by lower carcass weights. This effect was produced even by comparatively small changes, such as a rise from 3½% crude fibre to about 5% crude fibre. The results also show that carcass weight was positively correlated with back-fat thickness to a marked degree.4. It is evident that raising the level of crude fibre in the food caused a change in the distribution of live-weight gains, so that when at the same slaughter weights, the high-fibre pigs had lighter carcasses and heavier offal than their low-fibre counterparts. Consequently the high-fibre pigs also had thinner back-fats, and they would tend to grade better under carcass grading systems based on backfat measurements and biased towards thin back-fats.5. It is suggested that these effects are likely to be produced even in pigs considerably advanced in fattening, and that in younger pigs the drawback of retardation in rate of live-weight gain may also be encountered. Thus the use of high-fibre diets in self-feeding systems, as a corrective against over-fatness, may not normally be the best means of attaining this objective under commercial conditions.