Utilization of salts of volatile fatty acids by growing sheep. 5. Effects of type of fermentation of the basal diet on the utilization of salts of acetic acid for body gains.

Abstract

1. An experiment is reported in which groups of six lambs were fed two basal diets supplemented at three levels with a mixture of sodium and calcium acetates.2. The basal diets were given in amounts that provided equal intakes of digestible organic matter and crude protein. One contained 85 % of concentrates (Hc), the other 40% of concentrates (Lc). Rumen contents from a sheep receiving diet Hc contained a lower molar proportion of acetate and higher proportions of propionate and butyrate than when diet Lc was given.3. The calculated metabolizable energy of the basal Hc diet was utilized more efficiently than that of the basal Lc diet, for promoting empty body-weight and carcass-weight gains.4. On both basal diets, lambs receiving the diets supplemented with acetate made greater live-weight, empty body-weight and carcass-weight gains than lambs given unsupplemented diets. The responses of weight gain to increasing levels of acetate were linear.5. The responses to acetate were greater when it was given with the Hc diet than with the Lc diet. This effect was most marked for live-weight gain (P < 0.001), intermediate for empty body-weight gain (P < 0.05), but not significant for carcass-weight gain. This order of effects was in part due to a greater weight of alimentary tract tissue, and its contents, in lambs fed the Hc diet supplemented with acetate.6. It is concluded that under certain circumstances the energy of acetate may be utilized less efficiently than energy from propionate or butyrate.