The utilization of diets containing acetate salts by growing lambs as measured by comparative slaughter and respiration calorimetry, together with rumen fermentation

Abstract

1. In a comparative slaughter experiment, growing lambs were given concentrate diets in which 14 or 19% metabolizable energy (ME) provided by barley was replaced by sodium, calcium and potassium salts of acetic acid. As the proportion of ME as acetate was increased, energy retention decreased. ME intake was 9271, 9430 and 9217 ± 67 kJ/d and energy retention was 2698, 2422 and 2280 ± 71 kJ/d for the diets containing 0, 14 or 19% ME as acetate respectively. There were no differences in protein deposition. The efficiency of utilization of acetate for energy retention (k_f) was calculated by difference to be 3 and 10 ± 13% respectively for the diets containing 14 and 19% ME as acetate.2. In a second experiment, growing lambs were given concentrate diets in which 4 or 16% ME provided by barley was replaced by salts of acetic acid, and utilization was measured by indirect calorimetry. There were no significant differences in the utilization of the diets for maintenance (k_m) or energy retention (k_f). The k_m values were 82.4 ± 2.3 and 81.2 ± 0.7%, and k_f values were 67.4 ± 4.5 and 65.8 ± 2.7% respectively for the diets providing 4 and 16% ME as acetate. The k_f of the additional acetate in the diet providing 16% ME as acetate was calculated by difference to be 54%.3. The acetate and Ca concentrations of the rumen digesta were increased by including acetate salts in the diet, but Na and K concentrations were not affected.4. It is concluded that the best explanation for the poor utilization of acetate in the comparative slaughter experiment is that acetate was poorly utilized for lipogenesis. The calorimetry experiment contained relatively large errors, but the results suggest that acetate may be utilized efficiently in some circumstances. It is suggested that these results and apparently conflicting results in the literature may be explained by the concept that the efficient utilization of acetate is dependent upon the supply of glucose or glucose precursor.