Effect of calcium salts of fatty acids on rumen function and the digestibility of rations by sheep

Experiments were conducted to determine the effects of supplementing chopped ryegrass hay with 0, 1.5, 3, 6 or 12% calcium salts of fatty acids (CaSFA; Megalac) on digestion in the rumen of cannulated cows and on nutrient digestibility by sheep. In-situ ruminal disappearances of dry matter (DM) and cell wall fractions (acid detergent fibre, ADF, and neutral detergent fibre, NDF) were measured by the nylon bag technique. The DM, ADF and NDF disappearances were reduced for diets containing CaSFA at the 1.5, 3 or 6% levels after 48 h of rumen exposure. For diets containing 12% CaSFA, irrespective of the time of rumen incubation, DM disappearance was decreased, while ADF and NDF breakdown was improved. CaSFA supplementation did not influence invitro fermentation characteristics (pH, volatile fatty acid patterns). A digestibility experiment with six mature sheep showed no difference in nitrogen digestibility between unsupplemented and CaSFA-supplemented diets. However, digestibilities of DM, ADF and NDF were higher relative to the basal for the 12% CaSFA: 63.1 versus 60.6%, 63.8 versus 58.7% and 67.4 versus 62.7%, respectively. Ether extract digestion was enhanced by increasing the level of CaSFA, the corresponding values being 49.1, 66.5, 78.6, 81.9 and 77.9% at 0, 1.5, 3, 6 and 12% CaSFA, respectively. Apparent digestibility of energy was higher for the 12% CaSFA than the control diet 68.8 versus 62.1%). Nitrogen and energy retention was improved due to the decreases in urine and faecal excretion, respectively.