Effects of calcium salts of unsaturated fatty acids supplementation on ruminal digestion by grazing dairy cows

The objective of this study was to evaluate the effects of calcium salts of unsaturated fatty acids (Ca-FA) supplementation on rumen digestion by dairy cows grazing high-quality pastures. Three cows with cannulas in the rumen were allocated to three dietary treatments in a 3×3 Latin square design. The cows grazed an alfalfa pasture with a herbage allowance of 30 kg dry matter (DM)/cow. Mean pasture quality was: 23% DM, 71% DM in vitro digestibility, 25% crude protein (CP), and 26% neutral detergent fiber (NDF). The treatments consisted in the supplementation with: T0 (5 kg of ground corn plus 0.4 kg of fishmeal), T1 (similar to T0 plus de addition of 0.8 kg de Ca-FA), and T2 (3.2 kg of ground corn, 0.4 kg of fishmeal, and 0.8 kg of Ca-FA replacing a similar part of the corn on an energy basis). The Ca-FA contained 65% of unsaturated and 31% of saturated FA. Total volatile fatty acids (105 mmoles/L), acetato to propionate ratio (3.0), and ruminal pH (5.8) were not affected by Ca-FA supplementation. Isobutyrate concentration in the rumen was increased in T0 (P<0.01). Parameters of in situ ruminal degradation of DM, NDF, and CP of the pasture were similar among treatments. Neither milk production nor milk composition was affected by the treatments. Overall, the results indicated that unsaturated FA supplementation in the form of Ca-FA avoided negative effects on ruminal pasture digestion, even when ruminal pH was relative low.