Efectos de la suplementación con sales cálcicas de ácidos grasos insaturados sobre la digestión ruminal en vacas lecheras en pastoreo

The objective of this study was to evaluate the effects of supplementation with calcium salts of unsaturated fatty acids (Ca-FA) 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 daily herbage allowance of 30 kg dry matter (DM)/cow. Mean values of herbage quality indicators were: 23% DM, 25% crude protein (CP), 26% neutral detergent fiber (NDF), and 71% in vitro DM digestibility (IVDMD). The in situ rate and extent of disappearance of the different herbage fractions were also determined. The treatments consisted of 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 of Ca-FA), and T2 (3.2 kg of ground corn, 0.4 kg of fishmeal, and 0.8 kg of Ca-FA in isocalaoric substitution for corn). The Ca-FA contained 65% of unsaturated and 31% of saturated FA. Total volatile fatty acids (105 mmoles/L), acetate to propionate ratio (3.0), and ruminal pH (5.8) were not affected by Ca-FA supplementation. Isobutyrate concentration in the rumen was highest in T0 (P < 0.01). Parameters of in situ ruminal degradation of DM, NDF, and CP of the pasture herbage 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 the negative effects on ruminal pasture digestion that often accompany dietary unsaturated fat addition, even through ruminal pH was relatively low.