Effect of calcium salts of polyunsaturated fatty acids with different particle sizes on lactation performance and milk fatty acid profile in dairy cows

The objective of the current study was to assess the effects of particle size of dietary Ca salts of fatty acids (FA) on their inertness in the rumen, animal performance and transfer efficiency of polyunsaturated FA from diet to milk fat. Commercially produced CS of unsaturated FA (166 g/kg c9 18:1, 105 g/kg c9c12 18:2, 317 g/kg c9c12c15 18:3) were sieved through a 1.9-mm screen, and the retained particles were identified as coarse CS. The small particles were ground through a 0.864-mm sieve, and identified as fine CS. A mixture of unprotected FA, as triacylglycerols (TG), with a composition similar to that of the CS served as control. Eight Holstein cows were used in a 4 × 4 Latin square design. Treatments were administration of FA at the rate of 600 g/d in the form of: (1) coarse CS in the rumen; (2) fine CS in the rumen; (3) TG in the rumen; and (4) TG in the abomasum for 14 days. Pre-planned contrasts were used to compare coarse CS with: (i) fine CS (effect of particle size); (ii) TG in the rumen (negative control); and (iii) TG in the abomasum (positive control). Actual milk yield was lower with abomasal infusion of TG (26.3 kg/d), but was not affected by ruminal supplies of TG (29.7 kg/d) or fine CS (29.5 kg/d) as compared with coarse CS (30.4 kg/d). Milk fat yield was similar with coarse CS (1.05 kg/d) and abomasal infusion of TG (1.02 kg/d), but was lower with ruminal supply of fine CS (0.95 kg/d; tendency) and TG (0.89 kg/d). Accordingly, milk fat concentrations of t10c12 18:2 were similar with coarse CS (0.35 g/kg) and abomasal infusion of TG (0.33 g/kg), but were greater with ruminal supply of fine CS and TG (0.59 g/kg for both treatments). The apparent transfer efficiency of c9c12c15 18:3, from diet and lipid supplements to milk fat, varied from 0.017 to 0.264 g secreted/g consumed with ruminal and abomasal infusions of TG, respectively. The recovery of c9c12c15 18:3 in milk was greater with coarse CS (0.084 g/g) than with fine CS (0.042 g/g). Results confirm the hypothesis that large particles of CS improved protection against ruminal biohydrogenation of unsaturated FA and milk performance in lactating dairy cows.