Effects of varying alfalfa hay-to-corn silage ratio and fat source on feed sorting behavior and chewing activities of lactating dairy cows

Feed sorting and chewing behavior of multiparous Holsteins were tested in response to diets containing different alfalfa hay (AH) to corn silage (CS) ratios and fat supplements. Experimental diets consisted of two AH:CS ratios (70:30 and 30:70), supplemented with either 3.5% Ca salts of fatty acids (CaS-FA; DM basis) or 3.0% C16:0-enriched palm fat (PFA). Increased sorting against long particles (> 19 mm) but in favor of the fine-length particles occurred when the ratio of AH to CS altered from 70:30 to 30:70. Cows fed PFA tended (P = 0.09) to sort in favor of 1.18-mm particles compared to those fed CaS-FA. Changing the ratio of AH to CS from 70:30 to 30:70 decreased meal length and meal size but did not affect the rumination patterns. Dietary fat source did not affect feeding and rumination patterns. Altering the ratio of AH to CS from 70:30 to 30:70 decreased eating time expressed as min/kg peNDF>8 intake but increased rumination and total chewing time (min/kg of DMI or NDF intake). Cows spent less time ruminating and chewing when fed diets containing CaS-FA vs. PFA. Chewing time (min/kg of NDF intake) was the greatest when cows consumed diets containing 30:70 AH:CS ratio + PFA. •Shifting the AH:CS ratio from 70:30 to 30:70 increased sorting in favor of fine particles and against long particles (>19 mm). •Cows fed PFA vs. CaS-FA tended to sort more in favor of 1.18-mm particles. •Feed sorting behavior, and feeding and rumination patterns were not affected by fat supplements •Cows spent less time ruminating and chewing when they fed CaS-FA vs. PFA. •Chewing behavior (min/kg NDF intake) was highest in cows fed the 30:70 AH:CS diet + PFA.