The Impact of Alfalfa Hay Particle Size on the Utilization of Soy Hull by Early Lactating Dairy Cows

The purpose of this study was to evaluate the effect of alfalfa hay (AH) particle size (PS) and replacement of soybean hull (SH) in the diet on the performance of early lactating dairy cows. Eight lactating Holstein cows averaging 590 ± 33 kg of body weight and 47 ± 13 days in milk in replicated 4 × 4 Latin square design were assigned to a 2 × 2 factorial arrangement of treatments: PS of AH (fine vs. coarse) combined with SH (zero or substituted as 50% of AH). Physically effective fiber (peNDF) and physically effective factor (pef) contents of the diets were increased by increasing the PS of AH and the inclusion of SH in the diets (P < 0.01). Intake of peNDF was increased by increasing the PS of AH (P = 0.08) and SH inclusion (P < 0.01) in the diets. Apparent digestibility of organic matter decreased as fine AH (P < 0.05) was added to the diets, but coarse particles of AH increased (P < 0.05) and SH tended to decreased fiber digestion (P = 0.06) of diets. Milk production was increased by feeding diets containing SH (P = 0.04) but was not affected by AH particle size. Addition of SH reduced milk fat content (P < 0.01) but coarse particle of AH increased milk fat content (P < 0.03). Cows fed coarse AH tended to spend more time chewing (P = 0.08). Coarse particles of AH increased total chewing activity (P < 0.05) and also tended to increased eating activity (P = 0.09). When chewing activity was expressed based on NDF intake, ruminating time and total chewing time tended to be increased by coarse AH (P < 0.1). Interestingly when chewing activity was reported based on peNDF intake, the SH inclusion in the diets decreased eating time (P < 0.02), total chewing time (P < 0.03) and decreased trend for ruminating time (P = 0.08). The inclusion of SH in the diets decreased fecal pH value (P < 0.05). Coarse particles of AH in the diets containing SH resulted in increasing of fecal cumulative DM > 4 mm, 0.43 mm and 0.3 mm. In conclusion although supplementation of diets contained SH with coarse AH to some extent interacted with SH and improved milk fat yield and chewing activity, this interaction resulted in decrease of eating and total chewing activities, decreased in fecal pH and probably passing more DM to lower tract.