Interaction effects of season and dietary forage particle size on milk yield and composition of lactating Holstein dairy cows during the early lactation period

To evaluate the interaction effects of season and dietary forage particle size on milk yield and composition, 100 early lactation Holstein cows in two seasons of spring and summer (each season with 50 heads) in the form of two treatments containing alfalfa forage with large particle size (geometric mean 7.7 mm) and fine particle size (with a geometric mean of 4.2 mm) were used. The amount of dry matter intake of cows was recorded in groups and the milk production of cows was recorded individually.The results showed that milk yield, protein, lactose and total solid percentage of milk were higher within spring compared to summer (P< 0.01). Milk yield (P= 0.09) and milk lactose percentage (P = 0.08) for cows fed fine forage particle size trended to be higher than cows fed long forage particle size. The amount of dry matter intake within two hours after feeding for summer was higher than spring (P< 0.01). Overall, results of the predent study indicated that cows fed with fine forage particle size had more homogeneous feeding behavior pattern within both studied season than cows fed long forage particle size.