Nutrient digestibility, rumen fermentation parameters, and production performance in response to changing dietary ratio of barley to corn grain of Holstein dairy cows

The effect of diets based on barley or corn، or their equal blend on nutrient digestibility، rumen fermentation characteristics، and production performance of lactating dairy cows were evaluated using nine multiparous Holstein cows in a triplicated 3×3 Latin square design with 21-d periods. Apparent total-tract digestibility of dry- and organic matter changed quadratically (P=0. 03) and was greater in cows fed barley-based diets than cows fed corn-based diets (P<0. 05). Apparent total-tract digestibility of crude protein increased in barley-based diets vs. corn-based diets fed cows (P=0. 001). Ruminal fluid pH and volatile fatty acids concentrations were remained unchanged among treatments. Dry matter- and energy intakes were similar among treatments (P>0. 05). Both actual and energy corrected milk yield were unchanged across treatments. Average percentage and yield of milk constitutes including milk protein، lactose، and total solids were similar across treatments (P>0. 05). Milk fat percentage increased linearly (P=0. 02) with increasing ratio of the corn in the diets and was greater in corn-based diets relative to barley- and corn-based diets but not barley-based diets. However، milk fat yield tended to show a linear increase as the ratio of corn included in the diet increased (P=0. 07). Regardless of occurred milk fat depression in all dietary treatments، changing dietary ratio of barley to corn grain had minimal effect on production performance of dairy cows.