Digestion, Lactation and Nitrogen Utilization in Dairy Cows Fed Regrowth Orchardgrass or Regrowth Orchardgrass-Alfalfa Mixed Silage

Abstract

We evaluated the effect of mix seeding orchardgrass (OG) with alfalfa (AL) on the dietary characteristics of regrowth silage and feed intake, digestion, milk production and N utilization in dairy cows fed regrowth silage. Eight multiparous Holstein cows were used in a crossover design with two dietary treatments: diets containing either OG or OG-AL mixed silage at 23% second-cut and 22% third-cut of dietary dry matter. Dietary treatment did not affect dry matter intake or milk yield and composition. The whole-tract digestibility of dry matter, organic matter and fiber decreased with the replacement of OG with OG-AL in diet. Crude protein digestibility was not different between diets. Feeding OG-AL instead of OG increased the N intake. Proportional to N intake, urinary N excretion increased, milk N secretion decreased with replacing OG with OG-AL. No dietary effect was observed on N retention. These results show that an equal replacement of OG with OG-AL (containing 17% AL) regrowth silage decreases N utilization due to increased N intake and reduces fiber digestibility but has little impact on lactation performance.