Effect of fibrous by-products on production and ruminal fermentation in lactating dairy cows

Lactating dairy cows were used in experiments to determine the effects of feeding a combination of fibrous by-products to replace a portion of alfalfa hay or grain. Cows were fed a control diet, consisting of alfalfa hay, corn, soybean meal, and corn silage or one of four treatment diets. In these diets, a combination of soy hulls, corn gluten feed, and wheat midds replaced approximately 30 or 60% of alfalfa hay or 25 or 50% of corn and soybean meal. A 56-d production study used 50 midlactation dairy cows in a randomized complete block design. No differences in milk production or composition among treatments were measured, except for the diet in which 60% of the alfalfa hay was replaced with fibrous by-products. Cows fed this diet had a significantly lower percentage of milk fat compared with other treatments. A fermentation study used five fistulated, multiparous lactating dairy cows in a 5 x 5 Latin square design. Cows were fed one of the five experimental diets used in the production study during five consecutive 14-d periods. Rumen acetate to propionate ratio was highest for the control and 50% concentrate replacement diets (3.27) and lowest for the 60% hay replacement diet (2.78). This shift in ruminal volatile fatty acid profile corresponded to the change in milk fat percentage, measured during the production study. A mixture of fibrous by-products fed as an alternative to hay or grain ingredients could potentially decrease feed costs without a resultant decrease in milk production by mid-lactation dairy cows.