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 f eeding 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, cor n, soybean meal, and corn silage or one of four treatment diets. In these d iets, a combination of soy hulls, corn gluten feed, and wheat midds replace d approximately 30 or 60% of alfalfa hay or 25 or 50% of corn and soybean m eal. A 56-d production study used 50 midlactation dairy cows in a randomize d complete block design. No differences in milk production or composition a mong treatments were measured, except for the diet in which 60% of the alfa lfa hay was replaced with fibrous by-products. Cows fed this diet had a sig nificantly lower percentage of milk fat compared with other treatments. A f ermentation study used five fistulated, multiparous lactating dairy cows in a 5 x 5 Latin square design. Cows were fed one of the five experimental di ets used in the production study during five consecutive 14-d periods. Rume n acetate to propionate ratio was highest for the control and 50% concentra te 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 mixt ure of fibrous by-products fed as an alternative to hay or grain ingredient s could potentially decrease feed costs without a resultant decrease in mil k production by mid-lactation dairy cows.