Influence of by-product feeds and tallow on lactation performance of Holstein cows during two seasons

Experiments were conducted to evaluate the impact of fibrous by-product feeds and tallow on lactation performance and ruminal fermentation. Diets were arranged as a 2 x 2 factorial of low and high NDF with or without added tallow. Corn and soybean meal were replaced with corn gluten feed, soyhulls, wheat middlings, and high moisture, whole ear corn. Forty-eight Holstein cows were used in two seasonal replicates of a randomized block design. Addition of tallow decreased intake of the low fiber diet, but not the high fiber diet, during winter. Intake was unaffected by diet during summer. Dietary NDF percentage did not change DMI. Milk production was unaffected by addition of tallow but was more persistent for cows fed low fiber diets. Tallow reduced milk protein percentage but did not change milk fat percentage. Fibrous feeds did not influence milk composition. Four fistulated cows were used in a 4 x 4 Latin square design. Fibrous by-product feeds decreased total VFA concentration. Acetate to propionate ratio increased when tallow was added to high fiber diets but decreased when tallow was added to low fiber diets. Tallow and fibrous by-product feeds can be used to support milk production.