Effects of source and amount of energy and protein on ruminal fermentation, nutrient passage to the small intestine, and performance of lactating Holstein cows

Abstract

Three experiments were conducted using lactating cows fitted with ruminal and duodenal cannulae to investigate the effects of source and amount of energy and crude protein (CP) on nutrient flow to the duodenum. In each experiment, four Holstein cows were used in a 4 x 4 Latin square with treatments arranged in a 2 x 2 factorial.

In experiment 1, treatments were: 14.5% CP, soybean meal (SBM); 11.0% CP, SBM; 14.5% CP, corn gluten meal (CGM); and 11.0% CP, CGM. Dry matter and organic matter (OM) digested in the rumen, and microbial N flow to the duodenum were not affected by treatments. Flows of nonammonia nitrogen (NAN), nonammonia nonmicrobial nitrogen (NANMN), and amino acids to the duodenum were greater in cows fed the 14.5% CP diets which resulted in increased production of milk and milk CP compared to 11.0% CP diets. Feeding SBM diets increased production of milk CP compared to feeding CGM diets.

In experiment 2, treatments were: SBM, no calcium salts of long chain fatty acids (fat); SBM, fat; fish meal (FM), No fat; and FM, fat. Dry matter intake and flows of NAN, NANMN, microbial N, and amino acids to the duodenum were not affected by fat or source of protein. Fat decreased the amount of OM truly digested in the rumen. Milk production was not altered by treatment. Milk fat percentage was increased and milk CP percentage was decreased when fat was fed to cows, but yields of milk fat and CP were not altered.

In experiment 3, treatments were: 50% forage (LF), no fat; LF, fat; 67% forage (HF), no fat; and HF, fat. Feeding fat decreased OM intake and OM truly digested in the rumen. Milk production and percentage of milk fat were increased by feeding fat. Feeding HF diets decreased intakes of OM and starch, but increased ruminal pH and the ratio of acetate to propionate compared to feeding LF diets. Feeding HF decreased milk production but increased percentage and yield of milk fat. Feeding LF did not alter the flows of NAN or microbial N to the duodenum compared to feeding HF diets.