Dietary forage and nonfiber carbohydrate contents influence B-vitamin intake, duodenal flow, and apparent ruminal synthesis in lactating dairy cows.

The objective of this experiment was to quantify intakes, duodenal flows, and ruminal apparent synthesis (AS) of B-vitamins in lactating dairy cows fed diets varying in forage and nonfiber carbohydrate (NFC) contents. Eight (4 primiparous and 4 multiparous) ruminally and duodenally cannulated Holstein cows were assigned to 4 dietary treatments in a replicated 21-d period, 4 x 4 Latin square design with a 2 x 2 factorial treatment arrangement. Diets, fed as TMR, contained (DM basis) 2 levels of forage (35 and 60%) and 2 levels of NFC (30 and 40%). The forage portion of the diets contained 50% corn silage, 33% alfalfa hay, and 17% grass hay. Soybean hulls and beet pulp (2:1) and corn meal and ground barley (2:1) were included to achieve desired NFC concentrations. No supplemental B-vitamins were fed. B-vitamin AS was calculated as the amount of a specific B-vitamin flowing to the duodenum minus its daily orts-corrected intake. Dry matter and organic matter intakes were higher for cows fed the 35% forage diets and the 40% NFC diets. Increasing dietary forage content decreased ruminal AS of pyridoxine, folic acid, and B12. Increasing dietary NFC content increased ruminal AS of nicotinic acid, nicotinamide, niacin, pyridoxal, B6, and folic acid but decreased AS of B12. Across diets, amounts of B-vitamins synthesized were highest for niacin, followed by riboflavin, B12, thiamin, B6, and folic acid. Biotin AS values were negative for all diets, suggesting either no ruminal synthesis or that destruction by ruminal microflora was greater than synthesis. B-vitamin intake, duodenal flow, and ruminal synthesis are influenced by dietary forage and NFC contents.

Lactation performance by dairy cows fed supplemental biotin and a B-vitamin blend.

The objective of Trial 1 was to evaluate in dairy cows the effects of dietary supplementation with biotin and a B-vitamin blend on dry matter intake (DMI), milk yield, composition and component yields, total tract nutrient digestion, and plasma metabolites. Twenty-four multiparous Holstein cows averaging 46 +/- 8 d in milk at trial initiation were randomly assigned to treatments in a replicated 4 x 4 Latin square design with 28 d periods. The four treatments were: 1) a control diet (C) with no supplemental B-vitamins; 2) C plus supplemental biotin at 20 mg/d (B); 3) C plus supplemental thiamin (150 mg/d), riboflavin (150 mg/d), pyridoxine (120 mg/d), B12 (0.5 mg/d), niacin (3000 mg/d), pantothenic acid (475 mg/d), folic acid (100 mg/d), and biotin (20 mg/d) (BBVIT1X); 4) C plus supplemental thiamin (300 mg/d), riboflavin (300 mg/d), pyridoxine (240 mg/d), B12 (1.0 mg/d), niacin (6000 mg/d), pantothenic acid (950 mg/d), folic acid (200 mg/d), and biotin (40 mg/d) (BBVIT2X). Intake of DM was increased 0.7 kg/d for B vs. C and BBVIT1X and 1.3 kg/d for B vs. BBVIT2X. Milk yield was increased 1.7 kg/d for B vs. C. For BBVIT1X, milk yield was similar to B and BBVIT2X and tended to be higher than C. Yields of milk protein and lactose but not fat were higher for B than C. For BBVIT1X, milk component yields were similar to B and tended to be higher than C, with the exception of lactose yield where BBVIT1X was higher than C. The objective of Trial 2 was to evaluate DMI and milk yield, composition and component yields by dairy cows fed diets supplemented with either 40 mg/d biotin or the B-vitamin blend (BBVIT1X) compared to cows supplemented with 20 mg/d dietary biotin. Neither the 40 mg/d biotin treatment nor the B-vitamin blend enhanced lactation performance over the 20 mg/d biotin treatment. Biotin efficacy in short-term trials suggests that biotin may improve milk yield directly via effects on intake and (or) nutrient metabolism rather than indirectly via improved hoof health. More research is needed to determine the mode of action for supplemental dietary biotin.

Processing and chop length effects in brown-midrib corn silage on intake, digestion, and milk production by dairy cows.

In this experiment, we evaluated the influence of increasing chop length and mechanical processing of whole-plant brown-midrib corn silage on intake, digestion, and milk production by dairy cows. Corn silage treatments were harvested at three-quarter milk line stage of maturity at 13- and 19-mm theoretical chop length without processing, or at 19- and 32-mm theoretical chop length with processing at a 2-mm roll clearance. Twenty-four multiparous Holstein cows that averaged 102 +/- 17 d in milk at trial initiation were randomly assigned to treatments in a replicated 4 x 4 Latin square design with 28-d periods. Preplanned orthogonal contrasts were used to evaluate effects of processing (19 processed vs. 19 mm unprocessed) and chop length (13 vs. 19 mm unprocessed and 19 vs. 32 mm processed). Treatments were fed in total mixed rations containing 60% forage (67% corn silage and 33% alfalfa silage) and 40% shelled corn and soybean meal-based concentrate (dry matter basis). Milk yield was unaffected by treatment. Dry matter intake was unaffected by corn silage processing, but increasing corn silage chop length reduced dry matter intake in unprocessed (26.6 vs. 25.5 kg/d) and processed (25.9 vs. 25.1 kg/d) chop length contrasts. Processing reduced milk fat content (3.36 vs. 3.11%) and yield (1.43 vs. 1.35 kg/d), increased total-tract starch digestion (92.9 vs. 97.4%), and decreased total-tract neutral detergent fiber digestion (51.0 vs. 41.8%). Total chewing time (min/d) was unaffected by treatment. Masticate mean particle length was unaffected by chop length in unprocessed and processed corn silage treatments. In this study with brown-midrib corn silage fed to dairy cows producing 43 kg/d of milk, there were no benefits from crop processing or increasing chop length on lactation performance.