title: Apparent ruminal synthesis of B vitamins in lactating dairy cows fed diets with different forage-to-concentrate ratios.
abstract: Effects of the forage-to-concentrate ratio on apparent ruminal synthesis of thiamine, riboflavin, niacin, vitamin B6, folates, and vitamin B12were evaluated in an experiment using 14 ruminally and duodenally cannulated Holstein cows. The experiment was a crossover design with two 15-d treatment periods and a 14-d preliminary period in which cows were fed a diet intermediate in composition between the treatment diets. Treatments were diets containing low-forage (44.8% forage, 32.8% starch, 24.4% neutral detergent fiber) or high-forage (61.4% forage, 22.5% starch, 30.7% neutral detergent fiber) concentrations. Both diets were formulated with different proportions of the same ingredients. Concentrations of B vitamins were analyzed in feed and duodenal digesta. Apparent ruminal synthesis of each B vitamin was calculated as the duodenal flow minus the intake. The high-forage diet had the highest concentrations of riboflavin, niacin, vitamin B6, and folates, whereas the low-forage diet had the highest thiamine concentration. Vitamin B12in the diets was under the level of detection. Consequently, despite a reduction in dry matter intake when the cows were fed the high-forage diet, increasing dietary forage concentration increased or tended to increase intakes of riboflavin, niacin, and vitamin B6but reduced thiamine and folate intakes. Increasing dietary forage concentration reduced apparent ruminal degradation of thiamine and apparent ruminal synthesis of riboflavin, niacin, and folates and increased ruminal degradation of vitamin B6, but had no effect on ruminal synthesis of vitamin B12. As a consequence, increasing the forage-to-concentrate ratio had no effect on the amounts of thiamine, riboflavin, and vitamin B12reaching the small intestine but decreased the amounts of niacin, vitamin B6, and folates available for absorption. Apparent ruminal syntheses of riboflavin, niacin, folates, and vitamin B12were correlated positively with the amount of starch digested in the rumen and duodenal flow of microbial N, whereas these correlations were negative for thiamine. Apparent ruminal syntheses of thiamine and vitamin B6were negatively correlated with their respective intakes, whereas folate intake was positively correlated with its synthesis in the rumen.
authors.affiliation: Agriculture and Agri-Food Canada, Sherbrooke Research and Development Centre, 2000 College, Sherbrooke, Québec, Canada, J1M 0C8; Département des Sciences Animales, Université Laval, 2425 rue de l'Agriculture, Québec, Québec, Canada, G1V 0A6.
authors.forename: M
authors.initials: M
authors.lastname: Seck
authors.affiliation: Department of Animal Science, Michigan State University, East Lansing 48824-1225.
authors.forename: J A Voelker
authors.initials: JAV
authors.lastname: Linton
authors.affiliation: Department of Animal Science, Michigan State University, East Lansing 48824-1225.
authors.forename: M S
authors.initials: MS
authors.lastname: Allen
authors.affiliation: Agriculture and Agri-Food Canada, Sherbrooke Research and Development Centre, 2000 College, Sherbrooke, Québec, Canada, J1M 0C8; Département des Sciences Animales, Université Laval, 2425 rue de l'Agriculture, Québec, Québec, Canada, G1V 0A6.
authors.forename: D S
authors.initials: DS
authors.lastname: Castagnino
authors.affiliation: Département des Sciences Animales, Université Laval, 2425 rue de l'Agriculture, Québec, Québec, Canada, G1V 0A6.
authors.forename: P Y
authors.initials: PY
authors.lastname: Chouinard
authors.affiliation: Agriculture and Agri-Food Canada, Sherbrooke Research and Development Centre, 2000 College, Sherbrooke, Québec, Canada, J1M 0C8. Electronic address: Christiane.Girard@agr.gc.ca.
authors.forename: C L
authors.initials: CL
authors.lastname: Girard
mesh_terms: D000821:Animal Feed; D000818:Animals; D002417:Cattle; D004032:Diet / Q000662:veterinary; D004043:Dietary Fiber / Q000378:metabolism; D004063:Digestion; D005260:Female; D005285:Fermentation; D007774:Lactation; D008892:Milk; D012417:Rumen / Q000378:metabolism*; D014803:Vitamin B Complex / Q000378:metabolism*
chemical_list: D004043:Dietary Fiber; D014803:Vitamin B Complex
keywords: B vitamin; dairy cow; duodenal flow; forage-to-concentrate ratio