Vitamin B requirements and duodenal deliveries in lactating dairy cows: Organization of a limited literature

Abstract

The eight vitamins of the B vitamin (BV) complex (i.e., thiamine, riboflavin, niacin, pantothenic acid, vitamin B6, biotin, folate, cobalamine) are vital to numerous facets of mammalian metabolism. However a lack of organized requirements and duodenal delivery predictions limits their ability to be used in formulating rations for dairy cows. The objective was to create a model to evaluate dairy cow diets for their predicted duodenal BV deliveries relative to predicted requirements. Requirements for each BV were calculated in a factorial fashion with the total requirement for each being the sum of its needs for maintenance (including gestation) and lactation. The amount of each BV exiting the forestomachs was also calculated factorially, with the total outflow of each BV being the sum of its outflow from the diet, from particle free rumen fluid and in rumen escape microbial biomass. Initial model evaluation revealed over- or under-prediction of some BV sufficient to suggest that net forestomach disappearance and/or endogenous secretions not captured in the model were impacting correct prediction of duodenal flows of some duodenal BV. After correction of flows of some BV based upon relationships of net forestomach BV disappearance or appearance derived from relationships with milk true protein production, the final model suggested the sequence and extent of potential BV oversupply for a representative dairy cow was biotin (∼3300% of requirement), niacin (∼2200%), cobalamine (∼1500%), riboflavin (∼340%), pantothenic acid (∼220%), vitamin B6 (∼190%), thiamine (∼140%), and folate (∼105%). Further evaluation of these predicted BV supplies using published studies, where available, of performance responses of lactating dairy cows to supplementation of individual BV suggested that only dietary supplementation of folate has consistently positively impacted performance of lactating dairy cows, although evaluations of riboflavin, pantothenic acid, thiamine and vitamin B6 were severely hampered by a lack of studies. Research on dairy cattle responses to supplemental BV, except biotin, cobalamin and niacin, is suggested, although it is recommended that all dietary BV levels, and an estimate of ruminal microbial outflow, be reported in such studies.