A52-75-2007E.pdf - AgroMedia International Inc

Feeding7Folic acid and vitamin B12 requirements of dairy cows: A concept tobe revisitedCorresponding AuthorGirard, C.L.AAFC Dairy and Swine Researchand Development CentreCollaboratorsMatte, J.J.AAFC Dairy and Swine Researchand Development CentreLivestock Production Science (2005) Vol. 98 p. 123-133.Until recently, it had been generally assumed that the ruminant animal’srequirements for folic acid and vitamin B12 were satisfied by the rumen microbialsynthesis of these compounds, combined with dietary sources thatescape rumen degradation. As a result, few studies have been undertakento define the requirements of the vitamins at high levels of production.Studies summarized in this review demonstrate that supplementation canimprove milk production and metabolic efficiency, particularly in early lactation.These results imply that microbial synthesis and basal dietary levelsof folic acid and vitamin B12 may not always be adequate to support theincreased productivity of today’s lactating cows. However, supplementationof unprotected sources is not very efficient because of their rapidbreakdown in the rumen. Identification of a benefit from providing supplementalamounts of these 2 vitamins may lead to the development of productsin which they are protected from rumen degradation.8Modeling nutrient supply to dairy cattle from a feedstuff usingNRC-2001 (a TDN-based model) with inputs based on in situ andmobile bag technique measurementsCorresponding AuthorYu, P.University of SaskatchewanCanadian Journal of Animal Science (2005) Vol. 85 p. 513-519.The 2001 edition of the US National Research Council’s (NRC) publication,‘Nutrient Requirements of Dairy Cattle’ introduced the concept of metabolizableprotein (MP) in its nutritional model. MP is defined as true proteinabsorbed in the intestine, derived from microbial protein, undegraded feedprotein, gastro-intestinal secretions and protein released from the normalturnover of digestive tract tissue. Protein synthesis by rumen microbes maybe limited by the supply of either degradable protein or energy-yieldingcomponents in the diet. When degradable protein is available in excessof energy, attempts are often made to rebalance the diet, increasing thecontribution of undegraded feed protein to MP. To this end, one strategyoften applied to oilseeds and pulse crops is to heat the seeds, decreasingthe rumen degradability of their constituent proteins. The objective of thisstudy was to assess the value of the 2001 NRC model in predicting the MPcontributions of raw or toasted whole lupin seeds. Ground seed sampleswere incubated in the digestive tract to estimate protein degradability anddigestibility. These estimates were used as inputs into the 2001 NRC model,in place of values derived from the model’s feed database. This approachsignificantly improved the prediction of microbial protein synthesis andMP supply.38 Highlights in Canadian Dairy Cattle Research - 2007