Interactions acide folique - vitamine B12 - méthionine : effets sur le métabolisme hépatique et la productivité des vaches laitières
|Advisor:||Thivierge, Carole; Girard, Christiane|
|Abstract:||The aim of the present study was to determine if the effects of supplementary folic acid on lactational performance were due to improved methylneogenesis and if the supply in vitamin B12 could interfere with this metabolic pathway. In this eventuality, supplementary methionine, a major source of preformed methyl groups, should reduce the requirement for these vitamins. Sixty multiparous cows were fed either a diet calculated to supply 76% of methionine requirement (M-) or the same diet supplemented with 18 g of rumen-protected methionine (M+). Within each level of methionine, cows received either no vitamin supplement (B9-B12-), weekly intramuscular injections of 160 mg of folic acid alone (B9+B12-) or combined with 10 mg of vitamin B12 (B9+B12+), from 3 wk before to 16 wk after calving. At 12 week of lactation, glucose and methionine kinetics were measured by isotope dilution using infusions of D-[U13C]glucose, [13C]NaHCO3 and L-[1-13C, 2H3]methionine on 24 cows in treatments M-B9-B12-, M-B9+B12+, M+ B9-B12- et M+B9+B12+. Milk, blood and liver samples were collected to measure lactational performance, different metabolites and gene expression of key enzymes of energy metabolism and methylation cycle. The results showed that, in parallel with an increase in folates and vitamin B12 concentrations in milk, plasma and liver, administration of folic acid and vitamin B12 together increased milk production. The supplements of methionine affected methylation cycle by acting on mRNA abundance of key enzymes of this cycle whereas supplementary folic acid decreased plasma concentrations of homocysteine without any effect on animal performance. Intramuscular injections of folic acid and vitamin B12 increased whole body flux of glucose with a similar quantitative magnitude as the observed increment in milk lactose yield. Vitamin supplements increased also gene expression of the methylmalonyl-CoA mutase, an essential enzyme for the entry of propionate in the Krebs cycle. These results indicate that the effects of the combined supplements of folic acid and vitamin B12 on lactational performance are probably due to an improved efficiency of glucose metabolism rather than an effect on methylneogenesis.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||16 April 2018|
|Collection:||Thèses et mémoires|
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