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Effects of Intramuscular Injections of Vitamin B₁₂ on Lactation Performance of Dairy Cows Fed Dietary Supplements of Folic Acid and Rumen-Protected Methionine^*

Agriculture and Agri-Food Canada, Dairy and Swine Research and Development Centre, Lennoxville, QC, Canada J1M 1Z3

Corresponding author: Christiane L. Girard; e-mail: girardch{at}agr.gc.ca.

The experiment was undertaken to determine the effects of i.m. injections of vitamin B₁₂ on lactational performance of primiparous dairy cows fed dietary supplements of folic acid and rumen-protected methionine from 4 to 18 wk of lactation. Fourteen primiparous Holstein cows were assigned to 7 blocks of 2 cows each, according to milk production during the third week of lactation. All cows were fed a basal diet supplemented daily with rumen-protected methionine (18 g of supplement, to bring the estimated supply of methionine to 2.2% of metabolizable protein) plus folic acid (4 mg per kg of BW). Within each block, the cows received a weekly i.m. injection (2 mL) of saline or 10 mg of vitamin B₁₂. Milk production was recorded daily. Milk and blood were sampled every 2 wk. Supplementary vitamin B₁₂ increased energy-corrected milk from 25.8 to 29.0 (SE 1.6) kg/d, as well as milk yields of solids [3.52 to 3.90 (SE 0.22) kg/d], fat [0.87 to 1.01 (SE 0.06) kg/d], and lactose [1.48 to 1.64 (SE 0.11) kg/d]. Supplementation also increased concentrations and amounts of vitamin B₁₂ secreted in milk but had no significant effect on dry matter intake and concentrations and amounts of folates in milk. Packed cell volume, blood hemoglobin, and serum vitamin B₁₂ were increased by supplementary vitamin B₁₂, whereas serum methylmalonic acid was decreased. Serum concentrations of sulfur amino acids were unchanged by treatment. These findings support the hypothesis that, in early lactation, supply of vitamin B₁₂ was not optimal and limited the lactation performance of the cows.

Key Words: lactation • vitamin B₁₂ • folic acid • rumen-protected methionine

Abbreviation key: ECM = energy-corrected milk, 5-methyl-THF = 5-methyl-tetrahydrofolate, SAM = S-adenosylmethionine, THF = tetrahydrofolate

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