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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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