Short communication: Relationships among plasma and milk vitamin B 12 , plasma free fatty acids, and blood β-hydroxybutyrate concentrations in early lactation dairy cows.

This study was undertaken to evaluate the relationship between plasma and milk concentrations of vitamin B ₁₂ as well as the relationship between plasma or milk concentrations of vitamin B ₁₂ and plasma concentration of free fatty acids (FFA) or blood concentration of β-hydroxybutyrate (BHB) of early lactating Ayrshire (AY) and Holstein (HO) cows. A total of 44 dairy herds (7 AY and 37 HO herds) and 62 AY (21 in first, 19 in second, and 22 in third and more lactations) and 228 HO (51 in first, 74 in second, and 103 in third and more lactation) cows between 3 and 40 d in milk were involved in the study. Hand-stripped milk samples and blood samples were taken 6 h after the morning milking. Milk and plasma samples were analyzed for vitamin B ₁₂ concentration and plasma samples were analyzed for FFA concentration. A handheld device was used for blood BHB concentration determination. Thresholds for elevated plasma FFA concentration and hyperketonemia were set at ≥0.70 and ≥1.2 mmol/L, respectively. Vitamin B ₁₂ concentration in milk of AY primiparous cows [2,557 (1,995-3,276) pg/mL] was lower than in milk from HO primiparous cows [3,876 (3,356-4,478) pg/mL], whereas no difference was observed among other parities and breeds. Regardless of breeds, plasma concentration of vitamin B ₁₂ of first and second parities was lower than plasma concentration of third and more lactation cows. Milk vitamin B ₁₂ concentration was positively correlated with plasma vitamin B ₁₂ concentration, but the relationship was stronger for AY (ρ averaging 0.63) than for HO cows (ρ averaging 0.36). For AY and HO breeds, a significant relationship between milk or plasma vitamin B ₁₂ concentrations and plasma FFA concentration (ρ between 0.29 and 0.59) was observed. Moreover, cows with elevated plasma FFA concentration had greater milk and plasma vitamin B ₁₂ concentrations than cows with normal plasma FFA concentration. No relationship between vitamin B ₁₂ concentration in milk or plasma and blood BHB concentration and hyperketonemia was noted. In summary, milk is not well correlated with plasma vitamin B ₁₂ concentration for HO. It could be hypothesized that elevated plasma concentration of FFA could have a negative effect on the use of vitamin B ₁₂ by cow cells, which increases the concentration of the vitamin in plasma and its secretion in milk.
(Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)