Assessment of Lactational Performance in Dairy Cows Receiving a Rumen Protected B Vitamin Blend during Lactation: Part 2: A Regression Analysis of 50 Studies

A previous series of meta-analyses demonstrated that a protected blend of B vitamins (RPBV: folic acid, B12, pyridoxine, pantothenic acid, and biotin;Jefo, St. Hyacinthe, QC, Canada) improved milk fat and protein yield, with variation in the extent of the response. These results represent additional analyses of the same dataset to determine if the degree of response to RPVB on milk, fat and protein yield might be related to the level of production, lactation number, or days in milk (DIM). Results from 50 on-farm switchback trials conducted in 7 countries between 2005 and 2015 were included in the analysis. All herds participated in monthly milk recording services, and all were Holstein herds. A total of 6483 cows, averaging 163 DIM on the first test date, participated in the studies. Data were analyzed using regression models that accounted for the effects of trial, period, days in milk (DIM) and lactation number on milk and component yield. Milk yield and fat yield increased with B vitamin inclusion, and the extent of change was determined to increase with lactation number (P < 0.05). Protein yield increased with the RPBV and was unaffected by lactation number (P < 0.05) Responses to the RPBV occurred throughout lactation but were found to decline with DIM for milk, fat and protein yield. The global equation revealed that milk yield with the rumen-protected B vitamin blend = 4.05 + [0.917 × control milk] - [0.0063 × DIM] + [0.246 × Lactation number] (R2 = 0.798) The use of regression models allows changes in milk, fat and protein yields with the rumen-protected B vitamin blend to be more accurately predicted.