The objective of this research was to evaluate the impact of a dietary supplemental rumen protected B vitamin blend (RPBV: Folic acid, B12, pyridoxine, pantothenic acid, and biotin; Jefo, St. Hyacinthe, QC Canada) on milk, fat, and protein yield in cows past peak lactation. Results from 50 double reversal design trials (control-test-control) were evaluated using meta-analyses. All herds participated in monthly milk recording services, and all were Holstein herds. Within each of the 50 trials, cows included in the statistical analysis were over 45 days in milk (DIM) at the first milk test, averaged 159 ± 26 DIM on the first test date, and were available for all milk collection periods. A total of 6483 cows from 7 countries were represented in the 50 studies, with an average herd size of 129.7 ± 118.0. Meta-analyses were conducted to determine effect size for milk, fat, and protein yield based on the treatment differences and standard errors (SE) from the individual trials. Results indicated that dairy cows responded positively to the inclusion of the rumen protected B vitamin blend. Forest plots revealed trial-to-trial variation and might be related to age, level of milk production, and stage of lactation of the cows.

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] (R 2 = 0.798) The use of regression models allows changes in milk, fat and protein yields with the rumenprotected B vitamin blend to be more accurately predicted.