Impact of dietary inclusion of field peas (Pisum sativum) on milk production, blood metabolites, rumen fermentation, and composition of rumen bacterial community of lactating dairy cows.

This study determined the effects of inclusion of field peas in the diet of lactating dairy cows on milk production, blood metabolites, rumen fermentation, and the rumen bacterial community. Twelve midlactation Holstein cows were used in a replicated 3 × 3 Latin square design with three 21-d experimental periods. Cows were offered either a control TMR or a TMR containing coarsely ground peas with a geometric mean diameter of 4.2 mm at inclusion rates of 3.9% (LP) or 7.8% (HP) of DM. Increasing the dietary inclusion rate of peas from 0% to 7.8% of DM increased DMI from 23.7 to 24.3 kg/d and milk fat from 4.16% to 4.38%. Milk and milk protein yields were not affected, averaging 36.1 and 1.22 kg/d across treatments. Increasing pea in the diet increased the milk fat proportion of C16:0, while reducing the proportion of PUFA. Including peas in the diet increased the ruminal concentrations of ammonia nitrogen (NH3-N) and branched-chain volatile fatty acids, BUN, and MUN from 6.17 to 8.67 mg/dL, 1.26 to 1.42 mmol/L, 4.20 to 4.46 mmol/L, and 11.4 to 12.7 mg/dL, respectively. The pH, VFA concentrations of rumen digesta, and Purine Derivative Index were not affected. Although the inclusion of pea did not alter the α diversity indexes of the rumen microbiota, comparisons of Euclidean distances revealed a trend toward compositional shifts in the rumen bacterial community between cows fed pea-including diets and those fed a control diet. Differential abundance analyses revealed increased relative abundances of Shuttleworthia and decreased abundances of Selenomonas in the pea diets compared with the control. This study showed that coarsely ground field peas can be included in the diets of dairy cows at up to 7.8% of DM without adverse effects on milk production or excessive rumen degradation of dietary protein.