Effects of phytogenic supplementation at different dietary protein concentrations on performance, rumen fermentation, and nutrient digestibility in lactating dairy diets.

We aimed to evaluate the effects of phytogenic supplementation at different dietary protein concentrations in lactating dairy cattle diets. We hypothesized that phytogenic supplementation with a blend of several plant-based ingredients providing saponins, encapsulated cinnamaldehyde, curcumin, capsaicin, and piperine would act synergistically with dietary protein supply to maintain or enhance lactational performance when CP is adequate. Twenty-four lactating Holstein dairy cows were used in a 4 × 4 Latin Square design with 4 28-d experimental periods (21 d adaptation + 7 d collection) and 4 treatments in a 2 × 2 factorial arrangement (CP concentrations and phytogenic supplementation): 16.5% without or with phytogenic and reduced CP concentration at 14.5% without or with phytogenic supplementation. Phytogenic supplement was top-dressed (7 g/d) on the TMR. Intake and milk yield were recorded daily, and milk samples were collected during the last week of the experimental period for milk components and FA analysis. Data were analyzed using PROC GLIMMIX of SAS 9.4 and the statistical model included the main effects of protein, phytogenic supplement and their interaction and period as a fixed effect, and cow nested in square as a random effect. Significance was declared at P ≤ 0.05 and tendencies were discussed at 0.05 <P ≤ 0.10. Milk yield (MY) and feed efficiency (MY/DMI) were greater with adequate protein diets whereas phytogenic supplementation had no main effect on these variables; however, DMI increased with phytogenic supplementation in reduced CP diets. Phytogenic supplementation increased milk fat concentration and yield, 3.5% FCM, ECM, and the proportions of de novo and preformed FA, while mixed FA tended to increase. In summary, phytogenic supplementation, irrespective of dietary CP concentration, enhanced FCM, milk fat concentration and yield, as well as the proportion of de novo and preformed FA. Additionally, adequate protein diets, regardless of phytogenic supplementation, increased milk yield and improved feed efficiency.