Potential benefits of phytogenic additives and inactivated yeast (Pichia guilliermondii) on performance and nitrogen utilization of dairy cows during summer

This study evaluated the supplementation of phytogenic additives and inactivated yeast, either alone or in combination with a blend of fermentation residues, on DM and nutrient intake, apparent total-tract digestibility, feed particle sorting, milk yield and composition, blood metabolites, and nitrogen utilization in dairy cows during summer. Thirty-nine mid- to late-lactation cows (174 ± 76.0 DIM; 31.0 ± 3.42 kg/d milk yield, 630 ± 72.5 kg BW) were grouped into 13 blocks based on DIM, milk yield, BW, and parity, and assigned to the following treatments: control (CON), phytogenic compounds + sanguinarin and magnolia extract, fed at 1.94 g/kg DM (Heat Stress Solution, ADM Animal Nutrition; PHY); and phytogenic compounds + blend of fermentation residues (mycelium strains, Aspergillus niger), fed at 1.94 g/kg DM (Thermal Care R, ADM Animal Nutrition; BLD). Cows were subjected to a 2-wk covariate period and treatments were provided during the following 9 wk. Data were analyzed as repeated measures, modeling the fixed effects of treatment, time, and their interaction, as well as the random effect of block. Covariate measures were included in the model as fixed effects and treatment means were compared through orthogonal contrasts (CON vs. PHY + BLD and PHY vs. BLD). The temperature-humidity index during the experiment was 73.9 ± 1.37. Cows supplemented with phytogenic additives and inactivated yeast, either alone or combined with a blend of fermentation residues, tended to have lower DM intake, which consequently led to reduced intake of CP, ether extract, and starch. Digestibility of NDF was decreased in cows fed phytogenic additives (PHY and BLD). Digestibility of DM tended to decrease and the selection of medium-sized feed particles (4-8 mm) was greater in the PHY group compared with BLD. No significant differences were found in milk yield, milk composition, nitrogen utilization, or excretion of purine derivatives. However, supplemented cows showed greater feed efficiency (FCM yield ÷ DM intake), and a trend toward reduced MUN levels, indicating improved nitrogen utilization. These results suggest that these additives can enhance feed efficiency and nutrient utilization without compromising milk yield in dairy cows during summer.