58 Effect of Autolyzed Yeast Feed Additives on the Function of Dairy Leukocytes and on the Milk Constituents of Holstein Cows

Mastitis is one of the leading causes of losses in dairy farming due to the cost of treatment and disposal rates. Yeast-based products can improve milk production and quality by stimulating immunity and ruminal efficiency. The different yeast derivative products and components can result in different effects. However, there are doubts about their real impact on the mammary gland. The yeast cell wall rich in β-glucans, considered an immunomodulator, acts mainly on phagocytes cells. The yeast cytoplasm is composed of metabolites, mainly amino acids, nucleotides, and vitamins, which impact in increasing the number of ruminal microorganisms and improve the feed conversion, resulting in an increase in milk production. The objective of this study was to evaluate two different autolyzed Saccharomyces cerevisiae feed additives supplemented in dairy cows and their effects on mammary gland phagocyte function, milk somatic cells count (SCC), and production. For this, 25 multiparous Holstein cows, in the middle third of lactation (average production of 25 L/day, and SCC below 200,000 cells/mL) were distributed into 3 treatments: Control group [CG] (n=8); Autolyzed Yeast [AY] (15 g/animal/day, RumenYeast, ICC Brazil Company, n=10); Yeast Metabolites [YM] (5 g/animal/day, MaxiDigest, ICC Brazil Company, n=7). Milk production, CSS, reactive oxygen species (ROS), and cytology of milk leukocytes were measured weakly for 56 days. AY increased phagocytes ROS from d40 and 42 compared to CG (P< 0.05); increased macrophages and decreased neutrophils percentage in milk, and decreased SCC at d48 and d56, compared to CG and YM (P< 0.05). YM increased ROS from d40 until D48 compared with CG (P< 0.05), with no change in the cellular profile of milk. There was an increase in milk production from d32 only in the YM versus CG and AY. In conclusion, AY demonstrated greater activation of the mammary gland cellular immune system, while YM promoted increased milk production and intermediate immune system stimulation.