Effects of autolyzed yeast and rumen–protected glucose on dry matter intake, blood metabolites, inflammatory response and milk performance in transition dairy cows

Supplementation with autolyzed yeast and rumen-protected glucose are proposed to support metabolic adaptation during the transition period in dairy cows, yet responses remain inconsistent. This study concurrently evaluated their effects on intake, production, metabolic, and inflammatory parameters in multiparous Estonian Holstein cows (n = 28), assigned to control (n = 10), autolyzed yeast (10 g/day; n = 9), or rumen-protected glucose (200 g/day; n = 9) treatment group from −7 to 21 days in milk. Neither supplement affected dry matter intake, body condition loss, or ruminal pH dynamics. Under current dietary conditions, autolyzed yeast supplementation had no measurable effects on performance or metabolic indicators, likely due to low ruminal challenge. Rumen-protected glucose supplementation was associated with deeper negative energy balance postpartum, accompanied by a tendency for higher milk yield and non-esterified fatty acids, suggesting altered nutrient partitioning toward lactation rather than improved energy status. Besides that, systemic metabolic indicators and hepatic enzymes were largely unaffected by treatment, indicating limited influence on metabolic adaptation. Inflammatory responses were primarily time-dependent, although reduced haptoglobin concentrations for rumen-protected glucose suggest modest modulation of the acute phase response. These results indicate that responses to studied supplements are context-dependent and may not translate into improved metabolic resilience at moderate inclusion levels.