Effect of dietary humic substances on rumen fermentation, blood parameters, immune function, milk composition, and mammary health in periparturient dairy cows.

Objectives: The present trial aimed to evaluate the impact of humic substances (HS) on rumen fermentation, blood and immunological parameters, milk yield and composition, and mastitis incidence in dairy cows during the first 50 days of lactation. Materials and Methods: Sixty healthy pregnant Slovak spotted cows in the 2 months preceding calving were allocated to two groups (30 cows per group). The control group (C-group) received total mixed ration (TMR) without HS, while the experimental group (HS-group) received HS at a dose of 100 gm/day per cow for 60 days antepartum (d.a.p.) and 8 days postpartum (d.p.p.). Results: HS supplementation increased ruminal pH and the acetate-to-propionate ratio (C2:C3; 3.46% vs. 2.56%), while ammonia concentrations decreased on the 8th d.p.p. At the same time, animals treated with HS showed reduced serum and milk urea levels. Furthermore, milk protein and non-fat dry matter content increased, while somatic cell count (SCC) decreased. This was reflected in fewer udder quarters infected with mastitis pathogens in the HS group on 8th d.p.p. The positive effect of HS supplementation was associated with a favorable modulation of the ruminal fermentation pattern and reduced irritation by pathogenic bacteria, leading to decreased blood leukocyte concentrations and reduced phagocytic capacity and engulfing ability on 8th d.p.p. in the HS group. Conclusions: As demonstrated in our study, HS can be efficiently used as a promising organic additive in the TMR for both dry and fresh cows as part of a comprehensive herd health program.