Effects of Chestnut Tannin Extract on Enteric Methane Emissions, Blood Metabolites and Lactation Performance in Mid-Lactation Cows

Dietary tannin supplementation represents a potential strategy to modulate rumen fermentation and enhance lactation performance in dairy cows, though responses remain inconsistent. A 21-day feeding trial was conducted to evaluate the effect of chestnut tannin (CNT) extract on the enteric methane emissions (EME), blood metabolites, and milk production traits in mid-lactation dairy cows. Thirty-six Holstein cows were allocated to three homogeneous treatment groups: control (CNT₀, 0 g/d CNT), CNT₄₀ (40 g/d CNT), and CNT₈₀ (80 g/d CNT). Measurements of EME, dry matter intake (DMI), milk yield (MY), and blood and milk parameters were carried out pre- and post-21-day supplementation period. Compared with the no-additive group, the CNT extract reduced methane production, methane yield, and methane intensity in CNT₄₀ and CNT₈₀ (<i>p</i> < 0.001). CNT₄₀ and CNT₈₀ cows exhibited lower blood urea nitrogen (<i>p</i> = 0.019 and <i>p</i> = 0.002) and elevated serum insulin (<i>p</i> = 0.003 and <i>p</i> < 0.001) and growth hormone concentrations (<i>p</i> = 0.046 and <i>p</i> = 0.034), coinciding with reduced aspartate aminotransferase (<i>p</i> = 0.016 and <i>p</i> = 0.045), and lactate dehydrogenase (<i>p =</i> 0.011 and <i>p =</i> 0.008) activities compared to control. However, CNT₈₀ had higher circulating NEFA and BHBA than CNT₀ (<i>p</i> = 0.003 and <i>p</i> = 0.004) and CNT₄₀ (<i>p</i> = 0.035 and <i>p</i> = 0.019). The blood glucose, albumin, and total bilirubin concentrations were not affected. MY and fat- and protein-corrected milk (FPCM), MY/DMI, and FPCM/DMI were higher in both CNT₄₀ (<i>p</i> = 0.004, <i>p</i> = 0.003, <i>p</i> = 0.014, <i>p</i> = 0.010) and CNT₈₀ (<i>p</i> = 0.002, <i>p</i> = 0.003, <i>p</i> = 0.008, <i>p</i> = 0.013) cows compared with controls. Feeding CNT₈₀ resulted in higher protein content (<i>p</i> = 0.015) but lower fat percentage in milk (<i>p</i> = 0.004) compared to CNT₀. Milk urea nitrogen and somatic cell counts were significantly lower in both CNT₄₀ (<i>p</i> < 0.001, <i>p</i> = 0.009) and CNT₈₀ (<i>p</i> < 0.001 for both) compared to CNT₀, while milk lactose did not differ between treatments. These findings demonstrate that chestnut tannin extract effectively mitigates EME while enhancing lactation performance in mid-lactation dairy cows.