Effect of fumarate and live yeast on ruminal fermentation, methane emissions, and blood metabolites in dairy goats

The objective of the current study was to evaluate the short-term effects of fumarate and active dry yeast (ADY) on ruminal fermentation, methane (CH 4 ) emissions, microbiota (composition and function), apparent total-tract digestibility, production performance, and blood metabolites in dairy goats using a 2 2 factorial design.Twenty-eight primiparous dairy goats were blocked and randomly assigned to 1 of 4 treatments: (1) control; (2) fumarate supplied at 34 g/d; (3) ADY supplied at 1.5 g/d; and (4) fumarate and ADY supplied in combination.The treatments lasted for 38 d.The results showed that fumarate supplementation reduced CH 4 production (L/d), yield (L/kg DMI), and intensity (L/kg milk yield) by 11.3%, 15.5%, and 21.9%, respectively, without affecting DMI, milk yield, or apparent nutrient digestibility.However, the CH 4 -depressing effect of fumarate began to decline 3 h postprandially and gradually diminished thereafter.Additionally, fumarate supplementation increased FCM with a higher NE L while reducing the ADG of goats with a lower NE G , resulting in no overall change in the net energy available for production.Fumarate supplementation also increased ruminal pH but reduced total VFA concentrations and microbial diversity.Although fumarate did not alter the ruminal microbial structure at the genome or gene level, it stimulated the growth of fumarate-and lactate-utilizing bacteria, which may contribute to CH 4 mitigation and raise rumen pH.Supplementation with ADY increased the NE L and the molar proportion of ruminal butyrate and tended to increase CH 4 production and FCM without affecting CH 4 yield or intensity.Most of the blood metabolites and enzymes influenced by fumarate were involved in the tricarboxylic acid (TCA) and the urea cycles.Fumarate reduced the substrate concentrations of the TCA cycle (e.g., glucose, malondialdehyde) and the urea cycle (e.g., ammonia) in blood, but it increased the end products of the urea cycle (BUN, MUN) and enhanced the activity of malate dehydrogenase, a key enzyme in the TCA cycle.These findings indicate that fumarate can reduce enteric CH 4 emissions and enhance the TCA and the urea cycles in host animals.