ABSTRACT The reduction of enteric methane emissions from ruminants is a central topic in research on sustainable livestock research. Feed additives targeting the rumen microbiome are among the strategies being explored to reduce methane emissions and improve nutrient efficiency. In this context, the aim of this study was to investigate the effects of an additive composed by condensed tannins and Saccharomyces cerevisiae yeast compounds on intake, productive performance, nitrogen metabolism, methane emission, and rumen microbial biodiversity of lactating Holstein and Holstein × Gyr dairy cows. Sixteen dairy cows (8 Holstein and 8 Holstein × Gyr) were allocated to 2 treatments following a randomized block design according to milk yield and DIM: a control treatment (CON; without additive) and an additive treatment (ADT), in which the diet contained 2.7 g/kg DM of a commercial feed additive composed of condensed tannins from Acacia mearnsii and yeast compounds derived from Saccharomyces cerevisiae (Muucare Nature®). The trial lasted 84 d, including a 24-d adaptation period. The animals were housed in tie stalls and kept under identical conditions. Between d 17–19 and 47–49, samples of orts and feeds offered to the animals were collected. On d 18 and 19, as well as 48 and 49, spot collections of feces and urine were performed. Rumen fluid was collected via an esophagus on d 22 and 52, and the microbial composition was later analyzed by 16S rRNA sequencing. The VFA concentrations and rumen ammonia nitrogen were also quantified. Methane emission was measured using the sulfur hexafluoride tracer technique. The additive increased the apparent digestibility of DM and OM by about 6% without affecting feed intake, milk yield, and feed efficiency. Methane emission per ECM (g/kg) was reduced by almost 30%, and methane emission per milk yield (g/kg) showed a similar trend. The ADT cows showed higher propionate production and a lower acetate-to-propionate ratio. The microbial diversity in the rumen was altered, with a reduced α diversity and a different community composition, including an increased abundance of Prevotella ruminicola. The total amount of methanogens was unchanged, although one species, Methanobrevibacter smithii, tended to be less abundant. The additive reduced methane emission and improved nutrient digestibility, rumen fermentation, and nitrogen efficiency. These results indicate that the additive based on Acacia tannins and Saccharomyces cerevisiae yeast is a sustainable tool to reduce methane emissions in dairy production systems without compromising milk production.
Sant'ana et al. (Wed,) studied this question.