Bacteriocin-producing lactic acid bacteria as silage inoculants to reduce methane emissions in late lactation dairy cattle

Enteric fermentation in ruminants is the largest agricultural source of methane (CH₄) and contributes to global warming. Practical mitigation strategies are therefore needed for sustainable dairy production. This study evaluated a silage inoculant composed of bacteriocin-producing lactic acid bacteria (LAB) strains, Lactococcus lactis subsp. lactis SL242 and Lactiplantibacillus plantarum LP58 in late-lactation, spring-calving Holstein cows. Thirty cows were housed indoors and fed inoculated or control silage for 7 weeks. Daily milk yield and CH₄ emissions were measured, milk composition was analysed weekly and body weight and body condition scores (BCSs) were recorded biweekly. Dry matter intake (DMI) was determined using the n -alkane technique in week 4 of the experimental period to allow the animals to be fully adapted to the experimental diets, with estimated LAB intake of ∼10 11 CFU/cow per day. Treatment had no effect on DMI (12.4 ± 0.34 kg/cow per day), concentrate intake (4.3 kg/cow per day), milk yield or BCSs. However, a significant treatment-by-week interaction was observed for milk composition, with transient increases in milk fat concentration and milk solids production in the LAB group during weeks 4 and 5. Rumen microbiota analysis (16S rRNA sequencing) revealed distinct beta diversity clustering between groups at weeks 4 and 7. No overall reduction in CH₄ was observed, but emissions were numerically lower (5.8%) during weeks 4–7, with the greatest decrease (7.7%) at week 5 in the LAB group. These findings suggest that bacteriocin-producing LAB may transiently influence rumen microbial communities and reduce CH₄ output. Further research is warranted to optimise delivery strategies and maximise their potential to support sustainable dairy production.