Effect of supplementation with mesquite piperidine alkaloid extract on the relative abundance of ruminal bacteria and archaea in finishing feedlot lambs

This study evaluated the effects of dietary supplementation with Prosopis juliflora (mesquite) piperidine alkaloid extract (MPA; 17 mg kg -1 DM) or sodium monensin (MON; 17 mg kg -1 DM) in diets containing Tifton 85 hay harvested after 28 or 60 days of regrowth on ruminal fermentation characteristics and microbiota composition. Forty-two uncastrated Santa Inês crossbred lambs (29 ± 3 kg initial body weight) were randomly assigned to a completely randomized 3 ×2 factorial arrangement consisting of dietary additive (without additive, MON, or MPA) and hay harvest age (28 or 60 days of regrowth). Diets consisted of corn, soybean meal, mineral supplement, and Tifton 85 hay. Ruminal fluid was collected at slaughter after a 16-h fasting period, which should be considered when interpreting fermentation parameters. A significant interaction between dietary additive and hay harvest age was observed for butyrate concentration and the relative abundance (RAb) of methanogenic archaea and most ruminal bacteria. Within 28-day hay, MON increased butyrate concentration compared with the without additive and MPA treatments. For methanogenic archaea, MON reduced RAb in lambs fed 28-day hay, whereas MPA reduced RAb in lambs fed 60-day hay, possibly associated with greater Eubacterium ruminantium RAb, suggesting increased competition for hydrogen between alternative fermentative pathways and methanogenesis. Within 28-day hay, MPA reduced the RAb of Ruminococcus albus , Streptococcus bovis , and Gram-negative bacteria. In conclusion, MPA modulated the ruminal microbiome in a diet-dependent manner, reducing the relative abundance of methanogenic archaea in lambs fed Tifton 85 hay harvested after 60 days.