Effect of plantain in perennial ryegrass-white clover pasture on the ingestive behaviour, rumen fermentation parameters, and enteric methane emissions of spring-calving dairy cows

Plantain (Plantago lanceolata L.; PL) is a forage herb that can reduce nitrogen (N) losses from pasture-based dairy systems. However, there is a paucity of information on its effect on dairy cows' ingestive behaviour, rumen fermentation, and enteric methane (CH₄) emissions during the grazing season. This study investigated the effect of including PL in perennial ryegrass (Lolium perenne L.; PRG)-white clover (Trifolium repens L.; WC) pasture on the ingestive behaviour, rumen fermentation parameters, and enteric CH₄ emissions of spring-calving dairy cows throughout the grazing season (34-week study). Six primiparous and 20 multiparous dairy cows were blocked on parity and assigned to a pasture treatment in a complete block design (n = 13 per treatment): (1) PRG-WC (GrC), (2) PRG-WC-PL (GCP). Treatment groups were balanced for economic breeding index, calving date, milk production, and body condition score and live weight at calving. Cows offered GCP had significantly (1) longer eating times (average +103 min/day); (2) lower rumen fluid pH in early lactation (6.46 vs. 6.69); (3) lower rumen fluid ammonia-N concentration in early (1.49 vs. 2.25 mg/dL) and late (4.98 vs. 6.33 mg/dL) lactation; (4) lower proportion of acetic acid in early lactation and a greater proportion of propionic acid in rumen fluid throughout the grazing season, and (5) lower (-9.2 %) enteric CH₄ emissions (327 vs. 360 g/day), than cows offered GrC. The results demonstrate that GCP can increase cows' eating time while reducing rumen fluid pH and ammonia-N concentration. The lower enteric CH₄ emissions of cows offered GCP are encouraging for the development of more sustainable pasture-based dairy systems.