Methane emissions and ruminal fermentation in 22-month-old dairy-beef heifers, previously weaned at different ages, grazing ryegrass or chicory herbage in summer

Early-life management can influence methane (CH₄) production in ruminants after weaning, and the type of forage fed to animals can interact with the early-life interventions. However, the persistence of the effect of early life interventions has been little studied in cattle. The study aim was to evaluate the interaction effect between weaning age (10 vs. 20 weeks) and diet on CH₄ production and ruminal fermentation from dairy-beef heifers when they were 22-months old. Hereford × Friesian female calves were weaned from milk at 10 weeks of age (n = 36) or at 20 weeks of age (n = 36). When the heifers were 22-months old and weighed 523 ± 33 kg (mean ± standard deviation), they grazed ad libitum mature ryegrass-based herbage ( Lolium perenne ; RG) or ad libitum chicory ( Cichorium intybus ; CHI) in a crossover design with two 21-day periods. Methane and carbon dioxide (CO 2 ) production were measured using GreenFeed units. There was no effect of weaning age or of weaning age × diet interaction on CH 4 (g/d) and CO 2 (kg/d) production, residual CH 4 and acetate plus butyrate to propionate plus valerate (AB:PV) ratio. Methane production was 6 % less (165 ± 25 vs 168 ± 26 g/d) and CO 2 production was 12 % greater (8.1 ± 0.6 vs 7.2 ± 0.5 kg/d) and AB:PV was 6 % greater in heifers grazing CHI compared to those grazing RG. Methane production was therefore lower from heifers grazing CHI than from heifers grazing RG, but the weaning age intervention resulted in a similar CH₄ production in 22-month-old cattle.