Early-life multi-component additive supplementation and its effects on ruminal development and methane emissions in dairy heifer calves raised on pasture during the first 180 days of life

Enteric methane (CH 4 ) emissions from ruminants are a major challenge for sustainable livestock production, particularly in tropical pasture-based systems such as those predominant in Brazil. Early-life nutritional programming has been proposed as a strategy to modulate rumen development, given the high microbial plasticity during neonatal stages. This study evaluated the effects of early supplementation with a commercial multi-component additive on performance, ruminal fermentation, microbial protein synthesis, and CH 4 emissions in dairy heifer calves raised under grazing Cynodon spp. conditions. At birth, 20 female Holstein × Jersey calves were assigned to two treatments: control (placebo) or multi-component additive (3.0 g/animal/day; containing Saccharomyces cerevisiae , essential fatty acids, organic minerals, crude protein, and mannan-oligosaccharides), administered from birth to 90 d of age. One calf from the control group was excluded during the experimental period; therefore, 19 calves were included in the final analyses (28.2 ± 5.01 kg BW). Animals were monitored for up to 180 d to assess potential persistent effects. Growth performance, dry matter intake (DMI), short-chain fatty acid (SCFA) profile, microbial protein synthesis, and CH 4 emissions, were evaluated. Treatments showed no effects on performance, DMI, SCFA profile, microbial protein synthesis, or CH 4 emissions ( P > 0.05). However, significant period effects ( P < 0.05) were detected for most variables, reflecting increased intake, fermentative activity, and microbial synthesis associated with ruminal development. The CH 4 emissions increased with age, driven primarily by higher DMI and dietary fiber intake, without changes in energy conversion efficiency (Ym). Under these conditions, early-life supplementation with the multi-component additive did not alter ruminal function, microbial efficiency, or enteric CH 4 emissions in pasture-raised calves. The observed responses were primarily associated with physiological development rather than supplementation.