Polyunsaturated fatty acids are less effective to reduce methanogenesis in rumen inoculum from calves exposed to a similar treatment early in life.

The aim of this study was to evaluate the dose response on in vitro methane (CH) production of PUFA to which the inoculum donor animals had been exposed early in life. Sixteen Holstein calves (160 ± 3 and 365 ± 2 kg BW) at 6 and 12 mo of age were used as inoculum donors. Half of the calves were given increasing amounts of extruded linseed from birth (22 g/d) until 4 mo of age (578 g/d) first mixed with milk and then included in their concentrate. Linseed oil (LSO) was supplemented in vitro at 5 different doses (0, 0.6, 1.2, 2.4, and 4.8 mg/mL). Supplementation of LSO in the rumen inocula at both ages linearly decreased ( < 0.05) the in vitro CH production. Total in vitro VFA production was not affected by LSO supplementation. Inhibition of CH was smaller when using the rumen inoculum from calves that had received a similar treatment early in life ( < 0.05). Differences in response to in vitro supplementation of a type of fatty acids similar to those applied during early life suggest some "changes" in the functioning of the rumen microbial community.