Methane emissions from dairy cattle divergently selected for bloat susceptibility

Bloat susceptibility is a genetically inherited trait and this study explored whether cattle divergently selected for this trait (low or high bloat susceptibility) also differ in methane (CH4) emissions. Twelve low bloat (402 ± 12 kg liveweight, LW) and 12 high bloat (334 ± 13 kg LW) Friesian × Jersey mixed age (2–4 years old) non-lactating and non-pregnant female cattle were used in a late autumn (June) grazing experiment involving two periods (P1 and P2). Methane emissions were measured during 5 (P1) or 4 (P2) consecutive days using the sulfur hexafluoride (SF6) tracer technique. In P1 only, titanium dioxide (TiO2) was used for faecal output and feed dry matter intake (DMI) estimations and it was found that the selection lines did not differ in DMI per unit of LW (17.3 ± 1.3 v. 15.4 ± 1.3 g DMI/kg LW, P > 0.05; for low and high bloat cows, respectively). In both periods, the mean absolute CH4 emissions from low bloat cows were significantly higher (P   0.05) either at P1 (346 ± 16 v. 312 ± 11 mg/kg LW) or P2 (345 ± 11 v. 347 ± 10 mg/kg LW). In P1, when DMI was estimated using TiO2, the selection lines did not differ (P > 0.05) in CH4 yields per unit of intake (20.6 ± 0.8 v. 21.3 ± 1.4 g/kg DMI for low and high bloat, respectively). Previous studies with the same herd showed that the selection lines did not differ in DMI per unit of LW, which was confirmed by the present study from estimations of DMI by TiO2 dosing in P1. It is concluded that low and high bloat susceptible genotypes did not differ in their CH4 yields per unit of feed intake.