Feeding frequency of bromoform in supplementary pellets influences enteric methane for sheep fed a forage diet

Previous sheep studies using bromoform-rich additives fed once a day have reported 6-23% enteric methane abatement, but these are lower compared with beef cattle or dairy cow studies (39-99%), where administration was more frequent. We investigated how changing the intake distribution of bromoform delivered in supplementary pellets (BromPellets) between days and within a day, without changing total bromoform intake, could influence enteric methane abatement in sheep. Seventy-two Merino weaners (BW 23.3 ± 1.7 kg, mean ± SD) were used in a complete randomised block design consisting of six pellet feeding frequencies: (1) control pellets fed daily in the morning only (CON-1), (2) control pellets fed daily in the morning and afternoon (CON-2), (3) BromPellets fed daily in the morning only (DLY-1), (4) BromPellets fed daily in the morning and afternoon (DLY-2), (5) BromPellets on alternate days in the morning only (ALT-1), and (6) BromPellets fed on alternate days in the morning and afternoon (ALT-2). A 50:50 lucerne (Medicago sativa) and wheaten chaff (Triticum spp.) basal diet was offered ad libitum. Pellet quantities accounted for ∼12% of total dry matter intake (DMI, formulated at 0 mg/kg DMI for control pellets and 31 mg/kg DMI for BromPellets). The allowance of BromPellets was the same for all bromoform treatments within the 48 h period. Sheep were housed in individual pens for 91 days, consisting of an experimental period of 61 days, which included four two-day methane measurement periods on each animal, four individual ruminal fluid samplings and BW measurements, with daily feed intake recorded throughout. Methane production (g methane/day) was measured in open-circuit respiration chambers at 19-day intervals and was significantly affected by the between-day (P < 0.001) and within-day (P < 0.001) variations in BromPellet supplementation frequency. There was no interaction between main effects (P = 0.168). In comparison with sheep on CON-1, sheep on DLY-1 reduced methane production by 38% and sheep on ALT-1 by 32%. Compared with CON-2 sheep, DLY-2 sheep reduced methane production by 60%, and by 51% for sheep on ALT-2. Average daily gain and feed conversion ratio were not significantly affected by feeding frequency of BromPellets over 48 h. The feeding frequency of BromPellets had a numerically greater effect on methane abatement if sheep received more supplement meals within a day than if sheep received supplements on more consecutive days. Grazing trials are required to validate these findings in a near-commercial environment.