Asparagopsis taxiformis concentrates halogenated compounds that are known to inhibit cobamide-dependent methanogenesis in vitro and, therefore, has potential to mitigate enteric methane production. The present study investigated the effect of Asparagopsis on methane (CH4) production from sheep offered a high-fibre pelleted diet (offered at 1.2 × maintenance) at five inclusion levels of Asparagopsis for 72 days (0% (control), 0.5%, 1%, 2% and 3% organic matter basis as offered). Individual animal CH4 measurements were conducted at 21-day intervals using open-circuit respiration chambers. Asparagopsis inclusion resulted in a consistent and dose-dependent reduction in enteric CH4 production over time, with up to 80% CH4 mitigation at the 3% offered rate compared with the group fed no Asparagopsis (P < 0.05). Sheep fed Asparagopsis had a significantly lower concentration of total volatile fatty acids and acetate, but a higher propionate concentration. No changes in liveweight gain were identified. Supplementing Asparagopsis in a high-fibre diet (<2% organic matter) resulted in significant and persistent decreases in enteric methanogenesis over a 72-day period. Granulomatous and keratotic ruminal mucosa changes were identified in several sheep with Asparagopsis supplementation. While the outcomes of the present study may be extrapolated to feedlot to achieve the antimethanogenic effect associated with Asparagopsis, further work is required to define the long-term effects on productivity and animal health.

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Old man saltbush (Atriplex nummularia) and river saltbush (A. amnicola) are widely used in commercial grazing systems on saline land in south-western Australia. Three hypotheses were tested during a 3-year study aimed at understanding the performance of weaner Merino sheep grazing saltbush-based pastures. The first hypothesis, that young Merino sheep grazing river saltbush would be better able to maintain live weight, body condition and would grow more wool than sheep grazing old man saltbush, was not supported by the data. Across the 3 years of the study, sheep grazing old man saltbush lost significantly less live weight and grew more wool (proportionately 0AE06) than sheep grazing river saltbush. Differences in animal performance were considered to be associated with differences between the plant species in in vitro digestibility, concentrations of fibre, sulphur and crude protein in the herbage and the architecture of the Atriplex plants. The second and third hypotheses concerned supplementation strategies for sheep grazing saltbush. Three supplements were offered, namely barley grain, cereal straw or cereal hay, at a rate that approximated to one-third of the daily metabolizable energy requirements for maintenance of live weight. The performance of the sheep was higher when the grain supplement was offered but there was no effect of feeding roughage supplements compared to no supplementation. The findings suggested that the practice of feeding saltbush with adjacent crop stubbles is unlikely to be beneficial once any fallen grain has been consumed.

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