Nigel W. Tomkins

Effects of marine and freshwater macroalgae on in vitro total gas and methane production.

This study aimed to evaluate the effects of twenty species of tropical macroalgae on in vitro fermentation parameters, total gas production (TGP) and methane (CH4) production when incubated in rumen fluid from cattle fed a low quality roughage diet. Primary biochemical parameters of macroalgae were characterized and included proximate, elemental, and fatty acid (FAME) analysis. Macroalgae and the control, decorticated cottonseed meal (DCS), were incubated in vitro for 72 h, where gas production was continuously monitored. Post-fermentation parameters, including CH4 production, pH, ammonia, apparent organic matter degradability (OMd), and volatile fatty acid (VFA) concentrations were measured. All species of macroalgae had lower TGP and CH4 production than DCS. Dictyota and Asparagopsis had the strongest effects, inhibiting TGP by 53.2% and 61.8%, and CH4 production by 92.2% and 98.9% after 72 h, respectively. Both species also resulted in the lowest total VFA concentration, and the highest molar concentration of propionate among all species analysed, indicating that anaerobic fermentation was affected. Overall, there were no strong relationships between TGP or CH4 production and the >70 biochemical parameters analysed. However, zinc concentrations >0.10 g.kg−1 may potentially interact with other biochemical components to influence TGP and CH4 production. The lack of relationship between the primary biochemistry of species and gas parameters suggests that significant decreases in TGP and CH4 production are associated with secondary metabolites produced by effective macroalgae. The most effective species, Asparagopsis, offers the most promising alternative for mitigation of enteric CH4 emissions.

How feasible is it to replace urea with nitrates to mitigate greenhouse gas emissions from extensively managed beef cattle

Reducing methane emissions from cattle in Australia will be dependent upon finding a strategy that can be readily adopted by its northern beef industry. The majority of the herd are located in this region and they graze low-quality tropical (C4) pastures, resulting in high methane output. There are few mitigation options that can be readily applied to extensively grazed cattle. The addition of nitrate to the diet of cattle has been shown to reduce methane production and may be an applicable strategy in northern Australia. Nitrogen is often the primary limiting nutrient in low-quality tropical pastures and it is common practice by industry to supplement with urea. Supplying an equivalent dose of nitrogen using nitrate as an alternative to urea has been demonstrated in cattle without adverse impacts upon animal productivity or health. These findings may not be directly applicable to grazing cattle in northern Australian because the diets and feeding management are not representative of the region. Nitrite toxicity can result from feeding nitrates to livestock and there is evidence that the composition of the total diet and feeding pattern influences the risk of toxicity. If nitrate supplementation in grazing beef cattle in northern Australia can be demonstrated to reduce methane and be applied safely, adoption rates will still depend on carbon market pricing. Current modelling suggests that the cost of supplementing beef cows with nitrate in northern Australia would be at least double the cost of urea supplementation.

The red macroalgae Asparagopsis taxiformis is a potent natural antimethanogenic that reduces methane production during in vitro fermentation with rumen fluid

Livestock feed modification is a viable method for reducing methane emissions from ruminant livestock. Ruminant enteric methane is responsible approximately to 10% of greenhouse gas emissions in Australia. Some species of macroalgae have antimethanogenic activity on in vitro fermentation. This study used in vitro fermentation with rumen inoculum to characterise increasing inclusion rates of the red macroalga Asparagopsis taxiformis on enteric methane production and digestive efficiency throughout 72-h fermentations. At dose levels ≤1% of substrate organic matter there was minimal effect on gas and methane production. However, inclusion ≥2% reduced gas and eliminated methane production in the fermentations indicating a minimum inhibitory dose level. There was no negative impact on substrate digestibility for macroalgae inclusion ≤5%, however, a significant reduction was observed with 10% inclusion. Total volatile fatty acids were not significantly affected with 2% inclusion and the acetate levels were reduced in favour of increased propionate and, to a lesser extent, butyrate which increased linearly with increasing dose levels. A barrier to commercialisation of Asparagopsis is the mass production of this specific macroalgal biomass at a scale to provide supplementation to livestock. Another area requiring characterisation is the most appropriate method for processing (dehydration) and feeding to livestock in systems with variable feed quality and content. The in vitro assessment method used here clearly demonstrated that Asparagopsis can inhibit methanogenesis at very low inclusion levels whereas the effect in vivo has yet to be confirmed.

The concordance between greenhouse gas emissions, livestock production and profitability of extensive beef farming systems

Here we examine the concordance among emissions, production and gross margins of extensive beef farming systems by modelling a range of scenarios for herd management, animal genotype and pasture nutritive quality. We based our simulations on a case-study farm in central Queensland, Australia, and studied the influence of interventions designed for emissions mitigation, increasing productivity, or increasing gross margin. Interventions included replacing urea supplementation with nitrate, finishing cattle on the perennial forage leucaena (L), herd structure optimisation (HO), higher female fecundity (HF), and a leucaena finishing enterprise that had net farm emissions equal to the baseline (leucaena equal emissions; LEE). The HO intervention reduced the ratio of breeding cows relative to steers and unmated heifers, and lowered the ratio of costs to net cattle sales. Gross margin of the baseline, nitrate, L, LEE, HO and HF scenarios were AU

The effect of feeding frequency and dose rate of nitrate supplements on blood haemoglobin fractions in Bos indicus cattle fed Flinders grass (Iseilemia spp.) hay

146 000, AU

Asparagopsis taxiformis decreases enteric methane production from sheep

91 000, AU

Nitrate supplementation has marginal effects on enteric methane production from Bos indicus steers fed Flinders grass (Iseilema spp.) hay, but elevates blood methaemoglobin concentrations

153 000, AU

The effect of nitrate supplementation on arterial blood gases, haemoglobin fractions and heart rate in Bos indicus cattle after exercise

170 000, AU

Effect of feeding forage characteristic of wet or dry season tropical C4 grass in northern Australia, on methane production, intake and rumen outflow rates in Bos indicus steers

204 000 and AU

Effect of Tropical Algae as Additives on Rumen in Vitro Gas Production and Fermentation Characteristics

216 000, respectively. Enterprises with early joining of maiden heifers as well as HO and HF further increased gross margin (AU