Abstract
Simple SummaryThe beef industry in Northern Australia is characterized by an extensive grazing system in dry tropical rangelands defined by climate change indices of very low rainfall, a prolonged dry season and feeds of low nutritive value. In response, beef cattle need to be more efficient in converting the available drought-tolerant feeds to muscle, in an attempt to minimize greenhouse gas emissions. This study addressed the problem of reducing methane emissions from tropical beef cattle with the goal of decreasing the impact of climate change and greenhouse gas emissions in Northern Australia. The primary objective was to compare the effect of supplementing tropical beef cattle with both good quality lucerne and poor quality hay with increasing levels of different Desmanthus cultivars on in vivo methane emission. The results showed that in tropical beef cattle on high-quality diets, irrespective of cultivar and emission evaluation method, Desmanthus does not reduce methane emissions.The main objective of this study was to compare the effect of supplementing beef cattle with Desmanthus virgatus cv. JCU2, D. bicornutus cv. JCU4, D. leptophyllus cv. JCU7 and lucerne on in vivo methane (CH4) emissions measured by open-circuit respiration chambers (OC) or the GreenFeed emission monitoring (GEM) system. Experiment 1 employed OC and utilized sixteen yearling Brangus steers fed a basal diet of Rhodes grass (Chloris gayana) hay in four treatments—the three Desmanthus cultivars and lucerne (Medicago sativa) at 30% dry matter intake (DMI). Polyethylene glycol (PEG) was added to the diets to neutralize tannin binding and explore the effect on CH4 emissions. Experiment 2 employed GEM and utilized forty-eight animals allocated to four treatments including a basal diet of Rhodes grass hay plus the three Desmanthus cultivars in equal proportions at 0%, 15%, 30% and 45% DMI. Lucerne was added to equilibrate crude protein content in all treatments. Experiment 1 showed no difference in CH4 emissions between the Desmanthus cultivars, between Desmanthus and lucerne or between Desmanthus and the basal diet. Experiment 2 showed an increase in CH4 emissions in the three levels containing Desmanthus. It is concluded that on high-quality diets, Desmanthus does not reduce CH4 emissions.
Highlights
The global greenhouse gas emissions from livestock supply chains represent 14.5 percent of all human-induced emissions
Despite the presence of these compounds in Desmanthus spp., no difference was observed in CH4 yield between the Desmanthus treatments, the backgrounding (Rhodes grass) or lucerne diets when CH4 was measured with respiration chambers (RCs)
The absence of tannin effect on CH4 emissions was highlighted with the addition of polyethylene glycol (PEG) which did not show any difference
Summary
The global greenhouse gas emissions from livestock supply chains represent 14.5 percent of all human-induced emissions. Durmic et al [6] reported lower CH4 emissions compared to the mean emissions from 23 tropical grasses of 48%, 41% and 45% for cultivar JCU1 (Desmanthus leptophyllus), cv. Vandermeulen et al [5] attributed the in vitro reduction in CH4 emissions to the presence of secondary compounds such as hydrolysable tannins (HT), condensed tannins (CT) and/or their combinations in Desmanthus spp. Secondary plant compounds such as phenols, which include CT and HT, have an important role in feeding strategies to mitigate CH4 emissions from ruminants [8,9]. The comparative impact of supplementing beef cattle on a basal diet of Rhodes grass with varying levels of the tropical forage legume Desmanthus spp. and the temperate legume lucerne on CH4 emissions may fill in this significant knowledge gap in tropical beef cattle nutrition
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