Abstract
Methane emissions from ruminant livestock have been intensively studied in order to reduce contribution to the greenhouse effect. Ruminants were found to produce more enteric methane than other mammalian herbivores. As camelids share some features of their digestive anatomy and physiology with ruminants, it has been proposed that they produce similar amounts of methane per unit of body mass. This is of special relevance for countrywide greenhouse gas budgets of countries that harbor large populations of camelids like Australia. However, hardly any quantitative methane emission measurements have been performed in camelids. In order to fill this gap, we carried out respiration chamber measurements with three camelid species (Vicugna pacos, Lama glama, Camelus bactrianus; n = 16 in total), all kept on a diet consisting of food produced from alfalfa only. The camelids produced less methane expressed on the basis of body mass (0.32±0.11 L kg−1 d−1) when compared to literature data on domestic ruminants fed on roughage diets (0.58±0.16 L kg−1 d−1). However, there was no significant difference between the two suborders when methane emission was expressed on the basis of digestible neutral detergent fiber intake (92.7±33.9 L kg−1 in camelids vs. 86.2±12.1 L kg−1 in ruminants). This implies that the pathways of methanogenesis forming part of the microbial digestion of fiber in the foregut are similar between the groups, and that the lower methane emission of camelids can be explained by their generally lower relative food intake. Our results suggest that the methane emission of Australia's feral camels corresponds only to 1 to 2% of the methane amount produced by the countries' domestic ruminants and that calculations of greenhouse gas budgets of countries with large camelid populations based on equations developed for ruminants are generally overestimating the actual levels.
Highlights
The quantification and abatement of methane (CH4) emissions from domestic ruminants have received major attention from the scientific community during the last decades [1,2,3,4]
Some of the features that characterize ruminants, like the ability to ruminate and a chambered foregut that enables the sorting of food particles according to size, are shared with another artiodactyl suborder, the camelids (Tylopoda) [7,8,9,10]. Given these similarities in digestive anatomy and physiology, it has been assumed that camelids produce similar amounts of CH4 as ruminants when compared at the same body mass range [6,11,12] and are responsible for the release of significant amounts of this greenhouse gas (GHG)
Despite the similarities to the ruminant digestive anatomy and physiology, there are some important differences between the two suborders: 1. The camelid foregut can be separated into three compartments [7,8]
Summary
The quantification and abatement of methane (CH4) emissions from domestic ruminants have received major attention from the scientific community during the last decades [1,2,3,4]. Some of the features that characterize ruminants, like the ability to ruminate and a chambered foregut that enables the sorting of food particles according to size, are shared with another artiodactyl suborder, the camelids (Tylopoda) [7,8,9,10]. Given these similarities in digestive anatomy and physiology, it has been assumed that camelids produce similar amounts of CH4 as ruminants when compared at the same body mass range [6,11,12] and are responsible for the release of significant amounts of this GHG. Despite structural similarities with the ruminant foregut, the camelid compartments cannot be considered as direct homologues [8]
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