Abstract
Lipid supplementation is a promising strategy for methane mitigation in cattle and has been evaluated using several different lipid sources. However, limited studies have assessed the effect of temperature on methane emissions from cattle and changes in incubation temperature have also not been extensively evaluated. The aim of this study was to evaluate the combined effect of pequi oil (high in unsaturated fatty acids) and incubation temperature on fermentation characteristics and microbial communities using the rumen simulation technique. A completely randomized experiment was conducted over a 28-day period using a Rusitec system. The experiment was divided into four periods of 7 days each, the first of which was a 7-day adaptation period followed by three experimental periods. The two treatments consisted of a control diet (no pequi oil inclusion) and a diet supplemented with pequi oil (1.5 mL/day) which increased the dietary fat content to 6% (dry matter, DM-basis). Three fermenter vessels (i.e., replicates) were allocated to each treatment. In the first experimental period, the incubation temperature was maintained at 39°C, decreased to 35°C in the second experimental period and then increased again to 39°C in the third. Pequi oil was continuously supplemented during the experiment. Microbial communities were assessed using high-throughput sequencing of the archaeal and bacterial 16S rRNA gene. Methane production was reduced by 57% following a 4°C decrease in incubation temperature. Supplementation with pequi oil increased the dietary fat content to 6% (DM-basis) but did not affect methane production. Analysis of the microbiota revealed that decreasing incubation temperature to 35°C affected the archaeal and bacterial diversity and richness of liquid-associated microbes, but lipid supplementation did not change microbial diversity.
Highlights
Methane (CH4) is produced in the rumen by a group of archaea known as methanogens
An interaction between pequi oil supplementation and incubation temperature was observed for total Volatile Fatty Acids (VFA), acetate, propionate and iso-valerate production and the acetate:propionate ratio (P ≤ 0.05; Table 3)
One of the strategies for lowering enteric methane emissions in ruminants has been the supplementation of diets with fatty acids due to their ability to decrease available organic matter fermented in the rumen, reduce methanogen activity and protozoal populations (Johnson and Johnson, 1995)
Summary
Methane (CH4) is produced in the rumen by a group of archaea known as methanogens. The production of CH4 during fermentation in the bovine rumen results in a loss of energy for the animal. Measures to mitigate enteric fermentation would reduce emissions, but may raise animal productivity by increasing digestive efficiency. Among documented methane abatement strategies, dietary modification appears to be one of the promising technologies to reduce methane emissions from ruminants (Beauchemin et al, 2008; Martin et al, 2010; Patra, 2013). The addition of fats to ruminant diets is one of the recognized means used to decrease enteric methane emissions (Beauchemin et al, 2008). Previous batch culture incubations in our research group indicated that pequi (Caryocar brasiliense) oil used at 1% v/v can reduce CH4 production by up to 74% (unpublished data)
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