Abstract
Twenty male Saanen goats were randomly assigned to four levels of lovastatin supplementation and used to determine the optimal dosage and sustainability of naturally produced lovastatin from fermentation of palm kernel cake (PKC) with Aspergillus terreus on enteric methane (CH4) mitigation. The effects on ruminal microbiota, rumen fermentation, feed digestibility and health of animal were determined over three measuring periods (4-, 8- and 12-weeks) and the accumulation of lovastatin in tissues was determined at the end of the experiment. The diets contained 50% rice straw, 22.8% concentrates and 27.2% of various proportions of untreated or treated PKC to achieve the target daily intake level of 0 (Control), 2, 4 or 6 mg lovastatin/kg body weight (BW). Enteric CH4 emissions per dry matter intake (DMI), decreased significantly (P<0.05) and equivalent to 11% and 20.4%, respectively, for the 2 and 4 mg/kg BW groups as compared to the Control. No further decrease in CH4 emission thereafter with higher lovastatin supplementation. Lovastatin had no effect on feed digestibility and minor effect on rumen microbiota, and specifically did not reduce the populations of total methanogens and Methanobacteriales (responsible for CH4 production). Similarly, lovastatin had little effect on rumen fermentation characteristics except that the proportion of propionate increased, which led to a decreasing trend (P<0.08) in acetic: propionate ratio with increasing dosage of lovastatin. This suggests a shift in rumen fermentation pathway to favor propionate production which serves as H+ sink, partly explaining the observed CH4 reduction. No adverse physiological effects were noted in the animals except that treated PKC (containing lovastatin) was less palatable at the highest inclusion level. Lovastatin residues were detected in tissues of goats fed 6 mg lovastatin/kg BW at between 0.01 to 0.03 μg/g, which are very low.
Highlights
Mitigation of ruminant methane (CH4) emissions helps protect the environment as enteric CH4 emissions account for approximately 17% of the total global anthropogenic CH4 production [1]
Dry matter intake (DMI) decreased with increasing level of lovastatin in the diet but only the dry matter intake (DMI) for the 6 mg/kg body weight (BW) treatment was significantly lower than the control (Table 4)
The above shortcomings have led to the search of specific compounds, such as statins, a class of HMG-CoA reductase inhibitors which interfere with the biosynthesis of cell membranes of archaea, and selectively suppressing growth of methanogens
Summary
Mitigation of ruminant methane (CH4) emissions helps protect the environment as enteric CH4 emissions account for approximately 17% of the total global anthropogenic CH4 production [1]. Many nutritional CH4 mitigation approaches such as feed supplemented with essential oils [2], nisin [3] and condensed tannins [4] have been reported, but they are unlikely to be accepted at the farm level because the effects are often temporary as rumen microbiota can adapt to changes in the rumen ecosystem created by the mitigating agents. Some CH4 mitigating agents inhibit growth of useful rumen microorganisms such as peptidase producing and cellulolytic bacteria [5,6,7] leading to lower fiber digestion in the rumen. Lovastatin, an inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMG-CoA reductase), has been reported to effectively inhibit the HMG-CoA reductase activity which is necessary for biosynthesis of the cell membranes of archaea and selectively suppressing growth of methanogens without affecting other microorganisms in the rumen microbial community [9,10]. One study [10] was an in vitro study
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