Narasin as a Manure Additive to Reduce Methane Production from Swine Manure
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Animal production systems are an important source of anthropogenic methane emissions. Production of methane results from microbial activity by anaerobic bacteria populations within the stored manure that breaks down organic material and converts it to biogas. Swine manures obtained from three deep pit storages in Central Iowa were dosed with Narasin, an ionophore, to evaluate its inhibitory effects on methane and biogas production. Four Narasin dosing rates were evaluated, these included 0 (Control), 7.5, 15, and 30 mg Narasin/kg of manure. Overall, the results indicated that Narasin had an inhibitory effect on methane and biogas production, with greater inhibition being seen at higher dosing rates. The inhibitory effect weakened with time such that after 120 days of incubation there was no statistical difference in cumulative methane production between samples dosed with Narasin and the control. Two additional treatments, based on the addition of an easily available carbohydrate, sugar, were also evaluated. Sugar (10 g per kg of manure) was added to manure both with (15 mg Narasin/kg) and without (0 mg Narasin/kg manure) Narasin amendment. The addition of sugar was performed to evaluate the impact an easily available substrate had on the inhibitory effects of Narasin. The results suggested that methane production was initially increased by the addition of sugar, but that the increased methane production lasted for less than 6 days, at which point cumulative methane production was similar to the control. When treated with both Narasin and sugar the inhibitory effect did not impact the gas production during the sugar digestion phase, but did result in reduced methane and biogas production thereafter. Overall the results indicated that Narasin can be an effective pit additive but further study is needed to recommend dosing frequency and to evaluate how the continuous addition of manure impacts Narasin effectiveness. Thus, this paper will describe a scaled up lab experiment that will be used to evaluate the effect of dosing frequency of Narasin to determine how producers could most effectively use it at the farm scale.