Ruminal methanogenesis and biohydrogenation reduction potential of papaya (Carica papaya) leaf: an in vitro study

Abstract

An in vitro gas production study was conducted to test the effect of papaya leaf (PL) at different concentrations of 0 (CON), 10% (Low PL: LPL), 15% (Medium PL: MPL) and 25% (High PL: HPL) of replacement with alfalfa hay (AH) in substrate (50% AH + 50% concentrate) on rumen methane (CH4) production, rumen biohydrogenation (BH) of polyunsaturated fatty acid (PUFA) and rumen microbial population. PL at different concentrations were mixed with 30 ml of buffered rumen fluid and were incubated for 24 h. Methane production (ml/250 mg DM) declined at a decreasing rate (linear p = 0.03) with increasing levels of PL. The acetic/propionic ratio (1.80) was lowest (p < 0.05) for HPL compared with CON (2.04), LPL (1.95) and MPL (1.89). Supplementation of the diet with PL significantly (p < 0.05) decreased the rate of BH of C18:2n-6 (LA) and C18 PUFA after 24 h of incubation especially at the higher inclusion rate, resulting in an increased production of rumen BH intermediates such as conjugated linoleic acid (CLA), whereas saturated fatty acid (SFA) decreased in the rumen fluid after 24 h of incubation. Estimates of rumen microbial population using real-time PCR assay showed a reduction in total methanogens (p < 0.05) in MPL (−12%) and HPL (−16%) and increase in total bacteria population (HPL: +5%) and Butyrivibro fibrisolvens (MPL: +20; HPL: +23%) among PL treatment groups compared with the CON group. These results emphasise PL as a beneficial feed material for ruminants.