A series of in vitro and in vivo experiments was conducted to evaluate the methane-reducing potential of some medicinal plant extracts in order to use them as alternative additives to replace antibiotics such as monensin. A methanolic extraction procedure was used to extract secondary metabolites from plants because these metabolites have been found to have rumen modulation properties, which may help to improve nutrient utilization in ruminants, thereby reducing methane gas production. This study assessed the beneficial effects of Aloe vera (AV), Moringa oleifera (MO) pods and leaves, Jatropha curcas (JA), Carica papaya (CP), Tithonia diversifolia (TD), Azadirachta indica (AZ) and Piper betel (PB) extracts and their two-way combination on methane reduction attributes when evaluated in in vitro and in vivo studies.
Plants extract that were obtained using pure methanol were screened for their effectiveness in methane reduction at graded levels in an in vitro production study. The standardized crude plant extracts were added at the rate of 25, 50, 75 and 100 mg plant extract powder per kg of feed dry matter. Gas measurements were taken at regular intervals during the incubation period. Methane emission was determined for each gas sample with the use of gas chromatography. In subsequent in vitro studies, combinations of extracted plant metabolites were incubated with feed samples to test methane-reducing abilities, their effect on gas production, feed degradability, and volatile fatty acids production. The last in vitro study tested the effects of recommended dosages of plant extracts from previous in vitro studies on methane production, digestibility and volatile fatty acids of various feed substrates.
At the end of in vitro trials, plant extracts of Moringa oleifera, Jatropha curcas and Aloe vera were selected from the most promising and effective plant extracts for in vivo evaluation of feed digestibility, rumen fermentation parameters, methane emission, growth performance and blood profile of SA Mutton Merino sheep. Forty (40) Merino lambs were first ranked according to their body weight and divided into four groups with equal weight measurement. The four groups were randomly allocated to various plant extract treatments and the control. The plant extract treatments MO, JA and AV were drenched to the sheep, while animals in the control group were drenched with the same volume of water. All treatments were placed on the same total mixed ration formulated with 42% roughage component. Growth performance lasted 103 days, including adaptation, and the feed digestibility study lasted for 21 days, after which the animals were moved into the open circuit respiratory chambers for methane emission measurements in five batches.
Results obtained from the in vitro experiments indicated that plant extracts AV, MO, AZ, TD, CP, and JA had generally reduced (P<0.05) methane production without adversely affecting total gas production. All plant extracts significantly (P<0.05) increased the organic matter digestibility of Eragrostis curvula, while PB at all doses increased methane, total gas, volatile fatty acids and organic matter digestibility. Although the cocktails of promising plant extracts (MO, AZ, JA, AV, TD, and CP), which were effective against methane reduction, showed potential to increase propionic acid concentration, the effect was insufficient compared with the magnitude in which single plant extracts had reduced methane and increased digestibility. It was also recorded through the in vitro study that plant extracts are mostly effective in terms of methane reduction and increased organic matter digestibility when used on poor-quality forage.
Plant extracts MO and JA generally increased DM, NDF, ADF, CP and starch digestibility with significant effect on (P<0.05) on DM and CP digestibility compared with the control. Higher average daily gain and total weight gain were recorded for MO and JA. Better feed conversion efficiency was recorded for MO and JA, while feed dry matter (DM) intake was not significant across these treatments. Plant extracts MO, JA and AV significantly (P<0.05) reduced methane production from SA Mutton Merino (SAMM) sheep by about 20%, 35% and 28%, respectively, per kg of DM intake. Plant extracts MO, JA and AV reduced significantly (P<0.05) ammonia nitrogen (NH3-N) in the rumen with a corresponding increase in ruminal propionic acid concentration for MO and JA plant extracts. Significant reduction (P<0.05) by MO and JA was recorded only for white blood cells and lymphocytes in blood haematology. Thus, the findings of the in vivo study confirmed the in vitro results that plant extracts MO, JA and AV are able to reduce methane emission from ruminants with significant improvement in feed digestibility. This study also confirmed that supplementation of these plant extracts to animals is not toxic at inclusion level of 50 mg/kg DM feed. In addition, plant extracts of MO and JA can be used as additives to ruminants at the rate of 50 mg/kg DM feed to provide co-benefit in terms of improved performance. Further studies need to be conducted to encapsulate the plant extracts for better delivery and test the response of animals at 75 mg/kg DM feed for better improvement.