Effect of plant extracts used as a methane mitigation additive on carcass fat content and fatty acid composition of South African Merino sheep

Abstract

There is growing apprehension about the use of antibiotics such as monensin in the reduction of enteric methane emissions. This has initiated the utilisation of multipurpose medicinal plants as an alternative, although there are limited efforts to understand the effect of medicinal plant extracts on animal product quality. This research used Moringa oleifera and Azadirachta indica (A. Juss) leaf extracts to replace monensin with aim of assessing the effects of the plant extract on tissue fat content and fatty acid composition of South African (SA) Mutton Merino sheep. The experimental treatments involved 40 ram lambs in a randomised complete block design into four feed additive treatment levels (i.e., negative-control, Azadirachta indica, Moringa oleifera, and monensin). Twenty-four sheep were randomly selected at 60 - 65kg bodyweight, slaughtered, and the post mortem samples were collected over a 23 weeks trial period.

The univariate analysis revealed a significant increase (p < 0.05) in the carcass fat content of the Azadirachta indica treatment group as compared to the monensin and Moringa oleifera groups, even as the groups were adjusted for any difference in the initial body weight. On the other hand, the multivariate analyses on the subcutaneous fatty acids showed a significant rise (p < 0.05) in polyunsaturated fatty acids of the monensin treatment group. The Moringa oleifera group resulted in a significant increase (p < 0.05) in monounsaturated fatty acids molar composition. The interaction effect of days-on-trial with lipid pigment absorbance was significantly higher in the negative control group compared to monensin and Azadirachta indica treatment groups. These results indicate that the addition of either Moringa oleifera or monensin reduces carcass fat and improves the unsaturated fatty acid proportion in SA Mutton Merino sheep. Azadirachta indica treatment increased the carcass fat content and the non-essential fatty acid proportion. However, both monensin and Azadirachta indica groups caused limited deposition of carotenoid (or lipid pigment) in the adipose tissue.