The proximate and secondary metabolites of the leaf fodder of Searsia species are affected by seasons in the North West province of South Africa

Abstract The study was carried out to assess seasonal variation in the proximate principles, secondary metabolites, and in vitro dry matter degradability (IVDMD) of Searsia species. The leaves of Searsia lancea and Searsia pyroides were harvested during the autumn, winter, spring, and summer seasons. Samples were analysed for proximate principles, qualitative and quantitative secondary metabolites, and IVDMD. Solvents (methanol and distilled water) were used to prepare cold extracts for qualitative analysis of secondary metabolites. Data were analysed using a two-way analysis of variance. The lowest ( P < 0.05) neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), and cellulose were recorded for S. lancea compared to S. pyroides . The highest ( P < 0.05) crude protein (CP) content ( P < 0.05) was produced in summer. The lowest ( P < 0.05) NDF, ADF, ADL, and cellulose ( P < 0.05) was in the summer season, compared to other seasons. Within each species, both species had the lowest ( P < 0.05) NDF and ADL in summer. There was no variation ( P > 0.05) in the content of ADL, cellulose, and hemicellulose between species in each season. Saponins were highly present in all seasons of both extracts in S. lancea , while they were moderately present in S. pyroides . Phlobatannins were moderately present in the methanol extract while absent in the water extract in all seasons. Searsia pyroides had the lowest ( P < 0.05) total phenolic, total tannins and condensed tannins (CT) content compared to S. lancea . The highest ( P < 0.05) IVDMD was recorded for S. pyroides at 36 and 48 h in all seasons. Both species have potential to be used as feed due to high CP and low fibre. However, in all seasons, these species had the highest CT concentration, which may reduce their feeding value when CTs are not deactivated.