Influence of season and phytochemicals on the elemental composition of kobs’ diets in Old Oyo National Park, Nigeria

Phytochemicals or plant secondary metabolites (PSMs) are known to counteract mineral nutrients (MNs) utilisation in herbivorous wildlife, yet studies on the interactions between PSMs and MNs in relation to herbivory, particularly for kobs (Kobus kob) are scarce. Composite samples of each of five major forage plants of kobs’ (Grewia mollis, Afzelia africana, Gardenia aqualla, Maranthes polyandra and Andropogon gayanus) were randomly collected in and around feeding sites of kobs in both dry and wet season. Using standard procedures, samples were analysed for PSMs (alkaloids, phenols, saponins and tannins) and MNs [copper (Cu²+), iron (Fe²+), manganese (Mn²+), calcium (Ca²+), magnesium (Mg²+), zinc (Zn²+), sulphur (S²-), sodium (Na+) and potassium (K+)]. With appropriate statistical tools, data obtained were analysed, compared and correlated. Almost all plants were significantly higher in all the tested MNs and PMSs in the wet season, except for Maranthes polyandra which showed the inverse trend for Cu²+, Mn²+, S²-, Na+ and K+. Apart from tannins that were absent, the concentration of other PSMs (in Grewia mollis) and Ca²+ (in Gardenia aqualla and Andropogon gayanus) were significantly higher in the dry season. In conclusion, the concentration of Na+, K+, S²-, Fe²+ and Zn²+ in selected forage plants of kobs were highly influenced by the presence of PSMs.