Nutritional manipulation of sheep and goats for the control of gastrointestinal nematodes under hot humid and subhumid tropical conditions

Gastrointestinal nematodes (GIN) could have a negative impact on the nutritional efficiency and productivity of sheep and goats. However, feeding of the hosts can also affect parasites. This paper reviews literature data on nutritional manipulation of small ruminants as a tool for the control of GIN under hot humid and subhumid tropical conditions. Parasites are integrated into the food chain of foraging small ruminants. A balanced grazing system provides an adequate source of nutrients and an acceptable GIN burden that allows an optimum level of productivity. However, a breakdown in such balance may induce severe parasite infections. Diet manipulation strategies have been tested under tropical conditions. Animals receiving supplementary feeding may achieve an improved resilience against GIN infections. However, the improvement of resistance of sheep and goats against GIN through supplementation has been less studied and many confounding factors should be considered (pattern of fodder consumption, dilution of eggs in the faeces, direct anthelmintic (AH) effect of some ingredients, etc.). Some supplements cause a direct AH effect (i.e. copper wire particles against Haemonchus contortus). Meanwhile, bioactive plant secondary metabolites (PSM), such as tannins, are more complex. Some PSM may cause negative effects in the host (i.e. reducing feed digestibility), and yet animals consume bioactive plants at levels that can cause evident negative effects to the parasites. The GIN can be affected in different stages of their life cycle (i.e. adults with fewer eggs in utero or reduced worm burdens). Meanwhile, they can also affect new infections for the host (affecting egg hatchability and larvae motility in the faeces or avoiding exsheathment of incoming infective larvae in the host). Grazing management should be explored in most hot humid and subhumid tropical regions. Available results suggest that alternate and rotational grazing can both provide opportunities to reduce dependence on AH and can easily be complemented with supplementary feeding. More basic knowledge of animal nutrition and GIN epidemiology under hot humid and subhumid tropical conditions is needed to improve the applicability of nutritional strategies for the control of GIN infections.