Abstract :
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.
