Abstract :
This review addresses the question whether host resistance to gastrointestinal nematodes
is sensitive to metabolizable protein (MP) or metabolizable energy (ME) scarcity. Several
ruminant studies have addressed this question, and with additional data from monogastric
models and post-rumen infusion methodologies, there is convincing evidence that host
resistance to gastrointestinal nematodes is sensitive to MP scarcity and not (moderate) ME
scarcity. A possible evolutionary reason for this variation has been evoked. Attempts to
dissect the role of MP and ME scarcity on resistance to parasites in ruminants is hampered
by the modifying role of the rumen, as ME supplementation usually results in confounding
MP supply, arising from increased microbial protein synthesis. The latter contributes
less to intestinal MP than by-pass protein, and has an amino acid composition that is less
compatible with that of immune proteins, compared to MP arising from animal protein
sources. Thus, the largest benefits from supplementation on host resistance to gastrointestinal
nematodes are expected to arise from protein-rich foods rather than from energy-rich
foods. In addition, dietary protein quality in terms of level of by-pass protein and amino acid
composition of resulting intestinal MP are important factors to consider in non-chemical
parasite control strategies in small ruminant production systems.
