Abstract
Gastrointestinal nematode parasitism is one of the major causes for reduced
performance, compromised health and welfare of grazing ruminants. The
extensive, and sometimes inappropriate, use of anthelmintics for
gastrointestinal nematode parasite control has led to anthelmintic resistance.
The latter has urged the development of alternative approaches that would
reduce reliance on anthelmintics (Chapter One). This thesis reports effects of
combining such alternative approaches on sheep productivity and
parasitism, investigated under both pen (Chapters Tivo and Three) and
grazing (C hapters Four, F ive and Six) conditions.
The first two experiments report the effects of periparturient metabolizable
protein nutrition of twin-rearing ewes, on the degree of resistance to an
abomasal nematode parasite, Teladorsagia circumcincta, and performance
under varying degree of experimental parasite infection (Chapter Two) and
with two breeds that differ in their production potential (Chapter Three). The
results suggest that maternal protein supplementation improves litter
performance independently of infection pressure and production potential,
and reduces nematode egg excretion by -60% in the more productive breed.
However, protein scarcity had only limited effects on resistance to parasites
in the less productive breed used.
The last three experimental chapters describe grazing studies where maternal
protein supplementation was combined with grazing chicory relative to
grass/clover from around weaning (C hapter Four) and early lactation
(Chapters F ive and Six) to lamb finishing. Maternal protein supplementation
and grazing on chicory consistently improved ewe and lamb performance
and reduced lamb parasitism in an additive manner. On an initially parasite
infested pasture (C hapter Six), maternal protein supplementation and
grazing on chicory reduced lamb drench requirement by 31 and 40%,
respectively. The grazing experiments strongly suggest that the effects of
chicory could be through (1) improved nutrient supply, boosting lamb
resilience and/or resistance, (2) reduced larvae intake and (3) direct
anthelmintic-like effects. The absence of significant interactive effects
between maternal protein nutrition and grazing on chicory suggests that
under the grazing conditions used, achieved level of ewe protein intake from
the combination was, at least, not more than adequate or the anthelminticlike property of chicory was subtle. Exploitation of the effects of combination
from the above alternative approaches should lead to sustainable sheep
production by minimizing reliance on anthelmintics.
Chapter Seven briefly discusses the results obtained in the above experiments
in relation to the current knowledge on the use of alternative approaches and
puts recommendations for future work in the area of parasite control in
sheep with minimal reliance on anthelmintics.
