Abstract:
High prevalence of anthelmintic resistant Haemonchus (H.) contortus nematode
has made the researchers to think about the animals with better natural resistance against
this parasite. The objective of the present study was to evaluate the resistance status of
three indigenous sheep breeds against H. contortus by artificial and natural pasture
challanges. After weaning at 3 months of age, 25 lambs each of Thalli, Lohi and Kachhi
breeds were dewormed. Each lamb was dosed with 10,000 L3 of H. contortus and kept
on stall feeding at livestock farms of Agricultural University, Faisalabad (Pakistan).
Breeds were assessed on the basis of parasitological, hematological and biochemical
parameters. After nine weeks, 10 lambs of each breed were randomly selected and
slaughtered to evaluate the differences in adult worm burden among aforementioned
breeds. Eggs per gram of feces and worm burden were lower in Lohi lambs (P>0.05)
followed in ascending order by Kachhi and Thalli, which was also least affected in terms
of packed cell volume, total serum protein and serum albumin. Artificial infection was
ended by an anthelmintic treatment nine weeks later and remaining animals of both
groups were shifted to contaminated pastures for their evaluation by natural infection.
Duration and parameters were kept the same as for artificial trial. Lohi also performed
better in the field trial but difference between breeds remained low. This is the first study
on the natural resistance of three sheep breeds in Pakistan. It is proposed that all existing
sheep breeds in Pakistan be evaluated for natural resistance using H. contortus as a model
organism since it is the most prominent. If significant resistance is discovered then use of
these breeds could lessen dependence upon chemical anthelmintics.
