Comparative intensity of infection and performance of lambs selected for resistance or susceptibility to Haemonchus contortus in semi-arid Rajasthan

Abstract

The present study aimed to determine the variation in intensity of strongyle infection and performance in lambs of three divergent lines (selected for resistance or susceptibility to Haemonchus contortus and unselected) in semiarid Rajasthan. From the year 2004 to 2014, a total of 13,515 faecal samples from lambs (5-6 month of age) naturally infected with gastrointestinal nematodes (GINs) were evaluated for intensity of strongyle infection and estimated pasture contamination rate by them. The monthly mean intensity of strongyle infection remained significantly higher in susceptible line compared to other lines. In the month of peak parasitism (September), minimum proportion (34.54-45.61%) of animals possess higher FEC in resistant lambs followed by unselected (44.32-50.50%) and maximum (53.58-56.27%) by susceptible lambs. In majority of months, resistant lambs had lower contamination rate (>30%) compared to susceptible lambs. The magnitude of average daily gain (ADG) in body weight exhibited significant variation among different lines only between 6-9 months of age in Malpura (31.1±1.2 g/day in unselected line to 38.5±2.3 g/day in resistant line) and Avikalin breed (27.1±1.8 g/day in unselected line to 35.6±1.7 g/day in resistant line). During peak wormy season, a significant and negative correlation was found between FEC and weight at 6 and 9 month of age in susceptible line only. The study suggested that management of gastrointestinal nematodosis in flock through selection of sheep for resistance to strongyle worms led to decreased pasture contamination, lower intensity of infection with better performance in resistant flock.