Monthly variation in worm burden exhibiting possibility of hypobiosis of Haemonchus contortus in sheep under farm conditions of semi-arid Rajasthan

A study was undertaken to investigate the hypobiosis in strongyle worms by examining the abomasi from sheep subjected to post-mortem at ICAR-Central Sheep and Wool Research Institute, Avikanagar (Rajasthan). From June 2012 to March 2015, a total of 151 abomasi were evaluated for total number of adult Haemonchus contonus worm and inhibited fourth stage larvae (L₄ A total of 75.5% abomasi were found positive for H. contortus infection with an average worm burden of 434.1 worms per abomasum. A sharp decline in abomasi harbouring only adult worms was from December to April (except in March). An increase in fourth stage H. contonus larvae (L₄) was observed during August to April. The number of L₄ in abomasal mucosa was ≤1.0/abomasum during May to June and started rising from August and reached to a peak in January (60 L₄/abomasi) followed by decline in subsequent months. The analysis of ratio of adult to L₄ in abomasi showed sudden rise in proportion of L. from October and persisted higher up to April. The study demonstrated the possibility ofoccurrence ofhypobiosis phenomenon in H. contonus during adverse climatic conditions might be a probable mechanism for survival of worm generations. With the onset of monsoon, the resumption ofdevelopment of hypobiotic larvae in host caused contamination ofpasture and served as sole source ofinfection for young animals.