Rhythmicity in thermal humidity index and regulation of Haemonchus contortus in sheep of semi-arid tropical Rajasthan

ABSTRACT

Over the period (2012–18) at Avikanagar, the average monthly thermal humidity index (THI) varied significantly (p < 0.001) from 15.62 ± 0.19 (January) to 32.76 ± 0.14 (June), revealing that for sheep flocks the periods of non-stress and extreme stress were from November to February and April to October, respectively. Under modified worm management programme (MWMP), the monthly average faecal egg counts (FECs), Haemonchus contortus (adult and L₄) counts in abomasum varied significantly (p < 0.001) from 251.52 ± 20.72 (January) to 2763.54 ± 162.07 (July), from 18.21 ± 1.21/sheep in February to 1510.41 ± 66.87/sheep in September and from 0.24 ± 0.02/abomasi (July) to 46.82 ± 1.41/abomasi (January), respectively. Over the years, the monthly interaction between THI and parasitological observations exhibited almost similar relation among parameters. Both FECs and abomasal worm count showed a positive relation with THI while a reverse pattern was exhibited for L₄ counts. Overall on Pearson correlation a significant (p < 0.001) positive correlation was found between FEC and adult worm counts (r² = 0.411) and FECs and THI (r² = 0.253). The significantly negative correlation between FECs and L₄ counts during December to March supports the occurrence of hypobiosis in H. contortus. However, significant positive correlation between FECs and L₄ count during July to September suggested acquisition of fresh infection from environment. A positive correlation between FECs and THI during April to June and October to December indicated resumption of development in hypobiotic larvae could be due to stressful environment for host and initiation of hypobiosis due to non-stressful status of host, respectively.

KEYWORDS:

• Faecal egg count
• Haemonchus contortus
• hypobiosis
• modified worm management programme
• sheep
• thermal humidity index

Acknowledgments

The facilities provided by Director, ICAR-CSWRI, Avikanagar are thankfully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by All India Network Program on Gastrointestinal Parasitism by Indian Council of Agricultural Research, New Delhi.