Lateral migration of Haemonchus contortus larvae on pasture
Skinner, W.D.; Todd, K.S.
American Journal of Veterinary Research 41(3): 395-398
1980
ISSN/ISBN: 0002-9645 PMID: 7369613 Document Number: 166063
Faecal pellets containing infective larvae of Haemonchus contortus were deposited in short grass (10 cm) and tall grass (20 cm) on pasture plots at the University of Illinois Veterinary Research Farm, USA, for a 4-month period. One, 2, 4, and 7 days later, grass and mat samples were collected at 10 equal distances within 1 m from the faeces, and the larvae were counted. Weather data were recorded and compared with lateral migration of larvae. A few infective larvae of H. contortus (0.001% of the larvae placed on the plot) were found as far as 90 cm from the faeces after 24 hours. Generally, over 90% of the larvae were found within 10 cm of the faeces, and the number decreased logarithmically as the distance from the faeces increased. Moisture and temperature were the most important weather factors associated with lateral larval migration. An insignificant amount of migration occurred during hot, dry weather. More migration occurred during cool, wet weather than during cool, dry weather. Temperatures recorded 5 cm below the ground and at ground level showed the closest linear correlation to lateral migration. During the late summer and fall, lateral migration increased as temperature decreased. Survival of larvae correlated closely with lateral migration except during moderately dry periods. In such situations, lateral migration was reduced, even though there was little larval mortality. When faecal pellets were spread away from the deposits by environmental factors such as heavy rainfall and wind, the larvae were also disseminated. Invertebrates also appeared to have a role in the dissemination of larvae. [AS].