Seasonal effect of three pasture plants species on the free-living stages of Haemonchus contortus

R.D Carneiro,A.F.T Amarante

doi:10.1590/s0102-09352008000400014

Abstract

To evaluate both the development and survival of free-living stages of Haemonchus contortus obtained from feces of infected ovine in the four seasons of the year, eggs of this nematode were deposited on three grass species commonly used as sheep pasture in Brazil (Brachiaria decumbens cv. Australian, Cynodon dactylon cv. Coast-cross, and Panicum maximum cv. Aruana). The grasses were cut 5 or 30cm height before depositing the feces. Samples of grasses and feces were collected in six sub-plots from each plot one, two, four, eight, 12, and 16 weeks after contamination to determine the recovery of infective H. contortus larvae. Most infective larvae were recovered from feces or grass samples deposited on 30cm height herbage. High temperature and precipitation levels during the rainy season reduced the infective larvae recovery period from the environment. The best weather conditions for larvae development and survival, in both feces and grasses, were lower temperatures, around 17ºC, in association with low precipitation levels. In general, more larvae were recovered when fecal samples were deposited on Aruana grass.

Highlights

In the environment, the type of forage can have considerable impact on both population dynamics and vertical migration of infective larvae of gastrointestinal nematode parasites that infect sheep
There was a low rate of larvae recovery in the environment, largely below 1%
The highest mean L3 percentages recovered from grass (0.2% of the deposited eggs) and feces (2% of the deposited eggs) were found when fecal samples were deposited on 30cm height Aruana grass in May (28 days and 14 days after contamination, respectively)

Summary

Introduction

The type of forage can have considerable impact on both population dynamics and vertical migration of infective larvae of gastrointestinal nematode parasites that infect sheep. As different herbages have distinct growth and morphological characteristics, it is likely that they provide different microclimates on the soil surface that could have a direct effect on larvae development and survival, or indirectly modifying the number of coprophagous or nematophagous organisms (Niezen et al, 1998a) Based on these findings, Niezen et al (1998a) suggested that selecting a type of forage that is unfavorable for larvae could significantly contribute to parasitism prophylaxis. Banks et al (1990) and Barger et al (1994) found that high temperature and moisture levels in wet tropical climates favor egg hatching and larvae development, and result in high infective larvae mortality rates on the pasture These authors report that larvae can survive in contaminated tropical pastures for no more than one or two months, and that their populations peak approximately one week after contamination. Gastrointestinal nematode prophylaxis could be achieved when goats were kept on a rotational

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Conclusion