EFFECT OF PLANT-SPECIES ON THE LARVAE OF GASTROINTESTINAL NEMATODES WHICH PARASITIZE SHEEP

Faeces containing Trichostrongylus colubriformis and/or Ostertagia cir cumcincta eggs were used to provide four contaminations in each of 2 y ears on plots of browntop, Yorkshire fog, ryegrass, tall fescue, lucer ne, chicory, cocksfoot, white clover, and prairie grass and in the sec ond year a mixed sward of ryegrass/white clover. Third stage larvae we re recovered from faeces and from four strata of herbage, 0-2.5, 2.5-5 , 5-7.5 and > 7.5 cm above the soil surface at 2, 4, 6, 8, 11, and 14 weeks after faeces were deposited on the swards. Herbage species had a significant (P < 0.0001) effect on the number of larvae recovered. Gr eatest numbers of larvae, as indicated by ranking analysis, were recov ered from Yorkshire fog, ryegrass, and cocksfoot and lowest numbers fr om white clover and lucerne. The difference between herbages in number s of larvae recovered was due to the ''development success'', the abil ity of larvae to develop to the infective stage and migrate on to herb age, rather than ''survival'', the rate of population decline once on the herbage. Faecal degradation was most rapid from white clover and b rowntop, intermediate from tall fescue, lucerne, prairie grass, cocksf oot, and ryegrass, and slowest from Yorkshire fog swards. The numbers of larvae recovered from herbages were related (r(2) = 0.59, P < 0.05) with the faecal mass remaining. A greater proportion of the total lar vae recovered from the herbage was recovered from the bottom stratum o f Yorkshire fog and prairie grass than from white clover, with the oth er herbages intermediate, indicating that larvae had greater difficult y migrating up Yorkshire fog and prairie grass than the other herbage species. In most herbage species, despite more larvae being recovered from the lowest stratum, larval density (L-3/kg herbage DM) was highes t in the top stratum. This study has demonstrated that herbage species can have a significant impact on the population dynamics and vertical migration of T. colubriformis and O. circumcincta larvae. (C) 1998 Au stralian Society for Parasitology. Published by Elsevier Science Ltd.