C. Giudici et al., Changes in gastro-intestinal helminth species diversity in lambs under mixed grazing on irrigated pastures in the tropics (French West Indies), VET RES, 30(6), 1999, pp. 573-581
The development of gastro-intestinal helminth diversity was monitored in la
mbs grazing alone or grazing with heifers in the ratio one heifer to four l
ambs. Five successive cohorts of lambs were studied from January 1994 to Ma
y 1996. Each cohort of lambs grazed irrigated pastures of Pangola grass for
4 months (from weaning to 6 months of age). A total of 50 lambs was necrop
sied and their worms counted and identified at the end of each grazing peri
od. Four heifers were also necropsied on one occasion. Special attention wa
s dedicated to the identification of the most pathogenic worm, i.e. Haemonc
hus spp. Malate dehydrogenase polymorphism in H. contortus was studied in o
rder to evaluate changes between cohorts and between grazing managements. T
he species diversity was estimated by Shannon diversity indices (main speci
es or all species). It was higher in the mixed grazing group than in the la
mbs that grazed alone. Diversity increased in successive cohorts. This was
due in part to the acquisition of Cooperia spp. of cattle origin. The incre
ase in diversity in the mixed sating lambs corresponded to the lower faecal
egg excretion and better weight gains recorded previously in that group. T
here seemed to be no cross-transmission of H. similis found in heifers and
H. contortus harboured by lambs. The latter species was not morphologically
or genetically different in the lambs grazed alone or with heifers, indica
ting that the presence of cattle did not modify qualitatively the transmiss
ion of H, contortus. (C) Inra/Elsevier, Paris.