Worm population characteristics and pathological changes in lambs after a single or trickle infection with...

The regulation of the worm population and of its pathological effects was studied after a single or trickle infection with T. circumcincta. One hundred and twenty lambs, 60 Romanov and 60 Mérinos d'Arles, 3 months old, were distributed in four balanced groups: non-infected (G0), infected with 7000 L3 per animal once and slaughtered after 4 weeks (G14) or 8 weeks (G18), and infected 8 times and slaughtered after 8 weeks (G88). Parasitological, histological, haematological parameters and weight gains were recorded on each animal. Female and artificially nursed lambs had lower worm burdens and egg counts (epg) than males and naturally suckled lambs. No difference in parasitological parameters was seen between the two breeds, but Mérinos lambs infected once, had a higher increase in pepsinogen concentrations than Romanov lambs. In the infected animals, a significant proliferation of mast and eosinophil cells was observed in the abomasum wall. Serum pepsinogen concentrations were significantly higher 3 weeks p.i. and the weight gain was depressed during the first month p.i. The worm population was more numerous and younger in group G14 compared with G18 in which 24% of the worms had been expelled during the second month p.i. The female worms in G18 were longer and had more eggs in utero and higher egg output. After the trickle infection (G88) the take was reduced, female worms were longer with more eggs in vagina (pars ejectrix) and there was a higher variability in the number of eggs (compared with G18 data). The pepsinogen rise was smaller but no specific effect was seen on histological and haematological parameters.(ABSTRACT TRUNCATED AT 250 WORDS)