Gibbs H C, Barger I A
Vet Parasitol. 1986 Nov;22(1-2):57-66. doi: 10.1016/0304-4017(86)90007-5.
From autumn (April) to spring (November), groups of pregnant and dry Merino ewes grazed pasture contaminated with infective larvae of Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus colubriformis. A periparturient rise in faecal egg counts occurred in the pregnant ewes, following the maturation in early spring of arrested fourth-stage larvae of H. contortus and failure of pregnant ewes to expel the resulting adult worms. Peak egg counts were seen in September, just before lambing. In dry ewes, egg counts were slightly elevated at the time of the rise in the pregnant ewes, but fell to very low levels as adult worms developing from previously arrested larvae were expelled. Lactating ewes acquired greater burdens of O. circumcincta and T. colubriformis than did dry ewes, but were equally refractory to new infections with H. contortus. It is therefore suggested that the impairment of immunity to helminth infection seen in reproductive ewes may be more specific than was previously envisaged.
从秋季（4月）至春季（11月），将成群的怀孕美利奴母羊和空怀母羊放牧于被捻转血矛线虫、环形奥斯特线虫和蛇形毛圆线虫感染性幼虫污染的牧场上。怀孕母羊粪便虫卵计数出现围产期升高，这是由于捻转血矛线虫的滞育第四期幼虫在早春发育成熟，且怀孕母羊未能排出由此产生的成虫。在9月产羔前，虫卵计数达到峰值。在空怀母羊中，当怀孕母羊虫卵计数升高时，其虫卵计数略有上升，但随着先前滞育幼虫发育而成的成虫被排出，虫卵计数降至极低水平。与空怀母羊相比，哺乳母羊感染环形奥斯特线虫和蛇形毛圆线虫的负担更重，但对捻转血矛线虫新感染的抵抗力相同。因此，有人认为，繁殖期母羊中所见的对蠕虫感染免疫力的损害可能比以前设想的更具特异性。
