Australian Sheep Industry CRC, CJ Hawkins Homestead, School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia.
Vet Parasitol. 2010 Feb 26;168(1-2):51-9. doi: 10.1016/j.vetpar.2009.12.012. Epub 2009 Dec 29.
The temporal association between the periparturient rise in worm egg count of grazing Merino ewes to infection with Trichostrongylus colubriformis and the underlying causal mechanisms was investigated in an experiment that incorporated two levels of pregnancy (pregnant or unmated), two levels of infection (infected with 6000 T. colubriformis L(3)/week or uninfected) and, following lambing, three levels of lactation (non-lactating/"dry", early-weaned 2 days after parturition, or suckled). In addition to parasitological and host immune responses reported in a previous paper (Beasley et al., 2010), a range of endocrine and body compositional changes were monitored from day -50 to day 42, relative to the midpoint of lambing (day 0). By day -19, pregnant ewes had begun to mobilise fat and eye muscle, and after 42 days of suckling had lost 31% and 8%, respectively, of their existing depots. In comparison to non-pregnant (dry) ewes, the endocrine profiles of late-pregnant ewes were characterised by low levels of cortisol and prolactin and high levels of progesterone and oestradiol. Lactating ewes had lower levels of cortisol and leptin and higher levels of prolactin compared to both dry and early-weaned ewes. The mobilisation of fat and protein reserves throughout lactation in suckled ewes was closely associated with leptin and cortisol profiles, and provided strong evidence of an underlying nutritional basis for the periparturient relaxation of immunity. Both leptin and cortisol concentrations were also associated with both parasite burden and the immune status of the ewe. It is suggested that lower blood cortisol levels in suckled ewes contribute to a Th1 biased immune response that leads to an increased susceptibility to gastrointestinal nematodes. The results provide a detailed characterisation of the physiology underlying the periparturient relaxation of immunity to T. colubriformis, from which further investigations will aim to expose potential causal factors.
本实验研究了放牧美利奴绵羊在感染旋毛虫（Trichostrongylus colubriformis）期间，围产期蠕虫卵计数增加与感染之间的时间关联，以及潜在的因果机制。该实验包括两个妊娠水平（妊娠或未交配）、两个感染水平（感染 6000 条旋毛虫 L(3)/周或未感染），以及分娩后，三个泌乳水平（非泌乳/“干”、分娩后 2 天早期断奶、或哺乳）。除了之前一篇论文（Beasley 等人，2010）中报道的寄生虫学和宿主免疫反应外，从分娩中点前 50 天到 42 天，还监测了一系列内分泌和身体成分变化。到第-19 天，怀孕的母羊已经开始动员脂肪和眼肌，哺乳 42 天后，分别损失了现有的脂肪和肌肉储备的 31%和 8%。与非妊娠（干）母羊相比，妊娠晚期母羊的内分泌特征是皮质醇和催乳素水平低，孕酮和雌二醇水平高。与干母羊和早期断奶母羊相比，哺乳母羊的皮质醇和瘦素水平较低，催乳素水平较高。在哺乳期间，脂肪和蛋白质储备的动员与瘦素和皮质醇的水平密切相关，为围产期免疫放松的潜在营养基础提供了强有力的证据。瘦素和皮质醇浓度也与寄生虫负荷和母羊的免疫状态有关。研究表明，哺乳母羊血液中皮质醇水平较低，有助于导致 Th1 偏向的免疫反应，从而增加对胃肠道线虫的易感性。这些结果详细描述了围产期免疫对旋毛虫放松的生理学基础，进一步的研究将旨在揭示潜在的因果因素。
