Douhard Frédéric, Matthey Xavier, Marcon Didier, Coffre-Thomain Camille, Estivalet Lucie, Serreau Delphine, Guégnard Fabrice, Sallé Guillaume, Drame Papa Moussa, Elleboudt Frédéric, Lecompte François, Adriaensen Hans
GenPhySE, Université de Toulouse, INRAE, ENVT, Castanet-Tolosan, France.
UMR INRAE/ENVT 1225 IHAP, UMT Santé des Petits Ruminants, Ecole Nationale Vétérinaire de Toulouse, Toulouse cedex 03, France.
Int J Parasitol. 2024 Dec;54(14):767-777. doi: 10.1016/j.ijpara.2024.09.004. Epub 2024 Sep 26.
Although benefits of selection for host resistance to gastro-intestinal nematodes have long been recognized, its costs on production traits remain unclear. A main difficulty when studying those costs is to disentangle genetic effects due to selection from plastic responses induced by infection. Putative costs of host resistance have been extensively investigated in growing sheep. However, while most of those studies have relied on live weight to assess body growth, more comprehensive assessments accounting for body composition are advocated to detect trade-offs. In this study we used 90 female lambs from lines divergently selected on resistance to Haemonchus contortus that we experimentally infected (n = 60) or not (n = 30) under controlled conditions. As those conditions were defined to enable uninfected lambs to fully express their growth potential, we sought to precisely identify the effects of selection for host resistance on health traits and on growth traits. We assessed muscular and fat growth based on repeated measurements with dorsal ultrasonography for all lambs on farm, and with whole-body computed tomography (CT) scans for a subgroup of 18 infected lambs. Lambs achieved a high growth rate, including infected ones despite their high worm burden (confirmed at necropsy in the subgroup). As expected, lambs from the resistant (R) line were less infected than those from the susceptible (S) line. However, the clear pathogenic effects observed on muscular growth and voluntary feed intake were similar between lines. In contrast, a line difference in body fat was supported both by dorsal and volumetric CT measurements. Specifically, lower fat in the R line compared with the S line was observed equally in infected and uninfected groups, thus providing evidence for a constitutive cost of host resistance. Although this cost is not necessarily disadvantageous in nutrient-rich environments exposing animals to excess fat deposition, its consequences in nutrient-scarce environments may be important to promote sustainable breeding strategies for host resistance.
尽管选择宿主对胃肠道线虫的抗性所带来的益处早已得到认可，但其对生产性状的影响仍不明确。研究这些影响的一个主要困难在于，要区分选择所导致的遗传效应和感染引发的可塑性反应。人们已经对生长中的绵羊宿主抗性的假定影响进行了广泛研究。然而，尽管这些研究大多依靠体重来评估身体生长情况，但有人主张进行更全面的评估，包括身体组成，以发现权衡取舍。在本研究中，我们使用了90只雌性羔羊，这些羔羊来自对捻转血矛线虫抗性有不同选择的品系，我们在可控条件下对其中60只进行了实验性感染，另外30只未感染。由于设定这些条件是为了使未感染的羔羊能够充分发挥其生长潜力，我们试图精确确定选择宿主抗性对健康性状和生长性状的影响。我们通过对农场所有羔羊进行背部超声重复测量，以及对18只感染羔羊的亚组进行全身计算机断层扫描（CT），来评估肌肉和脂肪的生长情况。羔羊实现了较高的生长速度，包括那些感染的羔羊，尽管它们体内寄生虫负荷很高（在亚组的尸检中得到证实）。正如预期的那样，抗性（R）品系的羔羊比易感（S）品系的羔羊感染程度更低。然而，两个品系在肌肉生长和自愿采食量方面观察到的明显致病效应是相似的。相比之下，背部和容积CT测量都支持了品系间在体脂方面的差异。具体而言，在感染组和未感染组中均观察到，R品系的脂肪含量低于S品系，从而为宿主抗性的固有代价提供了证据。尽管在使动物面临脂肪过度沉积风险的营养丰富环境中，这种代价不一定是不利的，但在营养匮乏环境中的后果可能对促进宿主抗性的可持续育种策略很重要。
