Zaralis K, Tolkamp B J, Houdijk J G M, Wylie A R G, Kyriazakis I
Animal Nutrition and Health Department, Scottish Agricultural College, Kings Buildings, Edinburgh, EH9 3JG, UK.
J Anim Sci. 2008 Aug;86(8):1891-903. doi: 10.2527/jas.2007-0698. Epub 2008 Apr 11.
A reduction in food intake is a prominent feature of many infectious diseases. However, the underlying mechanisms of parasite-induced anorexia in sheep are poorly understood. Here, we tested the hypotheses (a) that the degree of parasite-induced anorexia in lambs is influenced by their growth potential and (b) that nematode infection results in elevated plasma leptin concentration in lambs. The hypotheses were tested with Suffolk x Greyface (S) and Scottish Black-face (B) lambs that are known to differ in their growth potential (S lambs are of greater growth potential than B lambs). During a primary parasite infection, 24 out of 48 lambs per breed were trickle-infected with 7,000 infective Teladorsagia circumcincta larvae per day, 3 d/wk, for a period of 12 wk (experiment I). The lambs were then dewormed, and after a 2-wk interval, half of the 24 lambs per breed that were previously infected were reinfected for another 12 wk with the same parasite and dose as used in the primary infection (experiment II). In both experiments, infected lambs were fed grass pellets for ad libitum intake, whereas noninfected lambs were fed grass pellets for either ad libitum or restricted intakes. The S lambs were more susceptible than B lambs to nematode infection, as judged from the differences in fecal egg counts (P = 0.007). Parasitized lambs of the more susceptible breed (S) showed anorexia [i.e., a decrease in intake of 13% compared with uninfected controls (P = 0.01)], whereas no significant reduction in food intake was observed in lambs of the more resistant breed (B). Reexposure to nematode infection of previously infected animals tended to result in renewed anorexia in S lambs but not in B lambs (P = 0.08) in a similar extent as during primary infection. Plasma leptin concentrations did not differ between ad libitum-fed infected and control lambs but were greater in infected than in noninfected lambs at a similar level of food intake during both the primary (P = 0.02) and the secondary parasitic infection (P = 0.004) in both breeds. The results show that leptin may be involved in the response of lambs to infection but that it is unlikely that leptin alone is responsible for the parasite-induced anorexia in lambs.
食物摄入量减少是许多传染病的一个显著特征。然而，绵羊体内寄生虫引发厌食症的潜在机制却鲜为人知。在此，我们对以下假设进行了验证：(a) 羔羊体内寄生虫引发厌食症的程度受其生长潜力的影响；(b) 线虫感染会导致羔羊血浆瘦素浓度升高。我们选用了已知生长潜力存在差异的萨福克×灰脸（S）羔羊和苏格兰黑脸（B）羔羊来验证这些假设（S 羔羊的生长潜力大于 B 羔羊）。在初次寄生虫感染期间，每个品种的 48 只羔羊中有 24 只每周 3 天、每天感染 7000 条环纹奥斯特线虫感染性幼虫，持续 12 周（实验 I）。然后给羔羊驱虫，间隔 2 周后，每个品种之前感染过的 24 只羔羊中有一半再次感染相同的寄生虫，剂量与初次感染时相同，持续 12 周（实验 II）。在两个实验中，感染的羔羊自由采食草颗粒饲料，而未感染的羔羊则自由采食或限量采食草颗粒饲料。从粪便虫卵计数的差异判断，S 羔羊比 B 羔羊更容易受到线虫感染（P = 0.007）。更易感品种（S）的感染羔羊出现了厌食症 [即与未感染对照组相比摄入量减少了 13%（P = 0.01）]，而抗性更强品种（B）的羔羊未观察到食物摄入量有显著减少。再次感染线虫时，之前感染过的动物中，S 羔羊倾向于再次出现厌食症，而 B 羔羊则没有（P = 0.08），程度与初次感染时相似。自由采食的感染羔羊和对照羔羊的血浆瘦素浓度没有差异，但在两个品种的初次（P = 0.02）和二次寄生虫感染（P = 0.004）期间，在相似的食物摄入量水平下，感染羔羊的血浆瘦素浓度高于未感染羔羊。结果表明，瘦素可能参与了羔羊对感染的反应，但仅瘦素不太可能是导致羔羊寄生虫性厌食症的原因。
