Jacobson Caroline, Pluske John, Besier R Brown, Bell Kevin, Pethick David
School of Veterinary and Biomedical Sciences, Murdoch University, Western Australia 6150, Australia.
Vet Parasitol. 2009 May 12;161(3-4):248-54. doi: 10.1016/j.vetpar.2009.01.008. Epub 2009 Jan 23.
Effects of gastrointestinal parasitism on sheep productivity are usually described using live weight change, however carcass productivity is more accurately described using dressing percentage (carcass weight as a proportion of live weight). This experiment had a 2x2x2 factorial design whereby 10-month-old Merino wethers were fed lucerne (Medicago sativa) diets (fresh lucerne or lucerne chaff) with 2 levels of carboxymethycellulose (CMC) inclusion (0% or 8% CMC) and nematode larval challenge (no larval challenge or 10,000 Teladorsagia circumcincta and 10,000 Trichostrongylus colubriformis per week). Sheep were weighed and euthanased 50 or 51 days after larval challenge and CMC supplementation commenced. Weight of the carcass (hot standard carcass weight) and gastrointestinal organs (full and empty) were recorded and expressed as a proportion of live weight. Larval challenged sheep had a worm egg count (mean+/-standard error) of 173+/-38 eggs per gram of faeces and total worm count of 30,237+/-2013 at slaughter. Larval challenged sheep had 1.3% lower dressing percentage (p=0.048), and 2% heavier full (p=0.007) and 1.2% heavier empty gastrointestinal tracts (p=0.012) compared to unchallenged sheep. There was no effect of CMC inclusion or lucerne type (fresh or chaff) on gastrointestinal tract weight or dressing percentage. Larval challenged sheep had 1.1% heavier full (p<0.001) and 0.6% heavier empty (p<0.001) small intestines, and 0.6% heavier full (p=0.005) and 0.3% heavier empty (p=0.026) large intestines compared to unchallenged sheep. Use of live weight change or other measures based on live weight (e.g. feed conversion efficiency) to assess the impact of nematode challenge in sheep may underestimate carcass productivity losses associated with larval challenge in sheep even at moderate levels of larval intake and without overt clinical signs of parasitism. Measurement of carcass weight and/or lean meat yield may better reflect the true economic effects of parasitism in sheep.
胃肠道寄生虫对绵羊生产性能的影响通常用体重变化来描述，然而胴体生产性能用屠宰率（胴体重占活体重的比例）来描述更为准确。本试验采用2×2×2析因设计，将10月龄美利奴羯羊饲喂苜蓿（紫花苜蓿）日粮（新鲜苜蓿或苜蓿草粉），添加2个水平的羧甲基纤维素（CMC）（0%或8% CMC），并进行线虫幼虫攻毒（无幼虫攻毒或每周10000个环纹奥斯特线虫和10000个蛇形毛圆线虫）。在幼虫攻毒和开始补充CMC后50或51天对绵羊称重并实施安乐死。记录胴体重量（热标准胴体重）和胃肠道器官重量（充满内容物和排空），并表示为活体重的比例。攻毒幼虫的绵羊在屠宰时每克粪便的虫卵计数（平均值±标准误）为173±38个虫卵，总虫数为30237±2013条。与未攻毒的绵羊相比，攻毒幼虫的绵羊屠宰率低1.3%（p=0.048），充满内容物的胃肠道重2%（p=0.007），排空的胃肠道重1.2%（p=0.012）。CMC添加量或苜蓿类型（新鲜或草粉）对胃肠道重量或屠宰率没有影响。与未攻毒的绵羊相比，攻毒幼虫的绵羊充满内容物的小肠重1.1%（p<0.001），排空的小肠重0.6%（p<0.001），充满内容物的大肠重0.6%（p=0.005），排空的大肠重0.3%（p=0.026）。使用体重变化或其他基于体重的指标（如饲料转化效率）来评估线虫攻毒对绵羊的影响，可能会低估与幼虫攻毒相关的胴体生产性能损失，即使在幼虫摄入量适中且无明显寄生虫临床症状的情况下也是如此。测量胴体重和/或瘦肉产量可能更好地反映寄生虫对绵羊的真实经济影响。
