Riley D G, Van Wyk J A
Subtropical Agricultural Research Station, Brooksville, FL 34601, USA.
Vet Parasitol. 2009 Sep 16;164(1):44-52. doi: 10.1016/j.vetpar.2009.04.014. Epub 2009 Apr 15.
The objectives of this study were to estimate genetic parameters for FAMACHA score and related traits at different levels of worm challenge in sheep and to assess the effect of different methods for modelling records from treated lambs on estimates of genetic parameters. Data were collected over five consecutive Haemonchus seasons from a total of l671 Merino lambs using the FAMACHA clinical evaluation system, and anaemic individuals were treated as needed, until flock health necessitated mass treatment at the peak of the worm season. Records of each sampling occasion were classified into low, moderate, or peak levels of worm challenge. Animal models were run separately for traits within each data set. Alternative analyses were conducted in which records of treated lambs were (1) included without adjustment, (2) included along with a fixed effect representing treatment status of the lamb for each record, and (3) included after application of a penalty to offset any phenotypic improvement or advantage due to that treatment. Estimates of heritability for individual FAMACHA data sets ranged from 0.06+/-0.04 to 0.24+/-0.05, the highest estimates being obtained for peak worm challenge data. Estimates of genetic correlation for FAMACHA with other traits varied, but were always near negative unity for FAMACHA score with haematocrit value. When data of treated lambs were penalised, higher estimates of heritability were obtained than when not penalised, hence this may be an effective method for allowing for early treatment of overly susceptible animals before the level of worm challenge is at an optimum level for BLUP (Best Linear Unbiased Prediction) evaluation. The estimate of genetic correlation for FAMACHA score in moderate worm challenge with that in peak worm challenge was almost unity. This suggests that estimation of breeding values for this trait using data from moderate worm challenge may be as effective as that from peak challenge.
本研究的目的是估计绵羊在不同蠕虫感染水平下FAMACHA评分及相关性状的遗传参数，并评估对经治疗羔羊记录进行建模的不同方法对遗传参数估计的影响。在连续五个血矛线虫季节中，使用FAMACHA临床评估系统从总共1671只美利奴羔羊收集数据，对贫血个体按需进行治疗，直到羊群健康状况要求在蠕虫季节高峰期进行大规模治疗。每个采样场合的记录被分类为低、中或高蠕虫感染水平。针对每个数据集中的性状分别运行动物模型。进行了替代分析，其中经治疗羔羊的记录：(1) 未经调整直接纳入；(2) 连同代表每只羔羊治疗状态的固定效应一起纳入；(3) 在应用惩罚以抵消该治疗导致的任何表型改善或优势后纳入。各个FAMACHA数据集的遗传力估计值范围为0.06±0.04至0.24±0.05，最高估计值是从高蠕虫感染水平数据获得的。FAMACHA与其他性状的遗传相关性估计值各不相同，但FAMACHA评分与血细胞比容值的遗传相关性始终接近 -1。当对经治疗羔羊的数据进行惩罚时，获得的遗传力估计值高于未惩罚时，因此这可能是一种在蠕虫感染水平尚未达到最佳BLUP（最佳线性无偏预测）评估水平之前，对过度易感动物进行早期治疗的有效方法。中等蠕虫感染水平下FAMACHA评分与高蠕虫感染水平下FAMACHA评分的遗传相关性估计值几乎为1。这表明使用中等蠕虫感染水平数据估计该性状的育种值可能与使用高感染水平数据一样有效。
