Powell R L, Wiggans G R, Norman H D
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350.
J Dairy Sci. 1994 Mar;77(3):883-90. doi: 10.3168/jds.S0022-0302(94)77023-5.
Holstein bulls were assigned to sampling categories (AI stud, AI nonstud, or non-AI) based on bull code, controller number, and age at semen distribution. The AI stud bulls were sampled through traditional progeny-testing programs of 13 AI organizations; AI nonstud bulls had AI semen collection reported by another organization or by multiple organizations. The non-AI bulls had no reported AI semen collection. Actual daughter yield deviations for these three groups of bulls were compared with expected performance (parent average) to provide an indication of whether evaluations were free from bias for daughter yield deviations. Mean difference of daughter yield deviation from parent average was close to 0 kg for animal model evaluations of all 22,930 bulls but was positively biased by 46 kg of milk for AI nonstud bulls. Mean PTA and reliabilities for parents were highest for AI stud bulls and lowest for non-AI bulls. The AI stud bulls varied least and were intermediate for mean management, approximated as mean daughter yield minus bull PTA. Management was highest for AI nonstud bulls, which suggested that adjustment for heterogeneous variance might reduce bias. However, the effect of this adjustment on mean difference of daughter yield deviation from parent average was small.
根据公牛代码、控制编号和精液分发时的年龄，将荷斯坦公牛分为采样类别（人工授精种公牛站、非人工授精种公牛站或非人工授精）。人工授精种公牛站的公牛通过13个人工授精组织的传统后裔测试项目进行采样；非人工授精种公牛站的公牛由另一个组织或多个组织报告有人工授精精液采集情况。非人工授精公牛则没有报告人工授精精液采集情况。将这三组公牛的实际女儿产奶量偏差与预期表现（亲本平均值）进行比较，以表明对女儿产奶量偏差的评估是否无偏差。在对所有22930头公牛进行动物模型评估时，女儿产奶量偏差与亲本平均值的平均差异接近0千克，但非人工授精种公牛站的公牛在牛奶产量方面正偏差46千克。亲本的平均预测传递能力（PTA）和可靠性在人工授精种公牛站的公牛中最高，在非人工授精公牛中最低。人工授精种公牛站的公牛变化最小，在平均管理方面处于中间水平，平均管理水平近似为平均女儿产奶量减去公牛PTA。非人工授精种公牛站的公牛管理水平最高，这表明对异质方差进行调整可能会减少偏差。然而，这种调整对女儿产奶量偏差与亲本平均值的平均差异的影响很小。
