Leymaster K A
J Anim Sci. 1987 Jul;65(1):110-6. doi: 10.2527/jas1987.651110x.
Crossbreeding of sheep is practiced to exploit simultaneously the use of additive and nonadditive genetic effects. The goal is to achieve optimal levels of performance appropriate for defined systems of sheep production and marketing. Although the beneficial effects of individual and maternal heterosis on sheep production have been well documented and widely implemented, considerably less is known about the effects of paternal heterosis. Limited evidence suggests that crossbred rams are more sexually aggressive and exhibit greater testicular growth than do purebred rams. Average estimates of paternal heterosis effects were 1.4, -.7 and 2.3% for seasonal fertility, prolificacy and preweaning survival, respectively. The average effect of paternal heterosis on fertility during spring breeding was 29.5%. Progeny of crossbred and purebred sires were similar in birth weight, weaning weight and postweaning growth rate and in phenotypic variation for these growth traits. However, favorable paternal heterosis effects need not exist to warrant the use of crossbred sires. Composite or F1 sires can be used as an effective method to manage the composition of additive breed effects. For example, varying proportions of germ plasm from highly prolific breeds such as the Finnsheep and Romanov can be realized through the use of crossbred sires to set reproductive rates at desired levels. Crossbred sires may be used to a greater extent to optimize additive breed effects than to exploit effects of paternal heterosis. The role of composite breeds in managing both additive and nonadditive effects is discussed.
绵羊杂交育种旨在同时利用加性和非加性遗传效应。目标是实现适合特定绵羊生产和销售系统的最佳生产性能水平。尽管个体杂种优势和母体杂种优势对绵羊生产的有益影响已有充分记录并得到广泛应用，但关于父本杂种优势的影响却知之甚少。有限的证据表明，杂交公羊比纯种公羊更具性攻击性，睾丸生长也更大。父本杂种优势对季节性繁殖力、产仔数和断奶前存活率的平均估计分别为1.4%、-0.7%和2.3%。春季繁殖期间父本杂种优势对繁殖力的平均影响为29.5%。杂交父本和纯种父本的后代在出生体重、断奶体重和断奶后生长速度以及这些生长性状的表型变异方面相似。然而，使用杂交父本并不一定需要存在有利的父本杂种优势效应。复合或F1父本可作为一种有效方法来管理加性品种效应的组成。例如，通过使用杂交父本将繁殖率设定在期望水平，可以实现来自芬兰羊和罗曼诺夫羊等高产品种的不同比例的种质。与利用父本杂种优势效应相比，杂交父本可能在更大程度上用于优化加性品种效应。本文讨论了复合品种在管理加性和非加性效应方面的作用。
