INRA UR631 SAGA, Castanet-Tolosan F-31326, France.
Genet Sel Evol. 2013 Sep 30;45(1):37. doi: 10.1186/1297-9686-45-37.
The pre-weaning growth of lambs, an important component of meat production, depends on maternal and direct effects. These effects cannot be observed directly and models used to study pre-weaning growth assume that they are additive. However, it is reasonable to suggest that the influence of direct effects on growth may differ depending on the value of maternal effects i.e. an interaction may exist between the two components.
To test this hypothesis, an experiment was carried out in Romane sheep in order to obtain observations of maternal phenotypic effects (milk yield and milk quality) and pre-weaning growth of the lambs. The experiment consisted of mating ewes that had markedly different maternal genetic effects with rams that contributed very different genetic effects in four replicates of a 3 × 2 factorial plan. Milk yield was measured using the lamb suckling weight differential technique and milk composition (fat and protein contents) was determined by infrared spectroscopy at 15, 21 and 35 days after lambing. Lambs were weighed at birth and then at 15, 21 and 35 days. An interaction between genotype (of the lamb) and environment (milk yield and quality) for average daily gain was tested using a restricted likelihood ratio test, comparing a linear reaction norm model (interaction model) to a classical additive model (no interaction model).
A total of 1284 weights of 442 lambs born from 166 different ewes were analysed. On average, the ewes produced 2.3 ± 0.8 L milk per day. The average protein and fat contents were 50 ± 4 g/L and 60 ± 18 g/L, respectively. The mean 0-35 day average daily gain was 207 ± 46 g/d. Results of the restricted likelihood ratio tests did not highlight any significant interactions between the genotype of the lambs and milk production of the ewe.
Our results support the hypothesis of additivity of maternal and direct effects on growth that is currently applied in genetic evaluation models.
羔羊的哺乳期生长是肉类生产的重要组成部分，取决于母体和直接效应。这些效应无法直接观察到，用于研究哺乳期生长的模型假设它们是可加的。然而，有理由认为，直接效应对生长的影响可能因母体效应的价值而异，即这两个组成部分之间可能存在相互作用。
为了检验这一假设，我们在罗曼羊中进行了一项实验，以获得母本表型效应（产奶量和奶质）和羔羊哺乳期生长的观察结果。该实验包括将具有明显不同母体遗传效应的母羊与具有非常不同遗传效应的公羊交配，在 3×2 析因设计的四个重复中进行。通过羔羊吸吮重量差减法测量产奶量，在产后 15、21 和 35 天通过红外光谱法测定奶质（脂肪和蛋白质含量）。羔羊在出生时称重，然后在 15、21 和 35 天时称重。使用受限似然比检验测试基因型（羔羊）和环境（产奶量和质量）之间的平均日增重的相互作用，比较线性反应规范模型（相互作用模型）和经典的加性模型（无相互作用模型）。
总共分析了 166 只不同母羊所生的 442 只羔羊的 1284 个体重数据。平均而言，母羊每天产奶 2.3±0.8 升。平均蛋白质和脂肪含量分别为 50±4 克/升和 60±18 克/升，0-35 天平均日增重为 207±46 克/天。受限似然比检验的结果没有显示出羔羊基因型与母羊产奶量之间存在任何显著的相互作用。
我们的结果支持了目前应用于遗传评估模型的母体和直接效应对生长具有可加性的假设。
