A suggested mode of inheritance for wool shedding in sheep

Abstract

The ability of a sheep to shed its ownwool has an attraction in scenarios where the costs ofharvesting wool outweigh its value. Certain breeds andcomposites have the ability to shed their wool in thespring, and these are investigated in this work in anattempt to outline the genetics of wool shedding. Oneflock from a breeding group in Southern England (UK)containing sheep with wool-shedding characteristicsprovided shedding scores (1 to 5 scale; no shedding tocomplete shedding) that were used in a range of geneticanalyses. The particular nature of wool sheddingsuggested that there may be a major gene segregatingin these populations that facilitates wool shedding. Inaddition, there was clearly variation among wool sheddersin the speed and extent of shedding, so a polygenictrait was also investigated. The breeding group used arange of shedding breeds and composites in a regularprogram to introduce wool-shedding genes into theirflocks. This allowed the testing of Mendelian ratios forshedders:nonshedders in both first-cross and first-backcrossanimals. Four modes of inheritance were tested:autosomal recessive, sex-linked recessive, autosomaldominant, and sex-linked dominant. The most likelymode of inheritance was autosomal dominant (P <0.05), with a low level of incomplete penetrance. In firstback-cross animals, this mode of inheritance was confirmedbut with complete penetrance. Approximately11% of shedders did not exhibit the trait as lambs.Mixed-model analyses of shedding scores allowed an investigationof factors that affected wool shedding andalso the extent of any genetic and permanent animalvariance. Shedding score was found to have a heritabilityof 0.54 ± 0.07 in lambs and 0.26 ± 0.06 in animalsof all ages in one flock using Easycare, Wiltshire Horn,Katahdin, and Dorper shedding animals. Sheddingscore as a lamb had a genetic correlation of 0.94 ± 0.08with shedding score as a 2 yr old, but at the phenotypiclevel this correlation was only 0.39 ± 0.05. No permanentanimal effect was found for shedding score. Breedingfor increased wool-shedding ability is possible, butimprovement of the trait needs to be considered in 2stages. First, the dominant gene needs to be introducedinto the population, and then selection between animalscan proceed by using EBV for the polygenic trait(speed or extent of shedding) as the basis for selection. ©2011 American Society of Animal Science. All rights reserved.