Lethal genetic disorder in Poll Merino/Merino sheep in Australia

Objectives Characterise a lethal genetic disorder in Poll Merino/Merino sheep Design Pathological description of a new congenital multisystem disorder in a commercial sheep flock, and analysis of breeding data collected each lambing season between 2004 and mid-lambing season 2010. Procedure Necropsies were conducted on six affected lambs and the mode of inheritance of the disorder was determined by pedigree and segregation analyses. Results The affected lambs were dwarfs with multiple defects in several organs, including skeleton, heart, liver and kidneys. The disorder has been named brachygnathia, cardiomegaly and renal hypoplasia syndrome (BCRHS). Segregation analysis suggests the disorder is transmitted as an autosomal trait with a recessive mode of inheritance. An annual incidence of the disorder in the discovery flock of up to 2.5% was recorded. Conclusions As a lethal disorder, the occurrence of BCRHS raises potential ethical and economic concerns for Merino breeders. The development of a DNA test would be useful to investigate its distribution in the Australian wool-sheep population. As the disorder affects both the skeleton and several critical organs, including the heart, it may provide a potential animal model for investigating key developmental processes in humans and other animals.