Combined immunodeficiency of Arabian horses: confirmation of autosomal recessive mode of inheritance.

The research paper focuses on a breeding trial carried out over three years to determine the inheritance pattern of combined immunodeficiency (CID) in Arabian horses, confirming it as an autosomal recessive trait.

Overview of the Study

• The researchers conducted a three-year prospective breeding trial with the aim of verifying the inheritance pattern of CID in Arabian horses, a trait suspected to be inherited as an autosomal recessive trait.
• They selected 26 mares that had previously given birth to foals affected by CID and mated them with a stallion that had also sired CID-affected foals. These selective pairings were intended to increase the likelihood of producing offspring with CID, given the suspected autosomal recessive inheritance pattern.

Study Results

• A total of 53 foals were obtained from these breedings. Out of these, 15 or 28.3% were diagnosed with CID. The ratio of female to male foals was approximately 1:1 (28:25), and the same roughly equal ratio was observed among the CID-affected foals (8 females to 7 males).
• These results suggest that there indeed is an equal probability of both male and female foals inheriting CID, a characteristic of autosomal traits as they are not linked to the sex chromosomes.

Confirmation of Autosomal Recessive Inheritance

• The findings from this breeding trial provide substantial evidence to confirm that CID in Arabian horses is inherited in an autosomal recessive manner.
• In autosomal recessive inheritance, both parents must pass on the defective gene for the offspring to exhibit the disease. The approximately equal ratios of males to females among affected and unaffected foals suggest that the trait is not linked to sex chromosomes (which would lead to sex-specific patterns of inheritance).
• This confirmation provides important knowledge for future selective breeding in Arabian horses, helping to prevent the propagation of CID within this breed.