Evidence for multiple alleles effecting muscling and fatness at the ovine GDF8 locus

The current investigation surveyed genetic polymorphism at the ovine GDF8 locus and determined its contribution to variation in muscling and fatness in sheep.

Re-sequencing 2988 bp from a panel of 15 sires revealed a total of six SNP, none of which were located within exons of the gene. One of the identified SNP, g+6723G>A, is known to increase muscularity within the Belgian Texel. A genetic survey of 326 animals revealed that the mutation is near fixation within Australian Texels and present in additional breeds including White Suffolk, Poll Dorset and Lincoln. Using a resource population comprising 15 sires and 1191 half-sib progeny with genotypic data, the effect of this and other SNP was tested against a set of 50 traits describing growth, muscling, fatness, yield, meat and eating quality. The loss of function allele (g+6723A) showed significant effects on slaughter measurements of muscling and fatness. No effect was detected on objectively assessed meat quality however evidence was found for an association between g+6723G>A, decreased intramuscular fat and reduced eating quality. Haplotype analysis using flanking microsatellites was performed to search for evidence of currently unidentified mutations which might affect production traits. Four haplotypes were identified that do not carry g+6723A but which showed significant associations with muscling and fatness.

The finding that g+6723G>A is present within Australian sheep facilitated an independent evaluation into its phenotypic consequence. Testing was conducted using a separate genetic background and animals raised in different environments to the Belgian Texel in which it was first identified. The observation that the direction and size of effects for g+6723A is approximately consistent represented a robust validation of the effects of the mutation. Based on observed allele frequencies within breeds, selection for g+6723A will have the largest impact within the White Suffolk. GDF8 may harbour additional mutations which serve to influence economically important traits in sheep.