Boman et al. Genetics Selection Evolution 2010, 42:4 http://www.gsejournal.org/content/42/1/4 R E S E A R C H G e n e t i c s Se l e c t i o n Ev o l u t i o n Open Access Impact of two myostatin (MSTN) mutations on weight gain and lamb carcass classification in Norwegian White Sheep (Ovis aries) Inger A Boman1,2*, Gunnar Klemetsdal1, Ola Nafstad3, Thor Blichfeldt2, Dag I Våge4 Abstract Background: Our aim was to estimate the effect of two myostatin (MSTN) mutations in Norwegian White Sheep, one of which is close to fixation in the Texel breed. Methods: The impact of two known MSTN mutations was examined in a field experiment with Norwegian White Sheep. The joint effect of the two MSTN mutations on live weight gain and weaning weight was studied on 644 lambs. Carcass weight gain from birth to slaughter, carcass weight, carcass conformation and carcass fat classes were calculated in a subset of 508 lambs. All analyses were carried out with a univariate linear animal model. Results: The most significant impact of both mutations was on conformation and fat classes. The largest difference between the genotype groups was between the wild type for both mutations and the homozygotes for the c.960delG mutation. Compared to the wild types, these mutants obtained a conformation score 5.1 classes higher and a fat score 3.0 classes lower, both on a 15-point scale. Conclusions: Both mutations reduced fatness and increased muscle mass, although the effect of the frameshift mutation (c.960delG) was more important as compared to the 3’-UTR mutation (c.2360G>A). Lambs homozygous for the c.960delG mutation grew more slowly than those with other MSTN genotypes, but had the least fat and the largest muscle mass. Only c.960delG showed dominance effects. Background In Norwegian White Sheep (NWS), two myostatin (MSTN) mutations affecting conformation and fat classes are segregating: the 3’-UTR mutation creating an illegitimate microRNA site (c.2360G>A) that was identi- fied in Texel sheep [1] and a frameshift mutation explained by a deletion of one base pair in nucleotide position 960 (c.960delG), identified in NWS [2]. While c.2360G>A reduces the level of circulating myostatin to approximately one third, c.960delG generates a comple- tely non-functional protein. Initially, the aim of the current study was to investigate the effect of the c.960delG mutation on growth and car- cass traits in NWS under ordinary commercial manage- ment conditions. NWS is a synthetic crossbreed, composed of the Dala, Rygja, Steigar and Texel breeds [3]. * Correspondence: iab@nsg.no 1Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences (UMB), PO Box 5003, N-1432 Ås, Norway However, during the course of this experiment, another MSTN mutation (c.2360G>A) was published [1]. Since the Texel breed is one of the NWS founder breeds [3,4], the ongoing study was expanded in order to include this new mutation. Here we present data on how the two mutations affect weight gain and lamb carcass classification. Methods Genotyping Genotyping of the two MSTN positions, c.960 and c.2360, was carried out as described by Boman et al. [2]. First, the animals were genotyped only at position c.960, and then retyped at position c.2360, after publication of the second mutation. Experimental design The field experiment comprised two experimental years in the Vesterålen area, in the north of Norway. © 2010 Boman et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.