Evaluation of the ovine callipyge locus: III. genotypic effects on meat quality traits.

Abstract

ABSTRACT:A resource flock of 362 F 2 lambs provided phenotypic and genotypic data to estimate effects of callipyge ( CLPG) genotypes (NN, NC, CN, and CC) on meat quality traits. The mutant allele is represented as C, the normal allele(s) as N, and the paternal allele of a genotype is given first. Lambs of each genotype born in 1994 and 1995 were serially slaughtered in six groups at 3-wk intervals starting at 23 wk of age. Warner-Bratzler shear force and subjective evaluation of marbling were collected during both years from longissimus. Calpastatin activity was measured on longissimus from the 1994 group, and ELISA quantification of calpastatin protein was obtained from the 1995 group. Significant additive and paternal polar overdominance effects on meat quality traits were detected. This is in contrast to previous research that detected only polar overdominance effects on slaughter and carcass traits in this population. The magnitude of genotypic effects on shear force differed significantly between years; however, additive ( P < .01), paternal polar overdominance ( P < .001), and maternal dominance ( P < .01) effects adjusted for variation in carcass weight were detected within each year. Shear force data adjusted to the mean slaughter age or carcass weight indicated that the means and variances of CN and CC genotypes were greater than values of NC and NN. Shear force values were greatest for CN and were intermediate for CC. The difference in shear force (adjusted for variation in slaughter age) between homozygous genotypes (additive effect) was supported by calpastatin activity data with 2-df F-tests of 3.66 ( P < .05) and 11.84 ( P < .001) at d 0 and 7 postmortem, respectively. Corresponding values for the paternal polar overdominance effects on calpastatin activity were 53.80 ( P < .001) and 87.43 ( P < .001). Calpastatin ELISA data ( d 0, adjusted for slaughter age) exhibited a paternal polar overdominance effect exclusively with a 2-df F-test of 57.63 ( P < .001). Additive and paternal polar overdominance effects on marbling adjusted for slaughter age had F-tests of 6.41 ( P < .01) and 93.29 ( P < .001), respectively. Consequences of increased longissimus shear force must be addressed if the advantages of CN lambs for dressing percentage and carcass composition are to be realized. Further research is needed to establish whether selection targeted at changing the background genome can mitigate the negative effects of the C allele on meat tenderness.

Identification of the Single Base Change Causing the Callipyge Muscle Hypertrophy Phenotype, the Only Known Example of Polar Overdominance in Mammals

“…Dramatic effects on muscle development, carcass composition, shape, and meat quality are hallmarks of the callipyge syndrome (Koohmaraie et al 1995;Freking et al 1998bFreking et al , 1999. The muscle hypertrophy phenotype is expressed in a unique parent of origin-dependent manner referred to as paternal polar overdominance (Cockett et al 1996;Freking et al 1998a).…”

“…The only genotype that expresses muscle hypertrophy in this type of gene action is one in which the mutant callipyge allele (C) is inherited from the sire and a normal allele (N) from the dam (genotype CN). Interestingly, sheep with two copies of the mutant allele (genotype CC) did not express muscle hypertrophy even though other phenotypes such as increased longissimus muscle calpastatin enzyme activity and increased longissimus muscle shear force were observed relative to noncarrier (genotype NN) or maternal-derived heterozygous (genotype NC) genotypes (Freking et al 1999). Understanding the mechanism by which the CLPG mutation alters these phenotypes would improve our basic knowledge of factors involved in muscle growth, carcass leanness, and meat quality, as well as delineate unique forms of genomic imprinting regulation.…”

Human–Ovine Comparative Sequencing of a 250-kb Imprinted Domain Encompassing the Callipyge (clpg) Locus and Identification of Six Imprinted Transcripts: DLK1, DAT, GTL2, PEG11, antiPEG11, and MEG8

“…It was shown to be inherited and fully controlled by an autosomal locus (clpg) mapping to the telomeric end of sheep chromosome 18 (Cockett et al 1994;Freking et al 1998c). Subsequent marker-assisted segregation analysis revealed that the callipyge phenotype is subject to a unique parent-oforigin effect, referred to as polar overdominance, in which only heterozygous individuals having inherited the CLPG mutation from their sire express the muscular hypertrophy .…”

Genetic and genomic approaches to improving sheep meat quality

“…any animal inheriting the Callipyge allele from its dam does not display the phenotype) (Cockett et al, 1996). The effect on meat quality is large; animals expressing the Callipyge phenotype have remarkably tough meat as assessed through shear-force measures or sensory panels, and the meat is associated with high calpastatin levels (Freking et al, 1999;Duckett et al, 2000). Fine mapping of the Callipyge locus, and its impact on associated imprinted genes was described by Charlier et al (2001), leading to the identification of the causative mutation (Freking et al, 2002).…”