Association With Growth And Carcass MuscleTraits In Sheep

WFIKKN1, WFIKKN2, myostatin (MSTN), MYF5, MYF6and GDF11may playa role in the regulation of muscle development and growth, but to date there havebeen no reports on variations in these genes and their effect on growth and carcassmuscle traits in sheep with the exception of MSTN. In this study, a total of100-165un-related sheep from8different breeds, including Dorper, Corriedale, Merino,Perendale, Dorset Down, Poll Dorset, Suffolk and New Zealand (NZ) Romney, wereused to look for genetic variation in twelve regions from the six genes, usingPolymerase Chain Reaction Single-Stranded Conformational Polymorphism(PCR-SSCP). For three higher polymorphism regions, including intron1ofWFIKKN2, the promoter of MSTN and exon3of MYF5,357-800NZ Romeny lambsfrom thirteen un-related sire-lines were used to analysed associations between geneticvariation and variation in growth and carcass muscle traits. The results are shown asbelow:1. The six genes had different genetic variation characteristics.(1) In the intron1of ovine WFIKKN2, five unique DNA sequences and twelve single nucleotidepolymorphisms (SNPs) were detected. In the3’UTR region, two unique DNAsequences and one SNP were detected.(2) In the promoter of ovine MSTN, threeunique DNA sequences and two SNPs were detected. In exon3of ovine MYF5, fourunique DNA sequences and three SNPs were identified. In exon1and the5’UTR ofovine MYF6, two unique DNA sequences and one SNP were detected, respectively.(3)In exon1of ovine MYF5, exon2, intron2and5’UTR of ovine GDF11and twoamplified regions in exon2of WFIKKN1, no SNPs were observed.2. Effect of variation in intron1of ovine WFIKKN2on growth traits appears tobe gender-dependent in NZ Romney lambs.(1) A chi-square test revealed that therewas no difference in variant frequencies between395male and405female Romneylambs（P=0.984）. In both genders, A and B were the most common variants, followedby C. D and E were the least common variant, with a frequency less than5%.(2) Forthe most common genotypes AA, AB and BB, there was a significant differencebetween the expected and actual genotype frequencies in the male lambs (P=0.002).Genotyps AA and BB were less than expected and AB was more common. This effectwas not observed for the female lambs (P=0.994).(3) In male NZ Romney lambs, the presence of variant B in a genotype of ovine WFIKKN2was associated with decreasedbirth weight, tailing weight, weaning weight and pre-weaning growth rate; andincreased post-weaning growth rate (P<0.05). Variant B could therefore be used as agene-marker for improving lamb growth traits in Romney sheep. However, variationin ovine WFIKKN2was not found to have an effect on various growth traits in thefemale lambs (P>0.05).(4) In male NZ Romney lambs, the presence of variant B in agenotype was associated with an increased shoulder yield and proportion shoulderyield. Given that female lambs were kept as flock replacement, association betweenvariation in ovine WFIKKN2and variation in carcass muscle traits was not analysed.(5) No associations with growth or carcass muscle traits were detected for thepresence (or absence) of variants A and C.(6) Different parent-of-origin for variant Bhad a different effect on birth weight, weaning weight, shoulder yield and proportionshoulder yield in lambs.3．Variation in the promoter of ovine MSTN had an effect on some growth andcarcass muscle traits in male NZ Romney lambs.(1) Two SNPs c.-2449G>C andc.-2379T>C were identified in the promoter of ovine MSTN.(2) Pearson correlationcoefficients between growth traits revealed strong phenotypic correlations betweenbirth weight and tailing weight (r=0.542, P<0.01), and birth weight and weaningweight (r=0.449, P<0.01). There were weak phenotypic correlations between birthweight and draft weight (r=0.246, P<0.01), birth weight and pre-weaning growth rate(r=0.280, P<0.01) and birth weight and post-weaning growth rate (r=-0.338, P<0.01).There was no phenotypic correlation between birth weight and growth rate form birthto draft (r=-0.082, P>0.05).(3) In357male NZ Romney lambs, variant c.-2449C wasassociated with increased loin yield and proportion loin yield (P<0.05).(4) c.-2379Twas associated with decreased birth weight, tailing weight and weaning weight(P<0.05). However, no association was found with draft weight and any growthtraits.The effect of variant c.-2379T on weight traits suggests that the SNP appears tohave an effect that originates at, or before birth and this effect persists to weaning.(5)Of the114lambs with one copy of c.-2449C, only9.65%had c.*1232A. What ismore, five lambs that were homozygous for c.-2449C were not found to possessc.*1232A. This would suggest that variant c.-2449C was not in linkage with c*1232A.4. Variation in exon3of ovine MYF5had an effect on some growth and carcassmuscle traits in male NZ Romney lambs.(1) Variants B and C were only observed and variants A and D were absent in389male NZ Romney lambs.(2) Variant C tended tobe associated with decreased birth weight and draft weight (P<0.1).(3) The presenceof variant C was associated with decreased leg yield, loin yield, total yield andproportion loin yield (P<0.05). Variant C could therefore be used as a gene-marker forimproving lamb carcass muscle traits.