Genetics and Breeding

Genome-wide association studies (GWAS) provide a powerful approach for identifying quantitative trait loci without prior knowledge of location or function. To identify loci associated with wool production traits, we performed a genome-wide association study on a total of 765 Chinese Merino sheep (JunKen type) genotyped with 50 K single nucleotide polymorphisms (SNPs). In the present study, five wool production traits were examined: fiber diameter, fiber diameter coefficient of variation, fineness dispersion, staple length and crimp. We detected 28 genome-wide significant SNPs for fiber diameter, fiber diameter coefficient of variation, fineness dispersion, and crimp trait in the Chinese Merino sheep. About 43% of the significant SNP markers were located within known or predicted genes, including YWHAZ, KRTCAP3, TSPEAR, PIK3R4, KIF16B, PTPN3, GPRC5A, DDX47, TCF9, TPTE2, EPHA5 and NBEA genes. Our results not only confirm the results of previous reports, but also provide a suite of novel SNP markers and candidate genes associated with wool traits. Our findings will be useful for exploring the genetic control of wool traits in sheep. more »

Data from seven research resource flocks across Australia were combined to provide accurate estimates of genetic correlations among production traits in Merino sheep. The flocks represented contemporary Australian Merino fine, medium and broad wool strains over the past 30 years. Over 110,000 records were available for analysis for each of the major wool traits, and 50,000 records for reproduction and growth traits with over 2700 sires and 25,000 dams. Individual models developed from the single trait analyses were extended to the various combinations of two-trait models to obtain genetic correlations among six wool traits [clean fleece weight (CFW), greasy fleece weight, fibre diameter (FD), yield, coefficient of variation of fibre diameter and standard deviation of fibre diameter], four growth traits [birth weight, weaning weight, yearling weight (YWT), and hogget weight] and four reproduction traits [fertility, litter size, lambs born per ewe joined, lambs weaned per ewe joined (LW/EJ)]. This study has provided for the first time a comprehensive matrix of genetic correlations among these 14 wool, growth and reproduction traits. The large size of the data set has also provided estimates with very low standard errors. A moderate positive genetic correlation was observed between CFW and FD (0.29 +/- 0.02). YWT was positively correlated with CFW (0.23 +/- 0.04), FD (0.17 +/- 0.04) and LWEJ (0.58 +/- 0.06), while LW/EJ was negatively correlated with CFW (-0.26 +/- 0.05) and positively correlated with FD (0.06 +/- 0.04) and LS (0.68 +/- 0.04). These genetic correlations, together with the estimates of heritability and other parameters provide the basis for more accurate prediction of outcomes in complex sheep-breeding programmes designed to improve several traits. more »

There is widespread interest in the use of skin properties for the selection of superior Merino genotypes. This is despite the fact that no selection experiments to date have demonstrated beneficial effects on production traits from selection based solely on skin traits. Two studies have examined whether the inclusion of skin traits in a realistic selection program improves the rate of genetic progress towards a breeding objective emphasising fleece weight and fibre diameter. Both indicated little benefit from including the skin traits. However the impact of the skin traits will depend on their heritabilities and their genetic associations with one another and with the traits in the breeding objective. There is increasing evidence that the genetic parameters differ between the Merino strains so results from one strain cannot be extrapolated to another. In this paper we examine the effects of including classer assessed skin quality and two objectively measured skin characters, skin biopsy weight and follicle density, on the genetic and economic gain made over and above that made using a standard selection index in South Australian Strongwool Merinos. The results indicate that substantial additional genetic gain can be made by including the skin traits. This was particularly true at low micron premiums where addition of all three skin traits increased the economic gain by 25%. The genetic improvement in adult clean fleece weight by including all three skin traits at this premium, was increased from 0.9% per annum to 1.4% per annum with a corresponding slight reduction in the decrease in mean fibre diameter. At higher micron premiums the benefit of including the skin traits was substantially less, again reflecting the tendency for skin trait inclusion to influence fleece weight to a larger extent than fibre diameter. Inclusion of the skin traits had little impact on coefficient of variation of fibre diameter, staple strength and staple length. Our results suggest that consideration of some skin traits may lead to moderate genetic gains and be worthwhile including in breeding programs for Strongwool Merinos, but they do not lend support to notions that consideration of skin traits will produce dramatic increases in fleece weights with concomitant large decreases in fibre diameter. more »

Yearling fibre diameter profiles from the OFDA2000 instrument were used to derive records on mean and coefficient of variation (CV) of fibre diameter at multiple points in the post-weaning age window, from 20 to 90% of staple profile length. Genetic correlations were calculated between these traits and their yearling equivalents. Results showed that from 50% of the staple profile and higher, post-weaning fibre diameter is genetically the same trait as yearling fibre diameter. Although the derivation of CV of fibre diameter was less accurate, genetic correlations with the yearling expression were greater than 0.9 for all except one percentile point. The expected correlation between post-weaning and yearling fleece weight was also derived, and under simple assumptions it is not unreasonable to expect estimates of genetic correlations greater than 0.9. more »