Production Traits In Sheep Research Articles

Genome-wide association studies for growth and meat production traits in sheep.

BackgroundGrowth and meat production traits are significant economic traits in sheep. The aim of the study is to identify candidate genes affecting growth and meat production traits at genome level with high throughput single nucleotide polymorphisms (SNP) genotyping technologies.Methodology and ResultsUsing Illumina OvineSNP50 BeadChip, we performed a GWA study in 329 purebred sheep for 11 growth and meat production traits (birth weight, weaning weight, 6-month weight, eye muscle area, fat thickness, pre-weaning gain, post-weaning gain, daily weight gain, height at withers, chest girth, and shin circumference). After quality control, 319 sheep and 48,198 SNPs were analyzed by TASSEL program in a mixed linear model (MLM). 36 significant SNPs were identified for 7 traits, and 10 of them reached genome-wise significance level for post-weaning gain. Gene annotation was implemented with the latest sheep genome Ovis_aries_v3.1 (released October 2012). More than one-third SNPs (14 out of 36) were located within ovine genes, others were located close to ovine genes (878bp-398,165bp apart). The strongest new finding is 5 genes were thought to be the most crucial candidate genes associated with post-weaning gain: s58995.1 was located within the ovine genes MEF2B and RFXANK, OAR3_84073899.1, OAR3_115712045.1 and OAR9_91721507.1 were located within CAMKMT, TRHDE, and RIPK2 respectively. GRM1, POL, MBD5, UBR2, RPL7 and SMC2 were thought to be the important candidate genes affecting post-weaning gain too. Additionally, 25 genes at chromosome-wise significance level were also forecasted to be the promising genes that influencing sheep growth and meat production traits.ConclusionsThe results will contribute to the similar studies and facilitate the potential utilization of genes involved in growth and meat production traits in sheep in future.

Investigation of polymorphisms and association of the ABCG2 gene with milk production traits in sheep

The ATP-binding casette sub-family G member 2 (ABCG2) gene was chosen as a candidate gene influencing milk production traits in sheep based on its function and chromosomal localization. A number of fragments were sequenced, including the 3′UTR region, 16 exons, and regions within introns 4, 5 and 6, in samples collected from 11 Awassi and 2 Gyimesi Racka sheep. A single 35-base insertion/deletion, and a total of 13 single nucleotide polymorphisms (SNPs) were identified. SNP mutations found in exons (n=3) were synonymous. Two SNPs (g.703T>C, c.863+40G>A) and the insertion/deletion (c.683-80_46del) were chosen for further investigation, and an association study between these three polymorphisms and milk production traits was performed in both breeds (Awassi n=310, Gyimesi Racka n=75). The analysis revealed significant effect of two of the studied SNPs in Gyimesi Racka. Mutation g.703T>C showed significant effect on protein percentage (p<0.05) while the c.683-80_46del had a significant effect on somatic cell score (p<0.01). However, further studies are needed to evaluate these possible associations more effectively.

Genetic polymorphism of β-lactoglobulin in sheep raised for milk production

To investigate β-lactoglobulin polymorphism using polymerase chain reaction – restriction fragment length polymorphism in Polish Mountain, East Friesian, Polish Merino and Austrian Bergschaf sheep raised for milk production, three β-LGB genotypes (AA, AB and BB) were found in all the groups, AB being the most frequent genotype in all the groups. The frequency of β-LGB A genes was 0.66 in Friesian, 0.55 in Bergschaf, 0.5 in Polish Mountain and 0.48 in Polish Merino sheep with no deviations from genetic equilibrium according to Hardy-Weinberg law. The relationship between β-lactoglobulin genotype and milk yield and milk composition was investigated, but no statistical differences were found. The present findings provide no conclusive evidence about the effect of different β-LGB variants on milk production traits in sheep.

SNP detection and haplotype analysis in partial sequence of MSTN gene in sheep

Polymerase chain reaction (PCR) products of the MSTN gene amplified from sixty sheep of nine Chinese indigenous sheep breeds and one imported sheep breed were sequenced to identify the single-nucleotide polymorphisms (SNPs) in a 378-bp fragment including intron 2 and exon 3 of the MSTN gene. A total of fifteen SNPs (A1937C, T1942G, C1956T, A1972C, A1990G, A2008C, A2011G, C2019T, A2025C, A2027C, T2085G, T2173C, C2198T, C2210T and C2213T) were detected among the sixty sequenced individuals and they were all located in intron 2. Twelve haplotypes were identified from these fifteen SNPs, of which haplotype I (CGTCGCGTCCGCTTT) and VIII (ATCAAAACAATTCCC) were the two major and basic ones with frequencies of 12.25% and 77.80%, respectively. Haplotype VIII was distributed in all sheep breeds and all individuals of the meat or meat-wool type sheep breeds were homozygous with respect to this haplotype. This suggests that haplotype VIII might be related to meat production traits in sheep. Haplotype I was only distributed in the fur, lambskin type and fur-meat type sheep breeds. This suggests that haplotype I may have some relationship with fur traits in sheep.

Polymorphism of the bovine ADRB3 gene

The β(3)-adrenergic receptor (ADRB3) is predominantly expressed in white and brown adipose tissue and mediates the lipolytic and thermogenic effects of high catecholamine concentrations. Variation in the ADRB3 gene (ADRB3) has been associated with obesity and the earlier onset of non-insulin-dependent diabetes mellitus in some ethnic groups, as well as some production traits of sheep, but to date variation of bovine ADRB3 has not been reported. In this study, variation in the promoter region of bovine ADRB3 was investigated in 737 cattle by polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) analysis. Six PCR-SSCP patterns representing six allelic variations and containing four single nucleotide polymorphisms (SNPs) and three nucleotide deletions/insertions were observed. Allele A was the most common allele (93.83%), whereas alleles C, D, E and F were rare (0.07, 1.09, 0.41, and 0.34%, respectively). The variation identified here might have an impact on both the function and level of expression of bovine ADRB3.

Mapping quantitative trait loci (QTL) in sheep. II. Meta-assembly and identification of novel QTL for milk production traits in sheep

An (Awassi × Merino) × Merino backcross family of 172 ewes was used to map quantitative trait loci (QTL) for different milk production traits on a framework map of 200 loci across all autosomes. From five previously proposed mathematical models describing lactation curves, the Wood model was considered the most appropriate due to its simplicity and its ability to determine ovine lactation curve characteristics. Derived milk traits for milk, fat, protein and lactose yield, as well as percentage composition and somatic cell score were used for single and two-QTL approaches using maximum likelihood estimation and regression analysis. A total of 15 significant (P < 0.01) and additional 25 suggestive (P < 0.05) QTL were detected across both single QTL methods and all traits. In preparation of a meta-analysis, all QTL results were compared with a meta-assembly of QTL for milk production traits in dairy ewes from various public domain sources and can be found on the ReproGen ovine gbrowser http://crcidp.vetsci.usyd.edu.au/cgi-bin/gbrowse/oaries_genome/. Many of the QTL for milk production traits have been reported on chromosomes 1, 3, 6, 16 and 20. Those on chromosomes 3 and 20 are in strong agreement with the results reported here. In addition, novel QTL were found on chromosomes 7, 8, 9, 14, 22 and 24. In a cross-species comparison, we extended the meta-assembly by comparing QTL regions of sheep and cattle, which provided strong evidence for synteny conservation of QTL regions for milk, fat, protein and somatic cell score data between cattle and sheep.

Quantitative trait loci underlying milk production traits in sheep

Improvement of milk production traits in dairy sheep is required to increase the competitiveness of the industry and to maintain the production of high quality cheese in regions of Mediterranean countries with less favourable conditions. Additional improvement over classical selection could be reached if genes with significant effects on the relevant traits were specifically targeted by selection. However, so far, few studies have been undertaken to detect quantitative trait loci (QTL) in dairy sheep. In this study, we present a complete genome scan performed in a commercial population of Spanish Churra sheep to identify chromosomal regions associated with phenotypic variation observed in milk production traits. Eleven half-sib families, including a total of 1213 ewes, were analysed following a daughter design. Genome-wise multi-marker regression analysis revealed a genome-wise significant QTL for milk protein percentage on chromosome 3. Eight other regions, localized on chromosomes 1, 2, 20, 23 and 25, showed suggestive significant linkage associations with some of the analysed traits. To our knowledge, this study represents the first complete genome scan for milk production traits reported in dairy sheep. The experiment described here shows that analysis of commercial dairy sheep populations has the potential to increase our understanding of the genetic determinants of complex production-related traits.

Genetic and Environmental Trends for Milk Production Traits in Sheep Estimated with Test-day Model

Data from milk performance testing were used to analyze genetic and environmental trends for purebred Tsigai, Improved Valachian and Lacaune sheep. 103,715 (Tsigai), 212,962 (Improved Valachian) and 2,196 (Lacaune) test-day records gathered by the State Breeding Institute of the Slovak Republic entered the analyses. The respective pedigree data comprised 23,724 (Tsigai), 51,401 (Improved Valachian) and 438 (Lacaune) records. The multiple-trait, mixed model methodology was used to predict the breeding values for daily milk yield, fat and protein content and to estimate the fixed and remaining random effects assumed to affect the above mentioned traits, separately for each breed. The breeding values for daily milk yield were adjusted for 150-day standardized lactation length by multiplying with the constant 150, as the breeding goal of the selection scheme in Slovakian sheep is to increase 150-day milk production and constant heritability throughout the whole lactation is assumed. The genetic trends were expressed as changes in averages of breeding values across birth years of animals. For Tsigai and Lacaune breeds, cumulative genetic changes over the analyzed period were 3.8 and 5.1 kg for 150-day milk, 0 and -0.16% for fat content and 0 and -0.12% for protein content. For Improved Valachian breed, either a low (1.6 kg for 150-day milk yield) or zero (fat and protein content) cumulative genetic change was found. The environmental trends were calculated as averages of solutions for flock-test day effect across years and months in which measurements were taken. A distinctive cyclical pattern which reflected short-time variation in milk production traits was found. Possible explanations for this phenomenon are given and discussed.

Associations between genotypes at codon 171 and 136 of the prion protein gene and production traits in market lambs

To determine whether selection for the homozygous A136 R171 genotype that confers resistance to classic scrapie infection negatively affects production traits in sheep. 996 commercial lambs obtained from 2 flocks at separate locations across 3 consecutive years. Procedures-Genotyping at codon 136 and 171 was performed by use of commercially available testing or a single-nucleotide polymorphism assay. Carcass data were collected without knowledge of genotype approximately 24 hours after slaughter by an experienced grader. The model to analyze associations between prion protein (PRNP) genotype and production traits was based on genotype, breed, or both as fixed effects and days on feed as a covariate. Average daily gain was significantly associated with only combined codons 136 and 171. In flock 1, weaning average daily gain was significantly greater in AA136 sheep than heterozygotes; the difference between QR171 and RR171 sheep, compared with QQ171 sheep, were not significant although QR171 and RR171 sheep had higher values. However, in flock 2, average daily gain was significantly greater in AV136 sheep than AA136 sheep and in QR171 sheep than QQ171 sheep. Findings suggest there is an advantage for average daily gain in lambs with an arginine allele at codon 171, but there were no other genotype effects on production traits. Thus, selection for the resistant arginine allele at codon 171 to comply with USDA scrapie eradication guidelines should not be detrimental to lamb production in commercial flocks. Effects of codon 136 on average daily gain were ambiguous.

Sensitivity of response of multi-trait index selection to changes in genetic correlations between production traits in sheep

Complex sheep breeding objectives and the inclusion of more traits in genetic evaluation requires more accurate genetic parameters. There are few estimates of genetic correlations, especially between the major sheep production trait groups and they are generally variable with large standard errors. This study examines the sensitivity of response to multi-trait index selection for a range of genetic correlations between major traits (growth, wool, carcass, reproduction and worm resistance) under 3 breeding objectives (fine wool, dual-purpose wool/meat and meat) relevant to Australian sheep enterprises. Factor analysis identified the major factors explaining the underlying variability in the matrix of base genetic correlations for each breeding objective. Monte Carlo simulation studied the effect of changes in the genetic correlations under 3 index scenarios with the genetic and environmental variance–covariance matrices sampled independently from a Wishart distribution. The sensitivity of responses to selection over the range of correlations varied with the breeding objective. Selection responses were sensitive under all objectives for the range of correlations for reproduction with wool traits and in at least some objectives for reproduction with growth, worm resistance and carcass muscling. Selection responses in the fine wool objective were highly sensitive to the correlation between growth and fibre diameter. The results provide a logical basis for setting priorities for studies to obtain more accurate estimates of genetic correlations among sheep production traits.

A review of genetic parameter estimates for wool, growth, meat and reproduction traits in sheep

Genetic parameters for a range of sheep production traits have been reviewed from estimates published over the last decade. Weighted means and standard errors of estimates of direct and maternal heritability, common environmental effects and the correlation between direct and maternal effects are presented for various growth, carcass and meat, wool, reproduction, disease resistance and feed intake traits. Weighted means and confidence intervals for the genetic and phenotypic correlations between these traits are also presented. A random effects model that incorporated between and within study variance components was used to obtain the weighted means and variances. The weighted mean heritability estimates for the major wool traits (clean fleece weight, fibre diameter and staple length) and all the growth traits were based on more than 20 independent estimates, with the other wool traits based on more than 10 independent estimates. The mean heritability estimates for the carcass and meat traits were based on very few estimates except for fat (27) and muscle depth (11) in live animals. There were more than 10 independent estimates of heritability for most reproduction traits and for worm resistance, but few estimates for other sheep disease traits or feed intake. The mean genetic and phenotypic correlations were based on considerably smaller numbers of independent estimates. There were a reasonable number of estimates of genetic correlations among most of the wool and growth traits, although there were few estimates for the wool quality traits and among the reproduction traits. Estimates of genetic correlations between the groups of different production traits were very sparse. The mean genetic correlations generally had wide confidence intervals reflecting the large variation between estimates and relatively small data sets (number of sires) used. More accurate estimates of genetic parameters and in particular correlations between economically important traits are required for accurate genetic evaluation and development of breeding objectives.

Estimation of genetic and environmental parameters of milk production traits in Slovak purebred sheep using test-day model

Covariance matrices and genetic parameters for milk production traits in sheep were estimated for the Improved Valachian and Tsigai breeds. These multipurpose breeds are of local importance, and are bred for milk, meat and wool. The traits under study were daily milk yield and fat and protein content. Genetic analyses were based on test-day records gathered over the period from 1995 to 2001. Each breed was analyzed separately. Only purebred animals with at least four test days per lactation were considered. The data set for the Improved Valachian consisted of 117,959 test-day records of 28,753 lactations belonging to 18,867 ewes. The corresponding pedigree comprised information on 32,804 animals. For the Tsigai breed, the data set consisted of 52,191 test-day records of 12,382 lactations belonging to 8,132 ewes and the pedigree comprised 14,576 animals. The three-trait animal model was used for analyses. To account for different lactation stage, a fixed regression on individual test days was employed. In addition to the function describing, effects of days in milk, effects of lactation, litter size, number of milkings per day, age at lambing, and flock-test day as well as additive genetic and permanent environmental effect of the animal were included in the model. Of these, flock-test day, additive genetic and permanent environmental effects were treated as random. Restricted maximum likelihood (REML) algorithm was used to estimate genetic parameters and covariance matrices. Heritabilities were 0.10 and 0.19 for daily milk yield, 0.06 and 0.12 for fat content, 0.07 and 0.17 for protein content for the Improved Valachian and Tsigai breeds, respectively. Genetic correlations between milk yield and fat content for the two breeds were −0.29 and −0.23 and those between milk yield and protein content were −0.30 and −0.27. Genetic correlations between fat and protein content were 0.58 and 0.57. Higher values (either positive or negative) were found for the breed with the larger number of records. Variance ratios and correlations were also estimated for nongenetic effects for both breeds. Variance ratios for the flock-test-day effects were rather high, ranging from 0.34 to 0.48. Higher values for these effects were found in the Improved Valachian sheep, reflecting more variability in management conditions in this breed. The genetic parameters estimated in this study should be used in routine genetic evaluation of milk production traits of local sheep breeds to replace present selection criteria based on phenotype values of dam milk yield.

Associations between transferrin type and facial eczema susceptibility and some production traits in sheep

Abstract (1) Two groups of Romney rams from a single source, six per group, were tested for susceptibility to facial eczema (FE), by measuring 223 of their progeny. The transferrin type for one group of rams was DD, and for the other group AA, AB, or AC. There were 64% of lambs (range 42-l00%) by the DD rams susceptible to FE (tested by measuring the response to a standard oral dose of sporidesmin), compared with 51 % (range 38-72%) by the other group. The difference was not significant. (2) Transferrin types were also determined on 332 lambs born in 1986 and sired by the 12 rams above and 5 other Romney rams. Forty percent of lambs carried at least one A and/or one G transferrin gene, 40% the DD type, and 20% other transferrin types. Frequencies of the three groups susceptible to FE were 47, 61, and 60% respectively (P<0.10). Similar ranking results (31, 47, and 40% respectively) were obtained from a preliminary sample of 273 Romney lambs born in the previous year. (3) The experimental farm was in an are...