Dairy Sheep Breeds Research Articles

Genetic diversity within economically important loci in European, Middle Eastern, and African sheep breeds: An insight into their development

The aims of this study were to analyze sequence variability within genes related to important economic traits in dairy and non-dairy sheep breeds, and to evaluate the genetic variability as an insight into their development. In total, 31 single nucleotide polymorphisms (SNPs), one indel, and one microsatellite, all located in ovine milk protein genes (CSN1S1, CSN1S2, CSN2, CSN3, LGB), and 13 SNPs located in genes associated with production and reproduction traits of economic importance (DGAT1, DGAT2, GHR, FASN, GHRHR, CTSB, MCR1, KRT1, IL2, IGF1, HR, GDF8, GDF9) were genotyped. The analysis included 752 samples derived from 23 different European, Middle-Eastern (Turkey and Israel) and African (Nigeria and Cameroon) sheep breeds, and the European Mouflon.We could not observe the often described decline of heterozygosity with increasing distance to the domestication centre maybe because of high gene flow and gene introgression between breeds following domestication. Tendencies of clustering according to the local origin of the animals were visible, whereas a clear breed grouping was not identified. No significant difference was found by principal component analysis of casein haplotypes between dairy and non-dairy breeds. However, using Canonical Discriminant Analysis most of the non-dairy individuals were correctly assigned to the non-dairy group, with an increasing precision when considering both casein haplotypes and the remaining SNP. The distribution of variation in the production-related SNP analyzed reflects both the long history of migrations, adaption, isolation, and the most recent effect of gene flow or isolation due to selection in the different breeds.

The genomic architecture of mastitis resistance in dairy sheep

BackgroundMastitis is the most prevalent disease in dairy sheep with major economic, hygienic and welfare implications. The disease persists in all dairy sheep production systems despite the implementation of improved management practises. Selective breeding for enhanced mastitis resistance may provide the means to further control the disease. In the present study, we investigated the genetic architecture of four mastitis traits in dairy sheep. Individual animal records for clinical mastitis occurrence and three mastitis indicator traits (milk somatic cell count, total viable bacterial count in milk and the California mastitis test) were collected monthly throughout lactation for 609 ewes of the Greek Chios breed. All animals were genotyped with a custom-made 960-single nucleotide polymorphism (SNP) DNA array based on markers located in quantitative trait loci (QTL) regions for mastitis resistance previously detected in three other distinct dairy sheep populations.ResultsHeritable variation and strong positive genetic correlations were estimated for clinical mastitis occurrence and the three mastitis indicator traits. SNP markers significantly associated with these mastitis traits were confirmed on chromosomes 2, 3, 5, 16 and 19. We identified pathways, molecular interaction networks and functional gene clusters for mastitis resistance. Candidate genes within the detected regions were identified based upon analysis of an ovine transcriptional atlas and transcriptome data derived from milk somatic cells. Relevant candidate genes implicated in innate immunity included SOCS2, CTLA4, C6, C7, C9, PTGER4, DAB2, CARD6, OSMR, PLXNC1, IDH1, ICOS, FYB, and LYFR.ConclusionsThe results confirmed the presence of animal genetic variability in mastitis resistance and identified genomic regions associated with specific mastitis traits in the Chios sheep. The conserved genetic architecture of mastitis resistance between distinct dairy sheep breeds suggests that across-breed selection programmes would be feasible.

Estimations of linkage disequilibrium, effective population size and ROH-based inbreeding coefficients in Spanish Churra sheep using imputed high-density SNP genotypes.

In this study, the availability of the Ovine HD SNP BeadChip (HD-chip) and the development of an imputation strategy provided an opportunity to further investigate the extent of linkage disequilibrium (LD) at short distances in the genome of the Spanish Churra dairy sheep breed. A population of 1686 animals, including 16 rams and their half-sib daughters, previously genotyped for the 50K-chip, was imputed to the HD-chip density based on a reference population of 335 individuals. After assessing the imputation accuracy for beagle v4.0 (0.922) and fimpute v2.2 (0.921) using a cross-validation approach, the imputed HD-chip genotypes obtained with beagle were used to update the estimates of LD and effective population size for the studied population. The imputed genotypes were also used to assess the degree of homozygosity by calculating runs of homozygosity and to obtain genomic-based inbreeding coefficients. The updated LD estimations provided evidence that the extent of LD in Churra sheep is even shorter than that reported based on the 50K-chip and is one of the shortest extents compared with other sheep breeds. Through different comparisons we have also assessed the impact of imputation on LD and effective population size estimates. The inbreeding coefficient, considering the total length of the run of homozygosity, showed an average estimate (0.0404) lower than the critical level. Overall, the improved accuracy of theupdated LD estimates suggests that the HD-chip, combined with an imputation strategy, offers a powerful tool that will increase the opportunities to identify genuine marker-phenotype associations and to successfully implement genomic selection in Churra sheep.

Variant discovery in the sheep milk transcriptome using RNA sequencing

BackgroundThe identification of genetic variation underlying desired phenotypes is one of the main challenges of current livestock genetic research. High-throughput transcriptome sequencing (RNA-Seq) offers new opportunities for the detection of transcriptome variants (SNPs and short indels) in different tissues and species. In this study, we used RNA-Seq on Milk Sheep Somatic Cells (MSCs) with the goal of characterizing the genetic variation within the coding regions of the milk transcriptome in Churra and Assaf sheep, two common dairy sheep breeds farmed in Spain.ResultsA total of 216,637 variants were detected in the MSCs transcriptome of the eight ewes analyzed. Among them, a total of 57,795 variants were detected in the regions harboring Quantitative Trait Loci (QTL) for milk yield, protein percentage and fat percentage, of which 21.44% were novel variants. Among the total variants detected, 561 (2.52%) and 1,649 (7.42%) were predicted to produce high or moderate impact changes in the corresponding transcriptional unit, respectively. In the functional enrichment analysis of the genes positioned within selected QTL regions harboring novel relevant functional variants (high and moderate impact), the KEGG pathway with the highest enrichment was “protein processing in endoplasmic reticulum”. Additionally, a total of 504 and 1,063 variants were identified in the genes encoding principal milk proteins and molecules involved in the lipid metabolism, respectively. Of these variants, 20 mutations were found to have putative relevant effects on the encoded proteins.ConclusionsWe present herein the first transcriptomic approach aimed at identifying genetic variants of the genes expressed in the lactating mammary gland of sheep. Through the transcriptome analysis of variability within regions harboring QTL for milk yield, protein percentage and fat percentage, we have found several pathways and genes that harbor mutations that could affect dairy production traits. Moreover, remarkable variants were also found in candidate genes coding for major milk proteins and proteins related to milk fat metabolism. Several of the SNPs found in this study could be included as suitable markers in genotyping platforms or custom SNP arrays to perform association analyses in commercial populations and apply genomic selection protocols in the dairy production industry.

Environmental and genetic factors affecting milk yield and quality in three Italian sheep breeds.

The aims of the study described in the Research Communication were to determine the level of influence of some environmental factors on milk yield and quality traits, including lactose, and lactation length in ewes belonging to three different Italian breeds and to estimate the heritability for the same traits. A total of 2138 lactation records obtained from 535 ewes belonging to three different Italian breeds (Comisana, Leccese, and Sarda) were used. Breed significantly affected all of the considered traits. Moreover, year of lambing affected milk yield and lactation length without influence on milk quality traits. Parity affected significantly only the milk yield, whereas type of birth showed its effect on milk yield, fat, protein, and lactose yield. On the whole, the presently reported heritability estimates are within the range of those already obtained in other dairy breeds by other authors, with values for lactation length being very low in all the investigated populations. Considering the heritability estimates for lactose content and yield, to the best of our knowledge, there is a lack of information on these parameters in ovine species and this is the first report on heritability of lactose content and yield in dairy sheep breeds. Our results suggest that genetic variability for milk traits other than lactation length is adequate for selection indicating a good response to selection in these breeds.

The effect of milking frequency reduction from twice to once daily on mammary physiology and animal welfare of two dairy Greek sheep breeds

The objective of this study was to investigate the effect of milking frequency reduction from twice (TDM) to once (ODM) daily on mammary physiology, activities of all milk enzymes implicated in the plasminogen activating cascade and animal welfare in dairy ewes. Thirty-eight dairy ewes (Chios, n=22; Karagouniko, n=16) under the same dietary and management conditions were used in a 14-wk experiment lasting from the 92nd to the 188th day of lactation period. The ewes were distributed in two equal groups of animals per breed. The first 14days served as an acclimatization period and once per day milking started at the 106th day following parturition and lasted 12 weeks. A significant decline in milk production of ODM ewes was observed compared to that of TDM ewes (−29.2%, P<0.001). Enzymatic activities of plasmin (PL), plasminogen-derived (PG) and plasminogen activator (PA) were significantly increased in the milk of ODM ewes compared to that of TDM. Furthermore, the sum of PL+PG activities was increased in ewes milked once daily and this indicates possible enhanced entrance of plasminogen towards milk. Increased blood lactose was observed in the ODM ewes at the 108th d following parturition, 2days after the milking frequency reduction was started, a finding indicating that the permeability of the tight junctions was compromised, although the leakiness of tight junctions was a transient phenomenon. Finally, no significant signs of distress were observed in ODM ewes. Thus, ODM treatment does not affect negatively the welfare of dairy ewes. Overall, the adaptation of the ODM practice is not recommended for the Greek farmers despite the apparent improvement of their quality of life.

Identification of novel SNPs of ovine PRL gene and their association with milk production traits

Prolactin (PRL) is a lactogenic hormone that plays a significant role in milk production; its depletion in sheep provokes a severe reduction of milk secretion. Thus, PRL also could be used as a positional marker gene associated with milk production and composition traits. Therefore, the purpose of the study was to identify genotype frequencies of single nucleotide polymorphisms the intron 2 in ovine PRL gene and its possible association genotypes with milk traits in dairy sheep breeds. The genetic structures of ovine PRL gene were examined by PCR-RFLP and DNA sequencing methods in three sheep populations. Four hundred and fifty blood and milk samples were used in the study, which included 150 samples from each of Sakiz, Akkaraman and Awassi ewes respectively. As a result, PRL genotype AA showed a strong association with milk yields content, whereas the animals carrying BB genotype had a higher fat percentage value in the three sheep breeds. Haplotype analysis of the obtained sequences showed the presence of 12 haplotypes in the PRL intron 2 region. In the present study, we have reported for the first time 48 SNPs of the PRL gene for intron 2 in dairy sheep breeds. These preliminary results indicate that the identified SNPs lend themselves readily for further research regarding physiological impacts such as milk production and reproductive traits in other dairy sheep populations.

Comprehensive RNA-Seq profiling to evaluate lactating sheep mammary gland transcriptome.

RNA-Seq enables the generation of extensive transcriptome information providing the capability to characterize transcripts (including alternative isoforms and polymorphism), to quantify expression and to identify differential regulation in a single experiment. Our aim in this study was to take advantage of using RNA-Seq high-throughput technology to provide a comprehensive transcriptome profiling of the sheep lactating mammary gland. Eight ewes of two dairy sheep breeds with differences in milk production traits were used in this experiment (four Churra and four Assaf ewes). Milk samples from these animals were collected on days 10, 50, 120 and 150 after lambing to cover the various physiological stages of the mammary gland across the complete lactation. RNA samples were extracted from milk somatic cells. The RNA-Seq dataset was generated using an Illumina HiSeq 2000 sequencer. The information reported here will be useful to understand the biology of lactation in sheep, providing also an opportunity to characterize their different patterns on milk production aptitude.

The effect of an herb mixture supplement on the performance of milking sheep during the summer feeding period

An experiment was conducted on 66 milking ewes of the Koluda prolific dairy sheep breed, housed indoors, during summer feeding based on alfalfa forage. The aim of the study was to determine the effect of our own herb mixture supplement added to concentrate feed (in the amount of 10 or 20 g/sheep/day) for milking sheep on consumption of feed and nutrients, as well as body weight, body condition, milk yield, chemical composition of the milk and condition of the udder. The addition of herbs to the concentrate feed increased its content of biologically active substances (ethereal oils and flavonoids) in proportion to the amount of herbs added. The use of the herb supplement had no effect on the body weight or body condition of the sheep. The addition of herbs in the amount of 20 g/sheep/day improved udder health, evaluated on the basis of the electrical resistance of the milk. The use of herbs increased lactation persistence and daily milk yield, which translated to greater milk production. Milk yield from sheep fed with supplements of 10 and 20 g of herbs was greater than in the control, by 8.2% and 16.4%, respectively. No effect of the herb mixture was noted on the content of the basic chemical components of the milk, other than a reduction in the content of milk fat in the case of the 20 g herb supplement.

Transcriptome expression analysis of candidate milk genes affecting cheese-related traits in 2 sheep breeds

Because ewe milk is principally used for cheese making, its quality is related to its content of total solids and the way in which milk constituents influence cheese yield and determine the technological and organoleptic characteristics of dairy products. Therefore, an in-depth knowledge of the expression levels of milk genes influencing cheese-related traits is essential. In the present study, the milk transcriptome data set of 2 dairy sheep breeds, Assaf and Spanish Churra, was used to evaluate the expression levels of 77 transcripts related to cheese yield and quality traits. For the comparison between both breeds, we selected the RNA sequencing (RNA-Seq) data at d 10 of lactation because this is the time point at which within and between breed differences due to lactation length are minimal. The evaluated genes encode major milk proteins (caseins and whey proteins), endogenous proteases, and enzymes related to fatty acid metabolism and citrate content. Through this analysis, we identified the genes predominantly expressed in each of the analyzed pathways that appear to be key genes for traits related to sheep milk cheese. Among the highly expressed genes in both breeds were the genes encoding caseins and whey proteins (CSN2, CSN3, CSN1S1, ENSOARG00000005099/PAEP, CSN1S2, LALBA), genes related to lipid metabolism (BTN1A1, XDH, FASN, ADFP, SCD, H-FABP, ACSS2), and one endogenous protease (CTSB). Moreover, a differential expression analysis between Churra and Assaf sheep allowed us to identify 7 genes that are significantly differentially expressed between the 2 breeds. These genes were mainly linked to endogenous protease activity (CTSL, CTSK, KLK10, KLK6, SERPINE2). Additionally, there were 2 differentially expressed genes coding for an intracellular fatty acid transporter (FABP4), an intermediate molecule of the citric acid cycle (SUCNR1), and 2 heat shock proteins (HSP70, HSPB8) that could be related to high protein production. The differential expression of these genes could have a direct influence on the different phenotypes observed between the 2 analyzed breeds.

Allelic polymorphism of Ovar-DRB1 exon2 gene and parasite resistance in two dairy sheep breeds

The Ovar-DRB1 gene locus is one of the most polymorphic genes of the Major Histocompatibility Complex (Ovar-MHC) and holds a functional role to antigen presentation. The aim of this study was: a) to describe the Ovar-DRB1 locus variability in two dairy Greek sheep breeds and b) to investigate associations between this variability with resistance to gastrointestinal parasitosis. Blood and faecal samples were collected from 231 and 201 animals of Arta and Kalarrytiko breeds, respectively. The identification of alleles was performed using the sequence–base method. Faecal egg counting (FEC) of the gastrointestinal parasites and measures of blood plasma pepsinogen levels were performed in order to evaluate parasitological parameters. From this study in the overall examined animals, thirty-nine Ovar-DRB1 alleles were identified, among them, ten new alleles, reported for the first time in the literature. In Arta breed a total of twenty-four alleles were found. Among the detected alleles, ten were breed specific and five were new. Regarding the Kalarrytiko breed, twenty-nine alleles were found, fifteen of them were unique and nine were new. The studied breeds differed in their allelic profile, with only 12 common from the total of 134 different recorded genotypes. A higher number of animals with high parasitic load and high plasma pepsinogen values were found in Kalarrytiko. Associations between Ovar-DRB1 alleles with FEC values were found with certain heterozygous genotypes to present significantly reduced FEC values. The large number of detected alleles with low frequencies and the fact that the majority of animals were heterozygous, make hard to find strong associations

Association study between β-defensin gene polymorphisms and mastitis resistance in Valle del Belice dairy sheep breed

Mastitis is generally caused by bacteria, and it is the most common disease in livestock species. Defensins are peptides with a broad spectrum of antimicrobial activity and β-defensin genes have been studied in several livestock species due to their important role in the innate immune response. The aim of this study was to establish an association between polymorphisms in the β-defensin 1 and 2 genes and mastitis resistance in the Valle del Belice dairy sheep. Data consisted of 1855 and 2804 observations for case and control group, respectively. Six single nucleotide polymorphisms and seven haplotypes were selected for association studies with mastitis. In particular, polymorphism G1747A on β-defensin 1 gene was associated with susceptibility to mastitis, while polymorphism G1659A on β-defensin 2 gene was associated with resistance to mastitis. Haplotypes ACAGGG and GCAGGG were associated with resistance to mastitis, whereas haplotype ACGGGG was associated with susceptibility to mastitis. The present study has firstly suggested the possible associations of β-defensin gene polymorphisms with mastitis resistance traits and showed the presence of interesting haplotypes in Valle del Belice dairy sheep breed. Results from association analysis provided preliminary evidence that β-defensins could be used as candidate genes or molecular markers for the improvement of ovine mastitis resistance traits in Valle del Belice dairy breed.

Characterization and Comparative Analysis of the Milk Transcriptome in Two Dairy Sheep Breeds using RNA Sequencing.

This study presents a dynamic characterization of the sheep milk transcriptome aiming at achieving a better understanding of the sheep lactating mammary gland. Transcriptome sequencing (RNA-seq) was performed on total RNA extracted from milk somatic cells from ewes on days 10, 50, 120 and 150 after lambing. The experiment was performed in Spanish Churra and Assaf breeds, which differ in their milk production traits. Nearly 67% of the annotated genes in the reference genome (Oar_v3.1) were expressed in ovine milk somatic cells. For the two breeds and across the four lactation stages studied, the most highly expressed genes encoded caseins and whey proteins. We detected 573 differentially expressed genes (DEGs) across lactation points, with the largest differences being found, between day 10 and day 150. Upregulated GO terms at late lactation stages were linked mainly to developmental processes linked to extracellular matrix remodeling. A total of 256 annotated DEGs were detected in the Assaf and Churra comparison. Some genes selectively upregulated in the Churra breed grouped under the endopeptidase and channel activity GO terms. These genes could be related to the higher cheese yield of this breed. Overall, this study provides the first integrated overview on sheep milk gene expression.

PrP genotype frequencies and risk evaluation for scrapie in dairy sheep breeds from southern Italy

Concerns regarding scrapie in sheep breeding have increased in the last few decades. The present study was carried out in dairy sheep breeds from southern Italy. In order to find breeding animals resistant to scrapie, the PrP genes of 1,205 animals from entire flocks of dairy native Apulian Leccese and Altamurana breeds, and Sicilian Comisana breed, were analysed for polymorphisms at codons 136, 154, and 171 related to scrapie resistance/susceptibility. The Altamurana breed was considered as two populations (Alt-Cav and Alt-Cra-Zoe), based on presumed cross-breeding. A total of five alleles and ten different genotypes were found. The ARQ allele was predominant for all breeds followed by ARR, the most resistant allele to scrapie, which was highly prevalent in Comisana (50%) and in native Alt-Cav (42.4%). The VRQ allele, associated with the highest susceptibility to scrapie, was detected at not negligeable levels in allocthonous Comisana (3.5%), at a low frequency (0.2%) in native Leccese and Alt-Cra-Zoe, while it was absent in Alt-Cav. The frequencies of PrP genotypes with a very low susceptibility risk to scrapie (R1) was higher in Comisana and Alt-Cav. The most susceptible genotype, ARQ/VRQ, was found only in Comisana. Within the Altamurana breed, there were notable differences between Alt-Cav and Alt-Cra-Zoe sheep. The Alt-Cav was characterised by the absence of VRQ and AHQ alleles and by the higher frequency of the ARR/ARR genotype (18.7%). Breeding programs, mainly in endangered breeds such as Altamurana, should be conducted gradually, combining resistance to scrapie, maintenance of genetic variability, and production.

Influence of the Season on the Metabolic Profile in Chios Sheep

Abstract Chios is a breed of sheep selected for milk production, with metabolic features typical for a dairy sheep breed. The energy requirements of pregnant sheep is increase in the last weeks of gestation. Metabolic imbalance in the late pregnancy in sheep, usually cause a metabolic disorder known as pregnancy toxemia. Additionally, a pregnant sheep exposed to low environmental temperatures has increased energy demands, due to its adaptation to undesirable environmental conditions. The aim of this study was to compare the metabolic profile of Chios sheep exposed to different environmental conditions.Two groups of ewes were instigated. First group included 8 pregnant ewes with clinical signs of pregnancy toxemia exposed to cold stress during the winter season. The second group included 8 non-pregnant, clinically healthy ewes, that were examined during the non-breeding period, in the spring season. Blood samples were taken and serum concentrations of glucose, beta-hydroxybutirate (BHBA), total protein, albumin, urea, creatinine, triglyceride and cholesterol, as well as activity of AST and ALP were determined. Pregnant ewes exposed to cold stress had significantly lower levels of glucose and total protein, and significantly higher levels of BHBA, albumin and AST in the serum compared to non-pregnant ewes that were in optimal environmental conditions. There was no significant difference between the serum levels of urea, creatinine, cholesterol, triglycerides and ALP among the groups. In conclusion, low environmental temperature and poor feeding during the winter season caused metabolic distress in pregnant ewes during the early winter season.

Effect of subclinical intrammamay infection on milk quality in dairy sheep: I. Fresh-soft cheese produced from milk of uninfected and infected glands and from their blends

Subclinical intramammary infection (IMI) is associated with a decrease in milk yield and changes in milk composition. The effects of IMI on fresh-soft cheese yield and quality were evaluated by: (i) the effect on the composition and coagulation properties; (ii) the effect of three levels of coagulating enzyme and three temperatures in the presence and absence of added CaCl2 on milk coagulation properties (milk from uninfected and infected halves and a blend of 50:50); (iii) the effect the milk source: uninfected, infected halves and a blend of 50:50 and 75:25 (uninfected:infected) on the production of small cheese blocks. Somatic cell count was significantly higher in infected glands of both Manchega and Lacaune dairy sheep breeds. In milk from infected glands, 25–30% of the milk did not coagulate. Rennet clotting time (RCT) of milk from infected glands was doubled and curd firmness (CF) was much lower in comparison to samples taken from the contra-lateral uninfected glands. Addition of Ca and temperature levels did not influence RCT in any of the milk combinations, while CF was significantly higher in milk from uninfected glands and 50:50 blends and also was higher as temperature increased. Enzyme concentration significantly influenced RCT and CF in milk from both uninfected and in the 50:50 blends but not in the milk from infected glands. IMI affected significantly milk syneresis, which was slower in the infected and in the 50:50 blends. The changes in syneresis were reflected in higher moisture in the curd of milk sampled from infected glands. The contents of fat, protein and dry matter in the cheese were significantly lower in the 50:50 blends compared to uninfected milk, whereas the contents of these organic components in the 75:25 blends were in-between. The distance required to penetrate the cheese before crushing was significantly deeper in cheese made from a 50:50 blend than that of cheese made from uninfected milk and 75:25 blend, which indicated that IMI modified cheese structure into softer and more elastic texture. The study also indicated that during storage of the milk before processing, milk quality (lower pH, increased RCT and decreased CF) from 50:50 blends deteriorated faster in comparison to uninfected milk.

Plasmin–plasminogen system and milk coagulation properties of two Greek dairy sheep breeds

The enzymatic activities of plasmin (PL), plasminogen-derived (PG) and plasminogen activator (PA) and their correlation with the milk coagulation properties and major milk components were studied in two Greek sheep breeds during their whole lactation. Individual milk samples were collected at 3-week intervals from 14 Karagouniko and 14 Chios sheep breed. The enzymatic activities of PL, PG and PA were measured by colorimetric assay. The milk coagulation properties (rCT rennet clotting time, K20 curd firming time, A30 final curd consistency) were determined with a Formagraph. The results showed that PL, PG and PA activities and rennet clotting time (rCT) did not differ between the two breeds. However, K20 and A30 differed significantly between Karagouniko and Chios milk. The stage of lactation (early, mid or late) significantly affected PL, PG and PA activities. PL and PA activity levels were lower during late lactation (after the 150 days of the lactation period) compared to the corresponding levels during early and mid lactation, while a significant reduction of PG activity was observed from mid to late lactation stage. Lactation stage also significantly affected milk coagulation traits: A decrease in rCT occurred at mid lactation (from 100 to 150 days) while K20 increased from the early to the mid stage of lactation. The activities of PL and PA were significantly affected by the health status of the udder; milk with >300,000 SCC had 51% higher activity of PL and 86% higher activity of PA than milk containing <300,000 SCC. PG activity was 12% lower in milk with low SCC in comparison with milk with high SCC, but the results were not statistically significant. The coagulation properties of milk were not affected by SCC. A weak significant correlation exists between plasmin, PL+PG and K20.

Prospects of dairy sheep farming in India: An overview

Basic idea of this paper is to review present status of dairy farming in sheep and explore the possibility for its establishment in the country to ensure more remuneration to farmers and quality milk products supply to consumers. Dairy sheep breeds are predominately found in Middle East and Mediterranean countries. The contribution of sheep milk to total milk production in the world is negligible (only 1.32%) but it is important in some of the countries like Greece, Syria, Jordon, Iraq, Somalia where sheep milk contributes 17–36% of total milk production. Awassi is a well-known dairy breed belonging to fat-tailed group and widely found in Middle East (Syria, Lebanon, Jordan, Iraq and Israel) countries. Awassi has proliferated, for breeding purposes, into at least 30 countries in all continents. Other dairy sheep breeds like Assaf (Israel), East Friesian (Germany), Lacaune (France), Sarda (Sardinia), Chios (Greece), Manchega (Spain), etc. are reared under intensive system for milk production. More than 95% of sheep milk is converted into cheese. Ewes ’milk is rich in proteins, minerals and lipids. Sheep milk is a medical necessity as an alternative to cow milk for many people and especially for infants. Bioactive peptides of sheep milk proteins have specific biological activities, such as antihypertensive, antimicrobial, opioid, antioxidant, immunomodulatory or mineral binding. These protein fragments are formed from the precursor inactive protein during gastrointestinal digestion and/or during food processing. Dairy sheep farming is more profitable and provides 2.2 times more net income per flock and per ewe over nondairy sheep farming.

Genome wide linkage disequilibrium and genetic structure in Sicilian dairy sheep breeds.

BackgroundThe recent availability of sheep genome-wide SNP panels allows providing background information concerning genome structure in domestic animals. The aim of this work was to investigate the patterns of linkage disequilibrium (LD), the genetic diversity and population structure in Valle del Belice, Comisana, and Pinzirita dairy sheep breeds using the Illumina Ovine SNP50K Genotyping array.ResultsAverage r2 between adjacent SNPs across all chromosomes was 0.155 ± 0.204 for Valle del Belice, 0.156 ± 0.208 for Comisana, and 0.128 ± 0.188 for Pinzirita breeds, and some variations in LD value across chromosomes were observed, in particular for Valle del Belice and Comisana breeds. Average values of r2 estimated for all pairwise combinations of SNPs pooled over all autosomes were 0.058 ± 0.023 for Valle del Belice, 0.056 ± 0.021 for Comisana, and 0.037 ± 0.017 for Pinzirita breeds. The LD declined as a function of distance and average r2 was lower than the values observed in other sheep breeds. Consistency of results among the several used approaches (Principal component analysis, Bayesian clustering, FST, Neighbor networks) showed that while Valle del Belice and Pinzirita breeds formed a unique cluster, Comisana breed showed the presence of substructure. In Valle del Belice breed, the high level of genetic differentiation within breed, the heterogeneous cluster in Admixture analysis, but at the same time the highest inbreeding coefficient, suggested that the breed had a wide genetic base with inbred individuals belonging to the same flock. The Sicilian breeds were characterized by low genetic differentiation and high level of admixture. Pinzirita breed displayed the highest genetic diversity (He, Ne) whereas the lowest value was found in Valle del Belice breed.ConclusionsThis study has reported for the first time estimates of LD and genetic diversity from a genome-wide perspective in Sicilian dairy sheep breeds. Our results indicate that breeds formed non-overlapping clusters and are clearly separated populations and that Comisana sheep breed does not constitute a homogenous population. The information generated from this study has important implications for the design and applications of association studies as well as for development of conservation and/or selection breeding programs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-014-0108-5) contains supplementary material, which is available to authorized users.

Milk protein variants are highly associated with milk performance traits in East Friesian Dairy and Lacaune sheep

In total, 403 milk samples of East Friesian Dairy (EFD) and Lacaune (LAC) sheep hold in three different flocks in Switzerland and Germany were analysed for milk protein variability at protein level by isoelectric focusing and at DNA-level by different DNA-based tests. Isoelectric focusing of all milk samples led to the identification of the alphas1-casein (αs1-CN; CSN1S1) alleles C and H, αs2-CN (CSN1S2) A, B, and C, as well as beta-lactoglobulin (β-LG; LGB) A and B. All animals were monomorphic for alpha-lactalbumin (α-LA; LALBA) A and kappa-casein (κ-CN; CSN3), and within beta-casein (β-CN; CSN2) only differences in the intensity and not in the position of the bands could be identified.DNA-based tests differentiated αs1-CN C into CSN1S1*C′ and C″, typed for CSN1S2*G, for an A>G single nucleotide polymorphism (SNP) in exon 7 of CSN2, for an A>G SNP in exon 2 of ovine CSN3, and for a microsatellite within intron 3 of CSN3. CSN1S2*G and the A>G-SNP within CSN2 occurred only in LAC, whereas the A>G SNP in CSN3 was identified only in EFD sheep. In total, 11 CSN3 microsatellite alleles were observed. Furthermore, 8 and 11 CN haplotypes (CSN1S1-CSN2-CSN1S2-CSN3) were identified in EFD and LAC sheep.Additionally, associations between milk performance traits and milk protein alleles and genotypes were analysed using 150-day-lactation data. Significant effects of milk protein alleles and genotypes on protein content were identified. In both dairy sheep breeds CSN1S1*C″ is significantly associated with a higher protein content. In EFD significant effects of the CSN3-SNP and the CSN3 microsatellite on protein percentage and of the LGB-SNP on protein and fat percentage were additionally identified. Further research is needed to clarify in more detail the effects of milk protein variability on milk performance also in other dairy sheep breeds, to aim the implementation in future sheep breeding programs.