Year and season effects on oestrus and ovarian activity in ewes of different breeds and crosses

The dates of onset and cessation of ovulation and oestrus and the duration of the ovulatory, oestrous, anovulatory and anoestrous seasons were determined for Suffolk, Rambouillet, Dorset, Finnish Landrace and reciprocal F₁ crosses between the last three breeds in a study which extended over 3 years. Ovulation rate, duration of oestrus and cycle length were also examined. Among the purebreds the major source of variation in these traits could be attributed to differences between the Rambouillet and the remaining breeds. Rambouillet ewes commenced and ceased ovarian and oestrous activity earlier than the Finn; first ovulation also occurred earlier in the Rambouillet than in the Suffolk and the duration of ovarian activity was longer for the Rambouillet than for either of these breeds. The oestrous season was 27 days shorter for the Rambouillet than for the Dorset, due to a higher incidence of ovulation without oestrus in the Rambouillet. The anoestrum was between 27 and 65 days longer for the Rambouillet than for any of the other purebreds. The period of anovulation was longest for the Suffolk breed. There was little evidence for heterosis in the duration of the breeding and non-breeding seasons. The repeatability of components of the breeding season was generally low. Ovulation rate increased slightly from early to mid-season and then declined significantly as the breeding season advanced, in all breeds.     

Genetic characterization and breed assignment in five Italian sheep breeds using microsatellite markers

The knowledge of the genetic relationship and admixture among neighbouring populations is crucial for conservation efforts. The aim of this study was to analyse the genetic diversity of five Italian sheep breeds (Appenninica, Garfagnina Bianca, Massese, Pomarancina and Zerasca) using a panel of 24 microsatellite markers. Blood samples from 226 individuals belonging to the aforementioned populations were obtained and genotyped. All the investigated breeds showed a significant heterozygote deficiency caused by the high level of inbreeding indicated also by the high level of F_IS (0.146). Genetic differentiation between breeds was moderate (F_ST = 0.05) but significant and the individuals could be assigned to their breeds with an high success rate even if the inter-individual distances showed that few animals clustered separately from the other individuals of the same breed, especially for Pomarancina breed. The genetic distances reflect the historical knowledge of these breeds and some patterns of ancestral and recent gene flow between neighbour populations arise. The clustering analysis detects the presence of six clusters. Massese and Zerasca breeds were grouped together as well as Appenninica and Pomarancina with the latter forming two distinct clusters equally represented. The formation of this last breed is occurred with the absorption of individuals of the Appenninica breed and the gene flow probably continued in these recent years allowing the presence of a population substructure for Pomarancina breed. Such substructure supports the high level of heterozygote deficiency found for this breed despite the relatively high population size. The five populations analysed presented some genetic similarities but a clear uniqueness of the populations has been showed for almost all of them. Special attention to monitor genetic variability and to organize mating plans should be given especially for the three endangered breeds.     

Evaluation of factors affecting individual assignment precision using microsatellite data from horse breeds and simulated breed crosses

Assignment tests have been utilized to investigate population classification, measure genetic diversity and to solve forensic questions. Using microsatellite data from 26 loci genotyped in eight horse breeds we examined how population differentiation, number of scored loci, number of scored animals per breed and loci variability affected individual assignment precision applying log likelihood methods. We found that both genetic differentiation and number of scored loci were highly important for recognizing the breed of origin. When comparing two and two breeds, a proportion of 95% of the most differentiated breeds (0.200 < or = FST < or = 0.259) could be identified scoring only three loci, while the corresponding number was six for the least differentiated breeds (0.080 < or = FST < or = 0.139). An identical proportion of simulated breed crosses, differentiated from their parental breeds by FST estimates in the range 0.050-0.069, was identified when scoring 12 loci. This level of source identification was not obtained for the less differentiated breed crosses. The current data further suggested that population sample size and locus variability were not critical for the assignment precision as long as moderately large sample sizes (> or = 20 animals per population) and fairly variable loci were used.     

Performance and utilization of Northern European short-tailed breeds of sheep and their crosses in North America: a review

The five Northern European short-tailed sheep breeds present in North America are the Finnsheep, Romanov, Icelandic, Shetland and Gotland. The Finnsheep and Romanov were first imported in 1966 and 1986, respectively, for their high reproductive performance. The Shetland, Icelandic and Gotland breeds were first imported in 1980, 1985 and 2005, respectively, for the uniqueness of their physical appearance and their unique fleeces desired by fiber craftspeople. There have been no scientific studies conducted on the performance of the Shetland, Icelandic or Gotland breeds relative to other breeds of sheep in North America. However, the Shetland and Icelandic breeds have become very popular in the United States and ranked 9th and 18th, respectively, among 35 breeds of sheep for number of purebred animals registered in 2008. The performance of the Finnsheep breed in North America relative to domestic breeds has been thoroughly investigated. Compared to several domestic purebreds and crosses, sheep with Finnsheep breeding had a younger age at puberty, greater fertility to autumn mating, greater litter size, greater survival to weaning, similar growth rate, similar subcutaneous fat thickness, smaller loin muscle area and greater percentage of kidney and pelvic fat. Each 1% increase in Finnsheep breeding in ewes was associated with approximately 0.01 more lambs born per ewe lambing. In North American studies, Romanov ewes were superior to Finnsheep ewes for reproductive rate and lamb production per ewe under both autumn and spring mating. Lambs of the two breeds were similar for survival, growth and carcass traits. Romanov and Romanov-cross ewes produced fleeces that were heavily contaminated with medulated and colored fibers and were of very low commercial value. Three composite breeds containing 25% to 49% Finnsheep breeding (Polypay, Rideau Arcott and Outaouais Arcott) were developed in North America and are now more popular than the Finnsheep breed.     

不同品种肉羊胚胎移植效率的研究

以无角多赛特、萨福克、德克赛尔、东福利生纯种肉用绵羊为供体,以内蒙古小尾寒羊为受体,利用辅助生殖技术对纯种群体进行扩繁,并对不同品种肉羊的超排及胚胎移植效果进行了比较.结果显示,无角多赛特和萨福克的平均超排胚胎数明显高于德克赛尔和东福利生(P<0.05);将2523枚A级囊胚进行移植,总产羔率为51.32%,以无角多赛特产羔率明显优于其他品种肉羊(P<0.05);手术和腹腔镜移植技术对引进的纯种绵羊产羔率没有影响,但腹腔镜移植技术对受体造成的创口小,操作快捷.     

Superovulation and recovery of zygotes suitable for microinjection in different breeds of sheep

This study investigated the appropriateness of different superovulatory protocols in various breeds of sheep for obtaining a maximum of zygotes suitable for microinjection. Animals were mated either once or two to three times to fertile rams. In Experiment 1, a 24 h interval between a two to three times mating and egg recovery resulted in 42.2% suitable zygotes whereas with single mating only 10.4% fertilized eggs were obtained. The extension of the interval to 40 h associated with a two to three times mating resulted in a recovery of 42.9% fertilized eggs but most (70%) of these were already at the two-cell stage. In Experiment 2, eCG resulted in similar superovulatory responses in Merino ewes as the more labour requiring FSH treatment (8.1 ± 4.5 versus 7.5 ± 4.1 corpora lutea (CL); 6.3 ± 3.0 versus 6.8 ± 4.0 oocytes/ zygotes; 39.4% versus 40.6% fertilization rate). In Experiment 3, following superovulation with pFSH (Folltropin®) the number of CL was not different among Merino, Finn, Crossbreds (Blackface X Finn) and Texel sheep (8.6 ± 5.2; 10.3 ± 4.5; 8.5 ± 3.8; 8.2 ± 2.8, respectively) as was the number of recovered oocytes/ zygotes (7.4 ± 5.6; 9.8 ± 4.3; 7.3 ± 3.8; 6.4 ± 2.9, respectively). However, the number of unfertilized ova was higher (P < 0.05) in Finn sheep as compared with Crossbreds and Texel sheep (5.0 ± 3.3 versus 2.2 ± 2.3 and 1.9 ± 2.6). Similarly, the fertilization rate was higher (P < 0.05) in Crossbreds and Texel sheep (64.4% and 65.5%) as compared with Finn and Merino sheep (38.3% and 42.5%). In Experiment 4, it was shown that in Merino sheep purified FSH supplemented with 68.6% LH resulted in lower (P < 0.05) superovulatory responses as compared with purified FSH supplemented with 133.1% LH or Folltropin (LH contamination 0.1%) (4.7 ± 3.3 versus 8.8 ± 3.8 and 8.6 ± 5.2 CL; 3.8 ± 2.5 versus 7.4 ± 3.6 and 7.4 ± 5.6 oocytes/zygotes, respectively). A three times repeated superovulatory treatment and oviductal flush per animal at monthly intervals did reduce (P < 0.05) the number of CL, but had no deleterious effect on zygote yields and the percentage of microinjectable zygotes. We conclude that (1) at least a two to three times mating is required to obtain acceptable fertilization rates; (2) the interval between mating and recovery should be 24–26 h in order to obtain zygotes; (3) eCG results in similar superovulatory responses as FSH; (4) Folltropin® is a suitable drug to induce superovulation in sheep; (5) the LH content of the FSH preparation plays a significant role in the superovulatory response of sheep; (6) superovulation and embryo recoveries can be repeated at least three times per animal without decrease in efficiency.     

Conservation priorities for Ethiopian sheep breeds combining threat status,breed merits and contributions to genetic diversity

Prioritizing livestock breeds for conservation needs to incorporate both genetic and non-genetic aspects important for the survival of the breeds. Here, we apply a maximum-utility-strategy to prioritize 14 traditional Ethiopian sheep breeds based on their threat status, contributions to farmer livelihoods (current breed merits) and contributions to genetic diversity. Contributions of the breeds to genetic diversity were quantified using Eding''s marker-estimated kinship approaches. Non-genetic aspects included threats (e.g. low population size, low preferences by farmers) and current merits (economic, ecological and cultural merits). Threat analysis identified eight of the 14 breeds as threatened. Analysis of current merits showed that sub-alpine and arid-lowland breeds contribute most to farmer livelihoods in comparison to other breeds. The highest contribution to the genetic diversity conserved was from the Simien breed. Simien showed high between-breed (low between-breed kinship = 0.04) as well as high within-breed diversity (low within-breed kinship = 0.09 and high H_E = 0.73 and allelic richness = 6.83). We combined the results on threat status, current breed merits and contributions to genetic diversity to produce a ranking of the 14 breeds for conservation purposes. Our results balance the trade-offs between conserving breeds as insurance against future uncertainties and current sustainable utilization. The ranking of breeds provides a basis for conservation strategies for Ethiopian sheep and contributes to a regional or global conservation plan.     

Hemotypes in Spanish sheep breeds

The structure and the genetic diversity of the Churra, Lacha and Manchega sheep breeds have been analysed using hemotypes observed in eight loci. The three breeds are different in their hemotypes in terms both of quantity and quality. The proportions of unique hemotypes in Churra (60%), Lacha (61%) and Manchega (67%) revealed a high level of individual diversity within each breed. Racial genetic diversity follows the descending order of: Manchega-Lacha-Churra. The value of N:H (number of animals: total hemotypes) in the multi-racial population was 3.05.     

The characteristics of the genetic relations between different breeds and crossbreeds of sheep

Frequency of occurrence of antigens belonging to 7 systems of blood groups in four breeds of sheep as well as two crosses of the first generation Tsigai X Ostfrisian; Ostfrisian X Tsigai) has been studied. A phylogenetic affinity between them is presented. Indices of genetic distances between breeds and crosses are calculated. The dendrogram demonstrates the existence of two clusters: the first has been formed with the Caucasian, Ostfrisian, Tsigai breeds and both crosses of the first generation: the second--with Astrakhan breed. The analysis of the results obtained shows that dendrogram constructed with regard for the frequency of blood antigens reflects real relations of the investigated sheep breeds according to the adopted systems.     

Analysis of different effects on longevity in four sheep breeds of northern Germany

The lifetime performance of female sheep is one of the most important economic traits in sheep husbandry. In this investigation, a Weibull model was used to study the effects of ‘breed’, ‘number of lambings’, ‘age at first lambing’, ‘type of birth’ and ‘farm’ on the length of productive life (LPL). The data included records of 5191 female sheep of four different breeds on 236 breeding farms in northern Germany. The observation period in which the sheep were born or were removed from the farm ranged from January 2003 to December 2007. About 12% of the records were right-censored. All variables had a significant effect on LPL at a level of p < 0.001 except ‘type of birth’. The German Blackheaded Mutton breed showed the lowest risk ratio with 0.77 (SE = 0.17), while the Texel had the highest hazard rate (1.00). The relative culling risk initially decreased from the first (5.73, SE = 0.09) to the seventh lambing (0.36, SE = 0.12), and then increased until lambing number nine. The highest relative culling risk was calculated at an age of 395 to less than 455 days at first lambing (1.00). Animals younger than 395 days at first lambing showed the lowest risk ratio (0.56, SE = 0.05). The culling risk for the effect ‘farm’ ranged from 0.3 to 3.1. A differentiation of environmental, housing or management effects was not feasible with this data. But the results offer some interesting options for further studies.     

Genetic and phenotypic aspects of foot lesion scores in sheep of different breeds and ages

Footrot is a costly endemic disease of sheep. This study investigates the potential to decrease its prevalence through selective breeding for decreased lesion score. Pedigreed mule and Scottish Blackface (SBF) ewes were scored for lesions on each hoof on a 0 to 4 scale for up to 2 (SBF ewes) or 4 (mules) times over 2 years. One score was obtained for SBF lambs. An animal was deemed to have lesions (severe lesions) if at least one hoof had a score of at least 1 (2). The prevalence of lesions was 34% in lambs, 17% in SBF ewes and 51% in mules. The heritability of lesions (severe lesions) analysed as repeated measurements of the same trait in a threshold model was 0.19 (0.26) in SBF ewes and 0.12 (0.19) in mules. Estimates for the sum and maximum of scores as well as the number of feet affected were much lower, as were estimates for permanent animal effects (i.e. non-genetic effects associated with an animal). When successive scores on the same animal were analysed as correlated traits, heritability estimates for most traits tended to be higher, except for severe footrot in mules where estimates varied greatly over time. The phenotypic correlations between successive scores in SBF ewes were close to 0, genetic correlations were moderately positive (0.18 to 0.55). Correlations in mules were generally of a similar size, but some genetic correlations were higher (up to 0.92). There was a clear trend for heritabilities for lesions and severe lesions to increase with higher prevalence of lesions, even when analysed in a threshold model. Heritability estimates for traits that combine scores over several events in mules, identifying the more persistently affected animals, ranged from 0.12 to 0.23 with the highest estimates for the average number of feet that were (severely) affected in animals scored for a minimum at two events. The heritability of all lesion traits in lambs was estimated as 0. It is concluded that selection for lower lesions is possible in ewes but not lambs, and that a simple binary score at an animal level is at least as effective as a comprehensive score at hoof level. Given the low repeatability of lesion scores, repeated measures over time will improve effectiveness of selection. Selection across environments (flocks, seasons) with different prevalences of lesions scores will need to take account of variation in the heritability.     

An ultrasonographic study of luteal function in breeds of sheep with different ovulation rates

Development and demise of luteal structures were monitored using daily transrectal ultrasonography in 2 breeds of sheep differing in ovulation rates (nonprolific Western white-faced cross-bred, n = 12 and prolific pure-bred Finn sheep, n = 7), during 1 estrous cycle in the mid-breeding season. Jugular blood samples were collected once a day for radioimmunoassay (RIA) of progesterone. The mean diameter of ovulatory follicles was higher in Western white-faced than in Finn ewes (6.4 +/- 0.2 and 5.3 +/- 0.2 mm, respectively; P < 0.001). The mean volume of luteal structures was higher (P < 0.05) in Western white-faced compared with Finn sheep from Days 5 to 15 of the cycle (Day 0 = day of ovulation). This accounted for the higher (P < 0.05) total luteal volumes recorded in Western white-faced ewes on Day 7 and from Days 11 to 15, despite the higher ovulation rate in Finn ewes (2.7 +/- 0.3 and 1.7 +/- 0.2, respectively; P < 0.05). Mean serum progesterone concentrations were higher (P < 0.05) in Western white-faced than in Finn ewes from Days 4 to 14. Daily total luteal volumes were positively correlated with daily serum progesterone concentrations throughout the cycle in Finn sheep (r > or = 0.40, P < 0.02), and during luteal growth and regression (r > 0.60, P < or = 0.00001) but not during mid-cycle in white-faced ewes (r = 0.16; P = 0.22). During the growth of the corpora lutea (CL), luteal tissue volume increased faster (P < 0.05) than serum progesterone concentrations in both breeds of sheep. During luteolysis, the decrease in luteal volumes parallelled that in serum progesterone concentrations in Finn (P = 0.11) but not in Western white-faced ewes, where luteal volumes decreased more slowly (P = 0.02) in relation to progesterone secretion. Increased ovulation rate in prolific Finn ewes resulted in more but smaller CL, and lower serum progesterone levels compared with nonprolific Western white-faced ewes. We conclude that breed-specific mechanisms exist to control the formation of luteal tissue and progesterone secretion in cyclic ewes differing in prolificacy. The mechanisms may involve ovulation of Graafian follicles at different sizes and inhibitory paracrine effects of CL on co-existing CL.     

Accuracy of genotype imputation in sheep breeds

Although genomic selection offers the prospect of improving the rate of genetic gain in meat, wool and dairy sheep breeding programs, the key constraint is likely to be the cost of genotyping. Potentially, this constraint can be overcome by genotyping selection candidates for a low density (low cost) panel of SNPs with sparse genotype coverage, imputing a much higher density of SNP genotypes using a densely genotyped reference population. These imputed genotypes would then be used with a prediction equation to produce genomic estimated breeding values. In the future, it may also be desirable to impute very dense marker genotypes or even whole genome re‐sequence data from moderate density SNP panels. Such a strategy could lead to an accurate prediction of genomic estimated breeding values across breeds, for example. We used genotypes from 48 640 (50K) SNPs genotyped in four sheep breeds to investigate both the accuracy of imputation of the 50K SNPs from low density SNP panels, as well as prospects for imputing very dense or whole genome re‐sequence data from the 50K SNPs (by leaving out a small number of the 50K SNPs at random). Accuracy of imputation was low if the sparse panel had less than 5000 (5K) markers. Across breeds, it was clear that the accuracy of imputing from sparse marker panels to 50K was higher if the genetic diversity within a breed was lower, such that relationships among animals in that breed were higher. The accuracy of imputation from sparse genotypes to 50K genotypes was higher when the imputation was performed within breed rather than when pooling all the data, despite the fact that the pooled reference set was much larger. For Border Leicesters, Poll Dorsets and White Suffolks, 5K sparse genotypes were sufficient to impute 50K with 80% accuracy. For Merinos, the accuracy of imputing 50K from 5K was lower at 71%, despite a large number of animals with full genotypes (2215) being used as a reference. For all breeds, the relationship of individuals to the reference explained up to 64% of the variation in accuracy of imputation, demonstrating that accuracy of imputation can be increased if sires and other ancestors of the individuals to be imputed are included in the reference population. The accuracy of imputation could also be increased if pedigree information was available and was used in tracking inheritance of large chromosome segments within families. In our study, we only considered methods of imputation based on population‐wide linkage disequilibrium (largely because the pedigree for some of the populations was incomplete). Finally, in the scenarios designed to mimic imputation of high density or whole genome re‐sequence data from the 50K panel, the accuracy of imputation was much higher (86–96%). This is promising, suggesting that in silico genome re‐sequencing is possible in sheep if a suitable pool of key ancestors is sequenced for each breed.     

Genetic diversity and variability in Alpine sheep breeds

The aim of this study was to analyze, through the use of microsatellite molecular markers, the genetic diversity and variability of nine Alpine sheep breeds reared in Italy (Bergamasca, Biellese, Schwarzbraunes Bergschaf, Tiroler Bergschaf, and Schnalserschaf), Germany (Brillenschaf and Weisses Bergschaf) and Slovenia (Bovška and Jezerzkǒ-Solčavska), and one Italian crossbreed population. Allelic richness was rather high in each breed highlighting a considerable genetic diversity. However, the study evidenced a significant departure from Hardy–Weinberg equilibrium in all analyzed breeds caused by a heterozygote deficiency. Such lack seems to be caused both to the presence of population substructure within breed and to a rather high level of inbreeding. The genetic differentiation among breed was rather low (F_ST = 0.057) but significant. The clustering analysis performed with STRUCTURE detected the presence of eight clusters; Schwarzbraunes Bergschaf and Tiroler Bergschaf were grouped together and Biellese and Bergamasca as well, evidencing a high similarity of their genetic make up. Reynolds’ genetic distance estimates confirmed the close relationship between these pairs of breeds. Moreover, Bovška, Jezerzkǒ-Solčavska and Brillenschaf resulted rather similar as expected according to their region of origin and to their common ancestors. Molecular coancestry confirmed as well such findings, suggesting that the studied breeds had origin from different ancestral populations. Concluding, microsatellite resulted a useful tool to investigate breed variability and to characterize Alpine sheep breeds. Obtained findings suggest the need to set up a conservation plan aiming to safeguard and increase the genetic variability of the studied breeds compromised by the high level of inbreeding. Microsatellites genotyping could help to monitor breed variability and to organize matings.     

Genetic structure of European sheep breeds

Large-scale evaluations of genetic diversity in domestic livestock populations are necessary so that region-specific conservation measures can be implemented. We performed the first such survey in European sheep by analysing 820 individuals from 29 geographically and phenotypically diverse breeds and a closely related wild species at 23 microsatellite loci. In contrast to most other domestic species, we found evidence of widespread heterozygote deficit within breeds, even after removing loci with potentially high frequency of null alleles. This is most likely due to subdivision among flocks (Wahlund effect) and use of a small number of rams for breeding. Levels of heterozygosity were slightly higher in southern than in northern breeds, consistent with declining diversity with distance from the Near Eastern centre of domestication. Our results highlight the importance of isolation in terms of both geography and management in augmenting genetic differentiation through genetic drift, with isolated northern European breeds showing the greatest divergence and hence being obvious targets for conservation. Finally, using a Bayesian cluster analysis, we uncovered evidence of admixture between breeds, which has important implications for breed management.     

Seasonal sexual activity and post-partum anoestrus in two Moroccan breeds of sheep: Beni-Guil and Sardi

Twenty-four Beni-Guil and twenty-six Sardi ewes were regularly checked for oestrus during 19 consecutive months following lambing using penis-deviated rams and for ovulation by endoscopy or plasma progesterone level. Fifty percent of the Beni-Guil and Sardi ewes had a first ovulation at 41 and 71 days and first oestrus at 85 and 132 days, respectively. The seasonal anoestrus in both breeds occurs from February to May and is characterized essentially by a lack of expression of oestrous behaviour.Compared to other breeds located at higher latitudes, the two breeds studied showed a more rapid resumption of sexual activity following lambing and a seasonal anoestrus of reduced length and intensity.