Genetic Improvement Of Sheep Research Articles

Progress in Research and Prospects for Application of Precision Gene-Editing Technology Based on CRISPR–Cas9 in the Genetic Improvement of Sheep and Goats

Due to recent innovations in gene editing technology, great progress has been made in livestock breeding, with researchers rearing gene-edited pigs, cattle, sheep, and other livestock. Gene-editing technology involves knocking in, knocking out, deleting, inhibiting, activating, or replacing specific bases of DNA or RNA sequences at the genome level for accurate modification, and such processes can edit genes at a fixed point without needing DNA templates. In recent years, although clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system-mediated gene-editing technology has been widely used in research into the genetic breeding of animals, the system’s efficiency at inserting foreign genes is not high enough, and there are certain off-target effects; thus, it is not appropriate for use in the genome editing of large livestock such as cashmere goats. In this study, the development status, associated challenges, application prospects, and future prospects of CRISPR/Cas9-mediated precision gene-editing technology for use in livestock breeding were reviewed to provide a theoretical reference for livestock gene function analysis, genetic improvement, and livestock breeding that account for characteristics of local economies.

Investigation for Mutation in BMPR-1B (FecB) Fecundity Gene in Awassi Sheep

Reproduction related traits in sheep such as ovulation rate and litter size are traits of high economic importance but as these traits are only expressed in one sex and in mature animals, thus inclusion of them in selection strategies is limited. Therefore, studying genes associated with reproductive events provides genotypic data, which is more useful in genetic improvement of sheep in a short period of time. Such reproductive traits in sheep are genetically controlled by genes having both additive and major effects. Booroola is the first gene identified in Booroola Merino sheep in Australia has major effects on ewe’s reproduction and has gained much popularity in sheep breeding for its immense economic value. Booroola or Bone Morphogenetic Protein Receptor -1B (BMPR-1B) gene is in chromosome 6 and FecB allele is the result of a single mutation in this gene where one copy of this allele results in a significant increase in ovulation rate thus outcome as increased lambing per parturition. The Awassi sheep is an indigenous breed of Turkey and identifying major genes for fecundity could greatly improve their breeding program. To identify the FecB gene in Awassi sheep, 88 blood samples were taken, and DNA was extracted by salting out method. After PCR amplification and AvaΠ digestion, the samples were analyzed for FecB mutation and all of 88 samples were found not to carry the mutant allele (FecB).

Whole-Genome Selective Scans Detect Genes Associated With Important Phenotypic Traits in Sheep (Ovis aries)

Sheep (Ovis aries) is one of the important livestock with diverse phenotypic traits. However, little is known about the molecular mechanism of diverse phenotypic traits in domestic sheep. Using the genome-wide high-density SNP data (600K) in 253 samples from 13 populations, we conducted the tests of selective sweeps (i.e., pairwise F ST and XP-CLR) associated with several important phenotypic traits (e.g., tail types, horn morphology, prolificacy, coat pigmentation, ear size, milk production, meat production, body size and wool fineness). We identified strong selective signatures in previously reported (e.g., T, RXFP2, BMPR1B, TYRP1, MSRB3, TF, CEBPA, GPR21 and HOXC8) and novel genes associated with the traits, such as CERS6, BTG1, RYR3, SLC6A4, NNAT and OGT for fat deposition in the tails, FOXO4 for fertility, PTCH1 and EMX2 for ear size, and RMI1 and SCD5 for body size. Further gene annotation analysis showed that these genes were identified to be the most probable genes accounting for the diverse phenotypic traits. Our results provide novel insights into the genetic mechanisms underlying the traits and also new genetic markers for genetic improvement in sheep and other livestock.

INSEMINACIÓN ARTIFICIAL POR LAPAROSCOPIA EN OVINOS BAJO CONDICIONES DE CAMPO EN EL VALLE DEL MEZQUITAL, HIDALGO

Objetivo: Evaluar la técnica de inseminación artificial por laparoscopia (IAL) bajo condiciones de campo en variables reproductivas en ovejas y sus impactos sociales con ovinocultores de la región del Valle del Mezquital, Hidalgo.
 Diseño/ metodología/ aproximación: El diseño experimental fue completamente al azar. Se utilizaron 387 ovejas distribuidas en 7 Municipios y 14 unidades de producción ovinas (UPO), de las razas: 162 Katahdin, 145 Hampshire, 45 Dorset y 35 Suffolk. El estro se sincronizó con esponjas intravaginales por 11 días, dos días antes del retiro se aplicó 400 UI de gonadotropina (eCG). La IAL se llevó a cabo a las 50 h post sincronización del estro en cada una de las UPO.
 Resultados: La respuesta e inicio del estro no mostró diferencias (P > 0.05) entre las diversas razas de ovejas. El porcentaje de ovejas gestantes presentó diferencias por la raza (P ? 0.05), la Katahdin mostró mayor tasa de gestación a pesar de las condiciones de campo y diversidad en las UPO; sin embargo, la prolificidad entre las razas fue semejante.
 Limitaciones del estudio/ implicaciones: Se sugiere la inclusión de nuevas razas de pelo que cumplan con las expectativas de los ovinocultores y satisfagan la demanda del producto para el comercio de la barbacoa.
 Hallazgos/ conclusiones: La técnica de IAL y el protocolo hormonal en la sincronización del estro presentan resultados favorables en gestación y prolificidad, por lo que resultan ser efectivos para el Programa de Mejoramiento Genético de Ovinos en la región del Valle de Mezquital, Hidalgo, México.

A Review on the Genetic Basis of Growth and Prolificacy Traits in Sheep

The performance of an animal for a particular trait is the result of its genetic merit and the effects of the environment where it exists. To set up genetic improvement in sheep, the genetic component attributed to the trait of interest need to be defined. The aim of this review was to describe major candidate genes influencing growth traits and prolificacy in sheep. Although growth and prolificacy are quantitative traits and are expected to be influenced by many genes with individual genes contributing small effects, there are major genes that have been identified with significant influence on growth and prolificacy. The CLPG, GDF8 and CAST genes are some of the major genes that have strong influence on sheep growth and carcass quality. The CLPG mutation can cause pronounced effect in the muscle found in the hindquarter and is responsible for the muscular hypertrophy phenotype in sheep. The GDF8 gene also play important role in increasing muscle depth due to mutation in the regulatory region and coding sequences. The CAST gene is an endogenous and specific inhibitor of calpain enzyme and thereby regulates the rate and extent of muscle tenderization following slaughtering. For prolificacy, BMP15, GDF9 and BMPR1B have been shown to exert significant influence on ovulation rate and litter size in various sheep breeds in the world. Both of the three genes are member of the TGF-beta family protein that encode protein product responsible for growth, differentiation and proliferation of ovarian follicles. The mechanism of action for such major genes are associated with the existence of mutation in the coding sequence resulting amino acid change as well as in the regulatory region that vary the expression level and inheritance of the genes. Up to now, better attempts have been made to describe the genetic basis of growth and prolificacy in sheep. However, more works are needed to characterize other genes influencing these traits. More importantly, making use of the identified genes in sheep breeding program through marker assisted and genomic selection should receive due attentions.

Review on challenges, opportunities and genetic improvement of sheep and goat productivity in Ethiopia

Review on challenges, opportunities and genetic improvement of sheep and goat productivity in Ethiopia

SNPs for Parentage Testing and Traceability in Globally Diverse Breeds of Sheep

DNA-based parentage determination accelerates genetic improvement in sheep by increasing pedigree accuracy. Single nucleotide polymorphism (SNP) markers can be used for determining parentage and to provide unique molecular identifiers for tracing sheep products to their source. However, the utility of a particular “parentage SNP” varies by breed depending on its minor allele frequency (MAF) and its sequence context. Our aims were to identify parentage SNPs with exceptional qualities for use in globally diverse breeds and to develop a subset for use in North American sheep. Starting with genotypes from 2,915 sheep and 74 breed groups provided by the International Sheep Genomics Consortium (ISGC), we analyzed 47,693 autosomal SNPs by multiple criteria and selected 163 with desirable properties for parentage testing. On average, each of the 163 SNPs was highly informative (MAF≥0.3) in 48±5 breed groups. Nearby polymorphisms that could otherwise confound genetic testing were identified by whole genome and Sanger sequencing of 166 sheep from 54 breed groups. A genetic test with 109 of the 163 parentage SNPs was developed for matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry. The scoring rates and accuracies for these 109 SNPs were greater than 99% in a panel of North American sheep. In a blinded set of 96 families (sire, dam, and non-identical twin lambs), each parent of every lamb was identified without using the other parent’s genotype. In 74 ISGC breed groups, the median estimates for probability of a coincidental match between two animals (PI), and the fraction of potential adults excluded from parentage (PE) were 1.1×10(−39) and 0.999987, respectively, for the 109 SNPs combined. The availability of a well-characterized set of 163 parentage SNPs facilitates the development of high-throughput genetic technologies for implementing accurate and economical parentage testing and traceability in many of the world’s sheep breeds.

Efficiency Assessment of a Swift Method to Enhance Substandard Viability Ram Ejaculates

Semen availability in ram semen processing facilities is of great importance for the genetic improvement of sheep. Accordingly, any method that would increase sperm viability in low viability ejaculates could be useful. In this study, the possibility of a glass beads filtration method by estimating the beads total surface provided (TSP) for adhesion of spermatozoa, was evaluated. Initially, two different TSP (102 and 154 cm(2)) achieved by various sizes of beads (1500, 2000 and 3000 microm) were tested and no significant difference in sperm viability improvement was noticed for the same TSP by different beads (p > 0.05). Next optimization tests were performed in which three different funnels were used for filtration at a standard TSP (154 cm(2)). The pear-shaped funnel was found to be the most appropriate for filtration, as semen volume recovery and sperm viability improvement were more pronounced (p < 0.05). Finally, filtration tests were conducted with pear-shaped funnels with different TSP (102 and 154 cm(2)) obtained by the aforementioned beads sizes (1500, 2000 and 3000 microm) in equal aliquots. Total surface provided of 102 cm(2) proved to be the more appropriate for filtration than 154 cm(2), as shown by the significant improvement of sperm viability (p < 0.01) and the significantly higher filtrate semen volume (p < 0.05). In conclusion, ram sperm viability improvement by more than 20% of its initial value and semen volume recovery by more than 60%, along with the fact that the total filtration time did not exceed 6 min in any case, suggest that through further development this method could be successfully used during ram semen processing.

Recent Technology of Genetic Selection Indices in Sheep Breeding

Abstract dalam bentuk hard copy

Factors affecting the survival of sheep embryos after transfer within a MOET program

Multiple ovulation and embryo transfer (MOET) has the potential to increase the rate of genetic improvement in sheep. However, better realization of this potential requires maximum survival rates of transferred embryos of high genetic merit after transfer into recipient ewes. These studies were therefore conducted to investigate the effect of both embryonic and recipient ewe factors on the survival rate of transferred embryos. Survival rate was similar after transfer of morula or blastocyst stage embryos, and these were higher ( P<0.05) than for very early morulae and early morulae. Advanced embryos (Day 5 blastocyst) had an advantage ( P<0.05) in survival rate over retarded embryos (Day 6 morula). Grades 1 and 2 embryos survived significantly ( P<0.05) better than Grades 3 or 4 embryos. There was no difference in embryo survival rate following transfer to recipients with different numbers of corpora lutea. In general, age or parity of recipient ewes did not affect embryo survival rate, although a higher ( P<0.05) embryo survival rate was observed for yearling recipients. Buserelin (GnRH agonist) treatment of recipient ewes 5 or 6 days after transfer of embryos (Day 12 of the cycle) did not improve embryo survival rate. These results confirm that both embryonic and recipient factors can play an important role in the success of a MOET program in sheep.

Effect of mating system, flushing procedure, progesterone dose and donor ewe age on the yield and quality of embryos within a MOET program in sheep

Multiple ovulation and embryo transfer (MOET) has the potential to increase the rates of genetic improvement in sheep. However, better realization of this potential requires a higher yield of transferable embryos. Thus we investigated some factors that may contribute to high embryo yield and quality under field conditions, as part of an ongoing MOET program. Comparison of the effects of 2 breeding systems (natural service plus laparoscopic intrauterine AI vs natural service only) on embryo yield and quality indicated that while AI did not affect embryo recovery, it significantly (P<0.05) improved fertilization rate and embryo quality, and increased (P<0.05) embryo survival rate after transfer to recipients. Two flushing procedures (the original semi-laparoscopic and a modified version) were compared for effects on embryo recovery. The modifications made to the original collection method increased (P<0.001) embryo recovery from 69.0 ± 2.4 to 83.2 ± 0.6%. The effects of the progestagen priming dosage during superovulatory treatment and ewe age on MOET outcome were also investigated. Donor ewes primed with 30-mg progestagen sponges came into estrus 1.9 h earlier (P<0.05) than those primed with 45-mg sponges, but there was no difference in ovulation rate or embryo recovery, or in embryo survival after transfer between the 2 regimens. However, Chi-square analysis indicated a significant benefit in favor of the higher progesterone dose on both fertilization (P<0.01) and embryo quality (P<0.001). Age of donor ewe did not significantly affect the timing of estrus, fertilization rate or embryo survival after transfer. While adult ewes had higher (P<0.05) ovulation rates and embryo yields, shearling ewes produced a much higher proportion of Grade 1 embryos (P<0.05).

AI and embryo transfer for genetic improvement in sheep: the current scene

SCIENTIFICALLY based programmes for the genetic improvement of sheep which combine the objective assessment of body composition with the reproductive technologies of artificial insemination (Al) and multiple ovulation and embryo...

A genetic analysis of early growth and ultrasonic measurements in hill sheep

AbstractGenetic parameters were estimated for early lamb growth and ultrasonic measurements taken on Scottish Blackface lambs reared under extensive conditions on two Scottish hill farms. Measurements were taken on approximately 2000 lambs born to unselected ewes, and sired by 32 rams previously selected for divergent predicted carcass lean content. Heritabilities for birth weight, marking iveight (at approx. 6 weeks of age) and weaning weight (at 17 weeks) were 0·07 (s.e. 0·04), 0·02 (s.e. 0·03), and 0·14 (s.e. 0·05), respectively. Heritabilities for ultrasonic muscle and fat depths at weaning were 0·27 (s.e. 0·09) and 0·16 (s.e. 0·06), respectively. There was a strong maternal effect on weight which declined from birth with lamb age and was relatively unimportant for the ultrasonic measurements. The rearing environment of the lambs (hill pasturev.‘improved’ (or ‘inbye’) pasture) was an important environmental effect on the heritability estimate for backfat thickness, with that for lambs reared on improved pasture being twice that of hill-reared lambs. The implications of the results from this work on genetic improvement of sheep in liill environments are discussed.

Genetic progress in the lleyn group breeding scheme using a multitrait selection index

Group breeding schemes were introduced into Britain in the 1970s as a means of increasing the rate of genetic improvement in sheep and providing a vehicle for breeders to cooperate and pool resources. The Lleyn Group Breeding Scheme was set up in 1978 with the aim of improving several maternal traits in a breed known for its prolificacy. Although the breed originates from North Wales members of the group were drawn from different parts of Britain. Flocks in the scheme were all recorded by MLC and sheep had the possibility of being selected using MLC's selection index, appropriately weighted for the traits of interest to group members.This analysis was designed to investigate the genetic progress made in the scheme between 1979 and 1993. Three traits were analysed; adjusted early lamb weight (LW) (at eight weeks of age), mature weight (MW) (at 18-months) and litter size (LS) in the form Number of lambs born per ewe lambing (NLBEL). These three traits were investigated in ten flocks which participated in the scheme, at varying levels, during the 14-year period 1979-1993. However, only genetic progress in the nucleus flock is reported in this paper.

Genetic progress in the lleyn group breeding scheme using a multitrait selection index

Group breeding schemes were introduced into Britain in the 1970s as a means of increasing the rate of genetic improvement in sheep and providing a vehicle for breeders to cooperate and pool resources. The Lleyn Group Breeding Scheme was set up in 1978 with the aim of improving several maternal traits in a breed known for its prolificacy. Although the breed originates from North Wales members of the group were drawn from different parts of Britain. Flocks in the scheme were all recorded by MLC and sheep had the possibility of being selected using MLC's selection index, appropriately weighted for the traits of interest to group members.This analysis was designed to investigate the genetic progress made in the scheme between 1979 and 1993. Three traits were analysed; adjusted early lamb weight (LW) (at eight weeks of age), mature weight (MW) (at 18-months) and litter size (LS) in the form Number of lambs born per ewe lambing (NLBEL). These three traits were investigated in ten flocks which participated in the scheme, at varying levels, during the 14-year period 1979-1993. However, only genetic progress in the nucleus flock is reported in this paper.

Opportunities for genetic improvement of sheep and cattle in the hills and uplands

AbstractThe principles of genetic improvement apply to hill sheep and cattle in just the same way as they apply to other livestock species. However, the breeding goals often differ, and will continue to change in the light of new economic and political circumstances. Also, there are particular problems of implementing breeding programmes in some of these areas, which do not apply to other livestock species. In this paper we aim to review or discuss (i) the current structure of the livestock industry in the hills and uplands, (ii) strategies for genetic improvement, (iii) the results of relevant selection experiments and industry breeding schemes, (iv) some of the difficulties of implementing breeding programmes and possible solutions, and (v) new opportunities for the genetic improvement of animals in the hills and uplands.

Applications of embryo transfer in animal breeding

Multiple ovulation and embryo transfer (MOET) offers new opportunities for genetic improvement in sheep and cattle breeding. While the techniques are still expensive, their use will mainly be for breed improvement, rather than in commercial production. Improved reproductive rates in females through MOET allow more intense selection, more accurate selection and, of most importance, a shorter generation interval. Each or all of these can contribute to faster rates of genetic change. To exploit the advantages of MOET different breeding systems may be required. Current progeny testing systems can be improved by MOET, but the highest genetic response rates are obtained with nucleus breeding-selection units bred by MOET. Adult MOET (after first breeding) may allow moderate (10–30 percent) gains in genetic response rates. Juvenile MOET (before first breeding) can yield higher (30–100 percent) gains in genetic response rates. Thus effective MOET of juveniles is required to fully exploit the possible advantages of MOET in genetic improvement in practice.

Transfer of superovulated sheep embryos obtained with different FSH-P

Embryo transfer is one way of accelerating genetic improvement in sheep. One of the main obstacles has been the production of good-quality embryos. The use of progestagens and the stimulation of ovulation with follicle stimulating hormone pituitary extract (FSH-P) has permitted the superovulation of donor and recipient ewes and the synchronization of their cycles. The injection of 16 mg FSH-P at the end of progestin treatment gave means of 9 ± 1.5, 12 ± 1.5, and 19.5 ± 2.6 corpora lutea per ewes in the Préalpes, Lacaune, and Romanov × Préalpes breeds respectively (this last breed is particularly prolific). Twenty Préalpes donor ewes produced 133 embryos that were recovered surgically at Day 6 of gestation; of these, 99 morulae were transferable. Forty-five morulae transferred surgically into 24 Préalpes recipient ewes yielded 16 pregnant ewes and 27 lambs (1.7 per ewe). Twenty-two Lacaune ewes yielded 204 embryos, of which 152 morulae were transferable. Of 76 recipients, 58 became pregnant and gave birth to 97 lambs (1.7 per ewe). During anoestrus, the mean ovulation rate decreased from 11.2 to 8.4; 40.6% of the embryos recovered were of transferable quality versus 74.5% during the normal breeding season. An improved superovulation technique, based on the use of FSH-P with a known follicle stimulating hormone to luteinizing hormonal (FSH/LH) ratio, provided us with good-quality embryos. This treatment must be adapted to the season.

Use of embryo transfer in genetic improvement of sheep

ABSTRACTEmbryo transfer following multiple ovulation could allow faster rates of genetic change in sheep, by increasing the effective female reproductive rate. The gains would come from lower generation intervals or increased selection among females, or both. They require good embryo transfer rates at 6 to 8 months of age. These are not adequate at present and need to be improved by research and development, justified by the extra genetic gains shown here to be possible. If high rates of embryo transfer (10 progeny per donor) could be achieved, then, with appropriate selection schemes, the rates of genetic change could be doubled compared with efficient schemes using normal reproduction. This applies to most traits, to those measured before reproductive age (growth traits and carcass traits estimated in the live animal), to female reproductive traits and to wool traits measured at 14 to 16 months of age. With moderate rates of embryo transfer (5 progeny per donor), gains of 50 to 70% in genetic response could be obtained. To limit the rate of inbreeding to moderate levels in a closed selection flock, some 100 to 200 females (1000 progeny) would be required. Application of the methods may be difficult with current breeding structures, and the development of special nucleus selection stocks i s proposed.