Booroola Fecundity Gene Research Articles

Impact of FecB Mutation on Ovarian DNA Methylome in Small-Tail Han Sheep.

In this study, adult Han ewes with homozygous FecB(B)/FecB(B) mutations (Han BB group) and ewes with FecB(+)/FecB(+) wildtype (Han ++ group) were selected. Methylated DNA immunoprecipitation and high-throughput sequencing (MeDIP-seq) was used to identify differences in methylated genes in ovary tissue. We examined differences in DNA methylation patterns between HanBB and Han ++ sheep. In both sheep, methylated reads were mainly distributed at the gene body regions, CpG islands and introns. The differentially methylated genes were enriched in neurotrophy in signaling pathway, Gonadotropin Releasing Hormone (GnRH) signaling pathway, Wnt signaling pathway, oocyte meiosis, vascular endothelial growth factor (VEGF) signaling pathway, etc. Differentially-methylated genes were co-analyzed with differentially-expressed mRNAs. Several genes which could be associated with female reproduction were identified, such as FOXP3 (forkhead box P3), TMEFF2 (Transmembrane Protein with EGF Like and Two Follistatin Like Domains 2) and ADAT2 (Adenosine Deaminase TRNA Specific 2). We constructed a MeDIP-seq based methylomic study to investigate the ovarian DNA methylation differences between Small-Tail Han sheep with homozygous FecB mutant and wildtype, and successfully identified FecB gene-associated differentially-methylated genes. This study has provided information with which to understand the mechanisms of FecB gene-induced hyperprolificacy in sheep.

Are Copy Number Variations within the FecB Gene Significantly Associated with Morphometric Traits in Goats?

Simple SummaryThe Booroola fecundity (FecB) gene, as a major fertility-related gene in sheep, is currently attracting considerable attention. While first discovered in sheep, determining whether FecB is a vital gene in goats has recently become a major research interest. Contemporary research has addressed this issue and discovered that several FecB variations in goats are significantly associated with litter size in goats. Given that growth development is positively associated with litter size, FecB may also exert a significant effect on goat morphometric traits. Five copy number variations (CNVs) of the FecB gene were tested in Shaanbei white cashmere (SBWC, n = 318), Guizhou Heima (GZHM, n = 203), and Nubian (n = 120) goats, all of which were significantly associated with body morphometric traits in the Shaanbei white cashmere goats (p < 0.05). Notably, individuals with the normal type of CNV3 consistently displayed a superior phenotype in litter size and morphometric traits, which allows its use as an effective marker for goat breeding.The Booroola fecundity (FecB) gene is a major fertility-related gene first identified in Booroola sheep. Numerous studies have investigated whether the FecB gene is a major fecundity gene in goats or whether there are other genes that play a critical role in goat fertility. Nevertheless, little attention has been paid to the role of the FecB gene in the body morphometric traits of goats, despite the positive relationship discerned between litter size and growth. We identified five copy number variations (CNVs) within the FecB gene in 641 goats, including 318 Shaanbei white cashmere (SBWC) goats, 203 Guizhou Heima (GZHM) goats, and 120 Nubian goats, which exhibited different distributions among these populations. Our results revealed that these five CNVs were significantly associated with goat morphometric traits (p < 0.05). The normal type of CNV3 was the dominant type and displayed superior phenotypes in both litter size and morphometric traits, making it an effective marker for goat breeding. Consequently, LD blocks in the region of 10 Mb upstream and downstream from FecB and potential transcription factors (TFs) that could bind with the CNVs were analyzed via bioinformatics. Although no significant LD block was detected, our results illustrated that these CNVs could bind to growth-related TFs and indirectly affect the growth development of the goats. We identified potential markers to promote litter size and growth, and we offer a theoretical foundation for further breeding work.

Effects of FecB Mutation on Estrus, Ovulation, and Endocrine Characteristics in Small Tail Han Sheep.

The Booroola fecundity gene (FecB) has a mutation that was found to increase the ovulation rate and litter size in Booroola Merino sheep. This mutation is also associated with the fecundity of small-tail han (STH) sheep, an important maternal breed used to produce hybrid offspring for mutton production in China. Previous research showed that the FecB gene affects reproduction in STH sheep, based on litter size records. However, the effects of this gene on estrus, ovulation, and endocrine characteristics in these sheep remain unclear. Here, we analyzed the traits mentioned earlier and compared them among the three FecB genotypes of STH ewes using estrus synchronization. Overall, 53 pluriparous ewes were selected from among 890 STH ewes and subjected to FecB genotyping for experiments to characterize estrous and ovulation rates. FecB heterozygous (+B) ewes presented an earlier onset of estrus (42.9 ± 2.2 h) and a shorter estrous cycle (17.2 ± 0.2 days) (P ≤ 0.05). The ovulation rates increased with the increasing copy number of the B allele (P ≤ 0.01). Ovulation time showed no significant differences among the three FecB genotypes. The serum concentrations of follicle-stimulating hormone (FSH), luteinizing hormone, estrogen (E2), and progesterone (P4) were measured in 19 of the ewes. Serum concentrations of E2 and FSH dramatically varied around the time of behavioral estrus. In FecB mutant homozygous (BB) ewes, E2 concentration had two peaks, which were higher (P ≤ 0.05) than those of ++ genotypes. FSH concentration of BB ewes was higher (P ≤ 0.05) than that of the ++ ewes just after estrus. The expression of the estrogen receptor 1 (ESR1) gene in the +B genotype was higher than in the other genotypes. Based on the data for the reproductive performance of STH ewes with the three FecB genotypes, our study suggests that the development of follicles in ewes with the B allele is dependent on the response to FSH regulated by E2 in the early stage. +B ewes, exhibiting moderate ovulation and litter size and a shorter estrous cycle, can be highly recommended in sheep crossbreeding systems for commercial mutton production. Moreover, this study provides useful information to conserve better and use the genetic resources of STH sheep in China.

Detection of mRNA Expression and Copy Number Variations Within the Goat Fec B Gene Associated With Litter Size.

The Booroola fecundity (FecB) gene, as the first major fecundity gene identified in Booroola sheep, has attracted careful attention. So far, previous research have uncovered the FecB mutation (Q249R) as the main mutation by virtue of which sheep exhibits multiple lambing phenomena. This mutation is now being intensively studied and widely used. However, such effect of the FecB mutation has not been applied to goats, and similar types of the FecB gene in goats still need to be studied. Thus, the current study attempted to verify potential mutations in the goat FecB gene as well as investigate their functions related to fecundity. First, FecB expression was investigated in six different goat tissues, and we found that FecB expression was highest in the mammary gland, followed by the ovary. Next, the influence of the FecB gene was analyzed from a new perspective, where five potential copy number variations (CNVs) (CNV1–5) within the FecB gene were identified for the first time, and then their effects on litter size were measured. Our results point out that CNV3 (P = 3.44E-4) and CNV5 (P = 0.034) could significantly influence the litter size of goats. Identically, the combination genotype of CNV3 and CNV5 which consisted of their dominant genotypes was also significantly associated with goat litter size (P = 7.80E-5). Hence, CNV3 and CNV5 could serve as potential DNA molecular markers applied to DNA editing and DNA microarray. Additionally, the abovementioned study has laid a theoretical foundation for the detection of potential fertility-related quantitative trait loci within the goat FecB gene.

Rapid visual detection of FecB gene expression in sheep.

Sheep play an important role in agricultural production and people’s lives, and fecundity is one of the most important economic traits of sheep for sheep breeders. The Booroola fecundity (FecB) gene has a certain correlation with litter size in sheep. Therefore, this study aims to detect FecB expression quickly, accurately and visually. Here, we used the nucleic acid dye SYBR Green I to detect FecB with the amplification refractory mutation system (ARMS), which can efficiently, rapidly, economically and visually detect FecB expression in sheep. After ARMS polymerase chain reaction (PCR), SYBR Green I was directly added to the ARMS products, and whether the sheep carried FecB was judged by directly observing the color change in the PCR tube. Homozygous (BB) or heterozygous (B+) samples with FecB mutation were bright green, while wild type (++) samples without FecB were orange yellow. This study suggested that this method has 100% accuracy and 0.5 ng/µL sensitivity. To our knowledge, this is the first report that shows the integration of the ARMS with SYBR Green I to detect FecB expression in sheep visually.

Genetic diversity and population structure of breeds of Askanian sheep by analysing polymorphisms in qualitative trait loci

Aim. To determine the level of polymorphism of some genes, pertaining to the quantitative traits of sheep and to study the genetic diversity and population structure of breeds of Askanian sheep and one of its hybrids. Methods. Molecular–genetic, population–statistical, biometric methods. Results. The genetic structure of populations of the Askanian Fine-Fleeced (AFF, n = 33), Askanian Meat-and-Wool (AMW, n = 22) and Askanian Karakul (AK, n = 46) breeds and a hybrid of Askanian Fine-Fleeced × Texel (AFFT, n = 40) has been studied for the fi rst time in terms of the polymorphisms of the following qualitative trait genes (loci) : meat productivity genes: ovine growth hormone (GH), calpastatin (CAST) and myostatin (MSTN); prolifi cacy genes: Booroola (fecundity gene FecB) and bone morphogenetic protein (BMP15). The sheep in all studied breeds and the hybrid mentioned above are characterized by the polymorphism of two loci, GH and CAST. The other three loci studied did not show polymorphism for the markers studied. GH is present as two genotypes (A/A, A/B), and CAST as three genotypes (A/A, A/B, B/B). The remaining genes were found to be in the monomorphic state. The frequencies of certain genotypes and alleles change in the direction from fi ne–fl eeced to meat animals. For instance, the concentration of heterozygous growth hormone (GH) genotype A/B increases from 0.0 % (AFFB) to 38.2 % (AMWB), and the concentration of allele A – from 0.083 to 0.191. The live bodyweight of fi ne–fl eeced lambs with GH genotype A/B at birth equaled 4.5 kg, and those with homozygous genotype A/A – 4.9 kg (P &lt; 0.001). Therefore, homozygous genotype А/А determined the increased level of meat productivity of sheep. A similar dependence was established at birth for the Askanian Karakul breed. Conclusions. The specifi city of genetic structure of Askanian breeds and hybrid is polymorphism of the GH and CAST and absence of polymorphism of BMP15 and FecB genes, determining the prolifi cacy (reproduction) trait. According to the distribution of polymorphic loci variants, the gene pools of Askanian Meat-and-Wool breed and the local Askanian-Texel hybrid are closely related and therefore explains the same direction of their productivity. At the same time, all populations are in a state of genetic equilibrium according to Hardy-Weinberg, which indicates a high level of their consolidation. Sheep which have the A/A homozygote of the gene growth hormone are characterized by an increased level of the body weight development.

Effect of the Booroola fecundity (FecB) gene on the reproductive performance of ewes under assisted reproduction

Reproductive traits are important factors in sheep production. The Booroola fecundity (FecB) gene—the first major gene for prolificacy identified in sheep—has a positive effect on ovulation rates and litter size under natural reproductive conditions. However, the effect of the FecB gene on reproductive performance under assisted reproduction, which uses many artificial hormones, remains unclear. In the present study, we evaluated the effect of FecB (BMPR-1B mutation) on reproductive performance under assisted reproduction, and examined offspring body weight at birth and weaning and survival rate at weaning. There were no differences among three genotype groups (homozygous carrier, BB; heterozygous carrier, B+; non-carrier, ++) in terms of estrus detection rate, time to estrus onset, or estrus duration following estrus synchronization (P > 0.05). The pregnancy rates at 60 d were similar among three genotype groups after artificial insemination (P > 0.05). However, the B allele had an additive effect on litter size (one copy resulted in an increase of 0.88 lambs and two copies produced an additional 0.41 lambs; P < 0.01), and increased lambing and fecundity rates (P < 0.01). After multiple ovulation, the average numbers of recovered embryos per ewe were 9.16 ± 0.79, 8.20 ± 0.77, and 8.44 ± 0.61 in the BB, B+, and ++ ewes, respectively (P > 0.05). There were no differences in the fertilization rate or numbers of grade 1–2 embryos among different groups (P > 0.05). The birth and weaning weights of lambs from BB and B+ ewes were lower than those of lambs born from ++ ewes (P < 0.01) owing to the high fecundity. The survival rate of lambs at weaning did not differ among groups (P > 0.05). Our results indicated that the presence of the B allele had an additive effect on litter size after artificial insemination, but it did not influence the parameters of estrus synchronization and multiple ovulation. Furthermore, the higher prolificacy in ewes carrying the B allele was associated with a reduction in offspring body weight at birth and weaning.

Effect of Booroola fecundity (FeCB) gene on litter size and scope for use in restoration of Nilagiri sheep from threatened status

Effect of Booroola fecundity (FeCB) gene on litter size and scope for use in restoration of Nilagiri sheep from threatened status

Quantitative expression of mRNA encoding BMP/SMAD signalling genes in the ovaries of Booroola carrier and non-carrier GMM sheep.

The GMM sheep is a carrier of Booroola fecundity (FecB) gene, which produces the twins and triplets in one lambing. The homozygous carrier GMM (FecBBB ), non-carrier GMM and Malpura (FecB++ ) ewes were synchronized by progesterone sponges, and the plasma progesterone concentration was measured by RIA. The results showed that the progesterone concentration did not differ significantly (p>.05) in homozygous carrier GMM (5.74±1.2ng/ml), non-carrier GMM (5.42±1.4ng/ml) and non-carrier Malpura ewes (5.67±1.5ng/ml). Further, quantitative expression of BMP factors/receptors and SMAD signalling genes were analysed in the ovaries of sheep by qRT-PCR. The study showed that the expression of BMP2 was slightly higher (p>.05) in carrier GMM than that of non-carrier GMM, but it was almost similar to Malpura ewes. Expression of BMP4 and BMP7 was significantly higher (p<.001; p<.05) in carrier GMM than that of non-carrier GMM and Malpura ewes. Although BMP6 expression was higher (p>.05) in carrier GMM than that of non-carrier GMM, but lower (p>.05) than the Malpura ewes. Expression of BMP15 (p<.05), GDF5 (p<.01) and GDF9 (p<.05) was significantly higher in carrier GMM than non-carrier GMM ewes. Surprisingly, BMPR1B expression was significantly higher (p<.001) in non-carrier GMM and Malpura than the carrier GMM ewes, while TGFβRI did not differ significantly (p>.05) among both GMM genotypes. On the other hand, expression of BMPR1A (p>.05) and BMPRII (p<.05) was higher in carrier GMM than the non-carrier GMM, but significantly lower (p<.001) than the Malpura ewes. It was interesting to note that the expression of SMAD1 (p>.05), SMAD2 (p<.001), SMAD3 (p<.05), SMAD4 (p<.001), SMAD5 (p<.001) and SMAD8 (p<.001) was lower in the carrier GMM than that of non-carrier GMM ewes. It is concluded that the FecB mutation alters the expression of BMPR1B and SMAD signalling genes in the ovaries of homozygous carrier GMM ewes.

Mechanisms regulating follicle selection in ruminants: lessons learned from multiple ovulation models.

Selection of a single dominant follicle from a cohort of growing follicles is a unique biological process, a key step in female reproductive function in monovular species, and lies at the core of reproductive technologies in cattle. Follicle growth and the number of follicles that ovulate are regulated by precise endocrine, paracrine, and autocrine mechanisms. Most of our current understanding about follicle selection focuses on the role of FSH, LH, and the IGF family in follicle growth and selection of the dominant follicle. However, more recently the role of members of the TGF-ß family has been highlighted, particularly in high fecundity genotypes in sheep. Intercellular signaling between the oocyte and granulosa cells (GC) regulates proliferation and differentiation due to actions of bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) within the follicle. Mutations that either knockout or reduce the activity of BMP15 or GDF9 have been found to increase ovulation rate in heterozygotes and generally cause severe follicle abnormalities in homozygotes. A mutation in the intracellular kinase domain of the BMPR1B receptor (Booroola fecundity gene) increases ovulation rate in heterozygotes with further increases in ovulation in homozygotes. The physiological mechanisms linking these mutations to increased ovulation rates are still not well defined. A recently identified high fecundity bovine genotype, Trio, causes increased expression of SMAD6, an intracellular inhibitor of the BMP15/GDF9 signalling pathways. This bovine model has provided insights into the mechanisms associated with selection of multiple dominant follicles and multiple ovulations in carriers of fecundity alleles. The present review focuses on the mechanisms involved in follicle selection in ruminants with a special emphasis on the contribution made by multiple ovulation models in both cattle and sheep. The evaluation of multiple ovulation models in ruminants has allowed us to construct a new physiological model that relates changes in the BMP15/GDF9 signalling pathways to the physiological changes that result in selection of multiple dominant follicles. This model is characterized by acquisition of dominance at a smaller follicle size but at a similar time in the follicular wave with multiple follicles acquiring dominance in a hierarchal sequence, delaying FSH suppression and, thus allowing additional follicles to continue to grow and acquire dominance.

Generation of gene-edited sheep with a defined Booroola fecundity gene (FecBB) mutation in bone morphogenetic protein receptor type 1B (BMPR1B) via clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas) 9.

Since its emergence, the clustered regularly interspaced short palindromic repeat (CRISPR)-CRISPR-associated (Cas) 9 system has been increasingly used to generate animals for economically important traits. However, most CRISPR/Cas9 applications have been focused on non-homologous end joining, which results in base deletions and insertions, leading to a functional knockout of the targeted gene. The Booroola fecundity gene (FecBB) mutation (p.Q249R) in bone morphogenetic protein receptor type 1B (BMPR1B) has been demonstrated to exert a profound effect on fecundity in many breeds of sheep. In the present study, we successfully obtained lambs with defined point mutations resulting in a p.249Q>R substitution through the coinjection of Cas9 mRNA, a single guide RNA and single-stranded DNA oligonucleotides into Tan sheep zygotes. In the newborn lambs, the observed efficiency of the single nucleotide exchange was as high as 23.8%. We believe that our findings will contribute to improved reproduction traits in sheep, as well as to the generation of defined point mutations in other large animals.

Advances in genomic strategies to improve growth and meat production traits in sheep: An overview

Growth and meat production traits (body weight at birth, 3-months and 6-months, eye muscle area, fat thickness, pre-weaning and post-weaning gains, average daily weight gain, chest girth, height at withers and shin circumference) are reviewed to know the relationship with the loci which are controlled by specific genes that are associated with these traits. Quantitative trait loci (QTL) for different body and carcass weight traits are identified. Chromosomes 1, 2, 3, 4, 5, 6, 16, 18 and 20 are considered as candidate genomic regions for body weight and some major gene effects like transferrin gene on chromosome 1, Belgium Texel double muscling and myostatin (MSTN) gene on chromosome 2, growth effect around insulin-like growth factor 1 (IGF-1) on chromosome 3, calpastatin gene on chromosome 5, leptin gene on chromosome 4, Booroola fecundity gene on chromosome 6, growth hormone receptor (GHR) gene in chromosome 16, callipyge effect and carawell muscle hypertrophy on chromosome 18 and MHC complex on chromosome 20 have been identified. High-throughput genotyping and next-generation sequencing technologies are the advanced techniques for the creation of the high-density SNP array as a tool for the genomic analysis of domestic animals. Genome-wide association studies (GWAS) and genomic selection are the ultimate use of SNP array for the improvement of economically important traits. Hence, genome-wide sequencing is an advanced tool which may help in better selection of animal genetic resources. It may be used for applying molecular breeding strategies in genetic improvement programmes oflivestock.

Allelic and genotypic frequencies in polymorphic Booroola fecundity gene and their association with multiple birth and postnatal growth in Chhotanagpuri sheep.

Aim:Chhotanagpuri breed of sheep reared for mutton in Jharkhand, India, having problem of low litter size and body weight. The response of genetic improvement for traits with low heritability through traditional selection method is time-consuming. Therefore, marker-assisted selection based on a polymorphism study of suitable candidate gene can response quickly. Thus, this study was aimed at identification of different allelic and genotypic frequencies of Booroola fecundity (FecB) gene and its association with multiple birth and postnatal growth in Chhotanagpuri sheep.Materials and Methods:DNA isolation and gene-specific amplification of FecB gene was performed from blood samples of from 92 Chhotanagpuri lambs maintained under similar feeding and management conditions. Custom nucleotide sequencing and single-strand conformational polymorphism analysis were performed to identify different genotypes with respect to the target gene. Statistical analysis was performed for determination of allelic and genotypic frequencies of FecB gene polymorphisms and its association with multiple birth and postnatal growth of lambs from birth to 52 weeks age.Results:“AA,” “AB,” and “BB” genotypes were found at locus-1 as it is polymorphic for FecB gene while locus-2 was found to be monomorphic for FecB gene. Higher frequency of “A” allele at locus-1 was found in single born lambs, whereas “B” allele was predominant among multiple born lambs. The lambs having “BB” genotype weighed significantly (p≤0.01) heavier than those of “AB” and “AA” genotype at 52 weeks of age.Conclusion:“BB” genotype has emerged as favored genotype for multiple births and better growth indicator. Therefore, homozygous lambs for “B” allele should be selected and utilized in breeding program for better growth rate.

Identification of the FecB mutation in Garole × Malpura sheep and its effect on litter size

High prolificacy in Garole sheep is due to the effect of the Booroola fecundity gene ( FecB) mutation. In the present study, Garole rams were crossed with non-prolific Malpura ewes with the aim to increase prolificacy into Garole × Malpura (GM) crosses. The FecB genotyping was carried out by Forced-Restriction Fragment Length Polymorphism PCR technique in Garole ( n = 64), GM crosses ( n = 53) and Malpura sheep ( n = 62). In 64 Garole samples genotyped, 55 were homozygous ( FecB BB ), 8 heterozygous ( FecB B+ ) and 1 non-carrier ( FecB ++ ). The results showed that most Garole sheep (∼98.0%) carried the FecB allele. Out of 53 GM samples, 36 were heterozygous, 14 non-carriers and 3 were homozygous. Fifteen GM ewes genotyped that had at least one record of twins or triplets, revealed 1 homozygous and 14 heterozygous and 9 GM ewes that never produced twins were all non-carriers of the FecB mutation. The mean litter size was 1.95 ± 0.08 and 1.60 ± 0.11 in Garole and GM ewes, respectively. All Malpura sheep did not carry the FecB mutation. The results indicated that a single copy of mutated FecB gene resulted in 0.93 extra lambs in GM ewes. The introduction of the FecB gene from Garole to Malpura sheep improved litter sizes in GM crosses.

277. Is the high level of circulating FSH in Booroola ewes due to the Bmp R1b mutation?

Booroola ewes are characterised by having high ovulation rate and litter size caused by the action of the Booroola fecundity gene (FecB), which encodes the bone morphogenetic protein receptor (BMPR) type 1b mutation (Q249R). The product of the FecB gene influences both pituitary and ovarian activity. In both neonatal and adult Booroola ewes carrying a double copy of the FecB allele, plasma concentrations of the pituitary-derived follicle stimulating hormone (FSH) are higher than in non-carrier females. BMPR-1b is expressed in the sheep pituitary gland and recent reports have shown that in addition to GnRH, TGF-β family members such as BMP 6, 7, and 15 induce pituitary FSHβ expression. Thus BMPs may function in regulating FSH synthesis in the pituitary. We are investigating whether we can detect induction/secretion of FSH in response to BMP treatment of ovine primary pituitary cell cultures, with the aim of elucidating whether the Booroola mutation is the cause of the increased FSH secretion. Due to the high variance between cultures from different animals, and between replicates from the same animal, we are attempting to determine the best method for approaching the question. Some results from these investigations will be presented.

Hormonal control of folliculogenesis: the key to successful reproduction.

Folliculogenesis is the process by which primordial follicles are promoted through a series of developmental steps until a mature oocyte is ovulated. The process of folliculogenesis is not fully understood and involves initial or primary recruitment from the primordial pool, development of small primary and secondary preantral follicles, formation of an antral cavity, and finally the selection of the ovulatory follicle(s) (Hirshfield 1991; Gougeon 1996). The growth and differentiation of the oocyte and the surrounding somatic cells which make up the follicle are subject to various carefully regulated steps which ensure that the number of eggs which are ovulated is reduced to that which is appropriate for the species. The disastrous consequences of dysregulation of this system are illustrated by sheep carrying the Booroola fecundity gene (Baird and Campbell 1998). Due to a mutation in the BMPRIβ receptor, these sheep ovulate up to ten eggs instead of one or two (de Souza et al. 2001; Mulsant et al. 2001; Wilson et al. 2001). The subsequent fetuses die due to either abortion or following premature birth. As a result, under natural circumstances the mutation only rarely persists in those few ewes carrying a single copy of the gene which ovulates twins.

The consequences of carrying the Booroola fecundity (FecB) gene on sheep liveweight

The increase in ovulation rate caused by the Booroola gene was first observed in the Booroola Merino strain of sheep (Davis et al., 1982) and the gene was subsequently mapped to sheep chromosome 6 (OOV6) (Montgomery et al. 1994). The low heritability of fertility traits and the desire to produce more lambs per ewe from meat breeds has lead to many crossbreeding programs seeking to obtain the benefits of the Booroola gene. However, many producers report animals carrying a Booroola allele to be lighter than non-carriers (G. Davis, personal communication). The Booroola Merino strain of sheep is typically lighter than recipient breeds used in the introgression programmes e.g. Romney. This study aims to determine whether the Booroola gene has a pleiotropic effect on liveweight or whether there is any evidence to suggest a closely linked quantitative trait locus (QTL) affecting liveweight that may ‘hitchhike’ with the Booroola gene.

Control of ovarian follicles activity in the ewe

During the ovine estrous cycles, three waves of follicular growth, closely associated with the FSH secretion pattern, were observed. The parameters of these follicular waves and the ability of follicles to produce steroids in vitro were studied in various conditions. In vivo, the follicular events were similar between the breeding season and the anestrus, except for the lack of ovulation; but at the end of the breeding season and in anestrus, the follicles lose a big part of their aromatization ability. In ewes carrying the Booroola fecundity gene or Cambridge fecundity gene, the reduction in follicular atresia seems to be one of the main follicular features implicated in the control of high ovulation rate. In vitro, the most relevant difference is an early acquisition of estrogen production ability of small follicles in Booroola fecundity gene barring ewes. Fluoro-gestone-acetate (FGA) pessaries reduced the number of growing follicles; despite this effect disappearing after the sponge withdrawal, the ovulation rate is significantly reduced. But an equine chorionic gonadotrophin (eCG) treatment restores the ovulation rate (OR) by reducing the atresia rate of pre-ovulatory follicles. In similar conditions, a pretreatment of the ewes with melatonin again reduced the atresia rate of large follicles and resulted in an increased ovulation rate. In vitro, FGA blocked aromatization ability, and melatonin inhibited both androstenedione and estradiol production, but a further treatment with eCG partly restores the steroid secretion. Immunization against androstenedione leads to a higher OR, owning to a reduced atresia of large follicles. Daily growth hormone injections for a hole cycle resulted in an increased follicular population and ovulation rate, while FSH plasma levels decreased and the follicle sensitivity to gonadotrophins was reduced.

Genetic variation of prenatal survival in relation to ovulation rate in sheep: A review

Varying rates of partial fertilization (2–40%) were found in literature. These data gave evidence that the `all-or-none' hypothesis on fertilization is not correct, at least in a number of sheep breeds and experimental conditions. Furthermore, there are indications for variability in prenatal mortality at different stages of pregnancy, as a function of ovulation rate (OR). Consequently, higher partial fertilization and foetal mortality rates interfere with the determination of prenatal survival (PS), based on the difference between OR and the number of living embryos at varying times before or at lambing, as was done in many studies on that subject. Indications for variability in PS within breeds were mainly an effect of differentiation between lines, depending on the selection criteria followed, e.g., growth rate vs. multiple ovulations. In some cases, this effect was associated with dam–embryo interactions or line–age interactions. Data on differences in PS between breeds and crosses were based, in most cases, on differences between twin and multiple ovulating ewes, or in ewes carrying multiple foetuses after egg transfer. Among twin ovulating ewes, all born to Romney dams, uterine efficiency (UE) was highest in Finnish Landrace (FL) sired ewes. The contribution of FL breeding to superiority in UE was supported in other FL crossbreeds and in crossbred genotypes with FL genes from their ancestry. Crossbreeding effects of the Booroola Merino on uterine capacity (UC) or on UE were variable, depending on the breeds used, on the presence of the Booroola Fecundity gene and on OR. A clear distinction should be made between UE (the marginal increase in LS as OR increases) and UC (the maximum number of foetuses a dam is able to support at birth) when comparing Finnish Landrace and Booroola Merino with other prolific breeds. There were indications of a higher genetic variability in PS, independent from the genetic variability in OR, in the Romanov breed than in other breeds and crosses. In conclusion, while genetic variation in litter size (LS) within some breeds can be statistically predicted on the basis of OR, between-breed variation in LS has consider the genetic variation in PS.

The effect of litter size, age of ewe and Booroola gene (Fee B) on the birth and placental characteristics of Texel ewes

It is widely recorded that placental weight varies a great deal in uniformly treated ewes, yet this variation remains unexplained (Mellor, 1983). The aim of this experiment was to assess the effects of differing parameters on birth weight, placental weight, and number and weight of cotyledons in Texel ewes carrying the Booroola fecundity gene.