InTechOpen uses cookies to offer you the best online experience. By continuing to use our site, you agree to our Privacy Policy.

Medicine » "Genetic Polymorphisms", book edited by Narasimha Reddy Parine, ISBN 978-953-51-3516-6, Print ISBN 978-953-51-3515-9, Published: September 6, 2017 under CC BY 3.0 license. © The Author(s).

Chapter 12

Genes Involved Litter Size in Olkuska Sheep

By Urszula Kaczor
DOI: 10.5772/intechopen.69205

Article top


Genes Involved Litter Size in Olkuska Sheep

Urszula Kaczor
Show details


Major genes increasing litter size were identified in certain sheep breeds. These genes include BMPR‐1B, BMP15, GDF9 and B4GALNT2, FecX2. Polish Olkuska sheep is a high‐fecundity sheep breed; while some animals might give birth to just one or two lambs, there are Olkuska ewes which have six or even seven lambs/lambing. Fertility of this breed is caused by mutation in the major gene FecXO (BMP15 gene), but analysis of polymorphism at the locus GDF9 revealed presence of four polymorphisms: G447A (L159L), A978G (G326G), G994A (V332I) and G1111A (V371M). Substitutions V371 and V332I are missense mutations found in the sequence encoding active GDF9 protein. V371 polymorphism has also an effect on litter size in Olkuska breed ewes. Study of genes associated with litter size in Olkuska sheep is of high importance, as they could be used in breeding programmes as selection markers for increasing production efficiency.

Keywords: fecundity, genes, litter size, Olkuska sheep

1. Introduction

Currently, more than 1200 sheep breeds differing in many production features, including fertility, are known globally. Ewes usually give birth to one or two lambs/litter. However, there are certain highly prolific breeds—such as inter alia Cambridge, Thoka, Javanese, Belclare, Lacaune, Woodland, Booroola, Aragonesa, Romney (Inverdale and Hanna), Garole (Bengal), Belle‐ile, small‐tailed Han, Hu and Kendrapada—whose litter size ranges from three to six lambs. Genetically conditioned differences in number of maturing and ovulating follicles in different breeds of sheep have been researched already since 1980 [1], when an attempt was made to explain the genetic basis for multiple births within a litter in various breeds around the world. It has been shown that sheep fertility depending on breed may be determined either polygenic or by a major segregating gene named the Fec gene.

Most mutations increasing ovulation levels and the number of lambs born to an ewe were identified in genes encoding proteins belonging to the family of transforming growth factors TGF‐β: BMPR1B (bone morphogenetic protein receptor‐1B), BMP15 (bone morphogenetic protein 15) and GDF9 (growth differentiation factor 9). In addition, mutations FecLL in Lacaune breed on chromosome 11 and FecX2W (fecundity gene X2) in Woodland sheep were identified. FecXL locus contains two genes IGF2BP1 (insulin‐like growth factor 2 mRNA binding protein1) and B4GALNT2 (beta‐1, 4‐N‐acetyl‐galactosaminyl transferase 2). It has been shown that B4GALNT2 is responsible for high prolificacy of Lacaune sheep [2]. The mechanism of action of the gene FecX2 on X chromosome in Woodland sheep is not yet exactly understood [3].

1.1. FecB mutation in the bone morphogenetic protein receptor 1B (BMPR1‐B) gene

Booroola was the first major gene (FecB) significantly influencing level of ovulation and litter size in sheep to be identified [4]. The effect of FecB mutation (Q249R) identified in Booroola Merino breed in the gene of bone morphogenetic protein receptor BMPR1‐B on chromosome 6 is an increase in ovulation level and litter size in carriers of one or two copies of the gene FecB. This mutation was also identified in Asian breeds: Garole, Javanese, thin‐tail Hu and Han. With regard to level of ovulation, the observed increase is additive in nature, while as concerns litter size—it is partly dominant. In ewes with heterozygous FecBB+ ovulation level increased by 1.3 CL (corpus luteum), while in ewes with FecBBB, the observed increase was up to 3.6 CL. The effect on litter size between homozygous++ and BB was +0.8 [6].

Many authors have shown high fertility of carriers of FecBB+ genotype, among others in Garole‐223% lamb production [6], Hu‐210%, Han‐240% [7] and Javanese breeds‐259% [8]. Research results in Indian sheep of Muzaffarnagari breed engendered some discussion, as presence of ewes with FecB gene that still had single births was proven, and share of sheep with genotypes FecBBBand FecBB+ was identified as 3.47 and 41.73%, respectively [9].

In antral follicles of FecBB+ ewes, a decrease in granulosa cell proliferation and premature expression of LH receptors were observed [10]. Appearance of FecB mutation in sheep compared with ewes devoid of mutation is associated with higher number of growing small cavitary (antral) follicles on the ovaries. Both total number of granulosa cells and total secretion of estradiol and inhibins in the ovaries of FecBBB ewes still remain the same as in ewes with FecB++ genotype. Significant impact of gene FecB on development of ovaries during foetal life is also observed, including, inter alia, a reduced number of oocytes from the 35th to the 50th day of gestation, a smaller number of class 1 follicles from 75th to 90th day of gestation and class 2 follicles (on 135th day). A small number of class 2 follicles were also observed in early neonatal life of FecBBB sheep [10, 11]. Significant effect of FecB gene on function of the hypothalamic‐pituitary system has been proven as well. It has been found that it may lead to increased secretion of follicle‐stimulating hormone (FSH) in FecBBB homozygotes, although it has not been confirmed in all of the animals investigated. No FecB influence on release of luteinizing hormone (LH) has been found [12].

1.2. Mutations in the gene of bone morphogenetic protein 15 (BMP15)

1.2.1. Protein BMP15

BMP15 protein together with growth factor 9 (GDF9) plays an important role in folliculogenesis [13, 14]. Its paracrine action affects granulosa cells, theca cells and the oocyte itself [15]. In vitro cultures indicate that recombinant protein BMP15 is a potent stimulator of granulosa cell proliferation, suggesting that both cell growth and their subsequent division and differentiation require BMP15 action [16]. The protein inhibits expression of FSH and LH receptors, as decrease in activity of BMP15 increases cell sensitivity to action of gonadotropins [17]. The conducted experiments showed that BMP15 inhibits expression of StAR protein, responsible for transport of cholesterol—specifically low density lipoprotein (LDL)—into cells. LDL is the substrate for production of steroid hormones. In rats, BMP may modulate the process of steroidogenesis in granulosa cells, modifies biological effects of FSH by inhibition of progesterone‐induced FSH secretion, without affecting production of estradiol [16]. BMP15 mRNA transcripts are observed from the primary follicle stage, in secondary, tertiary and dominant follicles stages, ending with atretic antral follicles [18]. In sheep, BMP15 affects proliferation rate and inhibits baseline and FSH‐mediated secretion of progesterone by granulosa cells of small antral follicles [11]. Presence of BMP15 mRNA was determined in the oocytes (class 1, 2, 3, 4 and 5 follicles), but it has not been demonstrated in granulosa cells and follicle theca [19].

1.2.2. Polymorphism in the BMP15 gene

In mammals, formation of BMP15 protein is determined by action of a single gene on chromosome X [20]. An encoded sequence with a length of 1179 bp is contained in two exons separated by an intron of 5400 bp in length. mRNA translation produces a peptide built of 393 amino acids, and the resulting mature protein has a length of 125 amino acids [21]. Mutations identified in the BMP15 locus (FecXI, FecXH, FecXL, FecXG, FecXB and FecXR) result in appearance of the same phenotype in different sheep breeds, and have different molecular basis. Heterozygous ewes give birth to more lambs, while homozygotes with two copies of a gene are infertile. Action of mutations marked FecXO and FecXGr identified in Olkuska and Grivette breeds differs from the above‐mentioned, as in the case of ewes with both one and two copies of the gene, an increase in prolificacy is observed (Table 1).

VariantBase changeCoding base bpCoding residue*Amino acids changeMutation/reference
175–18017 bp

Table 1.

Mutations identified in sheep at the BMP‐15 gene locus.

* Position of the coding residue in the Ovis aries bone morphogenic protein 15; BMP15 protein GenBank accession number AAF81688.1.

Substitution of FecXH detected in Hanna sheep causes introduction of a stop codon in place of glutamine in position 23 of amino acid residue of mature protein. Transition C>T observed in the case of FecXG in Galoway and Cambridge breeds, also introduces a premature stop codon in place of glutamine at position 31 of the polypeptide chain. As concerns carriers of these mutations, heterozygotes show increased levels of ovulation, while homozygotes with two copies of the gene are infertile [17].

A similar phenotype is observed for FecXI mutation, where hydrophobic valine is substituted for asparagine at position 31 of mature protein. This leads to changes in electrostatic potential of the region involved in formation of dimers—this, in turn, interferes with dimerization and consequently leads to the elimination of biological effects of BMP15. Homozygous ewes are infertile due to folliculogenesis being arrested at initial stage of the process [10].

FecXB mutation found in BMP15 gene locus in Belclare sheep is a result of polar serine being substituted for non‐polar isoleucine at position 99. This substitution has a significant impact on the ability of a protein to bind to type II membrane receptor; it determines the structure of the ligand‐receptor complex with BMP2, BMP7, activin A proteins. This polymorphism abolishes biological activity of BMP15, most likely by prejudicing the binding of protein and receptor [21]. Homozygous ewes are infertile due to hypoplasia of ovaries. Admittedly, presence of antral follicles was observed, but with oocytes of anomalous size, surrounded by a single layer of abnormal granulosa cells. Morphology of ovaries of such sheep is similar to image of ovaries of FecXI Inverdale ewes.

One copy of the allele FecXI (Inverdale) or FecXH (Hanna) results in ovulation level increase of +0.8–1.0 CL, significantly affecting size of the litter by +0.6 lamb. Homozygous FecXII and FecXHH Hanna ewes are sterile; in their small and poorly developed ovaries, follicles are provided with a single layer of granulosa cells [22]. In FecXI+ sheep, follicles were determined to be of a smaller diameter than those produced in ovaries of homozygotes devoid of mutation. However, FecXI+ ewes present a greater number of mature preovulatory dominant follicles of smaller diameter, and therefore do not differ in the level of estradiol and inhibin from non‐mutated ones [23]. Preovulatory follicles are also characterized by early maturation, which determines greater secretion of FSH and early formation of LH receptors [12].

Studies by Bodin et al. [24] on prolific sheep of Lacaune breed showed presence of FecXL mutation, leading to substitution of cysteine for tyrosine at position 53 of the BMP15 chain. Just as observed in the case of polymorphisms (FecXI, FecXH, FecXG and FecXB), also this change in gene structure causes increased level of ovulation in heterozygous ewes and infertility in homozygotes. In vitro studies revealed that the mutation FecXL is responsible for defective secretion of both precursors and active forms of BMP15. It is believed that this may be caused by damage to structure of one of the disulphide bonds whose formation involves cysteine, and that play an important role in stabilizing the structure of BMP15 [24]. In the case of presence of one copy of FecXL in ewes, ovulation level increase of +1.9–2.17 CL is observed [2, 25].

Lacaune sheep are, next to Hanna, Inverdale, Cambridge, Belclare and small‐tail Han breeds, an example where increase in litter size is determined by the presence of two major genes: FecXL and FecL on autosomal chromosome 11 [2].

In Aragonesa FecXR ewes, a 17 bp deletion results in a frameshift and appearance of a stop codon, even before the coding region of mature protein. The consequence of this mutation is an 85% modification in the propeptide sequence, specifically limitation of its size to 45 amino acids out of 245 present in the original propeptide. Heterozygous ewes are very highly fecund, while the presence of two copies of the mutated gene leads to a blockage of follicular development at initial growth state and female infertility. FecXR+ ewes have an average of 2.66 lamb/litter compared to flock average of 1.36. Presence of one copy of the gene resulted in litter size increase of +1.3 lamb [26].

A mutation in the gene BMP15 changing the amino acid sequence in the amino acid chain p.T317I was identified in French Grivette sheep. Ewes of FecXGrGr genotype have 2.5 lamb/litter, while FecX++ and FecXGr+give birth to 1.83 and 1.93 lamb in a litter, respectively. Sterilization of homozygotes with the FecXGrGr mutation has not been identified in the studied population [27].

Recent research in phenomenon of high fertility of ewes of the African breed Barbarine (167% annual lamb crop) showed presence of another substitution in the gene encoding BMP15, resulting in A119T mutation in the coding sequence of mature protein. Frequency of the mutated allele in the population of these sheep, or its impact of prolificacy are unknown [28].

1.2.3. Mutations in the growth differentiation factor 9 (GDF9) gene Protein GDF9

Growth differentiation factor 9 (GDF9) is another protein belonging to TGF‐β family. This peptide regulates development of ovarian follicles in rodents and ruminants (sheep), as well as humans [12, 29]. It has been shown that its synthesis, similarly as in the case of BMP15, occurs in the oocyte [30]. Mice lacking functional protein GDF9 (GDF9KO) were infertile, their follicle growth was arrested at primary follicle stage, with granulosa cells layer not properly formed, and changes in the zona pellucida. Oocytes were excessively enlarged and surrounded by a single layer of deformed granulosa cells, or oocyte was not observed in the follicle whatsoever [30, 31]. Growth differentiation factor 9 as a multi‐functional protein is responsible for follicular growth from its early stage—it initiates and regulates folliculogenesis and oocyte development. It has autocrine effects on oocytes, plays a role in their development and maturation, and paracrine effects on somatic cells, inhibits expression of luteinizing hormone receptor gene and stimulating synthesis of hyaluronic acid [32, 33]. GDF9 gene expression in sheep occurs in oocytes, with the presence of the transcript and protein demonstrated in the oocyte during formation of the follicle, in class 1 primary follicles as well as in follicles in the phase of intensive growth. In vitro experiments demonstrated that GDF9 is also found in degraded oocytes and in malformed follicular structures [34, 35]. In humans, GDF9 plays an important role in pathogenesis of polycystic ovary syndrome and premature ovarian failure [36]. Polymorphism in the GDF9 gene

The gene encoding protein GDF9 was found to be located in sheep on chromosome 5 [37]. The gene consists of two exons, with length of 397 and 968 bp, respectively. Its total length is 5644 bp, with coding sequence comprised of 1359 nucleotides [35].

A number of mutations (Table 2) were identified in gene GDF9; it was determined that the mutation FecGH (G8, Ser1184Phe) causes sterility in homozygous ewes. Impact of the mutations G1 (G260A, R87H), G2 (C471T), G3 (G477A), G4 (G721A, E241K), G5 (A978G), G6 (G994A, V332I) and G7 (G1111A, V371M) on fertility of sheep had not been initially analysed, but fertile homozygous animals with G1, G4 and G7 mutations were found [21, 30]. Effects of FecGH mutation are due to lack of active form of the protein, leading to arrest of follicular growth in the early stages of development [38, 39] (Table 2).

VariantBase changeCoding base bpCoding residue*Amino acids changeMutation/reference
S395FC>T1184395Ser>PheG8 (FecGH)/[21]

Table 2.

Mutations identified in sheep at the GDF9 gene locus.

*Position of the coding residue in the Ovis aries growth differentiation factor 9; GDF9 protein GenBank accession number AAC28089.2.

Mutation FecGH (G8) occurs within the sequence responsible for coupling a protein to the receptor and is a missense mutation. As a result, synthesized protein exhibits less affinity for the cell surface receptor. Ewes with one copy of the gene with FecGH mutation have higher ovulation level. Early maturation of small secondary follicles, inhibition of their growth and earlier ovulation of a larger number of oocytes were noted [21]. Most likely, early maturation of the developing follicles is associated with inhibition of FSH receptor expression at mRNA level due to the absence of biologically active GDF9 [19]. The fact that the FecGH mutation determines the decrease in quantity of active form of GDF9 was confirmed by immunization of ewes, which caused increase in ovulation level [30]. Presence of FecGH resulted in increased litter size in Belclare sheep, from 1.98 in animals lacking the mutation to 2.67 lamb/litter in heterozygotes; for Cambridge sheep, the litter size surged from 2.27 to 4.28 lamb/litter.

Phenotypic effect similar to FecGH was observed for FecGT mutation in Icelandic Thoka sheep breed [40].

The results of research conducted on Brazilian Santa Ines breed indicate that presence of a mutation called FecGE (Embrapa) in GDF9 gene has a completely different phenotypic effect than the mutations in the locus of this gene listed above, because ewes with identified two copies of the gene are prolific [41].

2. Genes determining litter size in Olkuska sheep

2.1. Mutations in the BMP15 gene

Analysing reasons behind high fertility of the prolific Olkuska sheep breed, neither FecXI mutation in BMP15 gene nor FecBB mutation in gene BMPR‐1B was identified [42]. However, a number of new mutations were detected in the BMP15 gene locus: A77A, L110L, P101, V135G [27] and N237K and N337H, defined as FecXO (synonyms: N69H or A1009C or p.Asn69His) (Table 3) [27, 43].

Substitution of N237K was identified outside the coding region of mature peptide in most studied ewes, and no connection with their fertility was demonstrated. FecXO was located in exon 2, in the coding sequence of mature protein (position 69 aa), right next to the sites of the mutations FecXI, FecXH, FecXL and FecXB found, respectively, at positions 39, 23, 53 and 99 aa of mature protein.

Two alleles (A and C) and three genotypes (AA, AC and CC) were found for the A1009C mutation identified in the sequence encoding BMP15 mature protein. The C allele (with N337H mutation) had a frequency of 0.55 and ewes with one (AC) and two (CC) copies of the gene constituted 56 (AC) and 27% (CC) of the animals, respectively [43].

2.1.1. Effects of N337H mutation on litter size of Olkuska sheep

Analysis of effects of mutation N337H on litter size of ewes showed a significant impact of polymorphism on prolificacy, which in sheep of genotype FecX++ was 1.74 ± 0.55 lamb/litter, with 2.47 ± 0.77 and 2.98 ± 1.50 lamb/litter for FecX+O and FecXOO genotypes, respectively [43]. Very similar results showed Demars et al. [27] for genotypes FecX++, FecX+O and FecXOO namely, 1.84, 2.46 and 3.05, respectively.

Changes in litter size in subsequent lambings of Olkuska ewes show an increase in fecundity correlated with increasing age of a mother. The maximum size of litter in FecXOO ewes was noted in their third lambing, with ewes giving birth to an average of 3 lambs/litter. However, for mothers with genotype FecX++, litter size continued to increase up to their fourth lambing, when the litter size reached 2.25 lambs [43]. Increase in the number of lambs in the first three consecutive lambings, and then subsequent decrease in litter size has been demonstrated in studies on other highly prolific sheep breeds. Liu et al. [44] showed that average litter size for FecBBB homozygotes in small‐tail Han sheep was 2.47 in the first lambing of an ewe, and 3.17 for older mothers. Increase in litter size as ewes were aging was also observed in Chinese Hu breed. Carriers of FecB gene bore an average of 1.92 lamb/litter in their first lambing, compared to 2.56 lamb in the third lambing [45]. The number of lambs in a litter was also positively affected by the number of prior lambings, an ewe has undergone in hybrids Garole × Marpura; heterozygous mothers gave birth into 1.51 ± 0.06, 1.55 ± 0.07, 1.70 ± 0.09 lamb/litter in their first, second and third lambing, respectively [46].

2.1.2. Litter size in Olkuska sheep population

In all herds of sheep breeds with a segregating major gene, distribution of litter size similar to the one determined in Olkuska sheep, that is, with high proportion of twin births and large share of triplets and larger litters, was determined. Distribution analysis of litters of Olkuska ewes showed that 29% of FecXOO mothers gave birth to four or more lambs in a litter, including sextuplets and septuplets. In the most numerous group of FecX+O ewes, only 14% of animals showed similar litter size, and among sheep of genotype FecX++ no litters of such size were observed (Table 4).

VariantBase changeCoding base (bp)Coding residue (bp)Amino acid changeReference

Table 3.

Mutations identified in Olkuska sheep in the BMP15 gene.

Gene/genotypeLitter size of ewes (lambs)
12345, 6, 7
BMP15 gene‐N337H (%)
FecX++ (AA)3751.811.2
FecX+O (AC)15.640.829.88.35.2
FecXOO (CC)18.623.928.39.719.4
GDF9 gene‐V371M (%)
GDF9 gene-V332I (%)

Table 4.

Percentage of litter types of ewes with N337H (BMP15 gene) and V371M, V332I (GDF9 gene) mutations.

In the case of FecX++, the proportion of triplets was also only 11.2% [43]. A much smaller share of quadruplet and lager litters was found in Javanese FecBBB ewes (16%) [8]. The most common litter sizes in Garole FecBB+ sheep were twins, single births and triplets; accounting for, respectively, 65, 21 and 5% of the total [47]. In turn, share of quadruplet and triplet litters in FecBBB ewes of Javanese breed was, 34 and 20%, respectively, with an average litter size of 2.5 lamb/litter [48]. Interestingly, in the flock of Olkuska sheep, for mothers with genotypes FecXOO and FecX+O singleton births were twice less frequent than for FecX++ ewes (16 vs. 33%). Share of twin births decreased along with appearance of additional alleles with the mutation; among FecX++ewes they accounted for 55% of litters, and for genotype FecXOOonly for 27%. In the population of Olkuska sheep with average annual lamb production of 218%, the distribution of litters of various sizes was: 21.7% of singletons, 41% of twins, 24.6% of triplets and 12.7% of quadruplets and larger. Thus, the share of litters larger than triplet is as high as 37.1%. In Garole sheep, characterized by slightly lower prolificacy (168–187%), the proportion of mothers with twins, triplets and quadruplets was 65, 21 and 5%, respectively [6]. Similar differences in distribution of litter size were observed in a herd of Chevoit‐Thoka sheep [49]. With an average litter size of 2.23 lamb/litter, the authors found similar share of twin litters (56.5%) in this population, but noted a much smaller share of births with quadruplet and larger litters (3.1%). High frequency of twin births, reaching 47% of the studied population, was demonstrated in Thoka‐Chevoit sheep; this breed was also characterized by a high share of singleton births (35%) [50]. A much smaller share of multiple births in comparison with data collected for Olkuska sheep was demonstrated in Aragonese breed with 120–150% fecundity: 66.4% of singleton litters, 28.4% of twin ones, but only 1.9% of triplets. It should be noted that among more than 2000 ewes studied, only three gave birth to quadruplets and only one to quintuplets. For sheep lacking the FecXR mutation, only singleton births were noted [26].

2.1.3. Effect of mutation N337H on litter size

In studies on effects of mutation N337H (FecXO) on litter size, it was shown that the effect on ovulation levels in O+ and OO ewes was an increase of +2 and +3.3 CL [27]. Effect of the O+ copy of the gene was measured at +0.73 lamb, with the effect of two copies of the gene estimated at +1.07 lamb/litter. Analysing litter size over three first lambings of an ewe, the effect on O+ ewes was +0.62 lamb/litter, and +1.07 lamb for the OO genotype (Table 5) [43].

Litter size of ewesGenotype BMP15 (N337H)Mutation effect [43]
Reproductive life span1.742.472.98O+: +0.73
OO: +0.34
Lambings: I–III1.742.362.81O+: 0.62
OO: +0.45
I1.762.362.51O+: +0.60
OO: +0.15

Table 5.

Estimated mutation effect for number of lambs born to ewes.

Comparative analysis carried out on the basis of studies by many authors between litter size for carriers of one copy of the gene versus wild sheep genotypes for populations with a major segregating gene revealed that the data vary depending on breed, age and environment. In the presence of one copy of the gene (FecBB+), effect varies from +0.48 in Booroola × Dorset hybrids in Australia [5] to +1.16 lamb/litter for offspring of Booroola × Romney and Booroola × Perendale hybrids in New Zealand [51]. Ewes with two copies of the gene had litters larger by +0.64 lamb for the Israeli Affec × Awassi hybrids, +1.61 for Chinese Merino meat strain [52, 53]. Garole × Malpura ewes of genotypes FecBB+ and FecBBB gave birth to, on average, 1.73 and 2.17 lamb, respectively, while litter size of FecB++ sheep was 1.03 lamb. Litter size for FecBB+ and FecBBB ewes compared to sheep of FecB++ genotype was higher by +0.70 and +1.14, respectively. The effect of one copy of the gene was increasing in consecutive lambings, from +0.52 in the first lambing to +1.03 in the ewes’ third lambing [46, 54].

2.2. Mutations in the gene GDF9

Identification of variations in the gene sequence of GDF9 revealed presence of point mutations G3, G5, G6 and G7—detected in 2004 in Belclare and Cambridge sheep by a team led by Hanrahan et al. [21]—also in Olkuska sheep (Table 6).

MutationBase changeCoding base (bp)Coding residue (bp)Amino acid change (aa)Reference

Table 6.

Mutations identified in Olkuska sheep in the GDF9 gene.

Presence of FecGH (G8) mutation was excluded [43]. Thus, the Polish Olkuska breed can be classified as one of the few breeds in the world, where presence of polymorphisms has been confirmed both in the gene BMP15 and the autosomal gene. Next to the N337H mutation in BMP15 gene, missense mutations V371M (G7) and V332I (G6) have been identified in the region encoding mature protein GDF9. It should be noted that in Olkuska sheep, the allele with mutation V371M occurs with very low frequency of 0.06, but GA heterozygotes demonstrate high annual lamb production of 346%, with the same for GG ewes at 236% (Table 7) [43].


Table 7.

Allele and genotype frequencies in the population of Olkuska sheep, (mutations V371M, V332I) in GDF‐9 gene.

Analysis of litter size distribution in sheep with GG and GA genotypes in the locus V371M (G7) revealed that the most frequently occurring litter size in GG ewes was twins (40.6%), followed by singletons (20.8%). Litters of quadruplets and larger accounted for 11.8% of all births. Among mothers with identified one allele with the GA mutation, the share of twin litters was twice smaller (20%), while litters with four and more lambs accounted for almost 50%. The share of single births was only 8.3% [43].

Also mutation V332I (G6) was found to be present in Olkuska sheep; with two alleles (G and A) and three genotypes (GG, AG and AA) found (Table 7).

The G allele appeared with a very high frequency of 0.84, and ewes of genotype GG accounted for 70% of all animals. Mothers with the GG genotype did not differ in average litter size from GA sheep, both over total duration of their productive life (2.24 ± 0.87 vs. 2.13 ± 0.91 lamb), and in the first three lambings (2.39 ± 0.90 vs. 2.30 ± 0.87) [43].

2.2.1. Effect of mutation V371M (G7) on litter size

Ewes with one allele with V371M substitution showed an increase in litter size of +0.55 lamb, while those with the V332I mutation showed a decrease of 0.18 lamb/litter [43]. Thus, only in the presence of the A allele, the mutation V371M resulted in an increase in litter size. Mutations described earlier by Hanrahan et al. [21], namely: G3, G4, G5 and G6 were also detected in the case of Olkuska breed. However, impact of these mutations on prolificacy of ewes has not been studied.

In ewes of the Brazilian breed Santa Ines, a mutation that does not cause infertility has been identified in gene GDF9. Melo et al. [55] and Silva et al. [41] identified substitution F345C (FecGE) to a significant degree determining fecundity of sheep. Alleles FecG+ and FecGEof frequencies 0.48 and 0.52, and genotypes FecG++, FecG+E and FecGEE with frequencies 0.17, 0.61 and 0.22, respectively, have been identified. Association between the genotype and level of ovulation and litter size has been confirmed. FecGEE ewes bore an average of 1.78 lambs/litter, FecG+E sheep 1.44 and FecG++ mothers 1.13 lambs/litter. Level of ovulation in FecGEE ewes (2.22 ± 0.12) was 82% higher than that observed for the FecG++ genotype. No statistically significant difference was identified between FecG+E heterozygotes and FecG++ ewes (1.34 ± 0.08 vs. 1.22 ± 0.11). As concerns litter size distribution, share of twin litters for ewes with the identified three genotypes was 44 and 12% for FecGEE and FecG+E ewes, respectively, while no twin litters were noted for FecG++ sheep [41].

Presence of the mutation G1 was also confirmed in Iranian Moghani and Ghezel breeds. Presence of three possible genotypes was identified, and all the ewes were fertile. Infertility was found in only one sheep, carrying also an additional copy of the gene FecXG in gene BMP15. Ewes with heterozygous genotype were more prolific compared to those with wild sheep genotype. Share of twin litters was small (6.3%) also among animals with the wild sheep genotype, while among heterozygotes twin births amounted to as much as 53.8%. Four homozygotic mothers with two copies of the gene G1 were fertile, but gave birth to singletons [56]. Mutation G1 was als identified in Indian Garole sheep, and frequency of the wild allele and of that carrying G1 mutation was, G‐0.82 and A‐0.18, respectively, with respective genotype frequency of 0.64 for GG and 0.36 for AG ewes [57]. Also in this case, presence of genotype with two copies of the AA gene was not detected. Mutation in the gene GDF9 was accompanied by the presence of FecB gene. In Chinese breeds, similar to the case of Olkuska sheep, several mutations in several different genes have been identified. In addition to gene FecB, also presence of mutations G2 (C471T) [58], and G3 (G477A) was revealed. Entirely new mutations G729T (Q243H) and T692C [59] were identified. The authors, however, found no impact of G3 on the number of lambs bore by ewes. While identifying mutation G729T outside the region coding mature protein, the researchers have found the allele T (0.091) as well as genotypes GG and GT (respective frequency of 0.817 and 0.183). In GT ewes, estimated litter size was 2.88 ± 0.19, while for GG sheep, it was only 2.11 ± 0.11. Effect on litter size was also recorded for the T692C mutation, where litters of CC mothers were larger by 0.63 lamb than litters of CG ewes [59]. In Hu sheep, A154G mutation at position 51 of the amino acid located outside the region coding mature protein GDF9 (Asn51Asp) was identified [60].

3. Effect of N337H and V371M (G7) mutations on litter size

Determining effect of simultaneous presence of N337H (A1009C) and V371M (G7) mutations on fertility of Olkuska breed ewes showed that the largest number of lambs was born to FecXOO mothers that were carriers of V371M mutation (3.32 ± 0.26 lamb/litter) (Table 8).

TraitCombined genotype in BMP15 and GDF9 loci
Litter size of ewes (LSM ± SE) (reproductive life span)1.64 ± 0.112.26± 0.082.56 ± 0.192.64 ± 0.083.32 ± 0.26

Table 8.

Estimated effect of N337H mutation in the BMP15 gene and V371M mutation in the GDF9 gene on number of lambs born to Olkuska ewes (combined genotype) [43].

Effect of presence of both the allele N337H and V371M in ewes was similar to how presence of two copies of gene N337H affected the sheep, and amounted to +0.92 lambs/litter [43].

Studies conducted so far on interaction and potential interdependencies between different mutations within the loci of genes encoding transforming growth factors TGF‐β have shown that presence of one copy of the gene with a mutation in the locus of BMP15 led to an increase in litter size; the result was sterilization in the case of homozygous genotype with two copies of the gene. This issue has thus far been researched only within a very narrow range. Presence of several alleles of various genes in the same animal was demonstrated by Hanrahan et al. [21] and Davis et al. [42], sheep carrying a copy of both FecXB and FecXGor FecXH and FecXI were infertile. Sheep carrying one copy of any of the above mutations on chromosome X and the mutation FecB (BMPR‐1B) had fully functional ovaries and ovulation levels higher than observed when these factors were occurring independently. The effect of simultaneous presence of one copy of FecX in BMP15 and one copy of FecGH (GDF9) was varied. Most observations showed that the effect of these two genes was additive, but in some cases the demonstrated impact of GDF9 was weakened when the FecX mutation was present alongside it. Estimated effect on level of ovulation due to the presence of FecXG in Belclare and Cambridge sheep amounted to 0.77 and 1.18 CL, respectively, while presence of FecXB in Belclare sheep resulted in 2.38 CL. The effect of carrying one copy of FecGH in Belclare and Cambridge ewes was much higher, and amounted to 1.79 and 2.35 CL, respectively. Generally, it can be assumed that the average stimulating effect on level of ovulation in case of mutations FecXG, FecXB and FecGHwas 0.70, 0.97 and 1.39 CL, respectively. Simultaneous appearance of different copies of a gene with a mutation in one animal resulted in a much greater increase in the observed number of corpora lutea in the ovaries. In sheep with genotypes FecGH/FecXG and FecGH/FecXB, the number of ovulatory follicles was 5.8 and 6.09, respectively, while for carriers of only one copy of the gene FecXG it was estimated at 2.69 CL, with 3.26 CL for FecXB ewes, and 2.67 CL for FecGH genotype [21]. Presence of FecXI and FecB genes in ewes resulted in high level of ovulation (4.4 CL), suggesting multiplicative effect of these mutations resulting from interactions between the genes BMP15 and BMPR‐1B [20].

4. Effect of N337H, G6 and G7 mutations on body weight

Mutations N337H, G6 and G7 detected in Olkuska sheep have no effect on body weight at 2, 28 and 56 days after birth [43]. These results are consistent with observations conducted for sheep breeds with the major gene FecB, such as hybrids Rambouillet × Booroola [61]. No effect of FecB on body weight at birth and weaning was identified for this population. Also, Kleemann et al. [62] and Abella et al. [63] found no impact of FecB on body weight and daily gains in the initial period of a lamb’s life. Visscher et al. [64] identified the weak effect of the gene FecB on initial and final body weight of lambs from 7 to 12 weeks of age in Booroola × Texel hybrids. In contrast to these observations, in nine breeds of Chinese sheep with FecB gene, its significant impact on litter size, body weight and body size has been identified. On day 90 after birth, the body weight of lambs with genotypes FecBBB and FecBB+ was higher than those of lambs with the genotype FecB++. However, these differences were age dependent and have not been detected with respect to weight measured at 2 and 120 days of age [45]. Gootwine et al. [65] have demonstrated lower body weight in lambs that were carriers of FecBB+ gene compared to FecB++ lambs that did not carry the mutation. Body weight at birth for lambs with various genotypes, but from the same birth type differed significantly; FecBBB lambs compared to FecB++ and FecBB+ ones had lower body weight. Comparing weight of Assaf breed sheep with different genotypes, lower body weight was identified in the case of lambs with two copies of the gene FecB [66]. Studies on Garole‐Malpura sheep aimed at assessing the impact of FecB genotype on body weight have shown that this gene significantly affects body weight at birth and at 12 months of age, as well as weight gains up to 3 months of life of a lamb. There was no effect on body weight at 3 and 9 months of age [46].

5. G617A polymorphism in inhibin‐α gene (INHA)

Proteins encoded by the genes GDF9 and BMP15, necessary for an oocyte to gain cytoplasmic maturity, are a group of more than 35 proteins in the transforming growth factor β family. Inhibin A and B is one of these proteins. A missense‐type substitution 617G > A—not causing amino acid substitution of proline—was identified in Olkuska sheep in exon 2 of the inhibin‐α gene (INHA) [43]. The highest frequency was found for allele G (0.86) and genotype GG (0.71), and no ewes with genotype AA were identified. No effects of the mutation on litter size were determined; while the difference between mothers of GG and AG genotypes did indeed amount to +0.3 lamb/litter, it was not statistically significant. The impact of the mutation was dependent on the age of the animals, and for an ewe’s first litter was only +0.1 lamb. This result confirms conclusions from other studies, which demonstrated the association among INHA, INHBA and INHBB and litter size of sheep [67]. Influence of variation in the inhibin gene on litter size of Merino and Friesian sheep at the level of, respectively, +0.04 and +0.09 lamb had been demonstrated previously [68]. The effect of TaqI/INHA polymorphism on the number of offspring has also been confirmed for Merino, East‐Friesian and Romanowska breeds [69]. After comparing frequency of allele A in sheep with varying prolificacy, the above authors found that with increasing fertility, an increase in the frequency of allele A could be observed as well. Ovis ammon and Ovis vignei presented only allele B, while high frequency of allele A (0.65) has been determined in romanowska sheep. Studies in fecund small‐tail Han and Hu breeds, as well as in low fecundity breeds Dorset, Texel and German Mountain Merino showed presence of polymorphism in the locus of inhibin βB A276G, in the untranslated region 3′‐UTR, only in Hu sheep. Presence of genotypes AA, AB and BB with respective frequencies of 0.636, 0.046 and 0.318, as well as alleles A (0.659) and B (0.341), has been identified. Evaluation of genotype influence on litter size of Hu ewes showed that sheep with genotype BB gave birth to +0.58 lambs more than sheep with AA genotype [59].

6. Conclusions

To summarize, Olkuska sheep are among the few breeds with significant polymorphisms in genes coding proteins of the TDF‐beta family. Fecundity of this breed is determined not only by the presence of major gene FecXO (N337H,1009 > C) in BMP15 locus, but also by the presence of a missense mutation V371M (1111G>A) in the gene locus of GDF9. Considerable polymorphism in GDF9 locus —where three other, low‐frequency mutations G3, G5 and G6 can be found—is particularly noteworthy. Ewes of Olkuska breed are highly prolific, both in the case of carriers as well as FecXOO animals, in contrast to sterilization observed in the majority of known homozygotes with mutations in the BMP15 gene. Research in genes determining prolificacy is an important factor for increasing fecundity of ewes and thus profitability of sheep production as well.


This work was supported by projects DS/KBZ/3242/2017.


1 - Davis GH. Fecundity genes in sheep. Animal Reproduction Science. 2004;82–83:247–253
2 - Drouilhet L, Lecerf F, Bodin L, Fabre S, Mulsant P. Fine mapping of the FecL locus influencing prolificacy in Lacaune sheep. Animal Genetics. 2009;40(6):1–9
3 - Feary ES, Juengel JL, Smith P, French MC, O’Connel AR, Lawrence SB, Galloway SM, Davis GH, McNatty KP. Patterns of expression of messenger RNAs encoding GDF9, BMP15, TGFBR1, BMPR1B and BMPR2 during follicular development and characterization of ovarian follicular populations in ewes carrying the Woodlands FecX2W mutation. Biology of Reproduction. 2007;77:990–998
4 - Davis GH, Montgomery GW, Allison AJ, Kelly RW, Bray AR. Segregation of major gene influencing fecundity in progeny of Booroola sheep. New Zealand Journal of Agricultural Research. 1982;25:525–529
5 - Fogarty NM. Enviromental modulation of FecB expession. Use of the FecB (Booroola) gene in sheep breeding programs. In: Proceedings of International Workshop ACIAR; 11–12 November 2008; Maharashtra. India, Pune: ACIAR; 2009;133. pp. 66–69.
6 - Fhamy MH, Mason IL. Less known and rare breeds. In: Fahmy MH, editor. Prolific Sheep. Willingford, UK: CAB International; 1996. pp. 178–186
7 - Feng W, Ma Y, Zhang Z, Zhou D. Prolific breeds of China. In: Fahmy MH, editor. Prolific Sheep. Willingford, UK: CAB International; 1996. pp. 146–151
8 - Inounu I, Iniguez L, Bradford GE, Subandriy O, Tiesnamurti B. Production performance of prolific Javanese ewes. Small Ruminant Research. 1993;12:243–257
9 - Singh RV, Sivakumar A, Sivashankar S, Das G. Evaluation of the Booroola FecB gene in Muzaffarnagari sheep. In: Proceedings of International Workshop ACIAR; 11–12 November 2008; Maharashtra. India‐Pune: ACIAR; 2009;133. pp. 223–224
10 - Monget P, Fabre S, Mulsant P, Lecerf F, Elsen JM, Mazerbourg S, Pisselet C, Monniaux D. Regulation of ovarian folliculogenesis by IGF and BMP system in domestic animals. Domestic Animal Endocrinology. 2002;23(1–2):139–154
11 - Fabre S, Pierre A, Mulsant P, Bodin L, Di Pasquale E, Persani L, Monget P, Monniaux D. Regulation of ovulation rate in mammals: Contribution of sheep genetic models. Reproductive Biology and Endocrinology. 2006;4:20
12 - Montgomery GW, Galloway SM, Davis GH, McNatty KP. Genes controlling ovulations rate in sheep. Reproduction. 2001;121:843–852
13 - Moore RK, Shimasaki S. Molecular biology and physiological role of the oocyte factor BMP15. Molecular and Cellular Endocrinology. 2005;234:67–73
14 - Yan C, Wang P, DeMayo J, DeMayo FJ, Elvin JA, Carino C, Prasad CV, Skinner SS, Dunbar BS, Dube JL, Celeste AJ, Matzuk MM. Synergistic roles of bone morphogenetic protein 15 and growth differentiation factor 9 in ovarian function. Molecular Endocrinology. 2001;15(6):854–866
15 - Rybak‐Krzyszkowska M, Grzyb A, Milewicz T, Krzaczkowska‐Sendrakowska M, Krzysiek J. Primary ovarian insufficiency in infertility clinic. Polish Journal of Endocrinology. 2004;6:766–768
16 - Otsuka F, Yamamoto S, Erickson GF, Shimasaki S. Bone morphogenetic protein‐15 inhibits follicle‐stimulating hormone (FSH) action by suppressing FSH receptor expression. The Journal of Biological Chemistry. 2001;276:11387–11392
17 - Moore RK, Erickson GF, Shimasaki S. Are BMP15 and GDF9 primary determinants of ovulation quota in mammals? Trends in Endocrinology and Metabolism. 2004;15:356–361
18 - Shimasaki S, Moore RK, Otsuka F, Erickson GF. The bone morphogenetic protein system in mammalian reproduction. Endocrinology Reviews. 2004;25:72–101
19 - McNatty KP, Smith P, Moore LG, Reader K, Lun S, Hanrahan JP, Groome NP, Laitinen M, Ritvos O, Juengel JL. Oocyte‐expressed genes affecting voulation rate. Molecular and Cellular Endocrinology. 2005;234:57–66
20 - Carabatsos MJ, Sellitto C, Goodenough DA, Albertini DF. Oocyte‐granulosa cell heterologous gap junctions are required for the coordination of nuclear and cytoplasmic meiotic competence. Developmental Biology. 2000;226:167–179
21 - Hanrahan JP, Gregan SM, Mulsant P, Mullen M, Davis G, Powell R, Galloway SM. Mutations in the genes for oocyte‐derived growth factors GDF9 and BMP15 are associated with both increased ovulation rate and sterility in Cambridge and Belclare sheep (Ovis aries). Biology of Reproduction. 2004;70:900–909
22 - Davis GH, Bruce GD, Dodds KG. Ovulation rate and litter size of prolific Inverdale (FecI) and Hanna (FecXH) sheep. Proceedings of Association for the Advancement of Animal Breeding and Genetics. 2001;14:175–178
23 - Shackell GH, Hudson NL, Heath NL, Lun S, Shaw L, Condell L, Blay LR, McNatty KP. Plasma gonadotropin concentrations and ovarian characteristics in Inverdale ewes that are heterozygous for major gene FecXI on the X chromosome that influences ovulation rate. Biology of Reproduction. 1993;48:1150–1156
24 - Bodin L, Di Pasquale E, Fabre S, Bontoux M, Monget P, Persani L, Mulsant P. A novel mutation in the bone morphogenetic protein 15 gene causing defective protein secretion is associated with both increased ovulation rate and sterility in Lacaune sheep. Endocrinology. 2007;148(1):393–400
25 - Bodin L, Lecerf F, Bessicre M, Mulsant P. Features of major genes for ovulation in the Lacaune population. In: Proceedings of the 8th World Congress on Genetics Applied to Livestock Production WCGALP, Belo Horizonte; 13-18 August 2006, Belo Horizonte, MG, Brazil; 2006; 04–04. pp. 1–4.
26 - Monteagudo LV, Ponz R, Tejedor MT, Laviña A, Sierra I. A 17 bp deletion in the Bone Morphogenetic Protein 15(BMP15) gene is associated to increased prolificacy in the Rasa Aragonesa sheep breed. Animal Reproduction Science. 2009;110:139–146
27 - Demars J, Fabre S, Sarry J, Rossetti R, Gilbert H, Persani L, Tosser‐Klopp, Mulsant P, Nowak Z, Drobik W, Martyniuk E, Bodin L. Genome‐wide association studies identify two novel BMP15 mutations responsible for an atypical hyperprolificacy phenotype in sheep. PLos Genetics. 2013;9(4):e1003482. DOI: 1010.1371/journal.pgen.1003482
28 - Vacca GM, Dhaouadi A, Rekik M, Carcangi, Pazzola M, Dettori ML. Prolificacy genotypes at BMPR 1R, BMP15 and GDF9 genes in North African sheep breeds. Small Ruminant Research. 2010;88:67–71
29 - McNatty KP, Galloway SM, Wilson T, Smith P, Hudson NL, O’Connell A, Bibby AH, Heath DA, Davis GH, Hanrahan JP, Juengel JL. Physiological effects of major genes affecting ovulation rate in sheep. Genetique Selection Evolution. 2005;37:25–38
30 - Juengel JL, Hudson NL, Heath DA, Smith P, Reader KL, Lawrence SB, O’Connell AR, Laitinen MPE, Cranfield M, Groome NP, Ritvos O, McNatty KP. Growth Differentiation Factor 9 and one Morphogenetic Protein 15 are essential for ovarian follicular development in sheep. Biology of Reproduction. 2002;67:1777–1789
31 - Elvin JA, Yan Ch, Wang P, Wolfman NM, Matzuk MM. Paracrine actions of growth differentiation factor‐9 in the mammalian ovary. Molecular Endocrinology. 1999;13:1035–1048
32 - Hayashi M, McGee EA, Min G, Klein C, Rose UM, Duin M, Hsueh AJW. Recombinant growth differentiation factor‐9 (GDF9) enhances growth and differentiation of cultured early ovarian follicles. Endocrinology. 1999;3:1236–1244
33 - Gilchrist RB, Ritter LJ, Cranfield M, Jeffery LA, Amato F, Scott SJ, Myllymaa S, Kaivo‐Oja N, Lnakinen H, Mottershead DG, Groome NP, Ritvos. Immunoneutralization of growth differentiation factor 9 reveals it partially account for mouse oocyte miogenic activity. Biology of Reproduction. 2004;71:732–739
34 - Bodensteiner KJ, McMNatty KP, Clay CM, Moeller CL, Sawyer H. Expression of growth differentiation factor‐9 in the ovaries of fetal sheep homozygous or heterozygous for the Inverdale Prolificacy Gene (FecXI). Biology of Reproduction. 2000;62:1479–1485
35 - McNatty KP, Moore LG, Hudson NL, Quirke LD, Lawrnce SB, Reader K, Hanrahan JP, Smith P, Groome NP, Laitinen M, Ritvos O, Juengel JL. The oocyte and its role in regulating ovulation rate: a new paradigm in reproductive biology. Reproduction. 2004;128:379–386
36 - Teixeira Filho FL, Baracat EC, Lee TH. Aberrant expression of growth differentiation factor‐9 in oocytes of women with polycystic ovary syndrome. The Journal of Clinical Endocrinology and Metabolism. 2002;87:1337–1344
37 - Sadighi M, Bodensteiner KJ, Beattie AE, Galloway SM. Genetic mapping of ovine growth differentiation factor 9 (GDF9) to sheep chromosome 5. Animal Genetics. 2002;33:224–248
38 - Liao WX, Moore RK, Otsuka F, Shimasaki S. Effect on intracellular interactions on the processing and secretion of bone morphogenetic protein‐15 (BMP15) and growth and differentiation factor‐9—implication of the aberrant ovarian phenotype of BMP15 mutant sheep. The Journal of Biological Chemistry. 2003;278:3713–3719
39 - Liao WX, Moore RK, Shimasaki S. Functional and molecular characterization of naturally occurring mutation in oocyte‐secreted factors BMP15 and GDF9. The Journal of Biological Chemistry. 2004;279(17):17391–17396
40 - Nicol L, Bishop S, Pong‐Wong R, Bendixen Ch, Holm LE, Rhind SM, McNeilly MS. Homozygosity for a single base‐pair mutation in the oocyte‐specific GDF9 gene results in sterility in Thoka sheep. Reproduction. 2009;138:921–933
41 - Silva BDM, Castro EA, Souza CJH, Paiva SR, Sartori R, Franco MM, Azevedo HC, Silva TASN, Vieira AMC, Neves JP, Melo EO. A new polymorphism in the Growth Differentiation Factor 9 (GDF9) gene is associated with increased ovulation rate and prolificacy in homozygous sheep. Animal Genetics. 2011;42(1):89–92
42 - Davis GH, Galloway SM, Ross IK, Gregan SM, Ward J, Nimbkar BV, Ghalsasi PM, Nimbkar C, Gray GD, Subandriyo Inounu I, Tiesnamurti B, Martyniuk E, Eythorsdottir E, Mulsant P, Lecerf F, Hanrahan JP, Bradford GE, Wilson T. DNA tests in prolific sheep from eight countries provide new evidence on origin of the Booroola (FecB) mutation. Biology of Reproduction. 2002;66: 1869–1874
43 - Kaczor U. 2011. Identyfikacja markerów plenności owiec olkuskich na podstawie polimorfizmu genów kodujących białka z rodziny TGF‐β [tesis]. Uniwersytet Rolniczy w Krakowie. Zeszyty Naukowe 479; 2011
44 - Liu SF, Jiang YL, Du LX. Study of BMPR‐IR and BMP15 as candidate gene for fecundity in little tailed Han sheep. Acta Genetica Sinica. 2003;30(8):755–760
45 - Guan F, Liu SR, Shi GQ, Ai JT, Mao DG, Yang LG. Polymorphism of Fec B gene in nine sheep breeds or strains and its effects on litter size, lamb growth and development. Acta Genetica Sinica. 2006;33(2):117–124
46 - Kumar S, Mishra AK, Kolte AP, Arora AL, Singh D, Singh VK. Effects of the Booroola (FecB) genotypes on growth performance, ewe’s productivity efficiency and litter size in Garole x Malpura sheep. Animal Reproduction Science. 2008;105(3–4):19–31
47 - Kumar S, Mishra AK, Kolte AP, Dash SK, Karim SA. Screening for Booroola FecB and Galway FecXG mutation In Indian sheep. Small Ruminant Research. 2008;80:57–61
48 - Roberts VJ, Barth S, El‐Roeiy A, Yen SSC. Expression of inhibin/activin subunits and follistatin messenger ribonucleic acids and proteins in ovarian follicles and the corpus luteum during the human menstrual cycle. The Journal of Clinical Endocrinology and Metabolism. 1993;77:1402–1410
49 - Adalsteinsson S, Jonmundson JV, Eythorsdottir E. The high fecundity Thoka gene in Icelandic sheep. Proceedings of the 40th Meeting of the European Association for Animal Production; 27–31 August 1989. Dublin, Ireland: EAAP; 1989;1.pp. 61–62
50 - Walling GA, Bishop SC, Pong‐Wong R, Russel AJF, Rhind SM. Detection of a major gene for litter size in Thoka Cheviot sheep using Bayesian segregation analyses. Animal Science. 2002;75:339–347
51 - Meyer HH, Baker RL, Harvey TG, Hickey SM. Effects of Booroola merino breeding and the Fec(B) gene on performance of crosses with long wool breeds. 2. Effects on reproductive performance and weight of lamb weaned by young ewes. Lives Production Science. 1994;39:191–200
52 - Gootwine E, Reicher S, Rozov A. Prolificacy and lamb survival at birth in Awassi and Assaf sheep carrying the FecB (booroola) mutation. Animal Reproduction Science. 2008;108:402–411
53 - Guan F, Liu SR, Shi GQ, Yang LG. Polymorphism of FecB gene in nine sheep breeds or strains and its effects on litter size, lamb growth and development. Animal Reproduction Science. 2007;99:44–52
54 - Kumar S, Kolte A, Mishra AK, Arora AL, Singh V. Identification of Fecb mutation in Garolex Malpura sheep and its effect on litter size. Small Ruminant Research. 2006;64:305–310
55 - Melo EO, Silva BDM, Castro EA, Silva TASN, Paiva SR, Sartori R, Franco MM, Souza CJH, Neves JP. A novel mutation in the growth and differentiation factor 9 (GDF9) gene is associated, in homozygosis, with increased ovulation rate in Santa Ines sheep. Biology of Reproduction. 2008;78:371
56 - Barzegari A, Atashpaz S, Ghabili K, Nemati Z, Rustaei M, Azarbaijani R. Polymorphism in GDF9 and BMP15 associated with fertility and ovulation rate in Moghani and Ghezel sheep in Iran. Reproduction in Domestic Animals. 2010;45:666–669
57 - Polley S, De S, Brahma B, Mukherjee A, Vinesh PV, Batabyal S, Arora JS, Pan S, Samanta AK, Datta TK, Goswami SL. Polymorphism of BMPR1B, BMP15 and GDF9 fecundity genes in prolific Garole. Tropical Animal Health and Production. 2010;42:985–993
58 - Chang JT, Luo YZ, Hu J. Polymorphism of GDF9 as a candidate gene for fecundity in sheep. Journal of Gansu Agricultural University. 2009;44(2):30–33
59 - Chu M, Zhuang H, Zhang Y, Jin M, Di X, Cao G, Feng T, Fang L. Polymorphism of inhibin βB gene and its relation sheep with liter size in sheep. Animal Science. 2011;82:57–61
60 - Li BX, Chu MX, Wang JY. PCR‐SSCP analysis on growth differentiation factor 9 gene in sheep. Yi Chuan Xue Bao. 2003;30:307–310
61 - Willingham TD, Wardon DW, Thompson PV. Effect of FecB allele on birth weight and post‐weaning production traits of Rambouillet‐Booroola cross wethers. Texas Agriculture Experimental Station Research Report. Sheep and Goat, Wool and Mohair CpR; 2002. pp. 1–6.
62 - Kleemann DO, Ponzoni RW, Stafford JE, Cutten IN, Grimson RJ. Growth and carcass characters of South Australian Merino and its crosses with the Booroola and Trangie Fertility Merino. Australian Journal of Experimental Agriculture. 1985;25:750–757
63 - Abella DF, Cognie Y, Thimonier J, Seck M, Blank MR. Effects of the FecB gene on birth weight, postnatal growth rate and puberty in Booroola x Merinos d’Arles ewe lambs. Animal Research. 2005;54:283–288
64 - Visscher AH, Dijkstra M, Lord EA, Suss R, Rosler HJ, Heylen K, Veerkamp RF. Maternal and lamb carrier effects of the Booroola gene on food intake growth and carcass quality of male lambs. Animal Science. 2000;71:209–217
65 - Gootwine E, Braw‐Tal R, Shalhevet A, Bor A, Zenou A. Reproductive performance of Assaf and Booroola‐assaf crossbred ewes and its association with plasma FSH levels and induced ovulation rate measured at prepuberty. Animal Reproduction Science. 1993;31:69–81
66 - Gootwine E, Rozov A, Bor A, Richer S. Carring the FecB (Booroola) mutation is associated with lower birth weight and slower post‐weaning growth rate for lambs, as well as a lighter mature body weight for ewes. Reproduction Fertility and Development. 2006;18(4):433–437
67 - Hiendleder S, Lewalski H, Jaeger H, Pracht P, Erhardt G. Nucleotide sequence of ovine α‐inhibin (INHA) gene and evaluation of RFLP marker effects on reproductive performance. Animal Genetics. 1996;27(2):91–92
68 - Hiendleder S, Lewalski H, Jaeger H, Pracht P, Erhardt G. Genomic cloning and comparative sequence analyses of different alleles of the ovine βA inhibin/activin INHA gene as a potential QTL for litter size. Animal Genetics. 1996;27(2):119
69 - Leyhe B, Hiendleder S, Jaeger C, Wassmuth R. Pronounced differences in the frequency TaqIβA inhibin allele between sheep breeds with different reproductive performance. Animal Genetics. 1994;25(1):41–43