Booroola Gene Research Articles

Fecundity Booroola Gene (FecB) Polymorphism in some Indigenous Sheep Breeds in Iraq

Fecundity Booroola Gene (FecB) Polymorphism in some Indigenous Sheep Breeds in Iraq

Assessing the performance of Moghani crossbred lambs derived from different mating systems with Texel and Booroola sheep.

In our ongoing project, which focuses on the introgression of Booroola/FecB gene and the myostatin (MSTN) gene into purebred Moghani sheep, we assessed the performance of second-generation Moghani crossbreds such as second crossbreds (F2) and initial backcross generation (BC1). These crossbreds were generated through different mating systems, including in-breeding, outcrossing, first paternal backcrossing (PBC1), and first maternal backcrossing (MBC1). Notably, F2 strains exhibited lean tail, woolly fleece and a higher percentage of white coat color compared to BC1. The impact of mating systems and birth types on pre-weaning survival rates was found to be statistically significant (P < 0.0001), with singleton offspring resulting from paternal backcross showing a particularly substantial effect. The F2 crossbred lambs carrying the Booroola gene did not show a statistically significant difference in survivability compared to those carrying the MSTN gene, implying the Booroola prolificacy gene had no significant impact on survival outcomes. However, the occurrence of multiple births had a significant negative impact on lamb survival (P < 0.0001). The PBC1 sheep strains, specifically Texel Tamlet ram strains carrying the MSTN mutation, exhibited superior growth rates compared to others (P < 0.05). Interestingly, the MSTN mutation in the homozygous variant genotype significantly impacts growth rate before weaning compared to other genotypes and pure Moghani sheep (P < 0.05). In conclusion, this study objectively underscores the pivotal role of genetic factors, specifically through strategic mating systems like paternal backcrossing, in enhancing desired traits and growth rates in Moghani sheep, thereby contributing valuable insights to the field of sheep breeding programs.

Aspects of follicular and oocyte maturation that affect the developmental potential of embryos

The ability to mature, be fertilized and finally to develop into a viable embryo is acquired gradually by the oocyte during progressive differentiation throughout folliculogenesis. This process starts with oocyte growth during the first steps of follicular development. As the oocyte is close to its final size, other modifications occur, less spectacular but at least as important in determining the resulting ability of the oocyte to accomplish its reproductive purpose (developmental competence). These modifications, referred to as 'oocyte capacitation', are probably influenced by the follicle. The proportion of developmentally competent oocytes increases with follicular size. However, the relationship between follicular growth and oocyte competence is not very strict, since a given oocyte may acquire its competence at any stage of follicular growth and since some examples of functional disjunction between follicular size and oocyte competence are described. Follicular atresia may impair the acquisition of oocyte competence, as evidenced by the parallel study of follicular characteristics and of the developmental potential of their oocytes treated individually through in vitro maturation, fertilization and development. However, when atresia is experimentally induced in large preovulatory follicles, oocytes remain competent, indicating that once competence is acquired, it is no longer sensitive to atresia. Oocyte maturation represents only the end of this long and progressive process and validates the preparation of the oocyte by conferring its final developmental ability. As evidenced by recent cloning experiments, the cytoplasmic aspects of oocyte maturation are crucial for the acquisition of developmental competence. This cytoplasmic maturation may be activated in vitro by the use of complex media supplement (serum, follicular fluid) but the use of defined media for maturation allowed the identification of some active factors (such as epidermal growth factor, growth hormone, inhibin and activin). The study of some differential models of oocyte competence (follicular size and atresia, Booroola gene, prepubertal oocytes) will provide a better understanding of oocyte capacitation and maturation, and allow the improvement of in vitro methods for oocyte maturation, which represent the most limiting step of in vitro production of embryos in large mammals.

Booroola Gene (Fec B) Polymorphism and its Liaison with Litter Size in Indigenous Sheep Breeds of Telangana, India

The present study was aimed to find out the presence of Fec B gene in Deccani and Nellore with its association to litter size. From forty ewes of each Nellore and Deccani breed, having variation in litter size, blood was collected and genomic DNA extraction was done. Animals were screened by PCR-RFLP method for the presence of Fec B gene. Digestion of the Fec B gene 190 base pair with Ava II restriction enzyme resulted in separation of non-carrier (++) 190 bp band (wild type) and heterozygous carrier (B+) 160+190bp indigenous sheep. Frequency of Fec B gene polymorphism distributions was different among these breeds. Among the forty Nellore sheep blood samples, there was only one ewe with (BB) homozygous (160bp) genotype, five ewes with (B/+) heterozygous (160+190bp) genotype and thirty four ewes with (+/+) homozygous (190bp) genotype in Fec B loci. There was only five ewes with (B/+) heterozygous (160+190bp) genotype and thirty five ewes with (+/+) homozygous (190bp) genotype in Fec B loci and none of the individuals carried homozygous genotype for the Fec B gene in Deccani sheep. The average litter size of ewes with the homozygous Fec B (BB) gene was 2.0, heterozygous Fec B (Bb) gene was 1.4 and 1.2, respectively in Nellore and Deccani breeds and others were 1.0 in respective genotypes of both breeds. The study revealed the presence of Fec B gene in indigenous sheep breeds of Telangana, India having good association with litter size in both the breeds.

Detection of polymorphism in booroola gene and growth differentiation factor 9 in Lori sheep breed

Purpose: This study was carried out for detection of possible polymorphisms in Booroola gene (FecB) and growth differentiation factor 9 [GDF9] in Lori sheep breed. Methods: Blood samples were taken from the jugular vein of the sheep and their DNA content extracted using modified salting-out method. The quantity and quality of extracted DNA was examined by absorption spectrophotometry and gel electrophoresis. Using two pairs of specific primers, two DNA fragments were amplified from FecB (190 bp) and exon 1 of GDF9 (462 bp) genes. The polymerase chain reaction (PCR) products were digested using AvaII and HhaI restriction enzymes for FecB and GDF9 genes, respectively. Results: In FecB locus, two genotypes, viz, wild type (+/+) and carrier-mutants (B/+), were detected with genotype frequencies of 0.948 and 0.052, respectively. Also, at GDF9 locus, two genotypes, namely, wild type (+/+) and carrier-mutants (+/-), were detected with genotype frequencies of 0.67 and 0.33, respectively. Heterozygous genotype frequencies for both loci showed higher than homozygous genotypes. None of the sheep carried homozygous genotype for both of the FecB and GDF9 variants in this breed. Conclusion: The results of the present study reveal slight polymorphism in FecB and GDF9 loci of Lori sheep breed. Keywords: Polymorphism, Lori sheep, Booroola gene (FecB), Growth differentiation factor 9 (GDF9), Polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP), Genotype, Mutants, Loci

Investigation of the Booroola Gene in Egyptian Ewes with Different Reproductive Status Using PCR- RFLP

OVULATION CAN BE regulated by group of genes, termed as fecundity (Fec) genes. The aim of this study was to identify genetic polymorphism in Booroola (FecB) gene in Barki, Rahmani, and Ossimi sheep breeds with different physiological status diagnosed by ultrasound. Accordingly, animals were early classified into three groups: carrying single fetus, twin fetuses and non-pregnant by ultrasonographic examination. Demonstration of fetal number was available as early as Day 35-40 post-mating transrectally, and trans-abdominally then after. The fetal viability could be checked through heart examination with M-Mode. Genomic DNA was extracted from blood samples of total number of sheep and two primers were used to amplify 190 and 140 bp fragments of FecB gene. The amplified fragments were digested using AvaII restriction enzyme. All sheep groups were non carriers for the FecB mutation and gave a 190 bp band (++) and 140 bp band (Fec++) for primer 1 and 2, respectively.In conclusion,no genetic polymorphism was detected in the three Egyptian sheep breeds in relation to pregnancy with single or twin fetuses. The study could be continue to search for other major genes.

Increasing ewe genetic fecundity improves whole-farm production and reduces greenhouse gas emissions intensities: 1. Sheep production and emissions intensities

Greenhouse gas (GHG) emissions from livestock constitute the largest proportion of Australian agricultural GHG emissions, necessitating development of strategies for mitigating GHG emissions from the livestock sector. Here we simulate a self-replacing prime lamb enterprise to examine the effect of increasing ewe genetic fecundity on whole farm GHG emissions, animal production and emissions per animal product (emissions intensity; EI).Breeding ewes were a cross-bred genotype containing the Booroola (FecB) gene with average lambing rates of 1.5–2.0 lambs per ewe. Lambs were born in winter on pastures of phalaris, cocksfoot and subterranean clover, and were sold at the beginning of summer. Flock dynamics were simulated using the model GrassGro and whole-farm GHG emissions were computed using equations from the Australian National Greenhouse Gas Inventory.Increasing ewe fecundity from a baseline of 0.96–1.54 lambs per ewe reduced EI from 9.3 to 7.3t CO2-e/t clean fleece weight plus liveweight (CFW+LWT) and GHG emissions per animal sold by 32%. Increasing fecundity reduced lamb sale liveweights and increased lamb mortality rates at birth, but this was offset by an increase in total liveweight turnoff. Greater ewe fecundity increased whole-farm productivity without increasing GHG emissions. For the same stocking rate as an enterprise running genotypes with lower fecundity, high fecundity genotypes either increased annual production from 449 to 571kg CFW+LWT/ha with little change in net emissions, or reduced emissions from 4.2 to 3.2t CO2-e/ha for similar average productivity. In both cases, EI decreased by ca. 2.1t CO2-e/t CFW+LWT.A foremost advantage of using high fecundity breeds is greater intra-annual variation in flock number, because such genotypes give birth to more lambs. This necessitates a reduction in the number of adult breeding ewes to maintain average annual stocking rate and benefits whole farm emissions, because breeding ewes contribute the largest proportion of farm emissions (77–80%), particularly enteric methane. We conclude that increasing ewe fecundity offers a win–win opportunity for the sheep industry by allowing sustainable intensification through greater production and lower emissions intensity, without adversely affecting net farm emissions or increasing stocking rate. High fecundity genotypes also present an opportunity for sheep producers to reduce stocking rates while maintaining current levels of farm production, thereby reducing labour and flock nutritional requirements.

Increasing ewe genetic fecundity improves whole-farm production and reduces greenhouse gas emissions intensities: 2. Economic performance

Ewes with the fecundity Booroola (FecB) gene produce more lambs per ewe on average than ewes without the gene and offers a potential way to decrease greenhouse gas emissions (net and per unit animal product) without reducing lamb production if the lambs can be reared to market weights. Using a case study farm in south-west Victoria, a biophysical modelling study has previously showed that increased ewe fecundity from 1 to 1.5 lambs per ewe increased production by 27% and reduced net farm emissions by 21% for the same long-term stocking rate. In this study, a whole-farm economic analysis was used to investigate the relative merit of the same case study farm, with high-fecundity ewes, compared with a baseline system that represented a typical prime lamb enterprise in the region. An additional system comprising ewes with high fecundity at a lower stocking rate than the case study farm was also examined. The analysis was undertaken to establish which farm systems represented the most economically efficient use of all the resources that are employed over a run of years, and involved estimating the net present value of annual profits earned by the farm in each scenario, taking into account the total value of capital used. The potential revenue from the sale of carbon credits through the Carbon Farming Initiative was also investigated. After accounting for the additional costs involved, increasing ewe fecundity resulted in an increase in annual whole-farm profit compared with the baseline system, but risk, considered as the variability in farm profit, also increased. Decreasing stocking rate for the high-fecundity system reduced annual operating profit and net present value at a 5% discount rate, but had less risk compared with the higher stocking rate system. While both systems that incorporated high-fecundity ewes reduced greenhouse gas emissions, revenue from the sale of carbon credits was small compared with revenue from the sale of lambs, wool and culled ewes. Despite this, and assuming the required increases in fertility and weaning rates could be achieved consistently on-farm, ewes with high fecundity may offer producers the opportunity to increase production and profit as well as decrease greenhouse gas emissions.

Genetic Polymorphism in FecB Gene in Iraqi Sheep Breeds Using RFLP-PCR Technique

This study was conducted to identify polymorphism in Booroola gene (FecB) in five Iraqi sheep breeds (Hamdani, Karadi, Arabi, Naeimi and Awassi). About fifty mature ewes (Ten for each breed used as pooled samples) were genotype for the Booroola (BMPRIB) receptor. The polymerase chain reaction (PCR) was used for amplification of a fragment with 140 bp at this locus. For genotyping of individuals at Booroola locus, the resulted amplified fragments were digested using AvaII restriction enzyme. AvaII restriction enzyme was used to detect possible mutation (G|GACC). The results showed no differences in the band patterns of digested products only the wild type alleles (Fec++) were detected and all breeds for this locus were monomorphism. Considering the phenotypic records in these breeds, the result revealed that the genetic factor responsible for litter size is not related to report of Booroola major gene and research should continue to search for other major genes ( such as FecH, FecX and FecG) in these sheep breeds.

Application of PCR-RFLP technique to determine Booroola gene polymorphism in the Sangsari sheep breed of Iran

Phenotypic evaluation and the culling of candidate animals for traits by applying traditional animal breeding are usually costly tasks, which need to be carried out over a considerable span of time. The use of molecular genetics as an alternative method enables animal breeders to select eligible animals for the desirable trait, or traits, at earlier ages. Selection based upon markers could result in increased accuracy as well as a better selection response of animals. The Booroola gene has long been recognized as a candidate gene responsible for a higher rate of ewe ovulation, which results in increased litter size. In this study, blood samples were taken from 150 Sangsari sheep breed (140 ewes and 10 rams) in the Damghan animal breeding center using Venojects treated with an anticlot substance (EDTA). The sample DNA contents were salted out and extracted. After extraction, and after undertaking quantitative and qualitative tests (including spectrophotometry and gel agarose, 8%), the required amounts of DNA for polymerase chain reaction (PCR) were determined. Using the relevant primer, the related part was reproduced (190 bp) and then the PCR products were cut by AvaΠ enzymes for the gene, and 2 parts (30 bp and 160 bp) were produced for the target site. The results obtained in this study revealed that only the wild-type allele (+) was observed in the samples, indicating that, most likely, only genotype ++ was present in the population under consideration.

Prolificacy Detection in Egyptian Sheep using RFLP-Specific PCR

Booroola gene (FecB) was the first major gene for prolificacy identified in sheep. In this study twenty two (11 twin producing female, 7 single lamb producing female, and 4 male) crossbred sheep were tested for the presence of the FecB mutation of BMPR1B. The females were selected for their twin production in three repetitive production cycles while the males were selected for being produced from prolific females as above. Forced restriction PCR of the FecB gene, 190 base pair (bp) was amplified using specific primer designed to introduce a point mutation in the resulting PCR products with FecB carrier sheep containing an AvaII restriction site (G|GACC). The FecB DNA test showed that there were no carriers for the FecB mutation in the selected prolific sheep sample.

Distribution of prolific Garole sheep in West Bengal, India

The Garole is a prolific breed of sheep. High prolificacy in sheep carrying the Booroola gene (FecB) is the result of a mutation in bone morphogenetic protein receptor-IB (BMPR-IB) (Wilson et al., 2001a,b) which had previously been identified in Garole sheep from the Sunderban region of West Bengal (Davis et al., 2002) . There is evidence that the breed has originated from the sheep brought by the Tibetan traders and traded in the plains of Bengal during the seventeenth till the nineteenth century. The present study was carried out to remap the distribution of the Garole sheep within the state of West Bengal (India) using the presence of the BMPR-IB mutation in the sheep flocks reared at different locations within the state of West Bengal. The breeding tract of Garole sheep was initially thought to be in the districts of 24 Parganas, South and North alone. However, the results from the present study indicate that the sheep is also reared in the district of Midnapur (East), besides in Jalpaiguri and Cooch Behar districts situated in northern parts of the state. The results of the present study indicate that the breeding tract of Garole sheep extends up to Jalpaiguri and CoochBehar districts of West Bengal at 26°16′ and 27°0′ North latitude and 88°4′ and 89°53′ East longitude. This study also indicates that the ancestors of the Garole sheep have migrated from China/Tibet, during the trading between West Bengal and Bangladesh during the seventeenth century till the early-twentieth century.

Türkiye’de Yetiştirilen Altı Yerli Koyun Irkında BMPR-IB (Booroola) Geninde FecB Allel Varlığının PCR-RFLP Yöntemiyle Araştırılması

Türkiye’de Yetiştirilen Altı Yerli Koyun Irkında BMPR-IB (Booroola) Geninde FecB Allel Varlığının PCR-RFLP Yöntemiyle Araştırılması

A developing country perspective on recent developments in animal breeders and intellectual property rights

Animal breeding and genetics have changed markedly, resembling those that have already taken place in the plant sector. These changes are going to be larger with sequenced genomes, transgenic livestock and cloned animals. Animal scientists have now started to protect their intellectual property and these protective measures have alarmed other scientists and the public. The challenge for developing countries is to guard against bio-piracy of their indigenous animal genetic resources, and to safeguard technologies that they have been using. A second concern is the export of genetic material to countries that did not ratify the Convention on Biodiversity. The first operational conflict resulted from a patent on a “Method of Bovine Herd Management”. The patent claims rights to a practice that has been public knowledge for nearly 100 years. The novel idea within the patent is the specific mathematical model and procedures developed for analysis of test day yields. Monsanto has recently applied for a series of patents on pig breeding in some 160 countries, whereas researchers in New Zealand and Australia obtained a patent for the Booroola gene. The east African Boran cattle breed has also been patented in Australia. Currently developing countries risk losing their intellectual property on indigenous livestock while research institutions require a stable regulatory framework in which to operate. There should be a balance between the needs of developed and developing countries and interim measures should be put in place in anticipation of the development of a legal framework on animal genetic resources. Keywords : keyword; keyword; keyword South African Journal of Animal Science Vol. 36 (5) 2006: pp.22-25

Effect of gastrointestinal nematodes on ovulation rate of merino Booroola heterozygote ewes (FecBFec+)

Twenty-five multiparous Merino ewes, each carrying one copy of the Booroola gene (Fec B Fec + ), were divided into two experimental groups (Control, n = 13 and Challenged, n = 12). The treatments were applied in the autumn between 14 March and 21 May. The sheep in the Control group were dosed orally twice-weekly with 10 mL water, and dosed with Levamisole every 14 days. Each sheep in the Challenged group was dosed orally twice-weekly with 6000 nematode larvae in 10 mL water. Challenged sheep shed more eggs per gram of faeces, lost live weight (40 vs. 38.2) and lost body condition score (3.5 vs. 3.0 condition score) during the study compared with the Control sheep. While live weight, body condition and the number of developing follicles all decreased in association with a nematode larval challenge, the proportion of developing follicles which formed a corpora lutea were unaffected. Thus a larval challenge during joining with nematode larvae at doses comparable to those encountered under field conditions can be expected to affect subsequent lambing performance.

Foreword to the international workshop on major genes and QTL in sheep and goats

This is the third international meeting dealing with major genes in small ruminants. The first was held in Armidale (NSW, Australia) in 1980, just after the discovery of the Booroola gene by B. Bindon and L. Piper. The discovery of a gene having such a large effect on ovulation rate and prolificacy in sheep was totally unsuspected at this time and a number of research teams all over the world concentrated their efforts to study its effects and identify the causal mutation. About 20 years were finally needed to obtain this information, which opened a new approach to the physiological regulation of reproduction.The second meeting was organised in 1990 in Toulouse along the same lines. Although its main concern was the Booroola gene, other major genes influencing ovulation in sheep were also considered. Indeed, an increasing amount of evidence demonstrated that, on the contrary to the current opinion in quantitative genetics laboratories before 1980, prolificacy is not always controlled by a very large number of genes each exhibiting a very small effect, but may also be influenced by genes with large effects, generalising the Booroola situation to other populations.Since then, mixed inheritance was also found for other production traits such as body conformation, seasonality or milk composition. However, the major evolution has been the inexpensive large-scale access to molecular genetic information, using PCR, microsatellites and SNP technologies. QTL detection experiments are performed in all domestic species, including sheep and goats, and the identification of genes having an average effect on the performance trait variability is now possible. The utilisation of these polymorphisms should also be a great help for a better management of populations, either through the selection of breeders or through the preservation of genetic diversity.This third meeting on major genes and QTL in sheep and goats was a unique occasion for the researchers involved in this area of Animal Science to present their latest results, exchange their experiences and progress in the organisation of scientific co-operation.

Association between PrP genotypes and performance traits in an experimental Dutch Texel herd

The Dutch scrapie eradication programme for sheep is based on selection for the resistant ARR/ARR genotype of the ovine prion protein (PrP) gene. The aim of this study was to estimate the possible association of the PrP genotype and performance traits. The data included 963 genotyped females born between 1991 and 1998 in an experimental Texel flock, in which the Booroola gene was introgressed. The associations of the PrP gene were evaluated using a single trait animal model. The allele frequency from the herd mostly corresponds with genotyped rams in the Netherlands in the same period. The results indicate no significant associations with litter size, and only 3 of 112 estimated associations with weight, growth and body measurements were significant, with a low significance level. Therefore it can be concluded that selection for ARR/ARR rams in this experimental herd seem to have no effect on the performance traits due to association. The included data from this study is compared to data from other studies estimating associations between PrP genotype and performance traits. The comparison suggests of a possible small effect, which is only detectable in large datasets, which could be a result of linkage to the PrP genotype.

Foreword to the international workshop on major genes and QTL in sheep and goats

This is the third international meeting dealing with major genes in small ruminants. The first was held in Armidale (NSW, Australia) in 1980, just after the discovery of the Booroola gene by B. Bindon and L. Piper. The discovery of a gene having such a large effect on ovulation rate and prolificacy in sheep was totally unsuspected at this time and a number of research teams all over the world concentrated their efforts to study its effects and identify the causal mutation. About 20 years were finally needed to obtain this information, which opened a new approach to the physiological regulation of reproduction. The second meeting was organised in 1990 in Toulouse along the same lines. Although its main concern was the Booroola gene, other major genes influencing ovulation in sheep were also considered. Indeed, an increasing amount of evidence demonstrated that, on the contrary to the current opinion in quantitative genetics laboratories before 1980, prolificacy is not always controlled by a very large number of genes each exhibiting a very small effect, but may also be influenced by genes with large effects, generalising the Booroola situation to other populations. Since then, mixed inheritance was also found for other production traits such as body conformation, seasonality or milk composition. However, the major evolution has been the inexpensive large-scale access to molecular genetic information, using PCR, microsatellites and SNP technologies. QTL detection experiments are performed in all domestic species, including sheep and goats, and the identification of genes having an average effect on the performance trait variability is now possible. The utilisation of these polymorphisms should also be a great help for a better management of populations, either through the selection of breeders or through the preservation of genetic diversity. This third meeting on major genes and QTL in sheep and goats was a unique occasion for the researchers involved in this area of Animal Science to present their latest results, exchange their experiences and progress in the organisation of scientific co-operation.

Case study of a Hungarian breeding program using imported Booroola rams

Abstract. The first major gene for prolificacy identified in sheep was the Booroola (FecB) gene. Since the recognition of its existence, the Booroola Merino has spread all over the world. In Hungary, a new breed – called Hungarian Prolific Merino – had been established based on the crossing of Hungarian Merino ewes and Booroola Merino rams, and was acknowledged in 1992. The only way to determine the FecB genotypes has been the measurement of the ovulation rate over a long period. In 2001, the Booroola mutation was identified. Mutation on the bone morphogenetic protein receptor – 1B gene was found to be associated with the increased ovulation rate in the Booroola Merino ewes. 138 ewes and 46 rams in the Hungarian Prolific Merino population were tested for this mutation by PCR-RFLP and their FecB genotypes were determined. One copy of the FecB allele increased (P &lt; 0,05) the ovulation rate by 0.89 ova and two copies increased by an average of 2.27 ova. Effectiveness of the FecB genotype estimation based on phenotype measurement was also compared to the results of direct DNA testing, and was found to have up to 80% accuracy.

Effect of Ageing on Hormone Secretion and Follicular Dynamics in Sheep with and without the Booroola Gene

It has been suggested that ewes carrying the Booroola gene (Fec(B)) consistently ovulate more follicles because they recruit more primordial follicles and/or have a lower rate of atresia. If the former is correct, the pool of follicles would be depleted sooner in Fec(B) animals. We have studied follicular dynamics and endocrine function during follicular and early luteal phases of the estrous cycle of older ewes with or without the fecundity gene and compared this data with data obtained 6 yr previously in the same animals. Older sheep carrying the Booroola gene maintained a significantly higher ovulation rate than noncarrier ewes [4.2 +/- 0.8 vs. 2.2 +/- 0.6 corpora lutea (CL), respectively; P < 0.05], and in keeping with data from young animals, both ovulatory follicles and CL (4.7 +/- 0.3 vs. 6.9 +/- 0.7 mm and 12.8 +/- 0.5 vs. 16.7 +/- 0.8 mm, respectively) were smaller than those of noncarrier ewes (P < 0.05). The interval from luteolysis to the onset of the LH surge increased with age in all the animals (from 52.0 +/- 8.0 to 67.0 +/- 7.5 h in gene carrier sheep and from 56.0 +/- 2.0 to 79.5 +/- 9.6 h in noncarrier sheep, P < 0.05). The concentration of estradiol and inhibin A in the early luteal phase was lower in older noncarrier ewes (P = 0.08 and P < 0.05, respectively), and the level of inhibin A was inversely related to the level of FSH in aged sheep of both genotypes (P < 0.0001). In contrast, the number of developing follicles in older ewes of both genotypes was similar to the number found in younger ewes, suggesting that increased ovulation rate in sheep carrying the Fec(B) mutation is related to a reduced rate of atresia.