Factors affecting differences between birth weight of littermates (BWTD) and the effects of BWTD on lamb performance.

The objectives of this study were to determine factors affecting lamb birth weight (BWT) and differences between BWT of the largest and smallest littermates (BWTD) and to assess the relative importance of BWT and BWTD on lamb survival and growth to weaning. Records from twin (n = 5369) or triplet (n = 1664) litters born on pasture were utilised. Breeds included Coopworth, Romney, Perendale, composite and Texel. Ewe and sire breed, age and weight of the dam, sex, and number of lambs born (NLB) affected BWT. Neither embryo loss nor ovulation pattern (i.e. all ova released from one ovary or some from each) were associated with BWT. Dam weight and NLB affected BWTD but dam age, sire or dam breed did not. Loss of an embryo reduced BWTD, and BWTD was lower when the ewe ovulated from both ovaries versus only one ovary for twins, but not triplets. Whereas BWT was moderately heritable (h2 = 0.20), BWTD was not heritable (h2 = 0.003). Lamb survival was positively associated with BWT. Lambs with BWTD > 1.3 kg were less likely to survive (73.3%) than those from litters of smaller BWTD (range 82.8-85.7% survival). Growth rate of twin and triplet lambs was positively associated with BWT. Surprisingly, lambs from litters with moderately high BWTD had slightly greater (approximately 3%) growth rate than those from lambs of low to intermediate BWTD. Thus, while large BWTD were negatively associated with survival, BWT itself, which was moderately heritable, appeared to be a stronger driver of lamb survival and average daily gain.

Activin A and follistatin during the oestrous cycle and early pregnancy in ewes.

The activin pathway has been postulated to be involved in regulation of multiple reproductive processes important for survival of the conceptus. These processes include luteinisation of the follicular cells and thus function of the corpus luteum, early embryo development and uterine function including implantation of the conceptus. Therefore, the aim of the current study was to determine whether the concentrations of activin A and follistatin (FST), an activin-binding protein, differed between ewes with a lifetime history of enhanced or reduced embryonic survival (ES). The mRNAs encoding FST and activin A (inhibin beta A subunit; INHBA) were present in the uterus and abundant in the uterine luminal or glandular epithelia by day 18 of gestation. A peak of activin A was observed in the systemic circulation around the time of oestrus, and activin A concentrations were elevated in animals with reduced ES during the oestrous cycle and early gestation. Concentrations of activin A in uterine fluid were approximately twofold greater on day 16 of gestation in ewes with reduced ES compared to those with enhanced ES. No consistent differences in FST were observed between these groups. Treatment of luteinising ovine granulosa cells with activin A in vitro suppressed progesterone secretion providing evidence of a potential pathway whereby increased concentrations of activin A may decrease ES.

Mutations in the leptin receptor gene associated with delayed onset of puberty are also associated with decreased ovulation and lambing rates in prolific Davisdale sheep.

The aim of this study was to determine if single nucleotide polymorphisms (SNPs) in the leptin receptor (LEPR) gene associated with delayed onset of puberty are associated with changes in other reproductive traits in adult ewes. The ovulation rate of ewes homozygous for the SNPs was ~15% lower (PPLEPR SNPs than their wild-type or heterozygous contemporaries. Partial failure of multiple ovulations was also increased (PLEPR had on average 0.2 fewer lambs at mid-pregnancy and at birth compared with the wild-type or heterozygous ewes (PLEPR were strongly associated with poorer reproductive performance in Davisdale ewes, which is likely to be linked to both a reduced number of ova available for fertilisation and an increased number of ewes failing to become pregnant. Increased partial failure of multiple ovulations in ewes with high ovulation rates (i.e. 3 or greater) may also contribute to the poor reproductive performance.

Single-nucleotide polymorphisms in the LEPR gene are associated with divergent phenotypes for age at onset of puberty in Davisdale ewes.

Attainment of puberty is a key developmental event influenced by genetic and environmental factors. In examining age at attainment of puberty, we observed closely related rams from the Davisdale line whose daughters differed in age at which they attained puberty. A candidate gene approach was used to identify mutations that may underlie these observed differences. Four rams with divergent phenotypes for their daughter's age at onset of puberty were selected for whole-genome sequencing. The coding regions of genes with known roles in regulating reproductive function were searched for single-nucleotide polymorphisms (SNPs) that altered the amino acid sequence of the protein. Of interest were three SNPs in the leptin receptor gene (LEPR). A Sequenom assay was developed to determine the genotype of these SNPs in daughters of 17 sons of a founding sire. A higher percentage of ewe lambs homozygous for the LEPR mutations failed to undergo puberty before 1 yr of age, and those that did undergo puberty during the first breeding season on average were approximately 17 days older than homozygous wild-type ewes. Heterozygous ewes were intermediate for both measurements. Given the predicted change in protein function produced by the mutation in LEPR and the strong associations between the genotype and onset of puberty phenotypes, we propose that this mutation in LEPR underlies the observed difference in age at onset of puberty in the Davisdale line. Furthermore, these animals will likely provide a useful model to better understand the role of leptin in the regulation of puberty.

Using sheep lines with mutations in single genes to better understand ovarian function.

Livestock populations have been subjected to strong selection pressure to improve reproductive success, and this has led to the identification of lines of animals with increased fecundity. These animals provide a rich biological resource for discovery of genes and regulatory mechanisms that underpin improved reproductive success. To date, three genes, all related to the transforming growth factor ß pathway, have been identified as having mutations that lead to alterations in ovulation in sheep. In addition, several other sheep lines have been identified with putative mutations in single genes with major effects on ovulation rate. This review is focused on the identification of the mutations affecting ovulation rate and how these discoveries have provided new insights into control of ovarian function.

An earlier rise in systemic progesterone and increased progesterone in the uterine vein during early pregnancy are associated with enhanced embryonic survival in the ewe.

Improved livestock production efficiency through greater embryonic survival (ES) is of economic and animal welfare benefit. Physiological characterization of animals that are extreme outliers for ES provides a valuable opportunity to identify a naturally occurring mechanism by which this trait may be enhanced. The objective was to determine the likely cause for the lifetime history of enhanced or reduced ES in a line of ewes selected for high fecundity. To address this question, progesterone concentrations in peripheral plasma as well as ovarian and uterine venous plasma samples were compared between groups of ewes with a lifetime history of either enhanced or reduced ES. The ability of the uterus to synthesize progesterone de novo at Day 5 of gestation was also tested. Ewes with enhanced ES had an earlier rise in progesterone concentration after estrus, irrespective of pregnancy status. In addition, there were increased concentrations of progesterone in the uterine vein in enhanced ES compared with reduced ES ewes on Day 5 of gestation (8.3 ± 0.8 ng/mL and 3.9 ± 1.4 ng/mL, respectively, P < 0.05). However, there were no differences in ovarian venous plasma (enhanced ES, 1725 ± 166 ng/mL; reduced ES, 1665 ± 268 ng/mL) at Day 5 of gestation. Although the endometrial tissue of some ewes (3/8) at Day 5 of gestation expressed three of the key genes necessary for regulation of de novo synthesis of progesterone, expression was not present exclusively in either of the two ES groups and therefore was unlikely to explain differences in the uterine vein progesterone concentrations between the enhanced and reduced ES groups. Collectively, the earlier rise in progesterone concentrations in peripheral plasma during the first week of gestation in the enhanced ES animals was independent of the presence of an embryo. Moreover, increased progesterone concentrations were also observed in the uterine vein at Day 5 of gestation of the enhanced ES ewes. It is proposed that the difference in uterine vein progesterone concentration was likely due to the differences in ovarian venous blood supply rather than de novo synthesis by the uterus.

Identification of a line of sheep carrying a putative autosomal gene increasing ovulation rate in sheep that does not appear to interact with mutations in the transforming growth factor beta superfamily.

Sheep lines with mutations in single genes that have major effects on ovulation rate have been very useful in gaining a better understanding of pathways important in controlling follicular development and ovulation rate. To date however, all known mutations are in the transforming growth factor beta (TGFB) superfamily. Ovulation rates were measured in 720 progeny of 20 rams that were descendants of a single prolific ewe. Evaluation of ovulation rates of daughters of closely related sires suggests the presence of a segregating major gene Fecundity Davisdale (FECD) that increases ovulation rate between 0.4 and 0.8 in heterozygous daughters. Key features of mutations in genes of the TGFB superfamily pathway, such as synergistic interactions with other family members, infertility in homozygous carriers, and increased responsiveness to exogenous gonadotropins, were not observed in this line; thus, the mutation does not appear to be acting in the TGFB pathway. Hence, there is likely a novel mutation being carried in this line of sheep that alters ovulation rate. Future identification of the causative mutation may provide new insights into regulation of follicular development and ovulation rate.

Postnatal uterine development in Inverdale ewe lambs.

Postnatal development of the uterus involves, particularly, development of uterine glands. Studies with ovariectomized ewe lambs demonstrated a role for ovaries in uterine growth and endometrial gland development between postnatal days (PNDs) 14 and 56. The uterotrophic ovarian factor(s) is presumably derived from the large numbers of growing follicles in the neonatal ovary present after PND 14. The Inverdale gene mutation (FecXI) results in an increased ovulation rate in heterozygous ewes; however, homozygous ewes (II) are infertile and have 'streak' ovaries that lack normal developing of preantral and antral follicles. Uteri were obtained on PND 56 to determine whether postnatal uterine development differs between wild-type (++) and II Inverdale ewes. When compared with wild-type ewes, uterine weight of II ewes was 52% lower, and uterine horn length tended to be shorter, resulting in a 68% reduction in uterine weight:length ratio in II ewes. Histomorphometrical analyses determined that endometria and myometria of II ewes were thinner and intercaruncular endometrium contained 38% fewer endometrial glands. Concentrations of estradiol in the neonatal ewes were low and not different between ++ and II ewes, but II ewes had lower concentrations of testosterone and inhibin-alpha between PNDs 14 and 56. Receptors for androgen and activin were detected in the neonatal uteri of both ++ and II ewes. These results support the concept that developing preantral and/or antral follicles of the ovary secrete uterotrophic factors, perhaps testosterone or inhibin-alpha, that acts in an endocrine manner to stimulate uterine growth and endometrial gland development in the neonatal ewes.

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.

Woodlands sheep have a putative genetic mutation (FecX2(W)) that increases ovulation rate. At present, the identity of FecX2(W) is unknown. The trait does not appear to be due to the previously described mutations in bone morphogenetic protein 15 (BMP15), growth differentiation factor 9 (GDF9), or bone morphogenetic protein receptor type 1B (BMPR1B) that affect ovulation rate in sheep. Potentially, FecX2(W) could be an unidentified genetic mutation in BMP15 or in the closely related GDF9, which interacts with BMP15 to control ovarian function. Alternatively, FecX2(W) may affect ovulation rate by changing the expression patterns in the molecular pathways activated by genes known to regulate ovulation rate. The objectives of these experiments were to sequence the complete coding region of the BMP15 and GDF9 genes, determine the patterns of expression of mRNAs encoding GDF9, BMP15, TGFBR1, BMPR1B, and BMPR2 during follicular development, and characterize the follicular populations in ewes heterozygous for the Woodlands mutation and their wild-type contemporaries. No differences in the coding sequences of BMP15 or GDF9 genes were identified that were associated with enhanced ovulation rate. The expression patterns of GDF9 and BMPR2 mRNAs were not different between genotypes. However, expression of BMP15 mRNA was less in oocytes of FecX2(W) ewes in large preantral and antral follicles. Expression of ALK5 mRNA was significantly higher in the oocytes of FecX2(W) ewes, whereas expression of BMPR1B was decreased in both oocytes and granulosa cells of FecX2(W) ewes. FecX2(W) ewes also had increased numbers of antral follicles <1 mm in diameter. These follicles were smaller in average diameter, with the oocytes also being of a smaller mean diameter. Given that a mutation in BMP15 or BMPR1B results in increased ovulation rates in sheep, the differences in expression levels of BMP15 and BMPR1B may play a role in the increase in ovulation rate observed in Woodlands ewes with the FecX2(W) mutation.

Prenatal diagnosis and management of mainstem bronchial atresia.

The prenatal diagnosis, natural history and management of mainstem bronchial atresia have not been described previously. We report two cases of prenatally diagnosed proximal bronchial atresia. The first patient presented at 18 weeks with sonographic and MRI findings consistent with bronchial atresia with fetal hydrops. The mother developed the mirror syndrome and labor was induced. A non-viable fetus was delivered at 25 weeks. The second patient presented at 16 weeks gestation with evidence of an intrathoracic mass that was subsequently prenatally diagnosed as a right mainstem bronchial atresia. The right lung increased rapidly in size and was associated with the onset of fetal hydrops. At 24 weeks, fetal pneumonectomy was performed but the fetus expired intraoperatively due to cardiovascular collapse. Post-mortem findings in both cases confirmed the presence of an atretic mainstem bronchus with massive enlargement of the lung. Bronchial atresia involving the mainstem bronchus is associated with a poor prognosis.

Physiological effects of major genes affecting ovulation rate in sheep.

Genetic mutations with major effects on ovulation rate in sheep were recently identified in two genes of the transforming growth factor (TGFbeta) superfamily and a TGFbeta receptor, namely bone morphogenetic protein 15 (BMP15), otherwise known as the growth differentiation factor 9b (GDF9b), GDF9 and activin-like kinase 6 (ALK6) otherwise known as the BMP receptor type IB (BMPRIB). Animals homozygous for the BMP15 or GDF9 mutations are anovulatory whereas animals heterozygous for BMP15 or GDF9 or heterozygous or homozygous for ALK6 have higher than normal ovulation rates. Immunisation of ewes against BMP15 or GDF9 shows that both are essential for normal follicular development and control of ovulation rate. Common features of fertile animals with the BMP15, ALK6 (and possibly GDF9) mutations are changes in oocyte development during early preantral follicular growth, earlier maturation of granulosa cells and ovulation of mature follicles at smaller diameters. In summary, these findings have led to a new paradigm in reproductive biology, namely that the oocyte plays a key role in regulating the ovulation rate.

Intrauterine repair of spina bifida: preoperative predictors of shunt-dependent hydrocephalus.

OBJECTIVE: The objective of this study was to determine which factors that are present at the time of intrauterine repair of spina bifida could predict the need for ventriculoperitoneal shunt for hydrocephalus during the first year of life. STUDY DESIGN: One hundred seventy-eight fetuses have undergone intrauterine repair of spina bifida at Vanderbilt University Medical Center since 1997. Among these, 116 fetuses had a postnatal follow-up period of at least 12 months. The primary outcome of the study was the need for a ventriculoperitoneal shunt for hydrocephalus during the first year of life. The following variables were analyzed: maternal demographics (age, race, gravidity, and parity), gestational age at the time of surgery, ventricular size, degree of hindbrain herniation (determined by magnetic resonance imaging in 33 cases), type of defect (myelomeningocele vs myeloschisis), upper level of the lesion, presence of talipes, and intraoperative use of a lumbar drain. Statistical analysis was performed with logistic regression (to test the association of fetal and maternal factors and the need for ventriculoperitoneal shunting), 2-sample t-tests for comparison of means, and receiver operating curves with the use of the probabilities that were generated by the logistic regression for both continuous and categoric versions of the factors. RESULTS: Sixty-one of 116 of the fetuses (54%) who underwent operation in utero required the placement of a ventriculoperitoneal shunt before the age of 1 year. The upper level of the lesion was the strongest predictor of shunt requirement (adjusted odds ratio per 1 level increase with the use of continuous variables [S1 through T10], 1.73 [95% CI, 1.22- 2.44]; adjusted odds ratio with the use of upper lesion level >or=L3 vs 25 weeks as a categorized variable, 3.3 [95% CI, 1.28-8.24]), and preoperative ventricular size (adjusted odds ratio per 1 unit increase with the use of continuous variables, 1.17 [95% CI, 1.01-1.36]; adjusted odds ratio with the use of ventricular size >or=14 mm vs <14 mm as a categorized variable, 3.5 [95% CI, 1.08-11.16]). Receiver operating curves with the use of the probabilities that were generated by the logistic regression analyses for both the continuous and categoric versions of the factors were compared. The area under the curve was approximately 0.81 for both methods. Thirty-eight of 48 of the fetuses (79%) with an upper level of the lesion >or=L3 required placement of a ventriculoperitoneal shunt, although 25 of 68 of the fetuses (37%) with lesions or=14 mm (27/32 fetuses) needed a shunt compared with 41% of the fetuses (34/81 fetuses) with smaller ventricles (P=.03). Seventy-one percent of the fetuses who underwent operation at >25 weeks of gestation also required shunt placement (37/52 fetuses); 39% of the fetuses (24/61 fetuses) who were treated

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).

Belclare and Cambridge are prolific sheep breeds, the origins of which involved selecting ewes with exceptionally high litter size records from commercial flocks. The variation in ovulation rate in both breeds is consistent with segregation of a gene (or genes) with a large effect on this trait. Sterile ewes, due to a failure of normal ovarian follicle development, occur in both breeds. New naturally occurring mutations in genes for the oocyte-derived growth factors growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are described. These mutations are associated with increased ovulation rate in heterozygous carriers and sterility in homozygous carriers in both breeds. This is the first time that a mutation in the gene for GDF9 has been found that causes increased ovulation rate and infertility in a manner similar to inactivating mutations in BMP15, and shows that GDF9 is essential for normal folliculogenesis in sheep. Furthermore, it is shown, for the first time in any species, that individuals with mutations in both GDF9 and BMP15 have a greater ovulation rate than sheep with either of the mutations separately.

Fetal hydrocephalus.

Fetal hydrocephalus is a dynamic process. Its natural progression is not completely understood, but it is almost always associated with other intracranial and extracranial anomalies. Fetal hydrocephalus might begin as mild ventriculomegaly and progress to a more serious state. Mild ventricular enlargement without an increase in head size might be a normal variant. Careful prenatal evaluation is always indicated when the diagnosis of ventricular enlargement has been made, and it should include a detailed anatomic survey and genetic amniocentesis. Therapeutic options need to be discussed in detail with the patient. If multiple associated anomalies--especially other CNS anomalies--are present, the prognosis for a viable outcome is dismal. If isolated hydrocephalus is seen, gender determination is appropriate in the consideration of X-linked hydrocephalus secondary to aqueductal stenosis. Communicating hydrocephalus can also be mistaken for obstructive ventriculomegaly, but it can usually be excluded by demonstration of dilation of the subarachnoid cistern. There is a small subset of fetuses that have isolated hydrocephalus that might benefit from prenatal surgical intervention. Feasibility studies are in progress to assess the therapeutic benefit of this type of therapy. Gestational age requirements and strict criteria are being evaluated. As with the multiple therapies discussed in this issue, many interventions are becoming more and more feasible, and antenatal surgery is likely to be limited only by the ability to think imaginatively and to act creatively.

DNA tests in prolific sheep from eight countries provide new evidence on origin of the Booroola (FecB) mutation.

Recent discoveries that high prolificacy in sheep carrying the Booroola gene (FecB) is the result of a mutation in the BMPIB receptor and high prolificacy in Inverdale sheep (FecX(I)) is the result of a mutation in the BMP15 oocyte-derived growth factor gene have allowed direct marker tests to be developed for FecB and FecX(I). These tests were carried out in seven strains of sheep (Javanese, Thoka, Woodlands, Olkuska, Lacaune, Belclare, and Cambridge) in which inheritance patterns have suggested the presence of major genes affecting prolificacy and in the prolific Garole sheep of India, which have been proposed as the ancestor of Australian Booroola Merinos. The FecB mutation was found in the Garole and Javanese sheep but not in Thoka, Woodlands, Olkuska, Lacaune, Belclare, and Cambridge sheep. None of the sheep tested had the FecX(I) mutation. These findings present strong evidence to support historical records that the Booroola gene was introduced into Australian flocks from Garole (Bengal) sheep in the late 18th century. It is unknown whether Javanese Thin-tailed sheep acquired the Booroola gene directly from Garole sheep from India or via Merinos from Australia. The DNA mutation test for FecB will enable breeding plans to be developed that allow the most effective use of this gene in Garole and Javanese Thin-tailed sheep and their crosses.