The role of genetic variability of the host on the resistance to Neospora caninum infection in cattle

Neospora caninum is one of the most frequently diagnosed abortifacient pathogens in cattle. There is abundant genomic information about the parasite itself, but very little is known about the genetic variability of resistance in the most common intermediate host. The aim of this review was to compile all the available information about the genetic variability associated with the resistance to N. caninum both between and within cattle breeds. We systematically searched for published studies that investigated the influence of genetics of the host on the prevalence of N. caninum and risk of abortion. Beyond the potential confounding effects of feeding systems, management and animal density, some lines of evidence suggest that Holstein, the most popular breed for milk production, has a comparatively higher risk of abortion due to infections by N. caninum, whereas some beef breeds from Continental Europe seem to be more resistant. It is still not clear if different genetic mechanisms of resistance are involved in the two known routes of infection: postnatal ingestion of oocysts or transplacental transmission from the infected dam to the fetus. Genomic information associated with susceptibility to infection and risk of abortion in different cattle breeds is still scarce. The information reported here could be useful to identify new research alternatives and to define novel strategies to deal with this major problem of animal production.

Development of PCR-based genetic test for detection of TTF1 mutation causing abortion in Holstein Friesian cattle

A stop-gain mutation (rs715966442; BTA11: 1,02,463,944 nucleotide position) in transcription termination factor, RNA polymerase I (TTF1) gene causes abortion in Holstein Friesian (HF) cattle. A PCR-restriction fragment length polymorphism (PCR-RFLP)-based genetic test has been developed and validated to screen the TTF1 mutation locus in HF cattle. The mutation locus was screened in 80 HF and HF crossbreds using the protocol, which revealed two animals as carriers of the mutant TTF1 allele. The test employed is cost-effective, rapid and precise and can be utilized as an effective tool for the screening of TTF1 mutation carriers in HF cattle population.

De novo synthesis of sphingolipids is essential for decidualization in mice

Sphingolipids play multiple roles in membrane structure, signal transduction, stress responses, neural development and immune reaction. The rate of de novo synthesis pathway of sphingolipids is regulated by two key enzymes, serine palmitoyltransferase (SPT), and ketoreductase (Kds). Here, we find that the mRNA levels of three subunits of the SPT holoenzyme (Sptlc1, Sptlc2, and Ssspta) are significantly up-regulated in mouse uterine stromal cells during decidualization. The expression of Kds, which reduces 3-keto-dihydrosphingosine to dihydrosphingosine, is co-localized with Sptlc1 in mouse uteri during early pregnancy. Moreover, l-Cycloserine, a specific inhibitor of SPT, can significantly decrease the weight and number of implantation sites, and impede the decidualization process in mouse uterine stromal cells, suggesting that blockage of de novo sphingolipid synthesis may cause defective decidualization and early pregnancy loss in mice. In addition, this study also shows progesterone (P4) can stimulate the expression of both Sptlc2 and Ssspta in mouse uterus. Therefore, our study shows that de novo synthesis of sphingolipids is necessary in implantation and plays a key role in decidualization of mouse.

Placental abnormalities in equine pregnancies generated by SCNT from one donor horse

Placental changes associated with SCNT have been described in several species, but little information is available in this area in the horse. We evaluated the ultrasonographic, gross, and histopathological characteristics of placentas from three successful and five unsuccessful equine SCNT pregnancies, established using cells from a single donor horse. Starting at approximately 6-month gestation, the pregnancies were monitored periodically using transrectal (TR) and transabdominal (TA) ultrasonography (US) to examine the placentas, fetal fluids, and fetuses. Of the five mares that aborted, one mare did so suddenly without any abnormal signs detected by US and four had enlarged umbilical vessels visible on TA-US before abortion. Placental edema (TR-US) and intravascular thrombi in the umbilical cords were seen (TA-US) in two of these four mares; one mare aborted shortly after acute placental separation was identified on TA-US. In three mares that delivered live foals, TA-US showed engorged allantoic vessels and enlarged umbilical vessels. Two of these mares had placental thickening visible on TR-US, interpreted as a sign of placentitis, that subsided after aggressive medical treatment. Seven of the eight placentas were submitted for gross and histopathological examinations after delivery. All placentas had some degree of edema, abnormally engorged allantoic vessels, and enlarged umbilical vessels. Placentitis, large allantoic vesicles, cystic pouches in the fetal part of the cord, and hemorrhages and thrombi in the umbilical vessels were detected only in placentas from mares that aborted. Equine pregnancies resulting from SCNT may be associated with placental pathologies that can be detected using ultrasonography. However, interpreting their severity is difficult. Although placental abnormalities have been observed in SCNT pregnancies in other species, to the best of our knowledge, placentitis has not been previously reported and may be an important complication of equine SCNT pregnancies, leading to pregnancy loss.

A novel mutation in the maternally imprinted PEG3 domain results in a loss of MIMT1 expression and causes abortions and stillbirths in cattle (Bos taurus)

Congenital malformations resulting in late abortions and stillbirths affect the economic wellbeing of producers and the welfare of cattle in breeding programs. An extremely high incidence of stillbirths of “half-sized” calves of normal karyotype and uninflated lungs was diagnosed in the progeny of the Finnish Ayrshire (Bos taurus) bull - YN51. No other visible anatomical abnormalities were apparent in the stillborn calves. We herein describe the positional identification of a 110 kb microdeletion in the maternally imprinted PEG3 domain that results in a loss of paternal MIMT1 expression and causes late term abortion and stillbirth in cattle. Using the BovineSNP50 BeadChip we performed a genome-wide half-sib linkage analysis that identified a 13.3 Mb associated region on BTA18 containing the maternally imprinted PEG3 domain. Within this cluster we found a 110 kb microdeletion that removes a part of the non-protein coding MER1 repeat containing imprinted transcript 1 gene (MIMT1). To confirm the elimination of gene expression in calves inheriting this deletion, we examined the mRNA levels of the three maternally imprinted genes within the PEG3 domain, in brain and cotyledon tissue collected from eight fetuses sired by the proband. None of the fetuses that inherited the microdeletion expressed MIMT1 in either tissue. The mutation, when inherited from the sire, is semi-lethal for his progeny with an observed mortality rate of 85%. The survival of 15% is presumably due to the incomplete silencing of maternally inherited MIMT1 alleles. We designed a PCR-based assay to confirm the existence of the microdeletion in the MIMT1 region that can be used to assist cattle breeders in preventing the stillbirths.

Anti-leucocyte antibodies and embryonic mortality in embryo transferred cows

Cows carrying unrelated transferred embryos (ET) produced anti-leucocyte serum antibodies (aLA) more often than cows carrying their own embryos. Cows carrying the ET showed a higher frequency of cytotoxic reactions against leucocytes from 40-60 randomly chosen cows than individuals carrying their own embryos. The percentage of animals with aLA was higher in cows carrying their second or third transferred embryo than in those with their first transferred embryo. There was no change in the frequency of cytotoxic reactions with repeated pregnancies from transferred embryos. There was no difference in the toxicity of aLA in normal pregnant cows and those carrying transferred embryos. Embryonic mortality (EM) of 35, 73 and 88% was noted during pregnancies from the first, second and third successful ET, respectively. Mortality of 48% occurred in the first pregnancy following an unsuccessful ET. Embryonic mortality of 31% occurred in cows simultaneously carrying their own and a transferred embryo. A direct relationship between the presence of aLA and EM in recipients was not proved. Other fertility problems may lead to EM in cows subjected to repeated transfer of foreign embryos.

Equine lymphocyte antigens and reproduction in the Standardbred mare

Equine lymphocyte antigen (ELA) gene frequencies were estimated for pacing and trotting Standardbred mares residing on a breeding farm in central Ohio. The ELA gene frequencies for Ohio Standardbreds did not differ significantly from the ELA gene frequencies of Kentucky Standardbreds, determined by Bailey (1983). No significant differences were found in the distribution of ELA class I antigens in horses with lower overall fertility or a history of abortion on the investigated breeding farm. Likewise, no significant association was observed when the ELA types of both the mare and the stallion to which she was mated were compared with the reproductive efficiency of the mare.

Selectin, Platelet Plays a Critical Role in Granulocyte Access to the Pregnant Mouse Uterus Under Physiological and Pathological Conditions1

Leukocyte recruitment to the pregnant mouse uterus is associated with highly regulated patterns of expression of vascular adhesion receptors. One striking observation is the localized expression of mucosal vascular addressin cell adhesion molecule (MADCAM1) and selectin, platelet (SELP, formerly P-selectin) by maternal vessels in the vascular zone (VZ) during the first half of pregnancy. From midgestation onwards, endothelial cells lining the maternal vessels of the VZ in addition express vascular cell adhesion molecule-1 (VCAM1). The predominant cell population within these vessels is monocyte-like cells. Granulocytes and low numbers of lymphocytes are also present. Murine fetal trophoblast cells are almost devoid of adhesion molecules, including SELP. In contrast, spontaneous abortions of allogeneic pregnancies are characterized by dramatic upregulation of SELP on maternal VZ vessels and on fetal trophoblast cells. Upregulation of SELP is associated with a dramatic influx of highly activated granulocytes, which infiltrate the vessels and tissue of the VZ and the trophoblast. The majority of the activated granulocytes within the trophoblast undergo nuclear fragmentation, which can be detected by TUNEL staining. To demonstrate that SELP is involved in the recruitment of granulocytes to the pregnant uterus, we undertook long-term in vivo inhibition studies using a monoclonal antibody to inhibit the contribution of SELP to leukocyte trafficking to the decidua. In addition, the pregnant uteri of syngeneic Selp(-/-) x Selp(-/-) mice were investigated and compared to the controls. Our results clearly demonstrate the importance of SELP for granulocyte access to the pregnant mouse uterus under physiological and pathological conditions.

NRAMP1 3' untranslated region polymorphisms are not associated with natural resistance to Brucella abortus in cattle

The NRAMP1 gene encodes a divalent cation transporter, located in the phagolysosomal membrane of macrophages, that has been associated with resistance to intracellular pathogens. In cattle, natural resistance against brucellosis has been associated with polymorphisms at the 3' untranslated region (3'UTR) of the NRAMP1 gene, which are detectable by single-strand conformational analysis (SSCA). This study aimed to evaluate the association between NRAMP1 3'UTR polymorphisms and resistance against bovine brucellosis in experimental and natural infections. In experimentally infected pregnant cows, abortion occurred in 42.1% of cows with a resistant genotype (SSCA(r); n = 19) and in 43.1% of those with a susceptible genotype (SSCA(s); n = 23). Furthermore, no association between intensity of pathological changes and genotype was detected. In a farm with a very high prevalence of bovine brucellosis, the percentages of strains of the SSCA(r) genotype were 86 and 84% in serologically positive (n = 64) and negative (n = 36) cows, respectively. Therefore, no association was found between the NRAMP1-resistant allele and the resistant phenotype in either experimental or naturally occurring brucellosis. To further support these results, bacterial intracellular survival was assessed in bovine monocyte-derived macrophages from cattle with either the resistant or susceptible genotype. In agreement with our previous results, no difference was observed in the rates of intracellular survival of B. abortus within macrophages from cattle with susceptible or resistant genotypes. Taken together, these results indicate that these polymorphisms at the NRAMP1 3'UTR do not affect resistance against B. abortus in cattle and that they are therefore not suitable markers of natural resistance against bovine brucellosis.

Allele frequency and likely impact of the glycogen branching enzyme deficiency gene in Quarter Horse and Paint Horse populations

Glycogen Branching Enzyme Deficiency (GBED), a fatal condition recently identified in fetuses and neonatal foals of the Quarter Horse and Paint Horse lineages, is caused by a nonsense mutation in codon 34 of the GBE1 gene, which prevents the synthesis of a functional GBE protein and severely disrupts glycogen metabolism. The aims of this project were to determine the mutant GBE1 allele frequency in random samples from the major relevant horse breeds, as well as the frequency with which GBED is associated with abortion and early neonatal death using the tissue archives from veterinary diagnostic laboratories. The mutant GBE1 allele frequency in registered Quarter Horse, Paint Horse, and Thoroughbred populations was 0.041, 0.036, and 0.000, respectively. Approximately 2.5% of fetal and early neonatal deaths in Quarter Horse-related breeds submitted to 2 different US diagnostic laboratories were homozygous for the mutant GBE1 allele, with the majority of these being abortions. Retrospective histopathology of the homozygotes detected periodic acid Schiff's (PAS)-positive inclusions in the cardiac or skeletal muscle, which is characteristic of GBED, in 8 out of the 9 cases. Pedigree and genotype analyses supported the hypothesis that GBED is inherited as a simple recessive trait from a single founder. The frequency with which GBED is associated with abortion and neonatal mortality in Quarter Horse-related breeds makes the DNA-based test valuable in determining specific diagnoses and designing matings that avoid conception of a GBED foal.

Effects of Nonadditive Genetic Interactions, Inbreeding, and Recessive Defects on Embryo and Fetal Loss by Seventy Days

Lethal recessive genes that cause early embryo loss are difficult to detect. Nonreturn rate at 70 d after first insemination (NR) was evaluated as a trait of the embryo using 1,739,055 first-service records from 1,251 Holstein bulls represented as both service sires and sires of cows. Effects modeled included herd-year-season, parity of cow, sire of cow, service bull, interaction of service bull with sire of cow, and regression on inbreeding of embryo. Variances of service bull and sire of cow were estimated using REML and estimated effects were removed from the data. Interaction variance was estimated from the residuals using the tilde-hat approximation to REML. An additive relationship matrix was used for sire of cow and a dominance relationship matrix for the interaction term. Service bull effects were assumed constant across time and unrelated. For each 10% increase in inbreeding, NR percentage declined by an estimated 1%. A regression of this size could be explained by > 20% of animals carrying defects that cause early embryo loss. Of the total variance, service bull contributed 0.36%; sire of cow, 0.24% (heritability of 1.0%); and interaction, 0.18% (dominance variance of 2.8%). Numbers of records exceeded 500 for 50 bull pair subclasses. Predicted interactions that included effects of inbreeding ranged from - 3.6% to +2.9%, compared with the mean NR of 56%. The largest negative interactions were not caused by known recessive defects. Complex vertebral malformation generally causes loss of pregnancies later in gestation, and few current bulls carry the gene for deficiency of uridine monophosphate synthase. Further study of the families with largest negative interactions could uncover new recessive defects.

Cumulative Discounted Expressions of Sire Genotypes for the Complex Vertebral Malformation and β-Casein Loci in Commercial Dairy Herds

Based on discounted gene-flow principles, a set of recursive equations was developed to quantify the value of using sires with a specific genotype for an identified gene in a commercial dairy herd. Two examples were used to demonstrate the usefulness of the method. The first example deals with the implications of using sires that are known carriers of the lethal recessive genetic defect, complex vertebral malformation (CVM). The second example examines the value of using sires homozygous for the A2 allele of beta-casein. Results are presented in terms of cumulative discounted expressions. These are then multiplied by the economic values of specific genotypes to determine the cost or benefit of using these sires. In general, the degree of mortality and the required price reduction for carrier sires increased as the proportion of carrier sires used, the duration of sire use, and the initial frequency in the cow herd increased. A semen discount of 3.10 pound sterling per CVM straw used would be required to offset the expected mortality when 20% of CVM carrier sires are used for 3 yr when 5% of cows are carriers. The cumulative discounted expressions' of using sires homozygous for the A2 allele of beta-casein also increased when the proportion and duration of carrier sire use and the initial frequency of the A2 allele increased. Assuming an A2A2 cow is worth 160 pound sterling more than a non-A2A2 cow, the expected benefit of using A2A2 sires in a 100-cow herd for 5 yr would be 57 pound sterling,120 for a 20-yr planning horizon. The results of this study demonstrate how the starting gene frequency in the herd, and the proportion and duration of use of sires of particular genotypes are critical to the economic implications of using single genes in commercial dairy farms.

Ovulation rate, litter size and prenatal losses in hair sheep of the French West Indies

Ovulation rate (OR) and litter size (LS) were recorded in local hair sheep of Martinique and in local x Lacaune-viande crossbreeds, in order to assess prenatal losses. Local hair sheep LS and OR were 1.91 and 2.41, respectively. Prenatal losses increased with OR, from 0.22 (OR = 2) up to 1.50 (OR > 3). The ewes (69.7%) with LS = 1 had actually lost at least one ovum, against 25.9% of the ewes with LS > 1. Ewes grazing Cynodon nlemfuensis (Stargrass) had lower LS than those grazing Digitaria decumbens (Pangola), in relation with a lower nutritional level and, maybe, more parasitism effects. No seasonal or age at lambing effect was shown. The OR and LS were dramatically decreased on local x Lacaune-viande crossbred ewes (minus 1.32 and 0.67 unit, respectively, P < 0.05). This suggests a possible negative effect of the tropical environment on the crossbreeds' reproductive function.

Murine abortion is associated with enhanced interleukin-6 levels at the feto-maternal interface

CBA/JXDBA/2J murine abortion is known to be associated with increased local and peripheral Th1-cytokines levels. The role of the pro-inflammatory interleukin-6 (IL-6) in murine abortion remains unclear. In humans, IL-6 was reported to be elevated at the onset of spontaneous abortion. The aim of our study was to evaluate the levels of IL-6 during murine pregnancy in (1) the normal murine pregnancy combination CBA/JXBALB/c and in (2) the CBA/JXDBA/2J abortion prone mating combination. We measured IL-6 serum levels by ELISA and local (placental and decidual) IL-6 levels by flow cytometry and immunohistochemistry. The expression of the IL-6 receptor gp80 was further analyzed. We additionally evaluated the number of mast cells and macrophages at the feto-maternal interface as a putative IL-6 source in reproductive tissues. IL-6 and gp80 were expressed in decidual cells as well as in different trophoblast types. Flow cytometry analysis showed increased numbers of IL-6+ cells in abortion placentas and deciduas compared to control pregnant mice. We observed an elevated number of mast cells and macrophages at the feto-maternal interface from abortion mice in comparison to control mice. Interestingly, we found very high numbers of mast cells, macrophages and IL-6+ cells in resorption tissue compared to control tissues. Flow cytometry studies confirmed that macrophages are being an important source of IL-6 at the feto-maternal interface. The mRNA IL-6 levels were also enhanced in placenta and decidua from mice with high abortion rate compared to normal pregnant mice, as analyzed by RT-PCR. Our results suggest that IL-6 produced not only by immunocompetent cells such as macrophages and mast cells, but also by trophoblasts and decidua cells, is directly involved in the pathology of abortion.

Extent, pattern and factors associated with late embryonic loss in dairy cows

Intensive genetic selection for increased milk production, coupled with increased dry matter intakes has led to significant improvements in cow milk yield, however, this increase in milk output has been accompanied by a decline in cow fertility. It has been suggested that there is a higher increment of late embryonic loss in high-yielding than in moderate yielding cows or in heifers. The objectives of this study were to establish the extent and pattern of embryonic loss, from days 28 to 84 of gestation, and to examine possible relationships between cow milk yield, cow genetic merit, parity, calving to insemination interval and embryonic loss in dairy cows managed mainly under pasture-based milk production systems. Multiparous dairy cows (n=1046) located on 8 farms and nulliparous dairy heifers (n=162) located on five of these farms were used in this study. The extent and timing of embryonic loss was measured by ultrasound scanning of the cows and heifers at 14-day intervals between days 28 and 84 of gestation. Positive diagnosis of pregnancy was based on the presence of an embryo or foetus with a visible heartbeat and, at the later scans, visible movement, whose size was compatible with stage of gestation and also on the presence of clear amniotic fluid of the cows and heifers presented as presumed pregnant on day 28 after insemination, 67 and 81%, respectively had a viable embryo. The subsequent embryonic loss rate between days 28 and 84 of gestation was similar (P>0.05) for cows (7.2%) and heifers (6.1%) and the pattern of loss over this period was also similar (P>0.05) for cows and heifers. There was no significant association (P>0.05) between level of milk production or milk energy output measured to day 120 of lactation and embryonic loss rate. Similarly, there was no significant relationship (P>0.05) between % milk fat, % milk protein and % milk lactose and embryonic loss rate. The extent and pattern of embryonic loss were not related (P>0.05) to either cow or to cow sire genetic merit. There was no significant (P>0.05) relationship between the calving to first service interval and embryonic loss. The extent of embryonic loss was greater (P<0.05) in cows that lost body condition between days 28 and 56 of gestation compared with cows than either maintained or improved in body condition.

Physical mapping of porcine seasonality genes

Seasonal infertility in sows is a problem in the pig industry characterized by delayed onset of puberty in summer and decreased farrowing rate resulting from silent oestrus and aborted pregnancy. Summer infertility is thought to be influenced by heat, sunburn and stress. However, the strongest contributory factor is photoperiod. The difference in seasonality between wild boar and commercial pig breeds suggests that there may be a genetic component to this trait. The maps and associated molecular tools emerging from the pig genome project have created opportunities to examine the genetic component of seasonal infertility. We are identifying and mapping genes that are likely to be involved in biological clock mechanisms and the melatonin pathways as candidate seasonality genes.

Participation of embryonic genotype in the pregnancy block phenomenon in mice

Pregnancy block by male pheromones in mice differs in incidence depending on the combination of strains. Female mice of BALB/cA strain mated with BALB/cA males show a 100% pregnancy block when exposed to males of inbred strain DDK shortly after copulation (Chung et al., Biol Reprod 1997; 57:312-319). In the present study, BALB/cA females mated with the males of other strains--CBA/J, C3H/HeN, C57BL/6Cr, and IXBL--showed higher pregnancy rates (66.6-87. 5%) even when they were exposed to DDK males. In the pharmacological induction of pregnancy block with dopamine agonist (bromocriptine, 4 mg/kg BW), BALB/cA females mated with BALB/cA males showed a 100% pregnancy block. In contrast, BALB/cA females mated with CBA/J, C3H/HeN, and C57BL/6Cr males showed higher pregnancy rates (40-70%). These results suggest that the better pregnancy rate of BALB/cA females mated with alien males may be due to the stronger viability of F(1) embryos. This interpretation was confirmed by an embryo transfer experiment in which a higher implantation rate was observed when BALB/cA embryos grown in BALB/cA females exposed to BALB/cA males were transferred into recipient BALB/cA females exposed to DDK males. These results suggest that the embryonic genotype or viability of the embryo is one factor contributing to the occurrence of pregnancy block by male pheromones in mice.

The conflict theory of genomic imprinting: how much can be explained?

In some mammalian genes, paternally and maternally derived alleles are expressed differently: this phenomenon is called genomic imprinting. Several-explanations have been proposed for the observed patterns of genomic imprinting, but the most successful explanation is the genetic conflict hypothesis--natural selection operating on the gene expression produces the parental origin-dependent gene expression--because the paternally derived allele tends to be less related to the siblings of the same mother than the maternal allele and hence the paternal allele should evolve to be more aggressive in obtaining maternal resources. The successes and failures of this argument have been examined in explaining the observed patterns of genomic imprinting in mammals. After a brief summary of the observations with some examples, a quantitative genetic model describing the evolution of the cis-regulating element of a gene affecting the maternal resource acquisition was presented. The model supports the verbal argument that the growth enhancer should evolve to show imprinting with the paternal allele expressed and the maternal allele inactive, whereas a growth suppressor gene tends to have an inactive paternal allele and an active maternal allele. There are four major problems of the genetic conflict hypothesis. (1) Some genes affect embryonic growth but are not imprinted (e.g., Igf1), which can be explained by considering recessive, deleterious mutations on the coding regions, (2) A gene exists that shows the pattern that is a perfect reversal (Mash2), which is needed for placental growth, and yet has an active maternal allele and an inactive paternal allele. This can be explained if the overproduction of this gene causes dose-sensitive abortion to occur in early gestation. (3) Paternal disomies are sometimes smaller than normal embryos. This is a likely outcome of evolution if imprinted genes control the allocation between placenta and embryo by modifying the cell developmental fate. (4) Genes on X chromosomes do not follow the predictions of the genetic conflict hypothesis. For genes on X chromosomes, two additional forces of natural selection (sex differentiation and dosage compensation) cause genomic imprinting, possibly in the opposite direction. Available evidence suggests that these processes are stronger than the natural selection caused by female multiple mating. Finally, the same formalism of evolution can handle an alternative nonconflict hypothesis: genomic imprinting might have evolved because it reduces the risk of the spontaneous development of parthenogenetic embryo, causing a serious threat to the life of the mother (ovarian time bomb hypothesis). This hypothesis can also explain major patterns of genomic imprinting. In conclusion, the genetic conflict hypothesis is very successful in explaining the observed patterns of imprinting for autosomal genes and probably is the most likely evolutionary explanation for them. However, for genes on X chromosomes, other processes of natural selection are more important. Considering that a nonconflict hypothesis can also explain the patterns in principle, we need a quantitative estimate of various parameters, such as the rate of dose-dependent abortion, the degree of female promiscuity, and the rate of spontaneous development of the parthenogenetic embryo, in order to make judgments on the relative importance of different forces of natural selection to form genomic imprinting.

Pregnancy block in house mice (Mus domesticus) as a function of t-complex genotype: examination of the mate choice and male infanticide hypotheses

Pregnancy block, whereby recently mated female mice abort their pregnancies when exposed to novel (strange) males, was studied in house mice (Mus domesticus) differing in t-complex genotype; t-mutations are deleterious and +/t females avoid +/t males as mates. The results of Experiment 1, in which the genotype of the female, stud male, and strange male was systematically varied, showed that pregnancy block was most frequent when the strange male was +/+. Because this effect was not enhanced among +/t females when stud males were +/t, the results cannot clearly be explained by the hypothesis that pregnancy block is a manifestation of mate choice. Moreover, the "strange male" effect in Experiment 1 is unlikely to be a female response correlated with the risk of male infanticide, as +/+ and +/t males did not differ in their infanticidal tendencies (Experiments 2 & 3). Alternative hypotheses, including a modified version of the mate choice hypothesis, are discussed.

Chromosomal aneuploidy associated with spontaneous abortions and neonatal losses in cattle

Pericardial sac samples from 77 bovine aborted fetuses and stillborn calves were submitted for tissue culture; cells from 55 of these samples were grown successfully in culture. Six of the 55 karyotyped fetuses (10.7%) had an abnormal chromosome complement, in 3 of which (5.5%) the abnormality was probably the cause of death. This level of abnormality is relatively high when one considers that most fetuses were >8 months gestational age. Approximately 5-7% of human stillbirths and 50% of first-trimester aborted fetuses have chromosome anomalies. If a similar situation exists in cattle, as suggested by these data, chromosome abnormalities may be a major cause of early fetal loss in cattle. Most chromosomally abnormal fetuses had multiple malformations, which suggests that the diagnostic use of chromosome analysis is most cost effective for malformed fetuses and newborns. Twins were present in a higher proportion of these fetuses than expected based on their incidence among liveborn cattle.

Stillborn triploid complex hybrid of lemurs (Eulemur macaco x E. coronatus)

The karyotype of a triploid lemur hybrid, issued from the backcross of an Eulemur macaco male with a female E. coronatus hybrid is reported. The differential negative effect of the multivalents on male and female fertility is discussed.

A survey of malformed aborted bovine fetuses, stillbirths and nonviable neonates for abnormal karyotypes

Postmortem examinations were performed on 30 morphologically abnormal aborted bovine fetuses, stillbirths and nonviable neonates. Fibroblasts from the pericardium were cultured for chromosome analysis. Karyotypes were successfully completed on 18 animals, of which three were trisomic, one was mosaic monosomic and one was chimeric. All aneuploid calves had multisystemic anomalies. Using chromosomal banding techniques, the abnormal karyotypes were determined to be: 61,XY,+27; 61,XX,+21; 61,XY,+?; 59,XY,-?/60,XY; and 60,XX/60,XY. Bacterial contamination or nonviability of tissues prevented the growth of fibroblasts in culture and cytogenetic analysis of the other 12 animals. It was estimated that 2.0% of all late gestation abortuses and stillbirths may have chromosomal abnormalities characterized by aneuploidy. The findings of this study suggest chromosomal abnormalities characterized by aneuploidy are a significant cause of multisystemic anomalies in aborted bovine fetuses and nonviable neonates.

Foetal and calf wastage in Bos indicus cross beef genotypes

The prevalence, stages and causes of foetal and calf wastage were determined in Brahman (1/2 B, 3/4 B) and Sahiwal (1/2 Sah, 3/4 Sah) and high grade Sahiwal (HGSah) genotypes over a 12-year period. The mean total loss from pregnancy being first diagnosed to weaning was 13.5% (range 9.4 to 19.0%) and was not influenced by cow age. Across all age groups total losses were significantly lower in 1/2 B (11.8%) and 3/4 B (11.7%) than in 1/2 Sah (16.3%) and 3/4 Sah (19.4%) which were in turn significantly lower than in HG Sah (26.5%). Mean prenatal, perinatal and postnatal losses were 3.5%, 4.4% and 5.6%, respectively. For prenatal losses, 42.4% occurred in early-, 34.8% in mid- and 23.0% in late gestation, the prevalence being influenced only by year effects. Perinatal losses were lowest in 3/4 B (2.9%) and highest in 3/4 Sah (8.3%) with other genotypes intermediate. Postnatal losses were lowest in 1/2 B (4.1%) and 3/4 B (5.0%), intermediate for 1/2 Sah (7.2%) and 3/4 Sah (6.2%) and highest in HG Sah (15.5%). In Brahmans, important causes of perinatal and postnatal losses were from unknown causes, and in Sahiwals from bottle teats, unknown causes and factors influenced by the cow. Bottle teats were mostly in cows older than 2 years with the majority being in Sahiwals. A high proportion (44%) of the postnatal losses occurred by 14 days after birth.

Chromosome mosaicism in a zebra (Equus burchelli) abortus provides evidence for a different in-vivo/in-vitro survival of balanced and unbalanced karyotypes

A fibroblast culture from the skin of a zebra abortus recovered from a pedigree known, in part, to be segregating for a chromosome centric fission was karyotypically mosaic. Some cells were balanced for the fission and the others unbalanced, being deficient for the shorter fission product. Initially, the latter were in the majority but after continued culture (101 days) they were outgrown by the former. This finding either suggests a differential in-vivo/in-vitro fitness of the two cell types or a change in proportions resulting from some other mechanism.

Selection and the transferrin polymorphism in rhesus monkeys (Macaca mulatta)

Rates of survival, infant growth and fertility of rhesus monkeys with two, one and no C allele(s) at the transferrin locus are compared. Infants with no C allele experience slower growth rates than animals with either one or two C allele(s). While heterozygous females exhibit the highest infant growth rates among females, their fertility is lower and incidence of abortions and stillbirths is higher than for females with two or no C alleles. It is hypothesized that opposing directions of selection at different life-cycle stages maintain a stable equilibrium at the transferrin locus.

Cytogenetic and DNA analyses of equine abortion

Although no major structural or numerical abnormalities were found in the karyotypes of 12 aborted equine fetuses, two unrelated abortuses each carried a large polymorphism for the amount of heterochromatin in chromosome 1. In both karyotypes this chromosome was shown to be larger than its homolog. To determine the nature of the extra DNA in these chromosomes, equine DNA was isolated and characterized by buoyant density analysis. Equine mainband DNA had a buoyant density in neutral CsCl of 1.699 g/cm3, while the highly repetitive (dG+dC)-rich fraction had a buoyant density of 1.715 g/cm3. A radioactive RNA probe complementary to the purified satellite fraction was used for in situ hybridization to chromosomal spreads containing the enlarged chromosome 1. The results indicated that an increase in highly repetitive (dG+dC)-rich DNA was responsible for the increase in the size of the abnormal No. 1 chromosomes. While two of the 12 aborted fetuses exhibited marked heterochromatic dimorphisms, none of the karyotypes obtained from individuals with no family history of abortion exhibited such obvious polymorphisms.