Showing papers in "Journal of reproduction and fertility in 1993"

Culture of pig embryos

Abstract: Pig embryos can be cultured using a number of different strategies including complex approaches like culture in vivo in a surrogate oviduct (rabbit, sheep, mouse), culture in mouse oviducts in organ culture, and co-culture of embryos with cells in addition to simple approaches like culture in defined media or salt solutions. Addition of serum to medium has been of particular importance where blastocyst development and hatching are required. Pig conceptuses (day 10-15), embryonic discs or cell lines derived from conceptuses can be cultured in complex media like Eagle's minimal essential medium or Dulbecco's modified Eagle's medium with serum, although embryonic discs can be cultured in the absence of serum. In contrast, early stage pig embryos (one-cell to blastocyst) are best cultured in simpler media such as those used for mouse embryos. The media that have been used are all relatively similar in composition. They contain salts and one or more energy sources such as glucose, lactate, or pyruvate with BSA as a macromolecular component. Early attempts to culture pig embryos were not very successful, but some embryos did develop to the blastocyst stage. More recent reports indicate a much higher rate of development with relatively little or no change in media composition. Some workers have reported improved development in medium lacking glucose, which is consistent with findings with laboratory animals such as hamsters. Glutamine can serve as the sole exogenous energy source in medium lacking glucose, lactate and pyruvate. Addition of taurine and hypotaurine to culture medium enhances development of pig embryos in vitro. We suggest, where possible, adoption of a standard medium that could be used by different laboratories and, perhaps, with different species. Use of one medium for different species would simplify experimental protocols, enhance studies of comparative embryonic physiology and metabolism, and expedite transfer of information obtained in different species.

Seasonal effects on fertility in gilts and sows.

Abstract: The ancestral wild pig is a short day length seasonal breeder. The domestic pig appears to have retained some of this seasonality as evidenced by a reduction in fertility during the summer-autumn period. The most important aspect of this seasonality is a reduction in the number of mated sows that farrow. Many of these sows conceive and embryos develop normally for 20-25 days before pregnancy is terminated and the sow returns to oestrus (25-35 days after mating). In other species, transduction of photoperiodic information is achieved by release of melatonin during the dark period. In the pig, the pattern of melatonin secretion and the subsequent hypothalamo-pituitary-gonadal responses appear to be more complex. A relatively high light intensity is required for pigs to generate a distinct diurnal melatonin rhythm and they appear unable to respond appropriately to abrupt changes in photoperiod. Pigs on restricted feeding and maintained under long photoperiods (but not under short photoperiods) have higher concentrations of melatonin than do similarly maintained pigs fed ad libitum. Continuous release melatonin implants have a deleterious effect on farrowing rate, suggesting that the abnormally high melatonin concentrations observed in sows in summer-autumn play a role in the pathogenesis of seasonal infertility. Ad libitum feeding of sows during the first few weeks of pregnancy may prevent the increase in melatonin concentrations and so remove the seasonal influence on fertility. The pituitary response to different photoperiods is also somewhat confusing. Although there is some evidence of increased sensitivity to the negative feedback of ovarian steroids in the prepubertal gilts and weaned sows during summer-autumn, LH concentrations are increased in early pregnant sows. It is proposed that the failure of sows to maintain pregnancy in summer-autumn results from disruption of maternal recognition of pregnancy causing regression of the corpora lutea, loss of pregnancy and return of the sow to oestrus.

Sperm morphology and fertility in the dog.

Abstract: Normal and abnormal dog spermatozoa were studied by means of bright field light and transmission electron microscopy and the effect of abnormal spermatozoa on dog fertility was evaluated. Semen samples were collected by digital manipulation from 67 dogs of 34 different breeds. Ten of the samples were examined ultrastructurally. The association between the percentage abnormal spermatozoa in the ejaculate and the fertility of the dog was statistically evaluated, based on insemination of 42 bitches. On this basis, the male dogs were divided into normal and subnormal groups. The percentage normal morphology below which fertility was adversely affected was found to be 60%: the fertility of dogs with > 60% normal morphology was 61% (14 of 23 inseminated bitches) whereas the fertility of dogs with < 60% normal morphology was 13% (two of 15 inseminated bitches). There was no statistical difference between the ages of the dogs in the two groups; from this it was concluded that subfertility may affect a dog at any age.

Cryopreservation of dog semen: a review.

Abstract: Success with artificial insemination of frozen dog semen has been limited. The major problems are associated with identifying the time of optimal fertility for insemination of the bitch, achieving intrauterine deposition of spermatozoa, the variation in post-thaw semen quality between individual dogs and poor spermatozoal survival after freeze-thawing. Many of these problems have been investigated and, to some extent, overcome; however, poor post-thaw spermatozoal longevity remains a problem and results from the lack of ordered logical studies of cryopreservation. The purpose of this paper is to review studies of dog spermatozoal preservation and insemination and to highlight those areas of cryopreservation that have been neglected.

Biology of gonadotrophin secretion in adult and prepubertal female dogs.

Abstract: Studies in the female domestic dog demonstrate that luteinizing hormone (LH) and follicle-stimulating hormone (FSH) have secretion patterns that are pulsatile, are inhibited by oestradiol during pro-oestrus and surge to maximal values before ovulation. Studies in ovariectomized bitches suggest that the periovulatory surge is triggered by a preovulatory decline at late pro-oestrus in the oestrogen:progesterone ratio. During the 3-8-month non-seasonal anoestrus, FSH concentrations usually are 50-100% of those of the periovulatory peak, whereas LH concentrations are only 10-20% of peak values. In ovariectomized bitches FSH concentrations are often 5-10 times preovulatory peak values, whereas LH concentrations are only the same as, or double, peak values. Increased LH concentration and pulse frequency are associated with the termination of anoestrus. Treatment with gonadotrophin-releasing hormone (GnRH) pulses or infusions of GnRH agonists can induce fertile oestrus in early anoestrous bitches, as can treatment with a dopamine agonist, presumably by suppression of prolactin secretion. Between 4 months of age and pubertal pro-oestrus at 8-12 months of age, serum concentrations of FSH and LH are similar to those in adult anoestrus, and are suppressed during chronic infusion of GnRH agonist. The latter resulted in a reversible inhibition of puberty during 1 year of treatment. Studies in vivo have shown that LH and prolactin are luteotrophic throughout most of the luteal phase. LH stimulated progesterone synthesis by bitch luteal cells in vitro in the presence or absence of stimulant factors or steroid precursors present in serum.

Premature ageing in transgenic mice expressing different growth hormone genes.

Abstract: Transgenic mice expressing various growth hormone genes have markedly reduced life spans, with few animals surviving beyond 12 months in some of the lines. Except for an increased incidence of mammary tumours in female mice expressing human growth hormones, pathological findings in debilitated or moribund transgenic mice resemble the well-documented degenerative changes that occur at a much greater chronological age in normal rodents. This study demonstrates that 10-month-old male transgenic mice expressing bovine growth hormone (known as 25-copy PEPCK. bGH transgenic mice) also show age-related changes in hypothalamic and striatal neurotransmitter metabolism that are not seen in normal litter mate controls until at least 24 months of age. Female mice and male mice with a lower circulating concentration of bGH (known as 5-copy PEPCK. bGH transgenic mice) live longer and fail to show the same magnitude of change in neurotransmitter synthesis and release. Although more work needs to be done to determine the physiological significance of these changes and to determine their relationship to the general effects of ageing on the CNS, transgenic mice expressing various growth hormone genes may provide an interesting and valuable model with which to study the ageing process.

Cytoplasmic inheritance and its effects on development and performance.

Abstract: In contrast to nuclear inheritance, cytoplasmic inheritance in mammals is derived mostly, if not exclusively, from the maternal line. Mitochondria, and their DNA molecules (mtDNA), are the genetic units of this method of inheritance. Mammalian mtDNA codes for 13 enzymes used in the mitochondrial energy-generating pathway, oxidative phosphorylation, 22 tRNAs and two rRNAs. Although all transcripts of mtDNA and their translational products remain in the mitochondria, most proteins used in mitochondria are from nuclear DNA and are imported after synthesis on cytoplasmic ribosomes. Spermatozoa introduce a small number of mitochondria into the cytoplasm of the egg at fertilization, which appear to be digested soon after penetration. Although the paternal contribution of mtDNA to the offspring is not believed to occur in mammals, some interspecific crosses have suggested that it does occur. Experiments with animals derived from reconstituted embryos, using nuclear or cytoplasmic transplantations, suggest that nuclear-mitochondrial interactions are important but not essential in the survival and replication of exogenous mitochondria introduced into the egg. As the levels of heteroplasmy varied in several tissues of animals derived from reconstituted embryos, it is suggested that differential partitioning of mitochondria occurs during embryogenesis. Mitochondrial morphology changes substantially during oogenesis and throughout early cleavage stages. Somatic morphology and normal replication patterns are regained at the blastocyst stage. In pig oocytes and embryos, mitochondria aggregate and are closely associated with endoplasmic reticulum, lipid granules and large vesicles. Although the direct correlation of mitochondrial genes with reproductive traits is still unclear, some human degenerative diseases and performance traits in cattle can be related directly to specific mtDNA polymorphisms. In pigs, reciprocal-cross comparisons have indicated greater offspring parent similarity with dam than sire for lean:fat ratio. A difference was also observed for oxygen consumption and oxidative phosphorylation, but not for anaerobic energy metabolism, in a pig reciprocal-cross experiment. Information on the transmission of mtDNA and its effects on performance will have many implications not only for our understanding of mitochondrial genetics but also for the increased productivity of animals. There are also potential ramifications to the animal cloning industry.

Early uterine development in pigs.

Abstract: The capacity of pig uterine tissues to recognize and respond to maternal and conceptus signals determines whether pregnancy can be established and defines the environment in which embryonic and fetal growth occur. Limits of uterine capacity may be defined genetically. However, the extent to which functional uterine capacity approaches genetic potential may be determined, in part, by the success of organizational events associated with growth, morphogenesis and cytodifferentiation of uterine tissues. It is important, therefore, that these events be identified and evaluated with respect to their potential effect on adult uterine function. Histogenesis of the pig uterus begins prenatally, but is completed postnatally. Transformation of the uterine wall from histoarchitectural infancy to maturity occurs between birth and day 120. Morphogenetic events characteristic of the first 60 days of neonatal life proceed normally in gilts ovariectomized at birth. These events include appearance and proliferation of uterine glands, development of endometrial folds, and growth of the myometrium. Endometrial development during this period involves alterations in patterns of epithelial and stromal DNA synthesis, coordinated changes in the distribution and biosynthesis of extracellular matrix glycosaminoglycans and cell surface glycoconjugates, and specific alterations in patterns of uterine protein secretion. The ovary-independent, spatially coordinated nature of these events suggests that neonatal uterine development is regulated locally via dynamic cell-cell and cell-extracellular matrix interactions. The extent to which such potentially critical interactions must be preserved to ensure developmental success remains unknown. However, the normal pattern of ovary-independent cellular and molecular events associated with development of the uterine wall was disrupted by treating neonatal gilts with oestradiol valerate, and daily administration of oestrogen to gilts from birth to day 13 did not affect ovulation rate, but did reduce embryonic survival by 22% on day 45 of gestation in adults that were exposed to oestrogen neonatally. These observations support the idea that some organizational events associated with development of the neonatal uterine wall must be allowed to proceed without interruption to ensure that adult uterine function is not compromised. Efforts to identify specific developmental determinants of uterine capacity may be facilitated by examining the consequences of xenobiotically induced interruption of uterine development on adult uterine function. Such studies may also contribute to identification of uterine factors affecting embryonic survival and fetal growth.

Effectiveness of in vitro maturation and in vitro fertilization techniques in pigs.

Abstract: In vitro maturation and in vitro fertilization techniques in pigs have progressed considerably in recent years. Many reports focus on the factors affecting in vitro maturation that lead to normal male pronuclear formation or monospermy after fertilization in vitro. It is suggested that pig follicular fluid (pFF), follicle somatic cells and various hormones are important factors for the maintenance of cytoplasmic maturation of oocytes in vitro, but that fetal calf serum (FCS), which is generally added to maturation medium, is detrimental. A series of experiments clearly indicate that the glutathione (GSH) content of matured oocytes increases greatly when maturation medium is supplemented with cysteine, a precursor of GSH, and the rates of male pronuclear formation increase in parallel with the increasing GSH content. To prevent polyspermy, conditions of maturation and of fertilization in vitro are important. Culture of oocytes in medium with FCS for the first 24 h and with BSA for the second 24 h decreases the incidence of polyspermy, without a significant effect on nuclear maturation. However, it has been shown that secretory macromolecules of the oviduct may reduce the incidence of polyspermy by interacting with fertilizing spermatozoa rather than with oocytes. A reduction of polyspermy by treating spermatozoa with pFF is also reported. In addition to the many improvements in the methodology of in vitro fertilization using unfrozen spermatozoa in pigs, techniques for fertilizing oocytes in vitro with frozen epididymal and ejaculated spermatozoa have also recently been developed.

Ovulation without cervical stimulation in domestic cats.

Abstract: Progesterone was measured by radioimmunoassay of serum collected at monthly intervals for 9 months (April-December) in 24 adult female American short-hair cats (age 25-11 years, mean 74 years); 20 cats were intact, and four were ovariohysterectomized controls One of the 20 intact queens was ovariohysterectomized after 7 months, when pyometra was diagnosed Cats could see and hear one another, and could see and hear male cats housed individually in the same room Direct contact with other cats was prevented Tactile stimulation of the cats' hindquarters and perineal regions by handlers was avoided Serum progesterone concentration > or = 48 nmol l-1 was defined as evidence of ovulation This concentration was exceeded in seven of 20 intact queens (35%) at one or more occurrences of non-coital ovulation; there were 13 such occurrences in all (1-3 per queen) Serum progesterone concentration ranged from 02 to 1034 (mean 1409 +/- 20) nmol l-1 in these seven cats, and was significantly greater than concentrations in the other intact and neutered cats In the remaining 13 intact and four ovariohysterectomized cats, serum progesterone concentrations ranged from 02 to 32 (mean 124 +/- 146) nmol l-1 These data suggest that, at least as far as cats housed in proximity to one another are concerned, intact female cats do not always require cervical stimulation to induce ovulation

Molecular biological methods for monitoring oocyte maturation and in vitro fertilization in bitches.

Abstract: Oocytes were collected from ovaries of bitches, at various stages of the oestrous cycle, after routine sterilization. Cumulus-enclosed oocytes were cultured for 0-72 h in a modified M-199 medium containing 10% oestrous bitch serum and 20 micrograms oestradiol ml-1. For oocytes surrounded by two or more layers of cumulus cells, an increase in the expression of mRNA transcripts for zona pellucida glycoprotein 3 (ZP3) was seen and reached peak levels after 48 h culture in vitro. Histological assessment showed that 39% of these oocytes had extruded their first polar body after 24 h culture in vitro. When these in vitro matured oocytes were transferred to oviduct cell monolayers and inseminated with fresh dog spermatozoa in Medium-199 supplemented with 10% fetal calf serum and 50 mg gentamicin sulfate ml-1, penetration of the zona pellucida started 1 h after insemination for oocytes that had been cultured for 48 and 72 h. At 12 h after insemination both male and female pronuclei were seen in 37.5% and 20% of the oocytes incubated for 48 and 72 h, respectively. No further development was seen.

Non-surgical intrauterine artificial insemination in bitches using frozen semen.

Abstract: A total of 46 bitches were inseminated directly into the uterus using non-surgical insemination procedures; the technique used in six bitches involved specially designed metal catheters and abdominal fixation of the cervix, whereas the remainder were inseminated by passing a flexible plastic catheter through the cervix using direct endoscopic visualization to facilitate the process. Twenty-seven bitches were inseminated with semen frozen at the clinic; the remainder were inseminated with imported semen. Insemination timing was based on endoscopic assessment of the vaginal mucosa, vaginal cytology and blood progesterone concentration determined using a rapid, qualitative enzyme-linked immunosorbent assay (ELISA) kit. Each bitch received between 50 x 10(6) and 200 x 10(6) total spermatozoa per insemination; post-thaw motility varied from 10 to 80%. Two inseminations were performed 48 h apart in the majority of bitches. An overall pregnancy rate of 80% (37/46) was obtained with a mean litter size of 5 +/- 3.14. Subsequent pregnancy rates were comparable for both techniques and both were considered to be effective methods of inseminating frozen semen. Considerably fewer spermatozoa were inseminated in many of these bitches than have previously been reported. In a series of seven bitches using the semen from one dog, each bitch received two inseminations of 30-35 x 10(6) live normal spermatozoa per insemination. A pregnancy rate of 85% (6/7) and a mean litter size of 7.8 was achieved. Rapid ELISA progesterone kits were used to identify the optimum time for insemination.

Biology of ovarian cycles, pregnancy and pseudopregnancy in the domestic cat

Abstract: Puberty in the female cat occurs between the ages of 8 and 10 months. Cats are seasonally polyoestrous, reflex ovulators. The oestrous cycle can occur as often as every 2-3 weeks. Ovulation usually occurs 24-36 h after copulation, and implantation occurs 12-13 days after copulation. The duration of gestation in the cat is 64-67 days (average 66 days). The corpora lutea secrete increasing amounts of progesterone, starting 1-2 days after ovulation. If implantation occurs, progesterone concentrations continue to increase throughout days 25-30, then slowly decline throughout the rest of pregnancy. In the absence of pregnancy, the corpora lutea reach their peak progestational activity within 10-15 days and then decline, with basal progesterone values being noted by days 30-35. Relaxin is produced by the fetoplacental unit beginning at about day 20 of gestation and continuing throughout the rest of pregnancy. Prolactin production increases from about day 35. Like those of prostaglandin F2 alpha, concentrations of prolactin plateau at about day 50 and increase abruptly just before delivery.

Genetic basis of prolificacy in Meishan pigs.

Abstract: Research in France and in the UK confirms the prolificacy of the Chinese Meishan breed to be about three to four piglets greater than that of control Large White females Crossbreeding studies clearly indicate that this breed difference is due to genes acting in the dam and not in the litter itself There is high heterosis for litter size in F1 Meishan x Large White crossbred females, such that their litter size is similar to or greater than that of purebred Meishan females There is some discrepancy between studies about whether the Meishan female has a higher ovulation rate than does the Large White breed and this can be attributed in large part to the different basis upon which breed comparisons have been made Nevertheless, there may be real genetic differences between Meishan pigs exported to different countries In young gilts at comparable numbers of oestrous cycles after puberty, the ovulation rate is similar in Meishan and Large White gilts, but in older gilts, and particularly in multiparous sows, Meishan pigs have a higher ovulation rate in British studies Once comparisons of prenatal survival between breeds have been adjusted for any breed difference in ovulation rate, the main cause of prolificacy in Meishan pigs can be seen to be an enhanced level of prenatal survival Crossbreeding studies show that this is controlled by the maternal genotype and not that of the embryos The advantage in prenatal survival to the Meishan pig is clearly present in the post-attachment period (after day 20 of gestation), but may also be present earlier in gestation Results from a study presented here suggest that Meishan sows have a higher uterine capacity than do Large White sows and this allows them to maintain their higher number of attached embryos through gestation F1 Meishan x Large White crossbred females achieve their high litter size via a different route than do purebred Meishan females These animals have a lower ovulation rate and fewer attached embryos than do purebred Meishan sows, but a very low level of fetal loss allows them to produce litters of similar size The low level of fetal loss in F1 females appears to be due to the higher uterine capacity of F1 females compared with purebred Meishan sows

In vitro fertilization in domestic and non-domestic cats including sequences of early nuclear events, development in vitro, cryopreservation and successful intra- and interspecies embryo transfer.

Abstract: The domestic cat may be used as a model for developing assisted reproduction techniques including in vitro fertilization (IVF), embryo culture, cryopreservation and embryo transfer (ET) for application to threatened and endangered species of non-domestic cats. Interoestrous domestic cats were injected with a total of 1.0-6.0 mg follicle-stimulating hormone (FSH) daily for 4 days and with 100 iu human chorionic gonadotrophin (hCG) on day 5. Follicular oocytes recovered at 26 +/- 1 h after hCG were co-incubated for 4-6 h at 38 degrees C in 5% CO2 with spermatozoa (1-2 x 10(5) motile spermatozoa ml-1) collected by artificial vagina. To determine the timing of sperm penetration and early fertilization events in vitro, oocytes were fixed and examined at intervals from 0.5 to 10 h after sperm exposure. The penetration rate of metaphase II (MII) oocytes at 0.5-3 h was equivalent to that at 3-6 h (95 versus 96%). Second polar body extrusion, pronuclear formation and apposition were observed at 2, 6-8 and 10 h, respectively. Simple (Tyrode's) and complex (F-10, M-199 and CMRL-1066) culture media with 10% fetal calf serum were compared for their ability to support development to the morula or blastocyst stage during culture periods of 96-168 h after IVF. The average number of cells per embryo was similar (P > 0.05) in the various media at each interval except that CMRL-1066 reduced (P or = 12 embryos (11/26) than if < 12 embryos were transferred (6/23).(ABSTRACT TRUNCATED AT 400 WORDS)

Results of 527 controlled artificial inseminations in dogs

Abstract: During 1990 and 1991, 527 artificial insemination (AI) procedures were performed by 40 veterinarians, under the Swedish Kennel Club control scheme, and reported to the Kennel Club within 14 days. The most common reason for AI (37.2%) was import of fresh and frozen semen or quarantine, i.e. introduction of new genetic material. Fresh semen (468 AIs) was deposited into the cranial vagina, and frozen semen (59 AIs) was inseminated transcervically into the uterus. Pregnancy rates were 54.7% with fresh and 39.0% with frozen semen. When corrected for stage of oestrus at the time of AI and semen quality, the pregnancy rates were 62.3 and 51.1%, respectively. Bitches inseminated with frozen semen had a 29.7% lower pregnancy rate and 30.5% smaller litter size than bitches receiving fresh semen; these differences were statistically significant. Forty-four bitches (8.4%) were also mated. Their pregnancy rate was significantly higher (88.6%; 90.7% corrected) than that of bitches inseminated with fresh semen only. Pregnancy rate was significantly higher in bitches inseminated twice with fresh semen than in those inseminated once only. Litter size and gestation length increased with the number of AIs. Most bitches whelped 62 days after a single AI with fresh or frozen semen, but the gestation period varied between 55 and 69 days. There were significant differences in fertility between breeds. Pup deaths occurred in 33.8% of the litters and the pup death rate during the first 3 weeks of life was 11.6%. The number of pups resulting from AI amounted to 1.1% of the total number of pups registered with the Swedish Kennel Club.

In vitro maturation and fertilization of preovulatory dog oocytes.

Abstract: Mature beagle bitches were injected with exogenous gonadotrophins to induce superovulation. Preovulatory oocytes were collected at 72 h after intravenous injection of human chorionic gonadotrophin and cultured for 72 h in a modified Krebs-Ringer bicarbonate solution containing 10% fetal calf serum and 30 mg gentamicin sulfate l-1. Control oocytes were collected from ovaries of anoestrous bitches and cultured for 72 h. All oocytes were at the germinal vesicle stage when collected. At 72 h of culture, a significantly larger population (31.9%) of preovulatory oocytes reached metaphase II, compared with the control group (12.1%). Ejaculated beagle spermatozoa were washed and preincubated for 4 h, then capacitated spermatozoa were added to the oocytes. The kinetics of sperm penetration into the ooplasm did not differ between the two groups of oocytes, but the development of male and female pronuclei was observed more frequently in oocytes collected from preovulatory follicles. These results suggest that preovulatory maturation is required for the normal development of canine oocytes, although they are ovulated at the germinal vesicle stage.

Optimizing semen production for artificial insemination in swine.

Abstract: Efficient production of high quality semen is of major importance to artificial insemination (AI) organizations. The semen produced should be free of contagious organisms, be of high quality, have good storage properties, fertilizing capacity and be of high genetic value. The best approach to prevent the spreading of microorganisms via semen in the process of AI is to collect semen from boars free from specific diseases, for example pseudorabies virus or leptospirosis. Antibiotics are added to the semen to suppress proliferation of microorganisms or even reduce their number. Sperm production is influenced by many factors such as season, collection frequency, breed and age. The average number of sperm cells produced per boar per week can vary more than 30% within one AI station, depending on the breed. Boar selection and boar management markedly influence the efficiency of sperm production. Sperm quality should be evaluated by fertility results obtained at breeding farms related to both farrowing rate and litter size to ensure a good quality monitoring system. A quality control system should be established to provide maximum reliability to customers.

Optimizing management of natural and artificial matings in swine

Abstract: A successful mating involves the coordination of many physiological events including insemination, gamete transport and ovulation. As more basic information about these processes becomes available, it is apparent that there are opportunities for manipulating these physiological events and enhancing the reproductive success of natural and artificial matings. The primary intent of this review is to examine the effectiveness of several of these strategies, as determined by their influence on farrowing rate and litter size. It is evident that the timing, duration and pattern of ovulation in pigs are extremely variable. Thus, increasing the frequency and changing the timing of matings during oestrus has received renewed interest. In general, if a female exhibits oestrus for more than 1 day, then increasing the frequency of matings has a greater influence on reproductive performance than does altering the timing of matings. In addition, litter size is more responsive to increased mating frequencies than is farrowing rate. Increasing the number of matings per oestrus via the use of combinations of natural service and artificial insemination, compared with the use of either alone, appears to enhance reproductive performance. It has been well documented that several aspects of the mating process itself can advance the onset of ovulation and enhance sperm transport and storage in the female reproductive tract. As a result, the use of these stimuli in conjunction with natural and artificial matings provide opportunities for enhancing fecundity. Pre- and post-breeding treatments with vasectomized boars, nonviable semen, oestrogens and seminal plasma have all been reported to increase farrowing rate and litter size. With artificial insemination, additions of prostaglandins, oxytocin, oestrogens and leucocytes to semen have been reported to enhance reproductive performance, albeit with varying degrees of success. Personnel and boar needs are important components in optimizing breeding management. Estimates of these needs for artificial and natural matings are discussed.

Effects of nutrition on pregnant and lactating sows

Abstract: It has been suggested that the long-term reproduction of the sow is best served by minimizing weight and fat loss in lactation. Such a strategy would require only a minimal restoration of weight in the following pregnancy, which would be beneficial, since the greater feed intake and weight gain in pregnancy, the greater the weight loss in lactation. Feeding ad libitum should be practised during lactation while gestation feed intake must be held low. A relationship between feed intake and embryo survival has been demonstrated in several studies, but the data are sometimes difficult to interpret. High energy feeding during the premating period and during early pregnancy, however, are often associated with increased embryo mortality. A short-term starvation in lactation decreased prolactin to post-weaning concentrations, and insulin and glucose to very low concentrations. Prolactin increased very rapidly after refeeding indicating that a neural mechanism might be involved. The increasing levels of cholecystokinin after refeeding and the neural reflex triggered might be related to this increase in prolactin. No changes in LH release were observed during the periods of starvation or refeeding. The catabolic rate during the first week of lactation is higher in sows with higher backfat thickness than in late gestation. As lactation progresses a more balanced metabolism is achieved regardless of backfat thickness before parturition. High-weight-loss primiparous sows need a longer recovery period from their negative energy balance during lactation than do low-weight-loss primiparous sows or multiparous sows. Several investigations have demonstrated that sows losing excessive amounts of body weight have extended weaning to oestrous intervals and an increase in anoestrus. Sows with low body-weight loss during lactation have higher plasma insulin and lower cortisol around weaning than do sows with high body-weight loss. What remains undefined is the degree of weight or condition loss below which an extension in the remating interval will occur and the level of dietary energy intake required to prevent this extension.

Studies of uterine secretions and products of primary cultures of endometrial cells in pigs.

Abstract: The uterus plays a central role in the reproductive biology of mammals. Adaptation of the uterus from an oviparous to a viviparous nature required changes that involved production of a uterine environment that could support the development of the embryo and fetus. Production of a suitable environment includes the synthesis and secretion of products by the uterine endometrium. However, the uterine endometrium is not a single homogeneous unit, but rather consists of several cell populations. Recent accomplishments in cell culture techniques provide a means for examining the contributions and secretory control of different endometrial cell populations. Furthermore, it is possible to recombine specific cell types to study their interaction. It is clear that the luminal epithelium, glandular epithelium and endometrial stroma produce different secretory products. Some secretions (for example uteroferrin) are secreted by only one cell type; others (for example prostaglandins, PGs) are secreted by all types of cell. There is much to be learned about the functions and regulations of endometrial secretions and there are important aspects of the role of the endometrium in pregnancy that present concepts do not address. For example, there is no explanation for the required synchrony between the embryo and uterus before day 10 and the implications of control of the uterine environment by progesterone from day 4 to day 10 are not understood. Almost all of the uterine secretory proteins are produced after day 10. In this review, we consider the protein and prostaglandin products from the different cell populations of the pig endometrium and propose a model to explain the integration of multiple sources of PGs and multiple regulators of PG secretion. Our purpose is to facilitate a more complete understanding of the individual uterine cell populations and a better understanding of how these cell types interact to function as a complete unit.

Hypo-osmotic swelling of dog spermatozoa.

Abstract: Dog spermatozoa were evaluated for their ability to swell when exposed to hypo-osmotic conditions. A medium was developed to allow spermatozoal swelling to be identified easily; both the number of swollen spermatozoa and their morphological appearance were influenced by the characteristics of this medium. The number of swollen spermatozoa was inversely proportional to the number of dead spermatozoa in a sample. Although spermatozoal swelling was highly repeatable there was no correlation with spermatozoal motility, morphology or vital staining. Electron microscopic studies demonstrated that swelling of spermatozoa was characterized by ballooning of the tail membrane and internal flexion of the axial filaments. Spermatozoa with damaged membranes were unable to swell. Hypo-osmotic swelling of dog spermatozoa is reliable and repeatable and may be a useful assay for the diagnosis of spermatozoal membrane function.

The regulation and mechanisms of action of growth hormone and insulin-like growth factor 1 during normal ageing.

Abstract: The decrease in tissue function that is observed in ageing animals has been linked to the decline in rates of protein synthesis. These changes may be caused, in part, by reduced secretion of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). It is well established that growth hormone-releasing hormone (GHRH) and somatostatin have an important role in the regulation of GH secretion and results from several studies suggest that an age-related increase in release of somatostatin has an important role in altering the secretion of GH. When the amounts of somatostatin mRNA were examined, there was a decrease in the aged rats but the amount of somatostatin mRNA bound to polysomes increased in these animals. This suggests that translational regulatory mechanisms are compromised in ageing animals. Moderate dietary restriction, which has been shown to increase life span, increases the amplitude of GH pulses and the capacity of tissues to synthesize protein. We have used the caloric restriction model to investigate the regulation and roles of GH and IGF-1 during ageing. Our results suggest that neuroendocrine regulation of GH secretion plays an important role in the process of biological ageing and that part of the beneficial effects of moderate dietary restriction may be mediated by altering the GH, IGF-1 axis.

Luteotrophic action of prolactin in dogs and the effects of a dopamine agonist, cabergoline.

Abstract: The purposes of this study were (1) to evaluate the effects of cabergoline (1.65 micrograms kg-1 injected subcutaneously for 5 days) on plasma progesterone concentrations in the pregnant bitch; (2) to assess its clinical value in terminating pregnancy in the bitch, and (3) to evaluate its side effects. Cabergoline, given to pregnant bitches, had an anti-prolactinic action and induced abortion. Plasma progesterone concentrations were reduced to below that value necessary to maintain pregnancy (2 ng ml-1 in all cases when the treatment was given 40 days after the first mating, and in four out of six cases when given from 30 days after mating). Fetal resorption occurred in 75% of cases, without clinical sign other than some vaginal discharge. The efficiency of cabergoline treatment can be monitored by plasma progesterone determination: concentrations < 2 ng ml-1 5 days after the start of treatment indicate success; in the event of failure, another treatment can be started. Ultrasonography was not always useful in predicting abortion, as in some cases this was not preceded by signs of fetal distress. The use of cabergoline as an abortifacient in the bitch appears to be of interest. Its efficacy in the second half of gestation, which is attributable to its antiprolactinic action, has been widely demonstrated and the probable multifactorial regulation of corpus luteum activity during the first half of gestation has suggested that earlier luteolysis could certainly be obtained without any side effects through a multiple approach, using different, mutually potentiating, luteolytic agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Embryo-uterine interactions in pigs during week 2 of pregnancy.

Abstract: The second week of pregnancy is a particularly critical period for embryonic survival in pigs. Within that time, conceptus oestrogen synthesis is initiated, spacing and final placement of conceptuses is completed, and the signal for extending the functional lifespan of the corpora lutea is received by the mother. There is also a marked increase in blood flow to the uterus and the uterine endometrium produces and secretes nutrient histotrophe. Conceptus-derived oestrogen has been implicated in many of these events. It is also during this period that the trophoblast elongates dramatically and the inner cell mass starts to differentiate into the embryo proper. Here, we critically review the evidence that oestrogen is the sole factor initiating long-term corpus luteum maintenance in pigs. We also review the functions and general properties of the major secretory proteins in histotrophe and the role of oestrogen in controlling their expression. It is now generally accepted that asynchrony within a litter underlies much of the losses of conceptuses that are otherwise genetically normal, but which are lagging in their development; however, the underlying mechanisms remain unclear. Here we hypothesize that oestrogenic compounds derived from more advanced conceptuses or provided prematurely, either by injection or in the diet, trigger a massive increase in uterine expression and secretion of retinol-binding protein laden with retinol. We propose that less developed, smaller conceptuses are least able to contend with the sudden exposure to this potential teratogen at a time when they are particularly susceptible to imbalance in retinol supply. Hence, even though their growth proceeds for a few days, their developmental potential is irrevocably compromised.

Comparative cryopreservation and capacitation of spermatozoa from epididymides and vasa deferentia of the domestic cat.

Abstract: Methods of cryopreservation for spermatozoa from domestic cat epididymides and vasa deferentia were compared as models for posthumous gamete salvage from non-domestic felids Spermatozoa were collected either immediately after castration (Fresh, n = 37) or after being cooled (5 degrees C) in tissue overnight (Cool, n = 37) and released into one of three extenders containing 20% egg yolk and 3% glycerol for cryopreservation: (1) TE: Tris buffer, citric acid and fructose; (2) TC: Tris buffer, citric acid and glucose, or (3) CP: lactose, and frozen over lipid nitrogen Before and after freezing, each sperm cell sample was evaluated for motility and percentage morphologically normal cells Samples were also evaluated for their ability to initiate fertilization using a zona attachment assay Neither percentage morphologically normal spermatozoa nor percentage motility differed among the three diluents for prefreeze and post-thaw samples, regardless of the collection treatment However, CP tended to provide lower post-thaw status than did the TE and TC cryoextenders Before freezing, there was no difference in percentage motility between the Fresh and Cool groups (mean: 76 versus 72%, respectively); however, progressive status and normal morphology were lower (P < 005) in Cool (30 and 57%) than in Fresh (34 and 64%) samples After thawing there was a greater decline (P < 005) in percentage motility in the Cool than in the Fresh group (34 versus 24%) and the number of intact acrosomes dropped from prefreeze values of 667 +/- 63 and 564 +/- 48% to 178 +/- 39 and 209 +/- 46% after thawing in the Fresh and Cool groups, respectively(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrasonographic monitoring of follicular development, ovulation and the early luteal phase in the bitch.

Abstract: Follicular development, ovulation and the early luteal phase in 15 oestrous cycles of 13 individual bitches were monitored daily by ultrasonography using a 7.5 MHz sector scanner transducer. These findings were compared with vaginal cytology and changes in the peripheral plasma concentrations of oestradiol, luteinizing hormone (LH) and progesterone. Both ovaries were imaged throughout the period of study. Follicles were identified as anechoic spherical structures as early as day 1 of pro-oestrus in two cases and on days 3-4 in 13 cases. The average follicular size increased from 3.7 +/- 0.6 mm to 6.9 +/- 0.7 mm (P < 0.001) between day -5 and the LH surge (day 0). The anechoic structures then increased in size to 7.5 +/- 0.7 mm (P < 0.05) until day 2 after the LH surge; their diameters continued to increase during corpus luteum development, up to 8.1 +/- 0.6 mm (P < 0.001) on the first day of dioestrus. The average number of follicles counted imaged on the day of the LH surge was 3.3 +/- 0.4 on the left ovary and 3.7 +/- 0.7 on the right ovary. The rapid disappearance of the anechoic antrum, corresponding to ovulation, was detected in only two bitches. In the remaining cases follicular rupture was not detected; however, starting at the LH surge, a gradual thickening of the antral wall occurred. This corresponded to a progressive obliteration of the anechoic region and was characteristic of the postovulatory corpora lutea. These changes led to a significant decrease (P < 0.05) in the number of anechoic structures to 2.4 +/- 0.5 on the left ovary and 3.3 +/- 0.5 on the right ovary by day 1 of dioestrus. During the follicular phase, the mean increase in oestradiol concentration was correlated with follicular size (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Early embryonic development in prolific Meishan pigs.

Abstract: Prenatal mortality in European pigs is estimated at 30-40%, the majority of which occurs between days 12 and 18 after mating. Chinese Meishan pigs are prolific, averaging three to five more pigs per litter than do European breeds. Early reports into the fecundity of Meishan females suggested that their prolificacy resulted from lower embryonic mortality when compared with European females exhibiting the same ovulation rate. The preponderance of evidence suggests that there are no differences between Meishan and European breeds in either morphological embryo diversity within a litter or embryo mortality before day 12 after mating. Recent studies from our laboratory suggest that preimplantation embryos from Meishan females exhibit markedly reduced growth rates and oestrogen secretory activities through day 12 when compared with embryos from Yorkshire females. The significantly reduced conceptus sizes of Meishan versus European breeds on day 30 of gestation provide additional evidence of the reduced growth rate of Meishan embryos. Furthermore, because embryonic oestrogen production is known to alter uterine secretion of histotroph, the lower oestrogen production by Meishan embryos in the Meishan uterus may result in more gradual alterations in the uterine environment that are beneficial for conceptus survival and subsequent litter size. Recent studies using cross-transfer of Meishan and Yorkshire embryos on day 2 after mating have led to the suggestion that there is a major effect of recipient genotype on embryonic growth rate and oestrogen secretion. In these studies, both Meishan and Yorkshire embryos transferred to Meishan uteri exhibited marked decreases in morphological development and oestrogen content on day 12 when compared with embryos transferred to Yorkshire recipients. These data suggest the presence of factor(s) in endometrial secretions from Meishan females that reduce the growth rate and oestrogen secretory potential of preimplantation conceptuses.

Aspects of the neuroendocrine control of growth hormone secretion in ageing mammals.

Abstract: In aged animals and humans the pulsatile secretion of growth hormone (GH), the mean amounts of GH released over 24 h, and the response of GH to the administration of GH-releasing hormone (GHRH) are lower than in young adults Pituitary somatotrophic cells in old male and female rats show an impaired responsiveness to GHRH, and the reduced secretion of GH in vitro is linked with a diminished stimulation of adenylate cyclase by GHRH Pretreatment with GHRH in vivo decreases the high basal adenylate cyclase activity in old male rats This pretreatment does not affect the rise of adenylate cyclase concentration in these rats that is subsequently induced by GHRH administration in vitro However, it does induce a small rise in adenylate cyclase concentration in old female rats In young rats of either sex the same GHRH schedule does not alter adenylate cyclase activity, but it does reduce the effectiveness of subsequent acute exposure to GHRH to stimulate enzymatic activity Short-term administration of GHRH in some aged subjects increases the response of GH to a subsequent acute challenge with GHRH However, primary or secondary alterations in somatotrophic cells are also present in aged mammals, such as a reduction in the number of GH-immunoreactive structures or post-receptor alterations In aged rats, major alterations in brain neurotransmitters and neuropeptides are present in hypothalamic and extrahypothalamic structures, especially in catecholaminergic and acetylcholinergic neurones These alterations are probably due to defects in neurosecretory GHRH and somatostatin neurones GHRH synthesis is impaired in the hypothalamus of senescent male rats, as shown by a reduction in GHRH mRNA levels and GHRH-like immunoreactivity Although the expression of somatostatin seems to decrease with age in the rat hypothalamus, secretion and activity of this hormone is increased, resulting in an altered relationship between GHRH and somatostatin gene expression and secretion Catecholamines induce GH release in most animal species by stimulating GHRH neurones and inhibiting somatostatin-releasing neurones Acetylcholine stimulates GH release via muscarinic receptors, and thus inhibits the effect of somatostatin neurones In male rats of various ages, except very young rats, systemic administration of pilocarpine, an agonist of muscarinic receptors, potentiates the GH response to GHRH during the entire lifespan(ABSTRACT TRUNCATED AT 400 WORDS)