Parturition and Postpartum Physiology

The physiological process of delivering foetuses and foetal membranes from the uterus to the external environment is called parturition or eutokia. It occurs in three stages with species-specific time duration (Table 23.17).

Table 23.17 Duration of various events of parturition (in hour)

Source: Compiled from various sources

Max maximum, avg average

23.4.1 Foetal changes before parturition

The foetus undergoes physiological and structural changes before the parturition for the extrauterine life.

1. Lung maturation and its expansion by the secretion of surfactants that reduce the alveolar surface tension.

2. Development of glycogen stored in the liver for energy supply till the initiation of suckling.

3. Increased output secretion of catecholamines and tri-iodothyronine for metabolic activity and thermoregulation.

The structural changes of the foetuses that occur before the parturition include

1. Closure of the ductus arteriosus.

2. Closure of foramen ovale within a few hours of birth.

23.4.2 Factors Responsible for the Initiation of Parturition

Throughout the gestation, the uterus remains quiescent under the influence of progesterone secreted from CL and placental. Uterine contraction initiates at the time of parturition due to decreased progesterone levels and increased oestrogen levels. Several other bio-molecules like prostacyclin, relaxin, nitric oxide and catecholamines begin the parturition process. The foetal glucocorticoid surge is the universal signal for the parturition in most domestic species. The physical,

Table 23.18 Factors responsible for the initiation of parturition

biochemical and hormonal signal factors to initiate the partu­rition process are presented in Table 23.18.

23.4.3 Mechanism of Parturition

At the end of gestation, the foetal hypothalamic-pituitary­adrenal (HPA) matures and increases cortisol secretion (Fig. 23.9). Foetal cortisol influences the functional matura­tion of foetal physiological systems, particularly the lungs and the cardiovascular system requires for the newborn immediately after birth. Increased foetal cortisol up-regulates cyclooxygenase 2 (COX2) and steroidogenic key enzyme 17a-hydroxylase-C17,20-lyase (CYP17) in the trophoblast cells. COX2 increases prostaglandin production. Activation of CYP17 leads to the metabolism of pregneno­lone to dehydroepiandrosterone, and the level of progester­one falls along with increased oestrogen level. The altered endocrine milieu (decreased progesterone, increased oestrogen) induces contraction associated proteins in the myometrium.

23.4.3.1 Ferguson Reflex

Ferguson reflex is a neuroendocrine reflex induced by the distension of the cervix caused by the foetus that stimulates a series of neuroendocrine responses to expel the foetus. The uterine distension signals the nucleus tractus solitarii (NTS) through spinal and vagal afferent nerves. NTS neurons proj­ect into the magnocellular oxytocin neurons at para ventricu­lar neurone (PVN). The neurones of NTS release nor-adrenaline that acts over the α1 receptors n PVN to activate the oxytocin neurons to release oxytocin that initiates myometrial contraction.

Melanin of the pineal gland controls the circadian rhythm through the suprachiasmatic nucleus (SCN) and stimulates the uterine contraction, determining the time of parturition. Melanin generally affects the uterus during the resting phase of the day; hence, parturition usually occurs in the daytime in the nocturnal animals like rodents (rabbits) and during late night or early morning hours in humans.

23.4.4 Inflammatory Changes During Parturition

The inflammatory process before and during the parturition is termed cervical ripening. It starts a few days before parturi­tion with a slow progression rate but immediately before, the inflammatory reaction accelerates rapidly. The types of cytokines involved in this process are species specific. In cows, the IL-1β, IL-8 and IL-10 increase, whereas TNF-α decreases. Granulocyte colony-stimulating factor (G-CSF), leukaemia inhibitory factor (LIF) and prostaglandin (PGE₂)

Fig. 23.9 Neuroendocrine mechanism of parturition. The cervical stretching induces oxytocin secretion from the posterior pituitary. Oxytocin initiates myometrial contraction. Higher secretion of PGF2α causes luteolysis and decreased progesterone secretion.

are increased during stage-1 of parturition. All these bio-molecules cause neutrophils into the cervical tissues and induce the release of matrix metalloproteinases (MMPs) from the stromal cells, fibroblast and smooth muscle cells. Some of the important MMPs are MMP-1 (Fibroblast colla­genase), MMP-2 (Gelatinase-A), MMP-8 (leukocyte collage­nase) and MMP-9 (Gelatinase-B). MMPs cause depletion of the collagen network and loosen the interactions between the bio-molecules present in the extracellular matrix of cervical connective tissue to decrease cervical rigidity and soften it.

23.4.5 Events of Parturition

There are three events of parturition that occurs sequentially. Stage-1 of parturition is the dilation of the cervix. It is also referred to as the onset of labour. The dilation of the cervix characterises it. Initially, the dilation is occurred slowly, called the latent phase, followed by an active phase. Stage- 2 or the expulsion or delivery of the newborn commences after full dilation of the cervix and continues till the expulsion of foetuses. The first phase of expulsion is passive. The foetus moves down through the vagina, followed by a short duration of active phase with the contraction of abdominal and uterine

Relaxin causes cervical dilation. Other associated endocrine factors of parturition are prolactin (induces maternal behaviour) and melanin (causes uterine contraction). The foetal cortisol also promotes myometrial contraction

muscle contraction that push the foetus to expel out. Stage-3 is the placental shedding stage when the placenta is expelled out after delivery of the young. Pluriparous animals require less time to complete each stage than primiparous animals. The species-specific characterised events of parturition are depicted in Table 23.19.

23.4.5.1 Stage-1

The cervix remains firmly closed during the entire gestation period in the form of a cervical plug.

Behavioural changes before parturition: Immediately before parturition is uneasiness or discomfort, anorexia, rising tail and mucous discharge from the oedematous and flaccid vulva. The softening and relaxation of the pelvic ligaments near the pin bones causing depression in the area generally occurs in domestic mammals. In a mare, the sinking

Table 23.19 Characteristic features of parturition in different animals

(continued)

Table 23.19 (continued)

of croup muscles is not so profound. Udder enlarges, becomes oedematous, and even secretion may appear from a teat in cow and litter bearing animals like the sow, bitch and queen. It occurs 2-4 weeks earlier in litter bearing animals and fourth months in the calf. Bitch and cat usually remain calm and quiet before parturition.

23.4.5.2 Stage-2

This stage begins with the entry of the foetus and foetal membrane into the pelvic canal. The allantochorion (com­monly known as the water bag) is expelled first, followed by the amnion, which contains the foetus. The rapid abdominal and uterine contractions expel the foetus through the vulva. The maximum contraction occurs during the expulsion of the foetal head. This maximum straining is followed by rest, but soon after that, the foetal thorax passes the vulva. The hips and hindlimbs are expelled simultaneously. The mare and sow usually lie in lateral recumbency while cow, bitch and ewe prefer to lie on their sternum. The offspring are generally born with the intact umbilical cord, but the movement of offspring and mother ruptures the cord. It takes longer to expel the foetuses in polytocous animals, depending on the number of foetuses. The duration between two successive piglets is about 10-20 min in the pig.

A longer time to complete the delivery process occurs in some abnormal conditions like twins, monster calf and abnor­mal posture of the foetus. During delivery, lateral recum­bency is the usual posture in most domestic animals but standing posture may also occur in pluriparous dams. The behavioural changes at this stage include licking and grooming. The licking in the nasal area facilitates the removal of mucous and placental tissues for the ease of respiration. The grooming behaviour is absent in sows, and the piglets

Table 23.20 Duration of parturition in different species

often die due to respiratory obstruction. Bitches and queen nurse their offspring in recumbency while cow, ewe and doe nurse their young in standing. A strong bond between mother and foetus is developed primarily due to pheromone per­ceived by olfaction.

23.4.5.3 Stage-3

Occasionally, the placenta is expelled within 3-8 h after the delivery of the foetus (Table 23.20). The expulsion of the foetal membrane is facilitated by the loosening of chorionic villi from maternal crypts. The expulsion of the foetal mem­brane occurs in two stages. The failure of placental expulsion within 24 h after parturition leads to retained placenta.

23.4.6 Foetal Presentation During Parturition

The foetus rotates from its position throughout the entire gestation period and orients itself to the normal parturition posture for smooth delivery at stage-1. Generally, the normal foetal presentations are of two types in domestic animals. These are either anterior presentations or posterior presentations. In the anterior presentation, two forelimbs and the head are present towards the vulva parallel to the animal’s spine. In the posterior presentation, one or both of the hind limbs and tail remain towards the opening of the birth canal parallel to the animal’s spine. In polytocous animals like pigs, the foetuses are positioned about half- and-half between facing forwards and facing backwards. Different abnormal presentation leads to parturition complications.

23.4.7 Parturition Complications

Difficulty during parturition is termed dystocia. Dystocia and retained placenta are the two major complications that arise during parturition. Each foetus has an individual placenta; hence, increased litter size may lead to dystocia. Positioning of the head between forelimbs in multiple foetuses causes dystocia on many occasions. Dystocia is mainly developed due to inappropriate cervical dilation and mostly occurs in cattle, goats, sheep and humans. The cervix of cattle is generally more cartilaginous; hence, incomplete cervical dilation is more. Several gestational anomalies like twins and uterine torsion may cause incomplete cervical dilation in cattle. The weak myometrial contraction due to hypomagnesaemia, hypocalcaemia, hyposelenemia and old age predisposes to incomplete cervical dilation and dystocia. Insufficient production of certain enzymes like 5α-reductase, and increased tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) fail cervical ripening. The deficiency of 5- α-reductase causes sustained progesterone production. A large size foetus may cause a hip lock. If the placenta is not driven out within the period of stage-3 (Table 23.20), the state is termed as retention of the placenta. Low oxytocin is considered one of the causes of retention of the placenta.

23.4.8 Induction of Parturition

In some cases, parturition is induced through therapeutic and managemental interventions to release the mother from sev­eral conditions like traumatic reticulo pericarditis, broncho­pneumonia, pre-partum cervical prolapse, downer cow syndrome and pregnancy toxaemia. Prolonged gestation is also required for parturition induction. The manipulation of the time of parturition is also desirable as calving in daylight facilitates better care for the newborn and the mother. The parturition can induce either through therapeutic interventions or managemental procedures.

23.4.8.1 Therapeutic Interventions for Parturition Induction

Several drugs like glucocorticoids, oxytocin and PGF2α are used alone or in combinations to induce parturitions in domestic and pet animals. The drugs’ choice and doses vary considerably among different species (Table 23.21).

23.4.8.2 Managemental Interventions

for Parturition Induction

Most parturition in cows happens in the hour of darkness. The easiest and most effective method for avoiding night calving is feeding cows at night. The exact mechanism is unknown, but it is postulated that feeding alters intra-ruminal pressure. The frequency of rumen contraction falls a few hours before parturition. Feeding increases the rumen con­traction, and hence the parturition can delay night feeding.

Table 23.21 Therapeutic intervention to induce parturition in different species

23.4.9 Postpartum Physiology

The time between the parturition and the occurrence of the first oestrous is called postpartum period (interval) or puer­peral period. The duration depends upon species, breed, nutritional status, age, parity and environmental conditions. Each species required a considerable time to exhibit the postpartum oestrus. It varies widely, only 24 h (rabbit) to 60 days (cow). The major physiological changes occur in the ovary, uterus, and mammary gland, together with behaviour changes to nourish the young.

Failure to exhibit oestrus and ovulate beyond such period after parturition is considered postpartum anestrus.

23.4.9.1 Postpartum Ovarian Changes

Pregnancy interrupts the HPO axis by secreting large quantities of the placental steroids, and resumption of ovarian cyclicity depends upon the interaction between hypothalamus-pituitary. The CL inhibits the growth of the antral follicles even 20 days after the parturition in cows and reduces the frequency of ovulation. The resumption of ovar­ian cyclicity occurs in three distinct phases. In the first phase, which occurs within 2-4 weeks postpartum, the pituitary LH secretion is increased. In the second phase, the sensitivity of the hypothalamus to the positive feedback of estradiol is restored. In the third phase, the HPO axis is recovered from the suckling induced suppression due to prolactin.

23.4.9.2 Uterine Involution

The restoration of uterine volume to its non-pregnant state is called uterine involution. It is characterised by decreased uterine volume, elimination of bacterial infections and regen­eration of uterine epithelium. In cows, the diameter and length of the gravid uterus are reduced to half by 5 days postpartum and 15 days postpartum, respectively, and completed with 40-50 days postpartum (Table 23.22). The constriction and occlusion of caruncular blood vessels lead to

Table 23.22 Uterine involution and occurrence of postpartum oestrus in different species

necrotic changes in the caruncle within 48 h of parturition. The necrotic layer is spread over the stratum compactum by day 5 postpartum. Some of the necrotic materials slough off through lochia (the uterine discharge secreted during early postpartum, composed of blood, mucus, remnants of foetal membranes, and maternal tissue together with foetal fluids). The shedding of necrotic caruncles is completed by day 15 postpartum, and the smooth surface of the uterus is restored by day 19 postpartum. Other than the inter- caruncular areas, the endometrial tissues start regenerating immediately after the parturition and completely regenerate by day 8 postpartum in the cow. The caruncular re-epithelialisation starts from 25 days postpartum and heals entirely by day 40-60. The constriction of the cervix begins within 10-12 h of parturition in cow and undergoes atrophy and shrinkage. PGF2α helps in uterine involution.

The important events in the ovary during this period are regression of corpus luteum, no follicular growth, decreased ovary size and appearance as anestrus. Uterine involution and repairing of the endometrium occur. Nursing to the young is common in most mammals after parturition, except mares and rats. Copious milk secretion with a positive energy balance has been found in the mammary epithelium cells. Suckling increases opioid peptides (β-endorphin) from the hypothalamus, which inhibits gonadotropin secretion, caus­ing to increase postpartum period. Thus, weaning favours to re-establishment of the HPO axis. It results in oestrous, and ovulation and the animal can conceive further. The oestrous after parturition is termed postpartum oestrus and can affect by light cycles, temperature and humidity. Any kind of stress negatively affects the HPO axis through cortisol, followed by a delayed postpartum period. Hot, dry and extreme weather cause delays in the postpartum period. Parturition in the non-favourable season to the seasonal breeder also delays the period. The development of anomalies during pregnancy and parturition may also cause delays in the postpartum period.

23.4.10 InitialCareofNewborn

23.4.10.1 TheOnsetofRespiration

During the parturition, PO₂ and blood pH is decreased, and PCO₂ is increased due to placental separation. High PCO₂ stimulates chemoreceptors at the carotid sinus and initiates respiration. Tactile and thermal stimulation is also required to initiate respiration. After birth, the fluid and mucous from the upper respiration tract need to be cleared first. Brisk rubbing the chest and scrapping of nostrils are the tactile stimuli to induce sneezing and clear the upper airways. Doxapram hydrochloride can also be applied to induce breathing. In extreme cases, oxygen therapy is required.

23.4.10.2 Thermoregulation

The newborn has inadequate sub cutaneous fat insulation and poor thermoregulatory control. The initial thermoregulation is achieved by producing metabolic heat and reduction in heat loss. For adequate metabolic heat production, sufficient nutrition is essentially required. The newborn should be placed in a warm environment to minimise heat loss. Appli­cation of body coat can also reduce heat loss. The ideal temperature for the newborn puppy is 95-100 °F during the first week, 85 °F during the second week and 70-85 °F during the third week.

23.4.10.3 CareofUmbilicus

The hemostatic clamp must be removed from the umbilical cord and must ligate to prevent further haemorrhage. Cutting the umbilical cord close to the abdomen is advisable, along with proper disinfection with antiseptic.

23.4.10.4 Feeding of Colostrum

Feeding of colostrums is required to boost the newborn’s immune system by transferring immunoglobulins. Nutrients and antibodies increase the immune system. Increased level of oxytocin induced by suckling stimulus facilitates colos­trum ejection. Cleaning of teats and physical assistants to a newborn is required for initial colostrum feeding. As a thumb rule, colostrum at the rate of 10% of a calf’s body weight can be fed to the newborn. Colostrums replacement therapy or colostrum from other animals should give in case of death of the dam.

23.4.11 Postpartum Reproductive Disorders

Due to stress and immune suppression around the peripartum, the animals are prone to infections. Some post­partum disorders like mastitis, metritis, retained placenta, and lameness may also occur from digestive or nutritional malfunctions directly affecting uterine development.

23.4.11.1 Mastitis

Mastitis has a direct effect on reproduction. Inflammation due to mastitis leads to stress and hyperthermia because of increased cortisol, reactive oxygen species (like NO) and cytokine (TNF-α). It affects locally and in the HPO axis, resulting in abnormalities in the oestrous cycle, ovulation, decreased oocyte competence, and failure of fertilisation. In addition, the pathogen-derived endotoxin and altered immune system cause endocrine imbalance and increased production of PGF2α, followed by luteolysis and an adverse uterine environment. It causes early embryonic mortality or abortions in dairy cattle. Mastitis affects reproduction in dogs also.

23.4.11.2 Metritis

Metritis and endometritis are uterine infections. They cause poor follicular growth and postpartum anestrus due to alter­ing GnRH secretion, decreased responsiveness of LH to the follicular cells and lower aromatase expression followed by less oestrogen secretion. The inflammatory response in the endometrial epithelium generates TNF-α, nitric oxide synthase (NOS) and prostaglandin-endoperoxide synthase 2 (PTGS2 or COX-2). It influences more PGE production than PGF (PGF2α). Thus, luteolysis is disturbed. Endome­trial immunity is also compromised through altered steroid hormone concentration, somatotrophins and local regulatory proteins due to LPS of the pathogens. Higher progesterone and IGF I, released in metritis, play an immunosuppressive role through the serine proteinase inhibitors, glycan-binding proteins (galectins) and galactose-β1,4-N-acetylglucosamine. Systemic inflammation and metabolic syndrome also affect reproductive function by a similar mechanism. Hence, metritis, endometritis and systemic inflammation directly affect the reproductive function to cause impaired fertilisation, twins, stillbirth, dystocia and retained placenta. It often occurs in cattle, sheep and dogs.

23.4.11.3 RetainedPlacenta

Retention of the placenta may occur due to certain venereal diseases and managemental and nutritional factors. It may cause chronic infection and alteration in hormonal balance and immune compromisation of the mother. It results in twin, abortion, stillbirth, dystocia, labour problem and shortened gestation. Subinvolution of the placenta after the first parturi­tion within 3 years of age is a common problem in the dog.

23.4.11.4 Lameness

Lameness is considered chronic stress to the animal. Hence, the HPO axis is inhibited through cortisol and other stress bio-molecules. So, LH pulse frequency and oestrogen level are reduced. It causes poor oestrus signs, failure of ovulation, delayed ovulation and low progesterone production from the immature corpus luteum. Thus, oocyte maturation and the process of fertilisation are disturbed. Infertility may develop due to the formation of an anovulatory cyst. Delay postpar­tum oestrus has also occurred.

23.4.11.5 Digestive or Nutritional Factors

Reproductive anomalies may also occur due to nutritional deficiency and toxicity of certain chemicals during in post­partum state. It causes improper placental growth and abor­tion with other reproductive hazards. The deficiency of vitamin A results in thickening and erosion of the placenta, followed by abortion in late gestation. It also causes an irregular oestrous cycle. The lack of vitamin D develops silent oestrus and delays ovulation. Iodine deficiency is also a cause of abortion. Deficiency of iron, copper, cobalt and protein leads to anaemia and energy-deficient condition leads to anestrus and irregular oestrus due to disturbance in the HPO axis and ovarian activity. Magnesium and phosphorus deficiency, mostly during postpartum of high yielder animals, also causes a similar effect. Selenium and vitamin E defi­ciency causes metritis. Excess blood urea nitrogen (BUN) due to protein-rich ration reduces fertilisation. Toxicity of nitrites and nitrates from fertiliser and some plants during drought, excess phosphorus (from the plant’s seed), and mycotoxins from fungus caused abortion and retained pla­centa. Diarrhoea, bloating, bleaching, constipation, nausea, poor gut health, chronic irritation and cramping cause anxiety and stress, lead to deviation in the HPO axis and ovarian dysfunction. Gluten (a protein found in wheat, rye and barley)-rich diet may develop an autoimmune disorder called celiac disease in the genetically predisposed dog, cats, rats and mice. It causes ovulatory problems along with osteopo­rosis, depression and anaemia. Various oestrogenic compounds like bisphenol A, DDT, polychlorinated biphenyls, polybrominated diphenyl ethers, petroleum by-products, pesticides, herbicides and plastics disrupt the steroidogenesis process during foetal growth.

23.4.12 Diseases Related to Embryonic Mortality and Foetal Abnormality

23.4.12.1 Congenital Disorders

Congenital deformity in the reproductive tract, like malfor­mation of the Mullerian duct, results in abnormalities in the fallopian tubes and uterine cavity. Like the Boxers breed of dog, some small animals have a small-sized uterus, causing dystocia. The ovarian bursal adhesion may occur in specific conditions due to improper ovarian manipulation by rectal palpation. It appears in large ruminants and results in inap­propriate capturing of ova during ovulation and fertilisation anomalies. Other placental abnormalities include small pla­centa, premature placental separation and umbilical cord complications. Common defects in dog foetal developments are canine congenital sensorineural deafness (CCSD, degen­eration of inner ear), canine-dilated cardiomyopathy and hypocalcaemia originated canine eclampsia (mostly in small-breed accompanying with more litter size).

Certain diseases like bovine viral diarrhoea (BVD), vibri­osis, brucellosis, chronic leptospirosis and trichomoniasis cause early embryonic mortality and infertility. Different pathogens affect different modes, but in general, adhesions in the region of the ovaries, obstruction in the oviducts, and inflammation in the uterus, placenta and cervix occur. Hence, the normal reproductive function is affected.

23.4.12.2 BovineViral Diarrhoea (BVD)

BVD causes early embryonic mortality or foetal death or birth of a malformed calf in cattle according to severity and time of infection. The infection also causes ovaritis and leads to the malfunctioning of follicular cells resulting harmful environment for the embryo or foetal development. It may also cause retention of the placenta.

23.4.12.3 Vibriosis

Vibriosis is caused by the bacterium Campylobacter foetus (earlier Vibrio foetus). It is common in cattle and sheep and also in humans. It is a venereal disease and spreads by infected bulls. The bacteria cause inflammation in the trophoblasts and chronic villi, resulting in necrotic placentitis and uterine infection. Infection may continue 1-8 months of pregnancy. The consequence is abortion and infertility.

23.4.12.4 Brucellosis

Brucellosis is a venereal disease caused by the bacterium Brucella abortus. It causes infection in the endothelial cells of the capillaries and sub-chorionic tissues. The oedematous growth results in the premature termination of pregnancy and retention of the placenta. It affects cattle, sheep, goats, pigs, dogs and humans.

23.4.12.5 Leptospirosis and Trichomoniasis

Leptospirosis caused by Leptospira genus of bacteria. Trans­mission occurs during natural mating, where young are more susceptible and cause early embryonic mortality. Cattle, sheep, goats, pigs and dogs are affected more. Trichomonia­sis is caused by a protozoon, Trichomonas foetus. The infec­tive organism transmits through the infected animal, semen and instrument used for insemination. It causes uterine infec­tion and abortion. It is common in cattle.

23.4.12.6 OtherPathogens

There are other organisms like streptococci, staphylococci, corynebacteria, diplococci, micrococci, and moulds that cause local infection in the reproductive tract; the conse­quence of this result in impaired gestation and infertility may arise in the chronic stage.

Learning Outcomes

• Fertilisation: Internal fertilisation occurs in all the primates and non-primates domestic mammals. Semen is deposited at the vagina by natural insemi­nation and around the cervix by artificial insemina­tion. The time of insemination depends upon the time of ovulation and it is species specific. After insemination, spermatozoa are transported to the ampulla, the site of fertilisation, through a uterine tube, and subjected to species-specific biochemicals and molecular changes known as capacitation and hyperactivation for final maturation. In most mammals, the secondary oocyte completes its mat­uration after ovulation in the oviduct immediately before fertilisation with the induction of spermatozoa. A series of biochemical reactions, like acrosomal reaction in the spermatozoa, cortical reaction in the oocyte, entry of sperm and initiation of meiosis and karyogamy occur to complete the fertilisation process. Several proteins and enzymes are involved in successful fertilisation or conception.

• Gestation: The period between conception and giv­ing birth to young is the period of pregnancy or gestation. Its duration depends upon the species. Several factors like genetic, maternal, foetal, endocrines and environment control the gestation. The embryo is implanted in the uterus during its blastocyst stage and then transforms into the foetus. During gastrulation, the foetus produces three germ layers for proper attachment with the uterine wall through the placenta. Various organs are developed at the organogenesis stage. The gestation is maintained by several endocrines and growth factors like interferon Tau (IFNT). The presence of these species-specific bio-molecules in the animal confirms the maternal recognition of pregnancy.

• Placenta: The placental types are species specific. According to layer involvement, these are epitheliochorial, endotheliochorial and hemochorial. These are cotyledonary, diffuse, dis­coid and zonary according to shape and attachment. The placenta supports the foetus to exchange nutrients and metabolites with the mother, physical and immunological protection, thermoregulation and proper development with the influence of sev­eral endocrines and bio-molecules. Placenta itself secretes some endocrines. Foetal sex-specific pla­cental activity has also occurred.

• Parturition: The species-specific complex physio­logical phenomenon occurs during the termination of pregnancy, the parturition. Interactions of several endocrines initiate the event involving various cel­lular and muscular activities in the female reproduc­tive tract to generate pressure and inflammatory processes for expelling the young and the placenta. Faulty foetal presentation causes the occurrence of dystocia. Several congenital and anatomical deformities may also occur.

Exercises

Objective Questions

Q1. Why do spermatozoa reach rapidly at the site of fertilisation immediately after insemination cannot fertilise?

Q2. Which part of the female reproductive tract is consid­ered a sperm reservoir in the cattle?

Q3. Which biological activity provides the zona penetrating ability to the spermatozoa?

Q4. Why is secondary oocyte not completely maturated before ovulation in cows?

Q5. Which stage of fertilisation causes the permanent blockage of polyspermy?

Q6. What is progesterone block?

Q7. The embryo is termed as a foetus from which morpho­logical stage?

Q8. What is the significance of zona hatching?

Q9. What is maternal recognition of pregnancy?

Q10. Eccentric type of implantation occurs mostly in which animals?

Q11. Which kind of placenta does not involve any endome­trial tissue?

Q12. What is hemotroph?

Q13. When eCG start to secret in a mare?

Q14. Why can relaxin determine pregnancy in dogs and cats, not progesterone?

Q15. In which sex the interferon tau is better expressed? Q16. What is cervical ripening?

Q17. Manipulation of which hormone is advised to correct retention of the placenta?

Q18. How many oocyte(s) are involved in the occurrence of fraternal twins?

Q19. Why dystocia mainly occurs in the Boxer breed of dog?

Q20. Why vitamin A deficiency causes abortion in late pregnancy?

Subjective Questions

Q1. Why is the concentration of spermatozoa reduced from the insemination site to the fertilisation site?

Q2. Describe the role of some bio-molecules involved in the capacitation.

Q3. Describe the process of fertilisation diagrammatically.

Q4. Describe the various factors affecting gestation.

Q5. Classify the mammalian placenta according to histolog­ical and morphological structure, shape and attachment.

Q6. Describe the endocrine role of the placenta.

Q7. Write the process of parturition in cow.

Q8. Neuroendocrine mechanism of parturition.

Answer to Objective Questions

A1. Lack of capacitation process

A2. Isthmus

A3. Hyperactivation

A4. Meiosis II is completed with the induction of spermatozoa at the oviduct

A5. Cortical reaction

A6. Reduce or block the muscular tone of the female repro­ductive tract in favour of gestation

A7. Gastrula

A8. The blastocyst can expand and proceed to the implan­tation process

A9. The state of the mother, caused by the conceptus, promotes the gestation

A10. Rat and mouse

A11. Hemochorial

A12. Substances that are directly transferred from the mater­nal blood by blood vessels through the placenta

A13. Around 25 days of gestation

A14. Corpus luteum persists more than during the pregnancy period in dogs, and placental progesterone can be synthesised in the cat with a luteal cyst and low pro­gesterone in the first 2 weeks. In contrast, placental relaxin is synthesised from about 4 weeks in the dog and 3 weeks in the cat.

A15. Female

A16. The inflammatory process in parturition

A17. Oxytocin

A18. Two

A19. Small-sized uterus

A20. Due to thickening and erosion of the placenta

Keywords for the Answer to Subjective Questions

A1. Vaginal toxic environment, cervical plug, transportation through the uterus, morphological and mucus barrier at UTJ

A2. Role of ions like bicarbonate and calcium; hormones like oestrogens and progesterone; various proteins, glu­cose and metabolites

A3. Acrosomal reaction in the spermatozoa, cortical reaction in the oocyte, entry of sperm and initiation of meiosis, karyogamy

A4. Genetic, maternal, foetal, endocrines and environmental factors

A5. Involvement of endometrium; shape and point of attachments between foetal and endometrial tissues; structure of the chorionic membrane and contact with the endometrium; loss of maternal tissue during parturition

A6. Placental steroid, placental protein hormones, placental proteins, placental prostaglandin

A7. Stage1, stage 2 and stage 3

A8. Role of progesterone, oestrogens, oxytocin, relaxin, melanin and foetal cortisol

Further Reading

Books

Carlson BM (2019) The reproductive system (Ch. 14). In: The human body. Andre Gerhard Wolff, London, pp 373-396. https://doi.org/ 10.1016/B978-0-12-804254-0.00014-4

Das PK, Mukherjee JM (2019) Immune responses of mammary gland (Ch. 2). In: Sar TK (ed) Mastitis: symptoms, triggers and treatment. Nova Science Publisher, Inc., New York, pp 89-118. ISBN: 978-1­53616-124-3

Lopes SMCS, Mummery CL (2014) Differentiation in early develop­ment (Ch. 10). In: Essentials of stem cell biology, 3rd edn. Academic Press, pp 121-139

Research Articles

Ardon F, Markello RD, Hu L et al (2016) Dynamics of bovine sperm interaction with epithelium differ between oviductal isthmus and ampulla. Biol Reprod 95(4):90. https://doi.org/10.1095/biolreprod. 116.140632

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