Reproduction in Male Animals
Anatomy of male reproduction:-
The male reproductive tract consists of primary sex organs (testes), secondary sex organs (efferent ducts of the testes, epididymises, vasadeferentia, urethra and penis) and accessory sex glands (ampulla, vesicular glands, prostate gland, and bulbourthral glands or Cowper gland).
The reproductive organs of the male animal have three major functions:
- Production of spermatozoa in the testis.
- Maturation, storage and transport of spermatozoa within the duct system.
- Deposition of semen within the female genital tract via the penis.
The testis is oval in shape with two borders (anterior and posterior), two surfaces (medial and lateral) and two extremities (proximal and distal).
The size divers according to deferent species. The largest testis weight is for the bull (300-400 g), followed by the ram (250-300 g),buffalo (200-300 g),stallion (150-250 g) buck(100-150 g), and camel(60-100 g).
The testicles of all domestic animals are normally located in the scrotum outside the body. They lies in the inguinal region, with their longitudinal axises in a vertical position for the bull, buffalo, ram and buck, but divers in the stallion that their axises are in a horizontal position. For camel, the testes are located in the perineal region just under the anus, with their longitudinal axises in an oblique position. Male cats have two testicles, which in an uncastrated cat sit just below the anus.
Each testis is suspended by a spermatic cord which contains the blood supply (internal spermatic artery) and venous drainage in the anterior portion and the vas deferens in the posterior portion.
Two agents produced by the fetal testis are responsible for this differentiation and development. Fetal androgen causes development of the male reproductive tract. Anti Mullerian hormone or Mullerian inhibiting substance is responsible for suppression of the Mullerian ducts.
The testes develop in the abdomen, medial to the embryonic kidney and descend from their site of origin. There are differences among farm animals concerning the time of testicular descent.
The testicular descent occurs in mid gestation for the bull, buffalo, ram and buck and just before or after birth for the stallion, camel, dog and tom cat (2-5 days after birth). The descent is probably under hormonal control (Testosterone and insulin3 are promote testicular descent and oestrogens inhibit it). The late descent of the stallion and camel gonads as compared to cattle can be ascribed to the high oestrogen content of the blood of the pregnant mare and female camel before the time of descent.
The scrotum is a two-lobed sac, which houses both testes. It keeps the testes out side animal’s body as production of spermatozoa requires temperatures below that of the body.
The wall of the scrotum is composed of four layers; skin, tunica dartos muscle, scrotal fascia and parietal layer of vaginal tunic. The tunica dartos forms the median septum which divides the scrotum into two distinct pouches.
The plexus of ducts within the testis becomes connected to the mesonephric duct (Wolffiain duct) to form the epididymis, ducts deference, and vesicular gland.
The epididymis is convoluted tube connecting the testis to the vas deferens and covered by an extension of the tunica albuginea testis.
Three anatomic parts of the epididymis are recognized. The head (caput), in which a variable number of efferent ductules. It continues as the narrow corpus epididymis (body), which terminates at the opposite pole in the expanded cauda epididymis (tail). The epididymis (head, body and tail) is less clearly differentiated in the stallion than in other farm species.
There are two vasa deferentia, each one is continuous with corresponding epididymis.
Each one is a thick duct extending from the cauda epididymis to the pelvic portion of the urethra. It runs dorsomedial to the urinary bladder to enter the pelvic urethra.
In the most species, the terminal part of the vas deferens is furnished, branched tubular glands to form the ampulla of the ductus deferens. The ampulla is absent in the boar and tom cat, but well developed in the stallion.
Vesicular glands (seminal vesicle) occupy a dorsal position in the urogenital fold lateral to the terminal part of the ductus deferens. The duct of the seminal vesicles and the ductus deferens may share a common ejaculatory duct that opens into the urethra. They are pair of compact lobular glands that are easily identified because of their knobby appearance in the bull, ram and buck. In the stallion, they are large pyriform glandular sac that evades identification because of their thin wall. The vesicular glands are absent in the dog, cat and camel.
The prostate and bulbourethral glands form from the embryonic urogenital sinus.
Prostate gland is a single gland with 2 parts, a body that stretches across the dorsal surface of the neck of the urinary bladder and disseminate or internal part that surrounds the pelvic urethra. The body of the prostate is small in the bull and large in the boar and camel, but absent in the ram and buck. The prostate gland in the stallion is bilobed and wholly external that can be identified by palpation per rectum.
Bulbourethral glands (Cowper) are paired round or oval compact bodies located above the urethra near its exit from the pelvic cavity. The bulbourethral glands are absent in the dog.
The penis form by tabulation and elongation of a tubercle that develops at the orifice of the urogenital sinus.
The penis either fibro-elastic (with sigmoid flexure) such as the bull, buffalo, rams, buck and camel or vascular, musclocavernosus and haemodynamic in the stallion.
The sigmoid flexure is post-scrotal for the bull, buffalo, ram and buck, but pre-scrotal for the camel and boar.
The fibro-elastic and vascular penises have retractor penis muscles, a pair of smooth muscles which relax to permit extension of the penis and contract to draw the penis back into the prepuce.
Male cat have a barbed penis and its points backwards, which will be painful for the female during mating, while the dog have an os penis.
The penis is cylindrical in shape and composed of root, body and glans penis.
The root is attached to the bony pelvis by two lateral branches, the right and left crus penis, which are covered by ischiocavernosus muscles. The body contains three erectile rods or cavernous bodies the two dorsal rods (corpora cavernosa) unite to form expansive cavernous body called corpus cavernosum penis 'CCP'. The ventral rod called corpus spongiosum penis 'CSP') which lie parallel to each other. In the stallion the cavernous bodies contain large cavernous space (increase in size during erection). In bull, boar and ram the cavernous spaces of are small.
The glans penis, the free end of the penis, is supplied with sensory nerves and is homologous to the clitoris in the female.
The urethra opens into a twisted groove in the glans penis of the bull and buffalo. The ram and buck have urethral process known as a filiform appendage extending beyond the glans penis. The glans penis of the camel is transverse, cartilaginous and hooked-shaped with a definite neck between the glans and the body of the penis. It has a small urethral process present on the lateral aspect of the external urethral orifice on the left side of the glans penis. The glans penis of the stallion is flattened, mushroom shaped, with a small urethral process extending beyond the flattened end.The dog has a fibro-cartilagenous end of os penis ventrally grooved, the glans penis includes the bulb, the long part of the head, and the crown,while the tom cat has spines on glans penis supposedly enhances vaginal stimulation to induce ovulation.
The penis of the camel is directed caudally, so that urination is towards the rear. However, when erection of the penis occurs, the cranial preputial muscles pull the prepuce and penis forward.
The prepuce is an invagination of the skin which completely encloses the free end of the penis. It sheds the non-erected penis. Has outer (prepenile) and inner (penile) folds which straighten out during erection.
In all species the head of the penis and the free part of the penis are within the preputial cavity, but in the dog, the head of the penis only is in the preputial cavity.
The orifice of the prepuce for the males of ruminants is surrounded by long and tough preputial hair.
The prepuce of the stallion is formed by a double fold (external and internal sheath).
The prepuce of the camel is pendulous, flattened from side to side and triangular shaped sheath, which open to the rear.
Anatomy of reproductive systemof malechicken:
The avian male reproductive system is all inside the bird - unlike the males of mammalian species which have their reproductive systems outside of the body.This is one of the really remarkable things about birds; the sperm remain viable at body temperature.
The male chicken possesses two testes, locatedalong the chicken’s back, near the top of the kidneys (cranio-ventral). The testes are elliptical shaped and light yellow in color and increase dramatically in size during the breeding season.
The vas deferens emerges medially and passes caudally to the cloaca where it has a common opening with the ureter (opens into a small bump, or papilla).The terminal vas deferens is swollen as a storage organ: the seminal glomus.
Poultry have no external penis, but rather a protuberance termed a "rudimentary phallus" is located on themiddle and front portion of the cloaca.
Physiology of male reproduction:
Puberty:
Is the age at which a growing male is able to mount, copulate and successfully impregnate a female. Practically, puberty is defined as the age at which an ejaculatefirst contains 50 million spermatozoa among them ≥10 % is progressively motile.
The age of puberty is influenced by genetic, nutritional, and environmental factors.
In the normal breeding conditions puberty occurs at 10-12 months for bulls, 4-6 months for rams and bucks, 13-18 months for stallions, 4-8 months for boars 24-40 months for camels, 6-8 months for dogand 4-5 months for cock (roosters).
When puberty is attained, the male exhibit external and behavioural changes, including changes in body conformation, increased aggressiveness, sexual desire, rapid growth of penis and testes, and separation of the penis from the prepuce for extension of the penis due to rupture of the penile frenulum.
Sexual maturity is a gradual process and it is may take years after puberty. Thus, puberty should not be confused with sexual maturity, as spermatogenic potential and size of the testes continue to increase when puberty is attained. For example, efficiency of spermatogenesis in the stallion reaches adult levels by 2.5-3 years of age, whereas daily spermatozoal production per testis and testicular weight continue to increase until 4-5 years of age.
As rule, mating is delayed few months after puberty for the bull, buffalo, ram and buck, or even years for the stallion and camel.
Libido and mating behavior:
Libido or sexual desire is the male interest in sexual congress or mating.
Libido is primarily dependent upon androgenic steroid hormones, which allow mating, and aggressive behaviour to occur, as well as maintaining the function of all parts of the male reproductive system.
Despite the dependency of male behaviour upon androgen, there has been much debate over the relationship between absolute concentrations of androgen and libido.
Some have argued a permissive role of androgen, while others have demonstrated positive correlations between testosterone concentrations and measures of libido.
Oestrous females of many species secrete pheromones to attract males, while others, notably the cow and some breeds of pig, exhibit homosexual behaviour as a signal to the male of the presence of oestrus. All males smell the perineal region of the female, and the odour of the oestrous female induces the so called ‘flehmen’ reaction in the bull, ram and stallion: a characteristic raised posture of the head an elevation of the upper lip.
Females that are not in oestrus signal their objection to the advances of the male and, at the least, will respond by moving away or, perhaps, by attacking the male in the offensive manner peculiar to the species.
Oestrous females signal receptivity by squatting, urinating, moving the tail to one side and remaining stationary. During this foreplay the male becomes progressively aroused; there are frequent erections of the penis, with emission of accessory fluid and many unsuccessful attempts to mount the female. Finally, mounting and copulation occur.
Ruminants:
Copulation in all of the domestic species of ruminants is brief. After detecting an oestrous female, mounting is followed quickly by the single ejaculatory thrust.
The male then immediately dismounts,but frequent subsequent matings occur.
Stallion:
Following intromission, the stallion performs a succession of copulatory movements of the hindquarters which, within a minute, culminate in ejaculation.
During ejaculation, successive waves of urethral peristalsis can be palpated on the lower surface of the penis, while the stallion exhibits a characteristic ‘flagging’ movement of the tail. The stallion then dismounts.
Dog:
The dog achieves intromission by vigorous thrusting of the hindquarters. Once intromission has been achieved, the bulbus glandis swells considerably, while the constrictor vulvae muscles of the bitch contract behind it, thus forming the ‘copulatory tie’.
The sperm-rich fraction of canine semen is ejaculated within as little as 80 seconds of intromission, so that conception may occur even if copulation does not proceed through to its second stage. In this second stage, the dog dismounts but remains connected and faces away from the bitch.
This change of position causes the penis to become bent through an angle of 180°; the efferent veins of the penis are thereby occluded and the penis remains turgid.
Cat:
During mating, the tom mounts the queen and grasps her neck with his teeth. As the tom adjusts his position the queen paddles her hindlegs, continuing to do so at an increasing frequency during the 10 seconds or so for which coitus lasts.
The queen cries out during copulation and, as the tom dismounts, she may strike out at him, displaying the typical ‘rage’ reaction. This is followed by a period of frantic rolling and licking at the vulva.
As soon as the postcoital reaction has ceased, the tom will attempt to mount again. Several matings may therefore occur within the first 30–60 minutes.
The cat is an induced ovulator , so the number and frequency of matings are important in ensuring that the LH surge is of sufficient magnitude to cause ovulation.
chickens:
The completed mating in chickens is the culmination of a sequence of behaviours.
The rooster will initiate mating by exhibiting courtship behaviour: dropping one wing and dancing in a circle (the lowered wing will be on the inside of the circle dance).
The hen will crouch (dip her head and body) to indicate receptiveness to the male.
The rooster will then mount the hen and grab her comb, neck feathers, or the skin on the back of her head or neck to help hold onto the hen's back.
The next behaviour is the tread (the rooster walks quickly in place on the hen's back) and finally the completed mating of the behavioural sequence.The completed mating occurs when the rooster dips his tail to the side of the hen's tail and spreads his tail feathers so that their cloacae come into contact ('cloacal kiss').At this point the rooster's ejaculate is released directly into the hen's vagina via her cloaca.
A rooster may mate from 10 to 30 or more times per day, depending on the availability of hens and competition from other roosters.
The rooster has a small phallus that becomes engorged with lymph to form a copulatory organ. The copulatory organ is rudimentary and at the time of mating there is practically no penetration. The hen everts her vagina during copulation, which helps to transfer the semen into the oviduct.
Hormonal control of male reproduction:
All aspects of male reproductive physiology are under the endocrine control of two major gonadotrophins LH and FSH.
The actions of LH are primarily upon the Leydig cell (adenylate cyclase). It promotes steriodogensis.
Testosterone is required for the production of sperm in testis and their subsequent maturation in the epididymis, for function of the accessory sex glands and for development of masculine secondary sexual characteristics.
The main target of FSH is the Sertoli cell (through adenylate cyclase – linked enzyme) to secret androgen binding protein (ABP) (maintain high androgen concentrations and prolong life span of epididymal sperm) and aromatize testosterone into oestrogens. Adequate FSH stimulation is also required to permit Sertoli cells to support spermatogenesis.