Animal Reproduction
ANIMAL REPRODUCTION CLASS
MEANING OF REPRODUCTION
Reproduction is the ability in animal to give birth to their young ones. The purpose of reproduction is to ensure continuity of life. The reproductive system includes all the organs and tissues concerned with reproduction in animals. Farm animals reproduce sexually and are mostly viviparous because they bear their young ones alive.
Poultry birds on the other hand are oviparous because they produce their young ones by hatching eggs after an incubation period.
Meaning of Hormones; Hormones are chemical substances which co-ordinates the activities of the body. Hormones are secreted by the ductless glands in the body and transferred through the blood to the target organs in which they exert their effect.
Types of Hormones
1. Androgen (Testosterone).
2. Oestrogen.
3. Follicle Stimulating Hormone (FSH).
4. Luteinizing Hormone (LH).
5. Progesterone (Pregnancy hormone).
6. Oxytocin.
7. Relaxin.
8. Prolactin.
Androgen is the only male reproductive hormone while others are female reproductive hormones.
Roles/Functions of Hormones in Animal Reproduction
1. Androgen (Testosterone) – It is stimulated by interstitial cell-stimulating hormone. Androgen promotes sperm production and maintenance. It promotes the growth and development of accessory glands. It brings about puberty in male animals. It stimulates the development of male secondary sexual characteristics and sexual behavior (sex drive).
2. Oestrogen/Estrogen – This hormone is secreted by graffian follicle. It helps in the production of ovulation and oestrus for heat period. It helps in the production of eggs or ovule in female animals. It stimulates mammary gland development. It brings about puberty in female animals.
3. Oxytocin – it is secreted during pregnancy. It is secreted by the posterior pituitary gland. It helps the female animals to produce milk after birth. It helps in contraction of the female uterine muscles during pregnancy.
4. Follicle Stimulating Hormone (FSH) – It is produced by anterior pituitary of both male and female animals. It stimulates the growth of ovarian follicle in females. Helps in the development of the seminiferous tubules.
5. Progesterone (Pregnancy hormone) – It produced by the placenta during pregnancy. It is essential for the implantation of the embryo in the uterus to form foetus. It inhibits oestrus (i. e procedure ripening). It helps to set the uterus for implantation.
6. Luteinizing Hormone (LH) – It is produced by anterior pituitary gland in males and females. Thisis called pregnancy hormone. It causes rupture of the follicle and subsequent release of ova (i.e ovulation).
7. Relaxin – This hormone is secreted during labour by the anterior pituitary hormone before parturition. It causes the relaxation of the pelvic ligament and cartilage during parturition.
8. Prolactin – It is hormone that is concerned with lactation or milk let-down from the udder or mammary gland. It is secreted some minutes after parturition.
REPRODUCTIVE SYSTEM CLASS: SS2
DEFINITION OF REORODUCTIVE SYSTEM
Reproductive system includes all the organs and tissues concerned with reproduction in animals. It consists of male and female systems.
Functions of the Reproductive System
It ensures the continuity of species by gamete for motion, coitus, mating or servicing.
It ensures the formation of eggs and spermatozoa (sperm cells).
It ensures the reproduction of reproductive hormones.
Terminologies Associated with Reproduction
Oestrus Cycle: Oestrus cycle is the interval from the of one heat period to the beginning of another.
Length of oestrus in farm animals
Species(s)
Name of Female(f)
Length of Oestrus(o)
s. Cattle
f. Cow
o. 21 days
s. Sheep
f. Ewe
o. 17 – 21 days
s. Goat
f. Nanny (Doe)
o. 17 – 21 days
s. Pig
f. Sow
o. 20 – 25 days
s. Horse
f. Mare
o. 21 -24 days
s. Rabbit
f. Doe
o, 7 – 10 days
2.Heat Period: The heat or oestrus period is the time when the female animal shows signs of its readiness to mate. It is the period of sexual receptivity in female, when the ovum or ova are released.
Heat period varies from one animal to another.
Cow
5 – 24 hours
Ewe
35 – 36 hours
Sow
40 – 48 hours
Doe (Goat)
40 – 50 hours
Mating: Mating is the act of in which the penis of the male is inserted into the vagina of the female, leading to the ejaculation of spermatozoa. Mating is also called coitus or copulation.
Gestation Period: This is the period between fertilization of an ovum to the birth of the young ones. It is also the period between conception and birth (i.e. period of pregnancy).
The period varies from animal to animal.
Gestation Period
Range
Cow = 283 days
275 – 285 days
Ewe = 114 days
112 – 116 days
Sow = 150 days
145 – 155 days
Doe (Goat) = 151 days
150 – 155 days
Doe (Rabbit) = 31 days
30 – 31 days
Ovulation: Ovulation is the rupturing of the ovary wall (Graffian follicle) to release mature eggs (ova or ovum) into the fallopian tube in animals. It occurs in- between or midway of oestrus cycle.
Time of ovulation varies among farm animals.
In Cow It occurs 10 – 14 hour after oestrus
In Sow It occurs 24 – 36 hours after oestrus
In Ewe It occurs 20 – 24 hours after oestrus
In Rabbit It occurs immediately after or during mating
Parturition: Parturition is the act of giving birth in farm animals. It marks the end of pregnancy and the beginning of lactation.
Fertilization: This is the fusion of the male sex cell or gamete (sperm) and the female sex cell or gamete (ovum or egg). It occurs in the oviduct or fallopian tube and when an animal is on heat period.
Lactation: This is the period during which the female animal releases milk from its udder immediately after parturition and thereafter.
MALE REPRODUCTIVE SYSTEM
The male reproductive system/organ is made up of the primary sexual character and secondary sexual character. The primary sexual character is made up of the testis (testes) which produce spermatozoa and sex hormones called testosterone. The secondary sexual character consists of the scrotum, Cowper’s gland, prostate gland, seminal vesicle, urethra, penis, vas deferens and spermatic duct.
Functions of the various parts of male reproductive system
Testis: Testis are located within the scrotum or scrotal sac. It is stimulated by the male hormone called testosterone. It secretes spermatozoa. The removal of testis is called castration.
Scrotum/scrotal sac: This help to house the testis. It regulates the temperature of testis at 40 C less than the body temperature of the animal. When the day is cold the scrotum constricts and when the day is hot, it drops or falls to a lower level.
Vas deferens: This is responsible for conducting the sperm from the epididymis to the neck of the urethra. The removal of the vas deferens is known as Vasectomy. Vas deferens can only be removed when sexual characters have developed in order to cull the poor quality of animal. Vasectomy is safer than castration, because the animal can still be stipulated but is not allowed to come down.
Epididymis: This is the coiled tubule in which sperms is stored for some time before it is being used.
Seminal vesicle: This is essential for secretion of certain fluids which are rich in food substances. It help in feeding the spermatozoa before fertilization takes place.
Prostate gland: This also secretes the Cowper’s fluid, which is alkaline in nature and help to reduce the acidity of spermatozoa.
Semen: This is the mixture of the seminal fluid and spermatozoa. Only about 25% of the quantity of semen ejaculated is spermatozoa, the remaining 75% are the seminal fluids.
Urethra: This is a narrow tract for the transportation of urine or excretion from the bladder to the external orifice.
Penis: Penis is organ which is used in introducing the spermatozoa into the vagina. The penis consists of arteries and veins. When penis is stimulated, the arteries dilate (expand) and veins constricts (close or contracts) then blood flows into the blood vessels thereby giving the penis a turgid nature and the copulation can take place.
FEMALE REPRODUCTIVE SYSTEM
The female reproductive system consists of the primary and the secondary sexual characters. The primary character is called ovary while secondary sexual characters include; infundibulum, oviduct, uterus, cervix, clitoris, vulva, vagina.
Functions of the various parts of female reproductive system
Ovary: This is similar to the testis in male reproductive system. It is located in the abdominal region. In young animals the surface is smooth but in mature animals the surface looks rough and blistered. The ovary is stimulated by the hormone called oestrogen. It secretes the female gamete or ovule or egg. The release of egg occurs during ovulation.
Fallopian funnel (Infundibulum): This is also known as infundibulum. It receives the egg when released during the ovulation.
Uterus: This is a muscular tubular organ made of a body consisting two horns. This is the place where implantation occurs. The period of pregnancy in animals also takes place in the uterus. The wall of the uterus is stipulated by the progesterone hormone.
Oviduct: This is also known as the fallopian tube. It is the point where fertilization occurs in the female animal.
Cervix: This is an organ which helps to prevent foreign bodies from entering the womb. It only relaxes during the oestrus (heat) and parturition.
Vagina: This is an elastic membrane which expands to cover the head of foetus and the penis. It is a tubular canal which receives the penis and in which spermatozoa is deposited. The vagina secrets much mucus during oestrogen, mucus secretion is very low after oestrus cycle.
Clitoris: This is like penis in the females. It is very sensitive, erotic and brings the female into the mating mood.
Vulva: This is also known as the labia majora. It is the posterior opening of the female genital tract into the exterior. During heat, the labia becomes red, turgid and mucus will be discharged.
PERIOD (II) REPRODUCTIVE SYSTEM IN BIRDS
In the male bird, the two testes are located inside the body. A narrow tube connects them to the cloaca in which the tube ends has a small raised papilla.
The process of egg formation are controlled by hormones. The female reproductive tract in hen consists of the following – ovary, infundibulum, fallopian funnel, oviduct, magnum, isthmus, uterus (shell gland), vagina and cloaca (vent).
Ovary: In female birds, only the left ovary is functioning while the right ovary degenerates very early in life about 7-9 days of incubation. The ovary produces eggs or ova in capsules attached to the ovary. The ovary also produces the yolk.
Infundibulum or fallopian funnel: The infundibulum receives the yolk released by the ovary. The internal terminal of the oviducts and sperms remain in the infundibulum for about 21 days.
Oviduct: Fertilization of the eggs takes place here as soon as the egg enters the oviduct when spermatozoa are present. The egg spends 15 minutes in the oviduct (fallopian tube) before it moves to magnum.
Magnum (Ampulla): In the magnum, the egg stays about 3 hours. Here is where the albumen and chalaza which hold the yolk and germ cell are formed. The egg now moves to the isthmus.
Isthmus: The egg stays here ab out one quarter hours (1/4hrs). The two lighter shell membranes and the shape of the egg are formed in this region and which it moves to uterus or shell gland.
Uterus or shell gland: The egg stays its longest time here. It remains for about eighteen to twenty one hours (18 – 21 hours). This is the place where all remaining parts of the egg are formed.
Vagina: The egg stays here for a very short time. The egg remains here for only 10 minutes before the egg will be laid.
Cloaca or vent: This is the portion where the egg is laid. It is also the point for the egestion of faeces. When the egg is laid, the outer shell become hard when it react with air.