ANIMAL REPRODUCTION (I)

The reproductive structures of many animals are very similar, even across different lineages, in a process that begins with two gametes–eggs and sperm–and ends with a zygote, which is a fertilized egg. In animals ranging from insects to humans, males produce sperm in testes, and sperm are stored in the epididymis until ejaculation. Sperm are small, mobile, low-cost cells that occur in high numbers. Females produce an ovum or egg that matures in the ovary. Eggs are large cells that require a substantial investment of time and energy to form, are non-mobile, and are rare relative to sperm numbers. When the eggs are released from the ovary, they travel to the uterine tubes for fertilization (in animals that reproduce via internal fertilization) or are released in the aqueous environment (in animals that reproduce via external fertilization).
The purpose of reproduction is to ensure continuity of life. As explained above, animals reproduces sexually. Those that bear their young ones alive are termed as Viviparous while those that produce their young ones outside the body by producing eggs which hatch outside the body after an incubation period are referred to as Oviparous.

MALE REPRODUCTIVE SYSTEM

Fig 3.1: The male Reproductive System (Bull)

Process of Male Reproduction.
Sperm are produced in the seminiferous tubules inside the testes. When the sperm have developed flagella and are nearly mature, they leave the testicles and enter the epididymis where it is stored and mature. During mating, the sperm leave the epididymis and enter the vas deferens, which carries the sperm, behind the bladder, and forms the ejaculatory duct with the duct from the seminal vesicles.
Semen is a mixture of sperm and spermatic duct secretions and fluids from accessory glands that contribute most of the semen’s volume. The bulk of the semen comes from the accessory glands associated with the male reproductive system. These are the seminal vesicles, the prostate gland, and the bulbourethral gland, all of which are illustrated in Fig 3.1 above. These fluids form the transport medium for the millions of spermatozoa that is expelled in the process of mating.
Other structures such as the spermatic cord supplies nutrients and oxygen to the testes while the urethra; a long tubular urogenital organ in the male animal helps inject the semen in the vagina as well as urine. These urethra ends externally in the organ called penis which is the organ necessary for copulation to take place. This gets engorged with blood providing necessary turgidity for its insertion.

FEMALE REPRODUCTIVE SYSTEM

Fig 3.2: Female Reproductive System (Doe).

The Process of Female Reproduction
Ovaries are the site of egg development. The eggs are known as know as Ovum (plural: Ova) which are enclosed by the graffian follicles. Egg development occurs in the follicles, which are lined with specialized cells called follicular cells that surround the egg and promote egg development. At ovulation or heat period, one follicle ruptures and one egg is released. The ruptured follicle, which remains in the ovary, is then called the corpus luteum, which secretes hormones that prepares the uterine wall for implantation if the egg is fertilized. If fertilization and implantation in the uterine wall occurs, then the corpus luteum continues to maintain the pregancy; if fertilization does not occur, then the corpus luteum degenerates as well as the uterine wall.
The oviducts, or fallopian tubes, extend from the uterus to the ovaries, but they are not in direct physical contact with the ovaries. The ends of the oviducts flare out into a trumpet-like structure and have a fringe of finger-like projections called fimbriae. When an egg is released at ovulation, the fimbrae help the egg enter into the tube and passage to the uterus. Fertilization (the union of sperm and egg) usually takes place within the oviducts and the developing embryo is moved toward the uterus for development. The process for attachment of fertilized ovum to the uterine wall is known as Implantation.
Other structures such as the vagina is the organ that receives the semen during copulation and the Vulva is the structure that is at the opening of the vagina.

EMBRYO DEVELOPMENT IN MAMMALIAN FARM ANIMALS
A mammal develops from a single cell called a zygote, which results from an ovum (egg) being fertilized by a single sperm. The zygote is surrounded by a strong membrane of glycoproteins called the zona pellucida which the successful sperm has managed to penetrate.
The zygote undergoes cleavage, increasing the number of cells within the zona pellucida.
After the 8-cell stage, mammalian embryos undergo what is called compactation, where the cells bind tightly to each other, forming a compact sphere.

Fig 3.3: Position of the developing foetus in the uterus of a cow.

Functions of the Reproductive System
i) It ensures continuity of species by gamate for motion,coitus,mating or servicing.
ii) It ensures the formation of eggs and spermatozoa (sperms cells).
iii) It ensures the reproductive hormones.
OESTRUS CYCLE
Oestrus cycle is the interval from the end of one heat period to the beginning of another.Estrus or “heat” is also a period during the reproductive cycle when female animals become sexually receptive, signaling they are ready for mating. It is under the influence of hormone called OESTROGEN.
OESTRUS CYCLE AMONG FARM ANIMALS

Animal Oestrus Cycle
Cow 20-21
Ewe 17-21
Sow 14-28
Doe(Goat) 17-21
Doe(Rabbit) spontaneous
Reasons Why Oestrous Detection is Important in Farm Animals
1) It enables thefarmer to know when best his animal can be serviced
2) It enables farmer to prepare for the impending pregnancy
3) It enables farmers to properly manage the animals

HEAT PERIOD
Heat or oestrus is the period a female animal is ready for ‘service’ (Service in animal husbandry means to mate and the act is called servicing). This period is very important in animal husbandry and breeding. It is the period when the ovum or ova are released. That is, the period when ovulation takes place.
Heat period varies from one animal to another e.g
Animal Heat Period
Cow 5-24hours
Ewe 35-36hours
Sow 40-48hours
Doe(Goat) 40-50hours

SIGNS OF HEAT IN FARM ANIMALS
Reduced or loss of appetite.
The reaction of the animal to feed is reduced or totally lost.
Increased body temperature:
The animal develops unusual high body temperature.
Vaginal discharge.
There would be mucus discharge from the animal vagina/vulva.
Frequent Urination
Standing still to be mounted
Frequent tail shaking

MATING
Mating is also known as coitus or copulation. Mating is the act which penis of the male is inserted into the vagina of the female, leading to the ejaculation of spermatozoa.Mating is necessary before farm animals can reproduce sexually. It takes place when the male animal mounts the female for sexual copulation.

TYPES OF MATING
1)Natural Mating: This occurs when a male, after identifying a female on heat period will mount on the female for mating the animal. Examples of natural mating are:
i) Flock Mating: Male and Female animals move together and mate freely.
ii) Pen Mating: Few number of males are kept together with limited number of females so that they can mate any time the female is on heat.
iii) Stud or Hand Mating: Male animals are taken to the female animal when on heat period. After mating the male is taken away.
2)Artificial Insemination : Is the process of collecting sperm cells from a male animal and manually depositing them into the reproductive tract of a female. Artificial insemination is commonly used instead of natural mating in many species of animals because of the many benefits it can reap.
There are several advantages by Artificial insemination over Natural mating or servicing.
• There is no need of maintenance of breeding bull for a herd; hence the cost of maintenance of breeding bull is saved.
• It prevents the spread of certain diseases and sterility due to genital diseases.
• Eg: contagious abortion, vibriosis.
• By regular examination of semen after collection and frequent checking on fertility make early detection of interior males and better breeding efficiency is ensured.
• The progeny testing can be done at an early age.
• The semen of a desired size can be used even after the death of that particular sire.
• The semen collected can be taken to the urban areas or rural areas for insemination.
• It makes possible the mating of animals with great differences in size without injury to either of the animal.
• It is helpful to inseminate the animals that are refuse to stands or accept the male at the time of oestrum.
• It helps in maintaining the accurate breeding and cawing records.
• It increases the rate of conception.
• It helps in better record keeping.
• Old, heavy and injured sires can be used.