ANIMAL REPRODUCTION (II)

TYPES OF MATING

Natural Mating: This occurs when a male mount on the female animal their heat period.  Examples of natural mating include Flock mating, Pen mating and Stud or Hand mating.

Artificial Mating: Artificial mating or Artificial insemination (AI) is the process of collecting sperm cells from a male animal and manually depositing them into the reproductive tract of a female. .

GESTATION PERIOD

This is the time interval between conception and parturition. This is also the period between fertilization of an ovum to the birth of the young ones. It is under the control of a hormone-progesterone (pregnancy hormone). Its  high secretion prevents further ovulation during pregnancy and maintains pregnancy. It is a period of swelling of the abdomen, udder and a period of increase in life weight.

OVULATION

Ovulation is the release of an egg from the ovary into the fallopian tube. It is under the control of pituitary gland hormones (Luteinizing hormone). It occurs mid oestrus cycle during heat period. Time of ovulation varies among farm animals. It is usually not more than 24 to 36 hours.

PARTURITION

This is the act of giving birth in farm animals. It marks the end of gestation/pregnancy. Lactation is expected to begin after this occurrence. The process involves the breaking away of the placenta from the uterine wall signaled by the maturation of the foetus. After this the membrane bag breaks, causing the amniotic fluid and the fetus itself to move through the cervix to the vagina. The placenta usually comes out after birth, this process is known as calving in cow, farrowing in sow, lambing in ewe, kidding in goat and rabbits, whelping in dogs, littering in cats. Read up signs of Parturition. 

FERTILIZATION

This is the fusion of the male sex cell/gamete (Spermatozoa) and female sex cell/gamete (ovum/egg). It occurs in the fallopian tube/oviduct. It leads to formation of diploid cell known as zygote.

LACTATION

This is the process of milk secretion from the female mammary gland also known as udder after parturition. This helps to feed the young animals. It is under hormonal control; Decreased progesterone and increase in oxytocin and oestrogen continuous sucking or extraction of milk from the udder stimulate the production of more milk.

STRUCTURE OF THE MAMMARY GLAND (UDDER)

Fig  :Mammary gland structure

COLOSTRUM

This is the first milk produced by the animal usually first 3 days of onset of lactation. It is yellowish white in colour and it is important because it contains several antibodies, vitamin and other nutrients that help boost the immunity of the younger ones. It is also highly digestible.

Parts of an Egg

Yolk. This is the most obvious part of the egg contents—the yellow part near the center.

Albumen. This is the clear part called the egg white. It’s called this because it turns white when cooked. There are two layers of albumen: thick (near the yolk) and thin.

Chalaza. It is a piece of thick protoplasm. It holds the yolk and the embryo in place within the albumen.

 Shell membranes. The egg contents are surrounded by two thin membranes called the inner and outer shell membranes.

Shell. This is the outer covering of the egg holding everything together. It is rich in calcium carbonate and it protects the egg.

PROCESS OF EGG FORMATION

The egg is formed in the reproductive tract of a female chicken, called a hen. The reproductive tract is divided into two major parts: the ovary and the oviduct. The ovary is where the yolk is added. When the yolk reaches the right size, it is released from the ovary by a process called ovulation. The released yolk is then picked up by the infundibulum. It is here that fertilization must take place. The yolk then passes to the magnum, where the albumen is added. It then goes on to the isthmus for the addition of the shell membranes. The developing egg spends most of its time in the shell gland, where the shell and any shell pigments are added. As the egg is being assembled it travels down the oviduct small end first. In the vagina it is pushed out the large end first. This prevents the egg from being contaminated by fecal material when it is laid. (Draw the reproductive system in birds)

REPRODUCTIVE HORMONE AND THEIR FUNCTION

FEMALE REPRODUCTIVE HORMONE

Luteinising Hormone (LH)

LH is a type of glycoprotein that is produced in the anterior pituitary via gonadotroph cells and serves to regulate the function of the gonads. In females LH stimulates the production of oestrogens and progesterone from the ovary via theca interna cells and luteal cells. Concentrations of LH increase during ovulation and with the formation of the corpora lutea with progesterone secretion. The secretion of LH is regulated via the secretion of GnRH (see earlier section).

As shown previously, in males there are between 4 to 12 GnRH pulses per day and this therefore means that LH also peaks throughout the day. During these peaks, the production and secretion of testosterone increases. Testosterone secretion also is pulsatile.

Follicle Stimulating Hormone (FSH)

FSH is a type of glycoprotein that is produced in the anterior pituitary via gonadotroph cells. FSH secretion is regulated by GnRH from the hypothalamus. In the female the granulosa cells of the ovary. FSH stimulates the maturation of germ cells within the ovaries. In the female it also stimulates follicular development and oestradiol synthesis.

Prolactin 

Prolactin is a protein that is produced from by the anterior pituitary via lactotroph cells. This hormone exerts a stimulatory effect on milk synthesis within the mammary glands. It has also been shown to have some degree of gonadal function in some domestic species and rodents. In birds increased concentrations of prolactin have been linked with brooding behaviours and the associated metabolic changes that birds undergo during brooding.

Oxytocin  

It affects mammary gland after birth by causing milk let-down or milk production. It also aids in the contraction of the female uterine muscles during pregnancy. It promotes the transport of spermatozoa in the female genital tract.
Oestrogen

Oestrogens have a number of functions related to reproduction and other areas of physiology. In relation to the reproductive role of oestrogens, they stimulate follicular growth and maturation, induce the female to begin displaying oestrous behaviour to facilitate mating, prepare the external genitalia for copulation and create favourable conditions for the development of fertilised egg cells. Oestrogens also contribute to the growth and development of mammary tissue and prepare the uterus for parturition.
Progesterone

Progesterone ensures the development of uterus and implantation of the fertilized ovum. It ensures the continuance of pregnancy.Progesterone prepares the uterus for reception of fertilized oocytes and is transported via the blood bound to plasma proteins. Progesterone also prepares the mammary tissues for milk production as well as inhibiting female reproductive behaviours associated with oestrous.

Relaxin

It causes the relaxation of the pelvic ligament during parturition for easy passage of the young ones
MALE REPRODUCTIVE HORMONE

Testosterone (T)

The male sex hormone is called testosterone and this hormone is required for spermatogenesis. Testosterone is a steroid hormone that is produced in the leydig cells within the testes. A relatively high concentration of testosterone is maintained within the testicular tissue and testosterone is circulated around the body by diffusion of the hormone from the spermatic cord into the testicular veins and arteries. The primary action of testosterone is anabolic growth, spermatogenesis promotion and promotion of secretion from the accessory sex glands.
It is responsible for the initiation of male secondary sex characteristics. It enhances muscular and skeletal growth. It sustains the life of sperms in the epididymis.s