OESTRUS CYCLE, MATING, GESTATION PERIOD, OVULATION, PARTURITION AND FERTILIZATION IN FARM ANIMALS
- Oestrus cycle is the interval from the end of one heat period to the beginning of another.
- It is also the period of “heat” or “oestrus” for coitus or mating.
- It is followed by a long period in which female animals will not show desire to mate.
- It is under the influence of hormone called oestrogen.
- The oestrus cycle varies among farm animals.
- Cow (20 – 21 days).
- Ewe (17 – 21 days).
- Sow (14 – 28 days).
- Doe (Goat) – 17 – 21 days.
- Doe (Rabbit) – spontaneous.
Reasons why oestrus detection is important in farm animals
- It enables the farmer to know when best his animals can be serviced.
- It enables the farmer to properly manage the animals.
- It also helps the farmer to start preparation for the impending pregnancy.
- 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 animal, when the ovum or ova are released. That is, the period when ovulation takes place.
- It occurs within the oestrus cycle and controlled by oestrogen.
- 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.
Signs of Heat in Farm Animals
- The vulva becomes large, red and swollen.
- There is undue noise making or grunting.
- A clear viscous secretion comes from the vagina and this arouses and excites the males.
- The animal becomes restless.
- It shows tendency to be ridden or mounted by other animals.
- There is loss of appetite.
- The animal has abnormal high body temperature.
- Frequent urination.
- Standing still to be mounted.
- Frequent tail shaking as in goat.
- Mating is also called coitus or copulation.
- Mating is the act in which the penis of the male is inserted into the vagina of the female, leading to the ejaculation of spermatozoa.
- Mating in farm animal may lead to fertilization.
- It is under the influence of hormone.
- Mating is necessary before farm animals can reproduce sexually.
- For mating to occur, the female animal must be on heat period.
- The penis must be erect before mating can occur.
- It takes place when the male mounts the female for sexual copulation.
- It leads to the occurrence of ejaculation of semen containing sperms which is deposited in the vagina.
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:
- Flock Mating: Both the male and female animals are allowed to move together and mate freely.
- Pen Mating: Very few number of males are kept together with limited number of females so that they can mate any time the female animal is on heat period, e.g, four males together with twelve females.
- Stud or Hand mating: The males are kept separately to be mated with individual females when on heat period. After mating, the male is taken away.
2) Artificial mating: This is called artificial insemination which involves the act of injecting spermatozoa artificially into the vagina of female animal on heat period. The sperms are collected from a male animal with desirable characters.
Such spermatozoa are stored at -196°C under liquid nitrogen until it is used.
Advantages of Artificial Insemination
- It is cheaper to import sperms than to import the male animal.
- Sperms collected can be used to fertilise many female animals of various sizes.
- It is more economical as it reduces the cost of feeding and managing male animals.
- Sperms (semen) can be used over a long time even after the death of the male animal.
- 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).
- Female animals, during this period, do not normally experienced heat period.
- 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.
- It is a period of swelling of the udder.
- It is a period of increase in life weight.
- The period varies from animal to animal.
- Ovulation is the rupturing of the ovary wall (Graafian follicle) to release mature eggs (ova or ovum) into the fallopian tube in animals.
- It is under the control of pituitary gland hormones (luteinizing hormone).
- It occurs in-between or midway of oestrus cycle.
- It occurs when female animals are on heat or show desire to be mated.
- Time of ovulation varies among farm animals, e.g, in cow, it occurs 10-14 hours 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 is the act of giving birth in farm animals.
- It marks the end of pregnancy.
- It marks the beginning of lactation.
- When the developing foetus has reached full term in the uterus, and is ready to be born, the placenta breaks away from the uterus wall.
- The foetus in the bag of membranes moves through the cervix and out through the vagina.
- At some point, the membrane bag breaks and the fluid inside is released.
- The umbilical cord constricts in the middle, withers and breaks naturally.
- The placenta and the broken membranes come out of the uterus as after-birth.
- The act of parturition varies with farm animals.
- Cow, it is called calving.
- Sow, it is called farrowing.
- Ewe, it is called lambing.
- Doe (Goat), it is called kidding.
- Doe (Rabbit) it is called kidding.
Signs of Approaching Parturition
- The mammary glands enlarge and begin to secrete milk substances.
- The vulva swells and becomes soft.
- There may be thick mucus discharge.
- The animal becomes restless, lies down and gets up frequently.
- The animal urinates frequently.
- The animal tries to build a nest and beds, e.g, as in rabbit.
- Loss of appetite.
- 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.
- It finally leads to the formation of zygote.
- It may occur when an animal is on heat period.