OESTROUS CYCLE
It is a rhythmic physiological cycle which takes place in the female animal’s reproductive tract that has reached puberty.
i) Oestrus is commonly referred as “Heat”
ii) Oestrus can also be spelled as “Estrus”
The Oestrous cycle in Cows can be divided into four stages:
i) Proestrum
ii) Estrum Follicular phase
iii) Metestrum
iv) Diestrum Luteal phase
Length of Oestrous cycle in cattle is 21 days.
i) Proestrum:
i. Ill-defined phase.
ii. Ovulatory follicle is formed in this stage.
iii. Follicle starts secreting Oestrogen.
iv. During the phase, the female reproductive system prepares for the onset of oestrus.
v. It lasts for 3 days.
ii) Estrum
i. Well-defined phase.
ii. It is the phase of sexual receptivity. It is only during oestrum the female animal allows to be mounted.
iii. It lasts for 24 hours.
Signs of estrum:
1. Increased locomotion.
2. Increased vocalization (Sound expression) Eg. Bellowing in cattle.
3. Mounts on other animals and allows to be mounted by other males. It indicates the willingness of the female to accept the male. This willingness is referred to as “Standing Oestrus”
4. Increased Urination.
5. Vulva and vagina become swollen and red.
6. Discharge of mucus from the vagina.
7. Other minor signs like anorexia, restlessness and decrease in milk yield may also be exhibited.
In cows, release of ova from the Graffian follicle (Ovulation) takes place 12 hours after the end of oestrum.
The optimum time for breeding the cattle is 12 hours after the onset of Oestrus (i.e. at Mid-heat).
(iii) Metestrum
i. Poorly defined phase.
ii. It is the period after the end of Oestrum, in which ovulation takes place leading to subsequent formation of Corpus luteum (CL). The CL starts producing Progesterone.
iii. In cattle, some capillary hemorrhage may occur in the uterus. This is called Metoestral bleeding.
iv. This phase lasts for 3 days.
(iv) Diestrum
i. Longest phase.
ii. It is the period of time when the CL is fully functional and progesterone production is high.
iii. It ends with the CL getting destroyed if the animal fails to conceive. If pregnancy is established, the CL remains functional through out the gestation period producing progesterone which protects the growing foetus.
iv. If animal is not pregnant, this phase lasts for 14 days.
ARTIFICIAL INSEMINATION (AI)
AI is a method of manual deposition of semen in the female reproductive tract with the help of AI gun instead of natural service (mating).
Merits:
1. Proven and genetically superior bull’s semen can be used for this method.
2. It helps to control Venereal (sexual) diseases.
3. The cost of rearing a bull for breeding purpose alone can be reduced.
4. By repeated use of semen from superior bulls, dramatic improvement in the performance of the female progeny can be expected.
5. Transport cost involved in the semen straws is very minimal.
Demerits:
1. It needs high standard of technical efficiency which requires skilled persons.
2. Correct detection of ‘Heat’ is necessary. Insemination of cows not in heat or faulty insemination will lead to infertility.
3. Moreover if the animal is pregnant, insemination will lead to abortion.
4. Hygiene and sanitary measures should be adopted throughout the procedure.
5. Selection of bulls as semen donors is very important. If they have defects in their genes or disease causing agents in the semen, it will lead to widespread deleterious effects.
Procedure:
1. The animal should be properly restrained in the Trevis.
2. The straw should be taken out from the LN2 container.
3. The straw is thawed by submersion in water at 37oC for 30 seconds.
4. The thawed semen straw is wiped cleanly, since even a small drop of water may be spermicidal (kill sperms) and the plug is cut off.
5. It is then loaded in AI gun and an AI sheath is put over.
6. By recto-vaginal technique, the semen is deposited in the uterus.
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