Reproductive System of Cattle

• The reproductive system produces male gametes, whereas the female produces female gametes.

• The male gametes are known as spermatozoa, while the female gametes are known as ova.

• Fertilization takes place when the male and female gametes fuse to form a zygote.

Functions of Parts of a Bull

• Testicles (Testes)

  • They produce spermatozoa.

  • They produce testosterone.

• Epididymis (Long Coiled Tube in Testes)

  • It transports sperm cells from the testicles to the vas deferens.

  • It helps in the maturation of developing spermatozoa.

  • It stores sperm cells in its tail.

Female Reproductive System of a Cow

• Oestrus Cycle in Cows

  • Exotic breeds of cattle attain puberty at the age of 15-19 months.

  • Indigenous breeds of cattle reach puberty at 27-30 months.

    • Variations also depend on management practices, especially feeding.

Factors That Affect Onset of Puberty

• Type and Breed of Animal

  • Some animals mature more quickly than others (e.g., exotic breeds).

• Genetic Make-Up

  • Dairy cattle breeds tend to reach puberty much earlier than beef cattle breeds.

• Body Weight

  • Most animals reach puberty when they have attained at least 30-50% of adult weight.

• Mating

  • It may hasten puberty (e.g., in rabbits).

• Environmental Factors

  • Puberty may be delayed due to unfavorable climatic conditions (e.g., during drought, feed and water become scarce).

• General Management, Especially Feeding

  • Calves that are properly fed and well looked after tend to reach puberty earlier than those that are poorly managed.

Oestrus Cycle

• Definition: Oestrus is the heat period for an animal. The oestrus cycle is the period between one heat period and the next.

  • In cattle, the heat period averages 21 days.

• Hormones:

  • Egg development is stimulated by a hormone known as oestrogen.

  • The egg takes six hours in the oviduct before disintegrating.

  • As soon as the egg is released, the level of oestrogen drops sharply, and the level of progesterone rises sharply.

    • Progesterone prepares the uterus to receive the embryo and maintains pregnancy if the egg is fertilized.

  • The sperm can stay in the reproductive tract of a cow for 20 to 30 hours.

Oestrus Cycle and Ovulation Periods

• Animal: Cow

  • Length of Oestrus Cycle (14 days): 19-23 days

  • Duration of Oestrus Cycle (hours): 10-26 hours

  • Ovulation Period (hours): 4-6 hours after the onset of oestrus

Phases of the Oestrus Cycle

1. Pro-Oestrus (Day 17-20)

   • Marks the animal’s coming in heat.

   • Follicles within the ovary are growing due to an increase in the secretion of follicular fluid.

   • Follicular fluid surrounds the ovum and contains the hormone oestradiol.

     • Causes the growth of the cells lining the oviduct.

     • Increases the number of cilia that transport the ova to the uterus.

   • The epithelial wall of the vagina increases in thickness to prevent possible damage during coitus.

2. Oestrous (Day One of New Cycle Begins)

   • Period of desire for mating.

   • Follicles are swollen, and the ovum is maturing.

   • Closed by ovulation (rupturing of the follicle).

   • Heat period lasts for 12 to 24 hours.

   • The vulva becomes swollen and congested with blood.

3. Met-Oestrous (2-4 Days)

   • Period when the organ returns to normal size.

   • The cavity of the follicle reorganizes and forms corpus luteum, which secretes progesterone.

   • Corpus luteum prevents further maturation of the follicles and thus prevents the occurrence of oestrous periods.

4. Di-Oestrous (Day 5-17)

   • Longest phase.

   • Corpus luteum is fully developed.

   • Uterine muscles also develop.

   • If pregnancy occurs, this stage is prolonged through gestation.

   • In absence of fertilization:

     • Corpus luteum undergoes changes.

     • The ovum becomes vacuolated and loaded with large lipid droplets.

     • Rapid re-absorption of the corpus luteum follows.

Signs of Heat in Cattle

• Behavioral Changes:

  • Smells other cows and attempts to mount them.

  • Becomes restless and isolates itself from the herd.

  • Starts bellowing frequently.

• Physical Changes:

  • Vulva becomes moist, red, and slightly swollen.

  • Clear mucus discharge from the vulva.

• Reproductive Readiness:

  • Stands still to be mounted by other animals (referred to as standing heat).

• Other Indicators:

  • Loss of appetite.

  • Increased frequency of urination.

  • Slight rise in body temperature.

  • In lactating cows, a sharp decline in milk yield.

Timing for Breeding a Cow

• When to Breed Based on Standing Heat Observation:

  • If standing heat is first observed in the morning: Breed in the late afternoon the same day.

  • If standing heat is first observed in the afternoon: Breed the next morning.

Gestation Period for Various Animals

• Animal: Gestation Period

  • Cattle (cow): 270-285 days

  • Goat (nanny): 150 days

  • Sheep (ewe): 145-150 days

  • Pig (sow): 112-116 days

  • Rabbit: 28-31 days