Reproductive Physiology of the Female
- In nature, animals usually breed once a year, with births in spring when conditions are ideal for offspring survival. Domestication has extended breeding seasons, but animals often revert to natural cycles, showing lower fertility in summer and early autumn.
- Female animals must attract males and be in heat to reproduce. Domestic mammals have regular heat cycles linked to ovary follicle development, leading to egg release. Successful mating can result in pregnancy.
Understanding the Oestrous Cycle
The oestrous cycle is a natural process that happens in female animals. It is similar to the menstrual cycle in humans but has some differences. Let’s break down what the oestrous cycle is and how it is traditionally divided into different phases.
What is the Oestrous Cycle?
- The oestrous cycle is a series of changes that occur in the reproductive system of female animals. It prepares the animal’s body for mating and potential pregnancy.
- This cycle is important for reproduction, which means having babies. It helps the animal know when it is the right time to mate.
Phases of the Oestrous Cycle
- The oestrous cycle is divided into several phases. Each phase has specific characteristics and changes that happen in the animal’s body.
- These phases help scientists and veterinarians understand the reproductive health and timing of animals.
Why Divide the Cycle into Phases?
- Dividing the cycle into phases makes it easier to study and understand. Each phase has different signs and changes, so knowing them helps in identifying what stage the animal is in.
- It is like breaking down a big task into smaller, manageable parts. This way, it is easier to focus on each part and understand it better.
Common Phases in the Oestrous Cycle
- Proestrus: This is the phase before the animal is ready to mate. The body starts preparing for mating, and there is growth in the reproductive organs. Prooestrus is the stage before oestrus where the reproductive system becomes more active, with follicle growth, changes in the uterus and vaginal area, and visible signs like swelling and discharge in females. The phase preceding oestrus is characterized by heightened activity in the reproductive system. This includes the final maturation of follicles in the ovaries, regression of the corpus luteum from the previous cycle (in polycyclic species), and noticeable changes in the uterus and vagina.
- Oestrus: This is the phase when the animal is ready to mate. It is often called “heat.” The animal shows signs that it is ready to mate, like being more active or seeking out a male. Oestrus is when a female animal is ready to mate, marked by increased mucus secretion and relaxed cervix. Ovulation happens during this phase, except in cows where it occurs after oestrus. In most animals, ovulation is spontaneous, but in cats, rabbits, and camelids, it is triggered by mating. During oestrus and prooestrus, follicles grow without functional corpus luteum, and oestradiol is the main hormone produced. These stages are collectively known as the follicular phase of the cycle. In another way it could be well summarize as “During this phase, the female is sexually receptive and will accept the male for mating. Ovulation, the release of the oocyte, typically occurs during oestrus in most domestic animals (exceptions include cows, cats, rabbits, and camelids)”.
- Metoestrus: After mating, the body starts to change again. This phase is when the body begins to prepare for a possible pregnancy. This phase follows oestrus, where cells from the ovulated follicle form luteal cells, leading to the creation of the corpus luteum (CL). During this time, mucus secretion from uterine, cervical, and vaginal glands decreases.
- Dioestrus: This is the phase when the body is either supporting a pregnancy or getting ready to start the cycle again if there is no pregnancy. Known as the luteal phase, the CL is active and produces progesterone. Uterine glands grow, the cervix tightens, and genital tract secretions become sticky. The cycle can be divided into oestrus and interoestrus, or follicular and luteal phases.
- Anestrus: This is a resting phase. The reproductive system is quiet, and there is little activity. It is like a break before the cycle starts again.
Why is Understanding the Oestrous Cycle Important?
- Knowing about the oestrous cycle helps in animal breeding. Farmers and breeders can plan the best time for mating to increase the chances of pregnancy.
- It also helps in veterinary care. Vets can diagnose and treat reproductive issues by understanding which phase the animal is in.
Examples of Animals with Oestrous Cycles
- Many domestic animals like dogs, cats, cows, and horses have oestrous cycles. Each species may have slight differences in the length and signs of each phase.
- For example, dogs usually have a cycle that lasts about six months, while cows have a cycle that repeats every 21 days.
Conclusion
- The oestrous cycle is a crucial part of animal reproduction. By dividing it into phases, we can better understand and manage the reproductive health of animals.
- This knowledge is valuable for anyone working with animals, from farmers to veterinarians, ensuring healthy and successful breeding practices.
