ReproductiveSystem
Evolution is the day-to-day process. According to evolutionary biologists, the three major functions of animals are growth, behaviour according to the environment, and reproduction.
The biological process by which new individual organisms are produced from their parents is called reproduction. Each organism exists due to reproduction, which is a fundamental characteristic of all forms of life. The offspring represents 50% from the paternal side and 50% from the maternal side. It is because the new-born shares genetic information from both parents. This mixing comes about because of sexual reproduction, which involves the fusion of two sex cells or gametes, called fertilisation. Male and female animals (Fig. 1.6) have different reproductive systems. During puberty, the reproductive organs develop to enable the production of offspring.The testes produce sperm, the male gametes. In most species, the testes are kept outside the body in the scrotum, except for elephants, rhinoceros, and a few marine animals, like whales and dolphins. The purpose of the external scrotum is to keep the scrotum cooler and is better to form sperm production. The sperm ducts carry sperm from the testes to the urethra, a tube running down the inside of the penis. Spermatozoa are mixed with secretion from glands to produce a liquid called semen. Semen helps carry the sperm into the female reproductive system. The female gametes eggs or ova are released from the ovaries through the process called ovulation. Immediately following ovulation, the egg travels through a tubular passageway called the fallopian tube away from the ovary and towards the uterus. During copulation, the semen is ejaculated from the penis into the female’s vagina. These ejaculated spermatozoa swim up through the cervix and uterus. If a sperm manages to reach the ova in the fallopian tube, then fertilisation will occur.
After ovulation, the egg only lasts 24 h, whereas the sperm can last up to 3 days (varies according to species). Once fertilisation occurs, the fertilised egg called the zygote will start to divide on reaching the uterus. This cluster of cells will settle into the lining of the endometrium of the uterus. Inside the uterus in a pregnant animal, the fertilised egg cell will continue to divide and differentiate to form different cells. Some will form structures in the embryo and others the placenta. The placenta is an external covering of the foetus where substance exchange between the mother and embryo occurs. Nutrients and oxygen will pass from the mother’s blood into the embryos. Embryos receive these nutrients through the umbilical cord. Usually, the embryo is called the foetus after fertilisation at the end of week 8 (varies according to the species). The foetus continues to develop for the entire pregnancy, also called gestation. After the designated gestation period with the combination of different endocrine hormones, parturition occurs. It is the glance at the complete process of copulation to start a new life.Various reproductive biotechnologies or assisted reproductive technologies (ART) have recently revolutionised livestock productivity to meet the increasing global population food demand. Recent biotechnologies in both males and females, particularly concerning livestock, have revolutionised the reproductive process in vitro and in vivo to improve reproduction and efficiency. Techniques like semen sexing are used to produce offspring of the desired sex. This technique is based on the flow cytometric principle of separating spermatozoa with fluorescently labelled X chromosomes from sperms and fluorescently labelled Y chromosomes. Using this technology, it can sort 15 million spermatozoa per hour into X- and Y-bearing sperms and predict the gender of calves with an accuracy of between 85% and 95%. Another technique is named sperm encapsulation, which encapsulates the spermatozoa for longer term preservation in vivo.
This technological innovation was intended to allow spermatozoa to stay alive longer in the body’s temperature and make the release of viable spermatozoa more progressive over a longer period in domestic animals. Coming to females, Ovum pick-up (OPU) is a non-invasive approach for obtaining large quantities of high-quality oocytes from living animals without invasive procedures. In India, using this technique first buffalo calf named Saubhagya was produced. This method not only improves reproductive efficiency over time but can also be used in follicle ablation to aid in follicle turnover during the embryo transfer protocol.Fig. 1.6 Description of the female reproductive system in animals. (Courtesy: BioRender)
Additionally, In vitro Maturation, Fertilisation, and Culture (IVMFC) involve the collection of oocytes from ovaries of slaughtered animals trailed by the production of viable embryos through in vitro maturation and fertilisation. The IVMFC approach is ideal for embryo transfer, cloning, transgenesis, and sophisticated in vitro techniques. Intracytoplasmic Sperm Injection (ICSI) is a micromanipulation procedure that involves generating healthy and desirable embryos by mechanically inserting high-quality spermatozoa into the oocyte cytoplasm. ICSI has also been performed on sexed sperm with an 80% success rate in cattle and 48-63% success rate in small ruminants using fresh and frozen- thawed sperm. There are many more techniques like embryo transfer technology (ETT), embryo cryopreservation, embryo sexing, somatic cell nuclear transfer technique, stem cell technologies, transgenesis to counter the demand of increased productivity. Although these techniques have the potential to be effective, they have been hampered by several factors, including the lack of a comprehensive database on indigenous livestock and its biodiversity (which includes traits such as production, reproduction, and disease resistance within species and breeds), which are necessary for their implementation. In the future, the use of these advanced techniques may provide additional insight into the molecular complexities of the reproductive process, including its insanity.
1.8