A male animal produces millions of sperms daily. Theoretically, it can inseminate females regularly and produce several offsprings. This excess capacity of male has been utilized through developing new technologies for artificial insemination which can be said as the first animal biotechnology.
The most effective factor that has increased the productivity of cattle is the artificial insemination. However, the breeder must replace the nature through artificial insemination if he ensures about the ovulation of female in herd together at a time. In contrast, if a breeder awaits for female to ovulate and then inseminate separately, the importance and economic significance of artificial insemination get reduced. Therefore, through artificial insemination technology increased number of females can be inseminated by a male.
Semen and its storage
In addition methods have been developed to produce semen from male by ejaculation. Semen ejaculate is collected and diluted (extended). Sperm motility and their number per milliliter are examined under the microscope. About 0.2 ml bull semen contains about 10 million motile sperms. The diluted sperms may be used fresh within a few days or cryopreserved at -196°C by using liquid nitrogen (for detailed description see Cryobiology
). The cryopreserved semen can be stored for a long time and easily transported across the states or countries. Thus, cryopreserved semen of a single male is capable of inseminating thousands of females of a country or other countries. For example, one ejaculate semen of a bull is sufficient to inseminate about 500 cows.
In many animals it is difficult to find out oestrous (sexual heat) in animals because it persists only for a few hours and occurs mostly at night. After ovulation (which is indicated by oestrous) females are inseminated. But in a herd it would be economical, easy and simplified management if females are inseminated at a times. However, it is possible only when all the female ovulate at a time; in practice it is not possible to get synchronization of oestrous. Moreover, it is possible to bring about ovulation in about 80 per cent of females by using hormones, for example progesteron and/or prostaglandin. These hormones regulate ovulation cycle of female and result in total synchrony of oestrous.
Sperms are produced in the testes of males and ova in female's ovaries. Sperms and ova contain half of chromosomes as compared to somatic cells. An ovum possesses autosomes and one X chromosome. Similarly, a sperm contains autosomes and one Y chromosome. In animals sex is determined genetically i.e.
by sex chromosomes. X chromosome determines femaleness and Y maleness. All the ova contain X chromosome, whereas a sperm consists of either X or Y chromosomes. One sperm ejaculate contains half X and half Y chromosomes.
In dairy industry demand of females is more than the males. Secondly, females have more desirable characteristics. The livestock industry prefers animals of one sex. Therefore, through artificial insemination technology X and Y chromosomes can be detected and sex of progenies determined accordingly.
There is a fluorescence dye (Hoechst 33342) that stains X and Y chromosomes with different intensities. Thus, these two chromosomes possibly can be separated by using an instrument, fluorescent activated cell sorter (FACS). Sperms are present in the form of suspension. The FACS converts a suspension of sperms into microdroplets. Each droplet consists of a single sperm cell. Individual microdroplet passes through a laser beam. Microdroplets of different intensities are deflected into separate collection tubes as the fluorescence of dye is measured electronically. The sperms separated by using FACS have recently been used and pre-sexed calves have been produced through in vitro
fertilization technique (see
Moreover, FACS is very expensive and slow. It takes about 24 h to process one semen ejaculate, whereas the sperm cannot remain viable for a long time. Therefore, more refinement in technique is required for its use on a large scale (Read and Smith, 1996).