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Fertilization is defined as union of male and female gamete to form zygote. During estrus phase, the cow is mated or inseminated with fertile semen. Ovum and spermatozoa undergo fertilization in ampulla of oviduct within few hours of mating. If no mating occurs, the ovum undergo degenerate and a new ovum is released in next estrus. For next ovum, a fresh insemination/copulation is necessary. With fertilization, two haploid cells (ovum & sperm) fuse to produce a diploid zygote which subsequently develops into embryo and later into fetus. Zygote moves into uterine horns by 4-5 days and becomes embryo and remains free in the lumen up to 32-35 days.
Implantation is defined as attachment of embryo to the uterus for taking nutrients from maternal blood. Implantation occurs after about 35 days and subsequently embryo is termed as fetus. After implantation placenta is formed. Placenta is specialized structure for maintaining connectivity between mother and fetus inside uterus. Placenta also acts as endocrine gland and produces hormones like progesterone placental gonadotropins required for maintenance of pregnancy.
Pregnancy is defined as the period during which young one remains in uterus. It starts from day of fertilization till the day parturition or delivery or birth of young one. Period of pregnancy is also termed as gestation length. During this period, development of fetus is completed.
Parturition is defined as act of expulsion of fetus out of reproductive tract after completion of gestation length. Before parturition, the fetus draws all nutrients and oxygen from maternal blood. After completion of gestation period, fetus is capable of living independent life. Mother approaching parturition exhibits some typical symptoms such as restlessness, sticky discharge from vagina, relaxation of pelvic ligaments, frequent change in posture etc. Parturition occurs in three stages. First stage is protrusion of water bag (allantois) during which a membranous bag containing fluid comes out. Second stage comprises of fetus expulsion (head comes first) from birth canal. Third stage is a longer phase during which placenta (fetal membranes) are expelled out. During parturition proper attention is required in terms of cleanliness and hygiene. Assistance of a qualified personal should be sought in case of any difficulty in parturition or when placenta is not expelled timely.
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