Pregnancy
One of the key for reproductive efficiency is a good observation of the signs of the estrus. Cows observed in estrus in the afternoon must be inseminated the next morning. Cows observed in estrus in the morning must be inseminated in the afternoon. The raison is because artificial insemination, or mating, performed in the later part of estrus tends to increase the conception rate, due the brief life of the ovum in the female reproductive tract.
Sperm travel from vagina to the oviduct in 10 to 15 minutes. However sperm undergo a series of biochemical reactions before they are able to fertilize an ovum. These reactions are called capacitation and six hours are required to complete the capacitation. Sperm will wait in the ampulla, which is a part of oviduct, at the time of ovulation so that fertilization can take place. Sperm can live in the female reproductive tract for 24 hours and the unfertilized ovum can live 6 to 12 hours. An ovum not fertilized will be resorbed by reproductive tract and an ovum fertilized will move to the horn of the uterus, which takes about three days. Development of the fetal and uterine membranes then takes place, during which time the developing embryo must live on the nutritive secretion that is produced uterine glands especially. This nutritive secretion is known as uterine milk, a substance that is produced during the early phases of mammalian gestation and that nourishes the embryo prior to implantation. Attachment of the fetus to the uterine wall begins day 28 of pregnancy and is completed by day 45. Then the blood progesterone will remain high and the cycle activity will be blocked. The embryo produces a protein known as interferon. The interferon is detected by the uterus and gives the first pregnancy signal and allows maintaining the integrity of the corpus luteum; thus there is continued production of progesterone.
Even though fertilization takes place and the development of the fetal membranes proceeds normally, in some cases pregnancy is terminated and the developing fetus is absorbed, mummified or expelled. If the termination is in early pregnancy, it is called early embryonic mortality, whereas it is called abortion in later pregnancy. Many embryonic deaths are unavoidable because they may be due to genetic abnormalities and it is nature's way of eliminating unfit genotype at a low biological cost.
The gestation is a period from fertilization to the birth of the calf (or parturition). This period it is average about 283 day (around 9.4 months), however there is breed variations. Male calves require 1.5 days more than female calves. Primiparous cows have a slightly shorter gestation period than multiparous cows.
