Fertilization and Pregnancy of Dairy Cows

1. Fertilization and fertilization is the process by which sperm and eggs combine to form a zygote (fertilized egg) in the fallopian tube ampulla. The physiological and biochemical mechanisms of fertilization are complex. The main processes include the entry of sperm into the egg; the sperm forms male pronucleus, the egg forms the female pronucleus; the pronucleus continues to develop and is replaced by the chromosomal group and forms a zygote, which begins normal cell growth and development and life processes. 2. Pregnancy begins with the fertilization of the egg, through cleavage, blastocyst formation, implantation of the embryo, differentiation and growth of the fetus, until the fetus matures and discharges together with the placenta and the accessory membrane before the maternal complex physiological process. It is a physiological phenomenon unique to the mother.

(1) The gestation period starts with the fertilized egg and goes through development until the mature fetus is produced. This period of time is called the gestation period. The gestation period of a cow is generally 270-285 days with an average of 280 days. Cows have a more stable heredity during gestation, but the length of the gestation period varies according to species, individual, age, season, and feeding and management conditions. Generally, early-maturing varieties are shorter than late-maturing varieties, and males are about 1 day more than females, and twins are 3-7 days shorter than singles. Breeding cows are about 1 day shorter than adult cows. The cows in winter and spring are farther than those in summer and autumn. Long, with an average difference of about 3 days, cows with poor feeding and management conditions have a longer gestation period.

(2) Development of embryos and attachment of fertilized eggs After a zygote is formed, the blastomeres continue to divide and proliferate, passing through mulberry embryos, blastocysts, and dilated blastocysts, and finally hatching from the zona pellucida to form a blister-like transparent. Blastocysts. The activity of the early blastocyst in the uterus was limited, and the position in the uterus gradually settled down and began to form a tissue-associated relationship with the uterine lining, and gradually implanted on the uterine mucosa. After the cattle are fertilized, they usually begin to implant 20-30 days. The time for implantation is about 60-75 days after fertilization. Blastocyst consists of two parts of cells, a part of which accumulates at the tip of the blastocyst, which will develop into the embryonic body, and the other part will constitute the blastocyst wall, covering the above part and becoming the outer membrane of the blastocyst, which will form the fetal membrane and fetal placenta.

(3) Fetal membranes and placental fetal membranes are the general term for the fetal body to outsource several membranes of the fetus. It is a temporary organ of the fetus during maternal intrauterine development. Its main role is to exchange material with the mother and protect it. The normal growth and development of the fetus. The fetal membranes mainly include yolk membrane, amnion, urine membrane and chorion. The yolk membrane exists for a short period of time. The cows disappear until 28-50 gestational ages. The amniotic membrane is on the innermost side and surrounds the fetus. Amniotic fluid forms in the amniotic cavities and the outer layer is chorion. The three membranes are in close contact with each other. The urine membrane amniotic membrane, urine membrane chorionic membrane and amnion membrane were formed. The urine membrane amniotic membrane and the urine membrane chorion together form a cavity called the urine cavity, with urine. Amniotic fluid within the amniotic cavity and the urinary water in the urine cavity are collectively referred to as fetal water. It plays the role of protecting the normal development of the fetus and preventing the fetus from interpenetrating with the surrounding tissues or the skin of the fetus itself. It is natural lubrication for the birth canal during childbirth. Agent to facilitate the discharge of the fetus. Placenta usually refers to the special structure formed by the connection between the urine membrane and the uterine mucosa, in which the urine membrane chorionic part is the fetal placenta and the part of the uterine mucous membrane is the mother's placenta. Placenta is rich in blood vessels, is an extremely complex multi-functional organs, with the substance transport, synthesis, decomposition, metabolism, secretion of hormones and other functions to maintain the normal development of the fetus in the womb. The placenta of the cow is a cotyledon type placenta, the villi on the cotyledon of the fetus closely match the glands on the mother's cotyledon, and the cotyledon of the fetus encloses the mother's cotyledon. The band associated with the fetus and the fetal membrane is called the umbilical cord. The umbilical cord of cattle is 30-40 cm long, with one umbilicus, two umbilical arteries, and two umbilical veins. When the arteries and veins reach the urinary chorion quickly, they are divided into two groups and divided into small branches. Into the chorion, it is divided into many small pieces on the urine membrane chorionic.

(4) Physiological changes in cows during pregnancy The cows undergo significant changes in the endocrine and genital organs during pregnancy to maintain the balance between the mother and the fetus. 1 During endocrinology, the endocrine system changes significantly, and various hormones coordinate the balance to maintain pregnancy. Estrogen: Larger follicles and placenta secrete a small amount of estrogen, but it is kept at a minimum level. Pre-delivery secretion increased until 9 months of pregnancy when the secretion increased significantly. Progesterone: During pregnancy, not only progesterone is secreted by the corpus luteum, but also the adrenal and placental tissues can secrete progesterone, and the progesterone content in the blood remains unchanged until the level of progesterone drops sharply in the days before delivery. Gonadotropin: During pregnancy, due to the effect of progesterone, the ability of the anterior pituitary to secrete gonadotropin gradually declines. 2 Changes in reproductive organs Due to the role of reproductive hormones, the fetus continues to develop in the mother's body, causing the reproductive system to change significantly. Ovaries: If mating without pregnancy, the corpus luteum subsides. If mating, the corpus luteum becomes a pregnancy corpus luteum and persists in the largest volume maintained throughout the pregnancy, continuing to secrete progesterone until the late corpus luteum gradually subsided. Uterus: During pregnancy, as the fetus grows, the volume and weight of the uterus continue to increase, the walls of the uterus become thinner, and the uterine glands grow and bend. Cervical: After gestation, the uterine sphincter is contracted and tense. The chemical substances secreted by the cervix changes, and the thickened mucous secretions form a cervix and close the cervix. Vagina and vulva: The vaginal mucous membranes turn pale, and the mucous membranes are covered with thick mucus secreted from the cervix. The labia is contracted and the vulva is closed until it becomes edematous and soft before the birth. Uterine Ligaments: The proliferation of smooth muscle fibers and connective tissue in the uterine ligament is thickened. Due to the increase in uterine weight, the uterus is pendulous and the uterine ligament is elongated. Uterine arteries: Uterine arteries become thicker, blood flow increases, and pregnancy pulses appear during and after pregnancy. 3 Changes in body condition Young cows in the first trimester can still grow normally during pregnancy. After pregnancy, the metabolism is strong, the appetite is increased, and the digestive ability is improved. Therefore, the nutritional status of the female animal is improved, the body weight is increased, and the color of the coat is smooth. The blood circulation system is strengthened, the pulse and blood flow are increased, and the blood flow to the uterus is significantly increased.

(5) Estimated date of pre-production period After the cows have been examined and judged to be pregnant, in order to reasonably arrange production, properly raise and manage the cows in different stages of pregnancy, and make every preparatory work before delivery, the cows must be accurately calculated. Expected date of production in order to prepare the production plan. Calculate the cow's expected date of birth can be reduced by 3 breeding months, mating date plus 7 methods, if the breeding months in January and February, you can add 12 months and then subtract 3. For example, the date of the last breeding of a cow was June 4, 2002, and the expected date of production was: 6-3=3 (that is, March 2003) 4+7=11 (that is, March 11). The pre-production date for this cow is March 11, 2003.

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