Early Embryonic Mortality

The rate of early embryonic death is 25%. Average conception rate is 60 %. While 5-15 % is rate of failure of fertilization. EEM is a way to get rid of undesirable genetic material at low biological cost because animal is wasting 21 days of his life in EEM. On the other hand if a cow born abnormal fetus, there will be a loss of 9 months.

Early embryonic mortality occurs between 8-19 days; mostly it occurs at day 14, 15.

Causes of EEM

Lack of PGF₂α:
When the embryo is implanting, the first contact of fetus to uterus sends signals to endometrium not to produce PGF₂α so that pregnancy may maintain. But if it is produced, the CL will regress and embryo will die before the attachment. As a result animal will come in heat at normal time in same cycle.

Nutrition Deficiency:
Nutrition deficiency is also the cause of EEM. Excess or deficiency of β carotenes, phosphorus, copper, and selenium has been considered the cause of embryo death.

Cytogenic Abnormalities:
Normal complement of chromosome is required for the proper development of new born. Expression will not be normal if chromosomes do not unite at proper site. First pair of chromosome should unite with first pair of chromosome of opposite sex. If these do not unite properly, it is cytogenic abnormality and embryo will not be normal. If the pairs unite correctly but there may be mutation, resulting embryo will be abnormal. Abnormal gametes can fertilize but shortly after fertilization they will die. In cattle 10 % of embryos have abnormal karyotype.

Intrinsic factors include chromosomal abnormality, single gene mutation, and mutagen induced irreversible changes in DNA. Chromosomal abnormalities either inherited or arise during gametogenesis. Some abnormalities may be acquired e.g. handling of embryos during transfer, permanent alterations in DNA induced by substances like superovulatory hormones, culture media and serum, UV, DNA binding dyes, radio activity, ethylene oxide and viral genes.

Immunological Factors:
When foreign body enters in body there is reaction. When fetus comes in uterus then there is no immune response because uterus has its own immunosuppressive mechanism. If any defect in this system, it will result in early embryonic mortality.

Age:
Cows which are older have higher incidence of early embryonic mortality.

Breed:
Breed does not affect rate of embryonic mortality. Those herds which have higher incidence of inbreeding have more chances of EEM.

Uterine Environment:
If environment of uterus is not proper, animal will not survive. There are two things for development of embryo.:

• Cellular development of uterus

• Secretion of nutrients (Chemical composition of pregnant and non pregnant uterus is different)

If there is problem in these two factors, there will be EEM. These are under the effect of estrogen and progesterone.

Hormonal Levels/ Imbalances:
Pregnancy is maintained by progesterone which is produced by coprus luteum. Proper amount of progesterone must be available; if sufficient amount is not available, the embryo will die. If progesterone is given in large amount, production of LH will go down and luteal activity will be less and there will be less production of progesterone. So calculated amount of progesterone should be given.

High Temperature:
If environmental temperature rises too much, body temperature will rise and uterus temperature still higher than body temperature then embryo will die off.

Effect of AI or Time of AI:
Life span of ovum is lesser than that of sperm. Sperm can survive for 18-24 hours and ovum for 6-8 hours. So when we inseminate animal, we should keep in mind the time for capacitation. If ovum has shed and then you inseminate, the sperms will take 6 hours for capacitation. This time will make the ovum more aged. So the aged gametes may fertilize but they may not be able to survive and EEM may occur.

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