VCP 511: Gynaecology and Obstetrics Section

REPEAT BREEDING - ETIOLOGY

All the major causes can be grouped into two categories of those causing

• Fertilization failure.
• Early embryonic death.

Fertilization failure

• Fertilization failure accounts for about 15% of reproductive wastage in normal cows. In repeat breeder cows the fertilization failure may be higher around 28-44%. Fertilization failures may be due to:
• Abnormalities in ovulation such as failure of ovulation and delayed ovulation. Both conditions are due to deficient LH release.
• Defects of the ovum like defective ovum and ageing of ovum – ova are viable for only few hours.
• Inability of the sperm to fertilize a viable ovum due to fertility differences in bull, high sperm abnormalities, low individual motility, low sperm concentration, inflammatory conditions of genital tract and very early A.I. or ageing of sperms.
• Inability of gametes to reach one another because of anatomical defects of genital tract both congenital and acquired, segmental aplasia, various affections of oviduct leading to obstruction and failure of ova pick-up.

Early Embryonic Death

• Embryo loss accounts for the major portion (25%) of the reproductive wastage.

Time of embryo death

• Major portion of the embryo death occurs gradually between days 8 and 19 after breeding.
• Most embryo death occurs before the critical stage of pregnancy recognition i.e. the cow will return to oestrus at within normal 18 to 25 days.

Etiology

Cytogenetic abnormalities

• Critical requirement for the embryo survival is the presence of a normal complement of chromosomes. Chromosomal aberrations play some unquantified role in early embryo loss.

Unfavourable uterine environment

•  Uterine environment enables the spermatozoa to ascend to site of fertilisation, provides adequate nutrients for different stages of embryonic development, maintains an appropriate milieu and fulfils immunologic requirements (both immunosuppressive and antibacterial requirement). Uterine environment can be affected by, hormonal imbalance, infections like endometritis, nutrition and environmental stress.

Hormonal imbalance

• Administration of progesterone in case of luteal deficiency tends to increase the pregnancy rate. Administration of hCG/GnRh on the sixth day after estrus during the luteal phase to induce steroidogenesis by the corpus luteum.

Non-specific uterine infections

• The presence of non-specific uterine infection or endometritis around the time of service is not an important cause of infertility in the cows. The bacteria may interfere with fertility by directly killing the gametes or conceptus, changing the uterine milk, causing endometritis (toxic products, luteolysis) and producing chronic histologic lesions.

Specific uterine infections

• Organisms which cause early embryonic death are T richomonas fetus, Campylobacter fetus, Brucella abortus and IBR – IPV.

Nutritional causes

• Extremes of nutrition are detrimental to the survival of embryo. Deficiencies of wide range of specific nutrients have been implicated in poor reproductive performance. Particularly selenium and Vitamin E were reported to cause early embryonic death. A very high plane of nutrition also leads to embryonic death. 

Environmental stress

•  Sustained elevated body temperature due to persistent fever or high environmental heat and humidity lead to early embryonic death.

Immunologic factors

• Following conception the cow comes into contact with both sperms and embryonic antigens and if the immunosuppressive mechanisms are not functioning properly, the antibodies produced may reduce the fertility.

Time of AI

• Improper timing of AI results in ageing  of gametes which results  in either fertilization failure or early embryonic mortality.