Embryonic mortality: definition, frequency and timing

Embryonic mortality is regarded as one of the major causes of reproductive failure in cattle resulting in reduced pregnancy rates, slower genetic improvement and substantial financial losses to dairy and beef production. Embryonic mortality refers to the losses which occur in the period between fertilisation and the completion of the stage of differentiation at approximately day 42.

Frequency and economic consequences

It is generally accepted that fertilisation rate in cattle is about 90%. Embryonic loss accounts for a 29-39% loss after fertilisation. Most cases are between days 8 to 16 after fertilisation (Roche et al., 1981; Dunne et al., 2000).

Figure 1: Frequency of embryonic mortality at different stages of pregnancy

Timing of Embryonic Mortality

• Early Embryonic Mortality
  • before day 15 post AI
  • does not affect the length of the cycle
  • no signs of abortion are diagnosed
    
• Late Embryonic Mortality
  • between 16 and 42 days post AI
  • the cow returns to oestrus after corpus luteum regression - length of the cycle increased
  • late embryonic mortality (after day 35-45) may be diagnosable as in some cases the embryo and the membranes are aborted. Remnants are frequently resorbed.
  • usually the only obvious sign is return to oestrous as late as 35-50 days after insemination.