When Cow should be Inseminated

 When should cows be inseminated?

If cows are inseminated too early the sperm will no longer be viable when they meet the egg; if they're inseminated too late then the reverse will occur.

However, there is more leeway with the former than the latter. The golden rule of timing of insemination remains: inseminate before the cow releases the egg ('ovulation') - we want the sperm to be in the oviduct before the egg gets there.

This means that the timing of insemination is based on predicting when ovulation is likely to occur not when it has occurred. In the cow, ovulation occurs 24 to 32 hours after the start of standing heat; this means that we can tie the timing of insemination to observing heat, with initial research showing that the best conception rates occurred when cows were inseminated  from mid oestrus until 2 to 3  hours after the end of oestrus.

The am/pm rule

This research led to the development of the 'am/pm rule' - where a cow which was seen on heat in the evening was inseminated the next morning, while a cow that was seen on heat in the morning was inseminated the following evening.

However, the modern dairy cow shows heat less intensely (fewer than 50% of cows in oestrus stand to be mounted compared to >70% in the 1980s) and shows it for a shorter period of time (duration of standing oestrus has decreased from an average of 15 hours to 5 hours), so the question is often asked as to whether the am/pm rule needs to be changed.

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