The Veterinary Column - Timing of AI is Essential
Date Posted: 17th November 2022
Timing of AI is Essential
Brian Kennedy MVB, DBR, MRCVS, FrAgs
Company Veterinarian, AI Services (NI) Ltd
Understanding the events associated with fertilisation allows us to time inseminations in such a way as to achieve best results. As with almost all biological processes, there is considerable variation from animal to animal, but on the whole average values provide a useful framework.
On average the modern high production dairy cow stays in heat for about 10 to 12 hours. During this time she will chin rest and sniff 25 times, mount 6 times and stand to be mounted 4 times, mainly within the second half of the heat period.
On the basis that much of this activity occurs during the hours of darkness, heats are easily missed without the aid of modern heat detection technologies.
Ovulation
Ovulation is when the oocyte is released from the ovary and occurs around 24 hours after the start of standing heat. The oocyte remains viable for approximately 6 hours, i.e. 24 – 30 hours after the first standing heat.
The goal is to have a supply of viable semen available in the oviduct at this time.
Insemination
Insemination with conventional (non-sexed) semen should happen anytime after 8 hours following the first standing heat. This semen remains viable for about 24 hours.
Sexed semen does not persist to the same extent (perhaps 12 hours) and to enhance the likelihood of fertilisation should not be introduced until 12 hours later than conventional semen, i.e. 20 hours after first standing heat.
