How Important is the Timing of A.I.?
David Mackey (College of Agriculture, Food and Rural Enterprise) and Brian Kennedy (AI Services Ltd)
Many farmers who use artificial insemination, whether conducted by a professional inseminator or DIY, wonder what is the best time for insemination to get the highest conception rates. A lot of farmers inseminate according to the am:pm rule, where cows seen on heat in the morning are served in the evening and cows seen on heat in the afternoon or evening are served the next morning – but is this the best way to time inseminations?
The am:pm rule
The am:pm rule regarding the best time to inseminate cows on heat came from when the practice of A.I. was first introduced in the 1940s. Research at that time showed that dairy cows were on heat for 18 hours on average so timing of insemination relative to onset of heat (early, mid or late oestrus) had a considerable effect on conception rates. However, in the modern dairy cow, cows are only on heat six to eight hours and exhibit much less mounting activity, if they demonstrate any overt signs of heat activity at all. Therefore farmers have to rely on seeing secondary signs of heat such as tail sniffing, restlessness and reduced appetite or milk production to help detect cows in heat. So, is timing your inseminations according to the am:pm rule still appropriate today?
Recent research
More recent research in Europe, the United States and New Zealand using larger numbers of cows and modern heat detection technology has shown that there is little if any difference between cows served using the am:pm rule or once daily service. Conception rates are at their maximum from 4-18 hours after onset of heat, but how long has a cow been on heat when you first see her being mounted?
When is the best time to inseminate?
Various studies have examined conception rates according to the time of day when cows were first observed in heat and time of insemination.
- For cows first observed in heat in the afternoon or evening the best time to inseminate is the following morning when conception rates are about 2 percent higher.
- For cows first seen on heat in the morning, the highest conception rates occur in the evening but these are not significantly higher. If cows are only inseminated at one time in the day, cows seen on heat in the morning are best served then rather than wait until the following morning (when the conception rate is typically 5 percent lower).
Overall, compared to conducting AI once daily in the morning, research evidence suggest that twice daily insemination according to the am:pm rule may increase conception rates slightly – but is twice daily insemination worth the extra effort? The practice of conducting inseminations on a once daily basis is already standard practice throughout Europe, New Zealand and Australia and no major decline in conception rates has occurred compared with the historic am:pm approach.
David Mackey and Brian Kennedy discuss the best time to inseminate cows