Heat Detection and Timing of Artificial Insemination
You have decided to use artificial insemination (AI) to breed your cows this spring. You have planned your heat synchronization protocol, selected the AI sire and ordered the semen. Now what? First, we address the signs of standing heat in cows and heifers. These include:
- Standing to be mounted by herd mates. This is the “silver bullet” sign of standing heat.
- Mounting other cows
- Clear mucus discharge from vulva
- Swelling and reddening of the vulva
- Bawling, trailing other cows and restlessness
- Rubbed hair on tail head and dirty flanks (from being mounted by other cows)
- Sniffing genitalia
- Chin resting on other cows
- Head raised and lip curled
- Decreased feed intake
- Bloody discharge from vulva (usually occurs after standing heat has ended)
The most limiting factor in AI programs is the proper detection in estrus or standing heat. A sexually mature, non-pregnant heifer or cow will have a standing heat every 21 days (on average). Heat synchronization protocols are designed to manipulate this process to make females come into standing heat on a schedule. Standing heat is the time in her estrous cycle when a cow/heifer is receptive mounting activity by a bull or other herd mates. Standing heat is the only external sign that cows are ovulating and should be bred (naturally or AI). Standing heat typically last 12 – 18 hours. Best heat detection practices include morning and evening (at 12 hour intervals) visual observation of standing heat. In spring calving Oklahoma herds, the morning heat detection is most effective in the very early daylight hours before high daily temperatures may suppress mounting activity. Applying bright colored paint or chalk to tail heads can be very helpful tool in heat detection.
When to AI?
Male bovine sperm are typically fertile for 24-30 hours after insemination. The cow typically ovulates 24 – 32 hours after the onset of standing heat and the ova (egg ovulated by cow) has a fertile life of eight – 10 hours. To get the needed overlap for conception, the best rule of thumb for AI breeding is to inseminate 12 hours after first observing the cow in standing heat. Furthermore, if/when cows are still standing after the first AI breeding, follow up again with another AI service 12 hours later. If using sexed semen and breeding off of observed standing heat, it is best to wait another four – six hours to AI for best conception rates.
Reference: Chapter 32, Oklahoma Cooperative Extension Service Beef Cattle Manual, Eight Edition
