Re-think a.m./p.m. rule
Old rules die hard. Among them is the a.m./p.m. breeding rule: See a cow in heat? Breed her 12 hours later.
The problem is that if you wait 12 hours after you see a cow in heat, it may be too late.
The a.m./p.m. rule is based on research that is now more than 70 years old. While somewhat correct in concept, it doesn’t take into account that you often don’t know when cows actually come in heat.
And today’s high-producing cows also have estrus periods that are of short duration. Seeing them in standing heat is often difficult, and then knowing when they first came in heat is nearly impossible.
"It’s really hard to see cows in heat," says Paul Fricke, a dairy reproductive specialist with the University of Wisconsin. Even if a cow is in standing heat for eight hours, she likely only has one standing event per hour. Each event last two to three seconds. So that means she has 16 to 20 seconds of standing activity per estrus.
If you’re observing heats even twice per day, seeing cows stand is difficult. And then knowing when estrus first started is impossible, Fricke says.
Ideally, he adds, you want to breed cows eight to 12 hours prior to ovulation. There is more risk to breeding a cow too late, by waiting 12 hours using the a.m./p.m. rule, than breeding once per day, he says.
Because heat detection is so difficult, particularly in large herds, most farmers have gone to heat synchronization programs. Then it’s critical that you time AI based on the protocol of your particular synch program.
Often, however, producers will still breed cows they see in standing heat. "If you do that and you see a cow in heat, breed her. The a.m./p.m. rule is too late," Fricke says.
If you are using activity monitors, follow the manufacturer’s recommendations, Fricke says. Even here, how-ever, cows don’t always go by the manual.
On a large Wisconsin dairy, Fricke and his team found that activity monitors were finding about 70% of cows in heat. About a third of the cows not showing heat were actually ovulating and were not anestrus. "About 10% of all cows were ovulating but not showing signs of heat," he says.
If you’re using activity monitors, Fricke recommends using a synchronization program on those cows that show no activity. The synchronization program will allow you to use timed AI on those cows that are ovulating. And it might jump-start those cows who are not, without the aid GnRH and prostaglandin shots.