Heat Detection in Cows and Buffaloes: Signs, Timing and the AM/PM Rule

Every missed heat costs a farm roughly three weeks of milk and feed with nothing to show for it. On many farms the biggest gap between a calf every 13 months and a calf every 16–18 months is not semen quality or the inseminator — it is noticing heat on time. This guide explains what to look for, how cows and buffaloes differ, and when to call for insemination.

How the heat cycle works

A healthy, non-pregnant cow or buffalo comes into heat roughly every 21 days (the normal range is about 18–24 days). Standing heat — the period when she accepts being mounted — usually lasts 12 to 18 hours in cows and can be shorter or harder to see in buffaloes. Ovulation happens after heat ends, which is why timing matters: semen needs to be waiting in the tract when the egg is released.

Signs of heat in cows

• Standing to be mounted by other animals — the most reliable sign.
• Mounting other animals, restlessness and bellowing.
• Clear, stretchy mucus from the vulva (often seen on the tail or hindquarters).
• Swollen, reddish vulva.
• A sudden drop in milk for one or two milkings.
• Reduced feed intake and more walking than usual.

Why buffaloes are harder: silent heat

Buffaloes are well known for silent heat: they ovulate normally but show few outward signs. They also tend to show heat more at night and in the early morning, and in Pakistan many buffaloes cycle mainly in the cooler months, with fewer heats in the hot summer.

To catch heat in buffaloes:

• Check them at least three times a day, including early morning and late evening.
• Watch for frequent urination, a slightly swollen vulva and clear mucus, especially when the animal is lying down.
• Use a teaser bull if you have access to one — buffaloes respond to the bull much more clearly than to people.
• Keep buffaloes cool in summer (shade, water, wallowing or sprinklers). Heat stress suppresses cycling.

When to inseminate: the AM/PM rule

The traditional guideline still works well for cows:

1. Heat first seen in the morning → inseminate the same evening.
2. Heat first seen in the evening → inseminate the next morning.

In practice this means insemination about 12 hours after you first notice standing heat. For buffaloes, many inseminators prefer the second half of heat, and some farms inseminate twice about 12 hours apart when the timing is uncertain. Ask your local inseminator or veterinarian which practice works best in your area.

After breeding

• Record the breeding date, the bull or semen used and who inseminated.
• Watch for a return to heat about 18–24 days later. No return is a good early sign but not proof of pregnancy.
• Confirm pregnancy with a veterinarian by rectal examination or ultrasound, usually from about 30–60 days after breeding.

Common reasons heats are missed

• Checking only at milking time.
• No written records, so nobody knows when the next heat is due.
• Poor body condition after calving — thin animals often stop cycling.
• Heat stress in summer, especially in buffaloes.
• Lameness or a slippery floor, which stops animals mounting.

If a cow or buffalo has not shown heat by about 60–90 days after calving, or keeps returning to heat after breeding, ask a veterinarian to examine her. Problems such as retained placenta, uterine infection or cystic ovaries are treatable when caught early.