How to Detect Heat in Dairy Cows — Signs Every Farmer Should Know

Heat detection is the single most impactful skill a dairy farmer can improve. Every missed heat cycle costs KES 3,000 to 5,000 in lost milk production, delayed calving, and repeat insemination costs. Over a year, across a herd of 10 cows, poor heat detection can cost your farm KES 60,000 or more.

The challenge is that cows do not announce it on your schedule. Heat lasts only 12 to 18 hours. If it happens overnight or while you are away, you miss it entirely — and wait another 21 days.

Here is how to catch every cycle.

Understanding the cycle

Dairy cows cycle every 18 to 24 days, with 21 days being the average. The cycle has four phases, but only one matters for breeding:

Standing heat (estrus): This is the 12-to-18-hour window when the cow will stand still while another cow or bull mounts her. This is when you should inseminate. Everything else is too early or too late.

The AM-PM rule is your guide: if you see a cow in standing heat in the morning, inseminate in the afternoon. If you see it in the evening, inseminate the next morning. This timing puts the sperm in the right place when the egg is released.

Primary signs of heat

These signs confirm that a cow is in or near standing heat:

Standing to be mounted. The single most reliable sign. If another cow mounts her and she stands still, she is in heat. If she walks away, she is not — she might be mounting others, but she is not the one in heat.

Mounting other cows. A cow in heat is more active and will mount herd-mates. She might mount 10 to 15 times in a day. But remember: the cow doing the mounting is not always the one in heat — watch who stands still.

Clear mucus discharge. A long, stringy, clear discharge from the vulva. This is cervical mucus, and its presence means the cervix is open and ready for breeding. You might see it directly or notice it on the tail or hind legs.

Secondary signs of heat

These suggest heat is approaching or in progress, but are not definitive alone:

• Restlessness — walking more, not settling down, vocalising
• Reduced milk yield — a sudden unexplained drop of 1-2 litres
• Chin resting — placing her chin on another cow's back (pre-mounting behaviour)
• Swollen, reddened vulva — visible oedema and colour change
• Roughed-up tail head — hair on the tail head is disturbed from being mounted
• Reduced appetite — less interest in feed, especially concentrates
• Sniffing other cows — particularly the vulva area of herd-mates

The timing problem

Research shows that 70% of mounting activity happens between 7pm and 7am. If you only check your cows at morning and evening milking, you are observing during the least active period.

Best observation times:

• Early morning before milking (5:30–6:00am)
• Mid-morning (10:00–11:00am)
• Late afternoon (4:00–5:00pm)
• Evening after feeding (7:00–8:00pm)

Three dedicated 15-minute observation periods per day — where you are watching the cows, not working near them — will dramatically improve your detection rate.

How records make detection predictable

If your cow last came into heat on May 1, she is expected back on May 22 (21 days later). If she was inseminated on May 1, you should watch especially carefully on May 22 — if she shows heat again, the insemination did not work.

Without records, you are relying on memory. With records, the app tells you: "Nyambura — expected heat: May 22. Watch closely May 20–24."

This changes heat detection from a game of chance to a scheduled task.

Cows that show weak signs

Some cows — especially high-producing ones — show very subtle heat signs. They may not mount, may not discharge visibly, and may only stand to be mounted for a few hours overnight.

For these cows, records are essential. If you know the expected date, you can dedicate extra observation time. You can also look for the secondary signs that, combined with the right timing, confirm heat.

After detection: what to record

When you detect heat, record immediately:

• Date and time of first signs
• Which signs you observed (standing, mucus, mounting)
• AI scheduled for (following the AM-PM rule)
• Semen details (bull name, straw number, technician)

After insemination, the app calculates:

• Expected return to heat: 21 days later
• Pregnancy check due: 30–45 days post-AI
• Expected calving date: 283 days post-AI (roughly 9 months and 10 days)

Common mistakes in heat detection

Checking only at milking time. Milking takes all your attention — you are not observing behaviour. Set separate observation times.

Confusing the mounter with the mounted. The cow doing the mounting is sexually active, but the one standing still is in heat. Watch who stands.

Waiting too long after detection. If you see heat at 6am and wait until 4pm for the AI technician, you are still within the window. If you see heat at 6am and wait until the next morning, you are too late.

Not recording. If you do not write down the date, you cannot predict the next cycle. Every unrecorded heat is a lost data point.

What one saved heat cycle is worth

One successful heat detection and timely insemination means:

• Your cow calves on schedule
• She peaks at the right time
• She produces a full lactation of milk
• You avoid 21+ extra open days of declining production
• You save KES 3,000–5,000 minimum

Over her lifetime, a cow that is bred on every first detected heat will produce significantly more milk than one where cycles are routinely missed.

The tool is observation. The multiplier is records.

Track every heat cycle at shira.farm.