On most Kenyan dairy farms the cow that does not get back in calf costs more than any piece of equipment in the shed. Every heat that passes unseen pushes the next calving back by about three weeks, and every three weeks of delay means a longer dry spell at the end of the lactation, fewer litres per year and a calf that arrives later than it should. The inseminator can only serve the cows you call him for, and the bull, if you still keep one, can only serve the cows he can reach.
Heat detection is not a vet skill or a laboratory test. It is a habit of watching, writing down and acting on what you see at the right time. This guide covers the signs of heat, how often and when to watch, the timing rule most inseminators in Kenya work to, the records that make it easier, and what to do when a cow keeps coming back. Figures below are general guidance from extension practice; your vet or AI provider can adjust them for your herd.
The 21-Day Cycle in Plain Terms
A healthy, non-pregnant cow or heifer comes on heat roughly every 21 days, with a normal range of about 18 to 24 days. The heat itself is short. Standing heat, the period when she will stand still to be mounted, is often given as around 12 to 18 hours, and in many high-yielding cows and in hot weather it is shorter and quieter than that. Ovulation follows some hours after standing heat ends, and the egg has a limited life, so the window for a successful service is measured in hours, not days.
That is why missed heats are so common. A cow can start and finish her standing heat between the evening milking and the morning milking, and nobody sees a thing. The answer is not to stare at the cows all day. It is to watch at the right times, know exactly which cows are due, and recognise the quieter signs.
The Signs, From Certain to Suggestive
Only one sign is close to certain: the cow stands still while another cow mounts her. A cow that walks away when mounted is usually not yet, or no longer, in standing heat. Everything else is supporting evidence that tells you to look harder.
Before and around standing heat, cows commonly become restless, walk more, bellow, sniff and lick other cows, and try to mount them. The vulva may look swollen, moist and redder than usual, and clear, stringy mucus may hang from it or smear the tail and thighs. Hair on the tail head can look rubbed or ruffled, and there may be dirt marks on her flanks from other cows' hooves. Milk yield often dips for a milking or two, and she may eat less.
About two days after heat, many cows show a small amount of blood-tinged mucus. This does not mean she is ready; it means the heat has already passed. Write the date down anyway, because it tells you to watch for the next heat about 19 days later.
| Sign | What it tells you | Action |
|---|---|---|
| Stands still when mounted | Standing heat | Call the inseminator using the timing rule below |
| Mounts other cows, restless, bellowing | Coming on heat or in heat | Watch her closely at the next check |
| Clear, stringy mucus; swollen vulva | Heat likely now or soon | Watch, and check for standing |
| Rubbed tail head, dirty flanks | She has been mounted | Watch; she may have been on heat overnight |
| Sudden drop in milk for one milking | Possible heat, or illness | Check her for heat and for sickness |
| Blood-tinged mucus | Heat was about two days ago | Record it; watch again in about 19 days |
When and How Long to Watch
Extension advice commonly recommends watching the cows at least two or three times a day, for about 20 to 30 minutes each time, when they are not busy feeding or being milked. Early morning before milking, midday and late evening are the usual choices. Many heats begin or show most strongly in the evening and at night, so the late evening check is the one most often skipped and the one that catches the most.
Cows show heat best on a floor where they can move and mount without slipping. On a zero-grazing unit, that means letting them into the exercise yard or walking area during the check, and keeping that floor rough enough to give grip. A slippery concrete floor or a deep mud patch makes cows reluctant to mount, so heats go unseen even when you are watching. Our guide to zero-grazing unit layout covers floors and yards, and the wet season management guide explains why mud in the short rains makes heat detection harder as well as causing lameness.
If you keep one or two cows, the herd effect is weak because there is no other cow to mount her. Watch her behaviour, her vulva and her milk more closely, and pay attention if she bellows towards a neighbour's cattle or the road.
The Morning and Evening Rule for AI Timing
Because the egg is released some hours after standing heat ends and semen needs time in the tract, insemination works best in the later part of standing heat rather than at the very first sign. The rule of thumb used widely by inseminators in Kenya and elsewhere is often called the AM to PM rule:
In practice, the bottleneck on many Kenyan farms is not the rule but getting the inseminator there in time. Save the numbers of at least two AI providers, whether county AI services, a cooperative or a private inseminator, and agree in advance how early you need to call. Tell them the time standing heat was first seen, not just that the cow is on heat. Semen is commonly sourced through providers who buy from the Kenya Animal Genetic Resources Centre (KAGRC) or from private importers; choose the bull with your inseminator or extension officer based on what you want from the daughters, and ask to see the straw details recorded on your card.
Handling the semen straw, thawing it and placing it correctly are the inseminator's job and need trained hands and a liquid nitrogen flask. What the farmer controls is a clean, calm, well restrained cow at the right time. A simple crush or a well built service gate makes the job quicker and safer for everyone, as our article on livestock handling equipment explains.
After Calving: When to Start Watching Again
Most cows show their first heat after calving within a few weeks, but the uterus needs time to recover before a new pregnancy. Many advisers suggest waiting until roughly 45 to 60 days after calving before the first insemination, and watching and recording any heats that come earlier, because a cow that has shown a heat before then is cycling normally. A common herd target is a calving interval of about 12 to 13 months, which leaves only a few weeks after the waiting period to get her in calf. Your vet can tell you the right waiting time for a cow that had a hard calving or a retained afterbirth.
Body condition matters here. A cow that loses a lot of weight in early lactation often shows weak heats or none at all. Good feeding after calving, with enough energy, protein, minerals and clean water, is part of fertility, not separate from it. Weigh or tape the cow each month, as described in our weighing tape guide, to see whether she is losing too much.
Heifers are served by size and weight more than by age. Ask your extension officer or inseminator what weight to aim for with your breed, then use the tape to track progress so you do not serve her too small or leave her waiting months too long.
Records: The Cheapest Fertility Tool
A heat that you recorded three weeks ago is the best warning that the next one is coming. Give each cow a clear ear tag number so nobody confuses two similar cows, and keep a simple record for every animal:
- Calving date and any problems at calving.
- Every heat seen, with date, time and the signs.
- Every service: date, time, bull or semen code, inseminator.
- The date she is next due on heat, 21 days after the last one.
- Pregnancy check date and result, and the expected calving date.
A wall calendar in the store, a notebook or a phone spreadsheet all work, as long as someone looks at it every morning and knows which cows are due. Many farmers add these columns to the same book they use for milk, as in our milk recording guide, because yield changes and heat dates explain each other.
When a Cow Keeps Coming Back
A cow that has been served two or three times without holding is often called a repeat breeder. Before blaming the semen or the inseminator, check the farm side: was the time of first standing heat really known, was she served at the right time, was she in good body condition, was she lame, and was she showing a clear heat or only some signs? Cycles much shorter or longer than the normal range, a dirty or smelly discharge, or no heat at all for many weeks after calving are all reasons to call a vet rather than serving again. Hormone treatments and infection treatments are for a vet to decide and give; do not buy and use them without a diagnosis.
Heat stress is worth thinking about too. Hot afternoons shorten and weaken heats and lower conception rates, which is one more reason for good shade, ventilation and plenty of clean water in the shed. A reliable drinking bowl in every pen keeps water in front of the cows all day.
Heat Detection Checklist
- Every cow tagged and listed with her last heat and next due date.
- Watch two or three times a day, including a late evening check.
- Let cows out onto a non-slip yard during checks.
- Record the time standing heat was first seen.
- Use the morning and evening rule, and call the inseminator early.
- Record service details and the date to watch for a return.
- Pregnancy check by a vet; act quickly on open cows.
Useful Equipment, With Prices
These prices are from the Fuga price list at the time of writing; check the site or call a branch for current prices and stock.
| Item | Stock code | Price |
|---|---|---|
| EAR TAGS - CATTLE _M | 6195 | KSh 20 |
| EAR TAG APPLICATOR | 6193 | KSh 2,000 |
| EAR TAG MARK PEN | 7116 | KSh 650 |
| WEIGHING TAPE | 6432 | KSh 800 |
| DRINKING BOWL- COW_CAST | 6189 | KSh 3,500 |
Watch at the right times, write down what you see, and call the inseminator on the morning and evening rule. For ear tags, an applicator, a weighing tape and drinking bowls for the shed, see our dairy and livestock equipment, visit any Fuga branch in Eldoret, Nairobi or Nakuru, or WhatsApp 0716 961 018. If the calf is already on the way, our guide to calf rearing equipment covers the next step.
Key Takeaways
- A non-pregnant cow comes on heat about every 21 days, with a normal range of roughly 18 to 24 days, and standing heat lasts only hours.
- Standing still to be mounted is the one reliable sign; mucus, mounting others, restlessness and a milk dip tell you to look harder.
- Watch two or three times a day for about 20 to 30 minutes, including a late evening check, on a floor where cows can move without slipping.
- Use the morning and evening rule: seen standing in the morning, inseminate that afternoon; seen in the evening, inseminate early next morning.
- Record calving, every heat, every service and the next due date, and have a vet confirm pregnancy rather than assuming it.
- Cows that repeat, show irregular cycles or no heat after calving need a vet, not another straw of semen.
Frequently Asked Questions
How often does a dairy cow come on heat?
A healthy cow or heifer that is not pregnant comes on heat about every 21 days, with a normal range of roughly 18 to 24 days. Standing heat itself is short, often around 12 to 18 hours and shorter in many high-yielding cows and in hot weather.
What is the surest sign that a cow is on heat?
She stands still while another cow mounts her. Other signs such as clear stringy mucus, a swollen vulva, mounting other cows, restlessness, bellowing and a drop in milk suggest heat is near, but standing to be mounted is the sign most inseminators rely on.
When should I call the inseminator?
Many inseminators use the morning and evening rule. If the cow is first seen in standing heat in the morning, inseminate that afternoon or evening. If she is first seen in the afternoon or evening, inseminate early the next morning. Tell the inseminator the time standing heat was first seen.
How soon after calving can a cow be served again?
Many advisers suggest waiting roughly 45 to 60 days after calving before the first insemination, while recording any earlier heats. Your vet may advise a longer wait after a difficult calving or a retained afterbirth.
What does blood in the mucus after heat mean?
A little blood-tinged mucus about two days after heat is common and means the heat has already passed. Record the date and watch for her next heat about 19 days later.
