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Heat Detection for Sick Cows

A sick cow often shows weak or missed heat signs, which can cause confusion about when to breed her. This guide covers how to watch, record and decide with your vet.

Why illness changes heat signs

Heat is the period when a cow is receptive to breeding, and the estrous cycle averages about 21 days. When a cow is sick, in pain or underfed, her hormones and her behavior change, and her signs of heat can be faint or absent.

A cow with a fever, lameness, mastitis, a uterine infection or a metabolic problem may not stand to be mounted, may not move around much and may not show the usual restlessness. That does not mean she is not cycling. It means you may not see it.

Sick cows also eat and move less, so even a normal heat may look different. Think of a missed heat as a question to ask, not a fact to accept.

Know what normal heat looks like

Learn the signs of heat in healthy cows first. Standing to be mounted is the clearest sign, along with mounting others, restlessness, clear mucus, a swollen vulva, sniffing and chin resting, and often a small drop in milk or feed intake.

Sick cows may only show some of these signs, in a weaker form. Look for small changes in behavior and compare them with her own pattern rather than with the herd. Watching at set times, such as early morning and late evening, and for a few minutes at a time, catches more activity than a quick glance during chores. Quiet time after milking is often best, when cows have settled and are not distracted by feed.

• Standing to be mounted
• Mounting other cows
• Restlessness and walking more
• Clear stringy mucus
• Swollen, red vulva
• Slight change in feed and milk

Watching cows that are sick or recovering

Give sick cows priority for treatment, not breeding. Wait for your vet to say she has recovered enough to be bred. Rebreeding too early can lower the chance of a pregnancy and can add stress to a weak cow.

Write down the date of illness, the treatment as your vet directs, the date she recovered and each heat sign you observe. Notes made at the time help your vet judge when a cow is ready.

If a cow does show heat soon after recovery, write it down but wait for your vet's go-ahead before breeding. A cow that seems fine may still be rebuilding body reserves and uterine health.

Using records and tools

Activity monitors, heat-detection aids and pedometers can help, but they are tools, not answers. A drop in activity because of lameness can look like a missed heat, and a sick cow may give false signals.

Combine tools with careful visual checks at set times of day. Keep breeding records by cow and review them regularly with your vet or reproductive adviser. Be careful with any tool that depends on activity. A cow that is sore or sick moves less, so the reading may be misleading in exactly the animals you most want to watch.

When to breed and when to wait

Do not breed a cow just because the calendar says she is due. Ask your vet to check any cow that is sick, thin, lame or fresh and has not shown heat, since a physical exam can find causes that watching cannot.

A cow that is treated with any product must have milk and meat withdrawal times followed exactly. Any treatment or reproductive program is a vet decision. If a cow is much thinner than she should be after an illness, ask your nutritionist whether her ration needs to change before she is bred, since a cow in poor condition may struggle to settle.

Common mistakes and what to ask

Common errors include breeding a cow that is still sick, missing heat because she is lame, breeding on guesswork and failing to record what was seen. Another is blaming the semen or the technician before checking the cow.

Ask your vet: Is she healthy enough to breed? Could pain or disease be masking heat? What exam should we do? When should she be rechecked?

Working with your vet and breeding team

Share notes with the person who breeds your cows, whether that is your vet, an AI technician or your own crew. Tell them which cows were sick, what happened and what you have seen since.

Agree on a clear rule for who decides when a recovering cow gets bred, so nobody acts on a hunch. Review the results every few months and adjust the routine if conception on recovered cows is poor.

• Share health history before breeding decisions
• Record each heat sign and date seen
• Set a clear owner for the breed-or-wait call
• Review outcomes with your vet each quarter

More in Herd Health & Disease Management

• Body Condition Scoring and Health Monitoring
• Annual Herd Health Calendar for Dairy Farms
• Common Fresh Cow Diseases and Early Warning Signs
• Mastitis Detection: A Practical Herd Checklist
• Clinical vs. Subclinical Mastitis: What Dairy Farmers Need to Know
• Milk Fever Prevention in High-Yielding Cows