The Cattle Breeding Cycle: A Practical Calendar from Heat to Weaning

A cow's breeding year has no slack in it. She is pregnant for roughly nine and a half months, needs about 80 days after calving to be ready to breed again, and a 365-day calving interval leaves almost no room for a missed heat.

Miss one cycle and the interval stretches by three weeks. Miss three and she calves a season late, which in most systems means a calf worth noticeably less. The farms with tight calving intervals are not luckier. They watch for heat properly and write down what they see.

This is the calendar, and the checks that hold it together.

The Oestrous Cycle

A non-pregnant cow cycles roughly every 21 days, though 18 to 24 is normal.

Standing heat — when she stands to be mounted — lasts only about 12 to 18 hours, and it is the only reliable sign of the fertile window. This is why heat detection is the hardest part of cattle breeding: the signal is short, and half of it often happens overnight.

What to watch for:

Standing to be mounted. The definitive sign. Everything else is secondary.
Mounting other cows. Often the cow doing the mounting is approaching heat rather than in it.
Clear, stringy mucus from the vulva
Restlessness, bawling, reduced feed intake
A drop in milk yield in dairy cows, sometimes the first thing noticed

Cows show heat most in the cool hours. Checking twice — early morning and late evening — catches far more than checking once at midday, which is when most missed heats are missed.

If you are running a herd with any size to it, record the date every time you observe a cow in heat, even when you do not intend to breed her. Three observed heats give you her cycle length, which lets you predict the next one within a day or two. That prediction is what turns heat detection from luck into a schedule.

Timing the Service

Once heat is confirmed, timing decides whether the service takes.

The egg is released around 24 to 32 hours after standing heat begins, and sperm needs several hours in the tract before it can fertilise. That gives the long-standing rule of thumb:

Cow seen in heat in the morning — serve that afternoon or evening. Cow seen in heat in the evening — serve the following morning.

Serving too early is generally better than too late. Once ovulation has passed, the window is gone and you wait another 21 days.

Natural service or artificial insemination? AI gives access to better genetics than most farms could afford to own, avoids keeping a dangerous bull, and lets you match sires to cows. It demands accurate heat detection and reliable access to a technician. Natural service forgives poor heat detection because the bull does the detecting, but it caps your genetics at whatever bull you own and you are feeding him year-round. Herds with good records usually do better on AI; herds without records usually do better with a bull.

The Calendar

| Stage | Timing | What to do | |---|---|---| | Heat observed | Day 0 | Record the date and the cow | | Service | 12–18 hours after standing heat | Record sire and date | | Return to heat | ~21 days after service | Watch closely — if she returns, she is open | | Pregnancy check | From ~30 days (ultrasound), ~40 days (palpation) | Confirm early; an open cow costs feed | | Nutrition step-up | Last 2–3 months | Two-thirds of foetal growth happens here | | Dry off (dairy) | ~60 days before calving | She needs the rest to calve well and milk again | | Move to calving area | ~2 weeks before due date | Clean, dry, supervised | | Calving | ~283 days after service | Range of about 279–287 days | | Colostrum | Within 6 hours | The single most important hour of a calf's life | | Back in heat | ~30–60 days after calving | Do not serve yet | | Ready to serve again | ~60–80 days after calving | Hitting this keeps a 365-day interval | | Weaning | 6–8 months typically | Depends on system and pasture |

Pregnancy Checking Is Not Optional

The most expensive animal on a cattle farm is a cow everyone assumes is pregnant and is not. She eats for months, produces nothing, and by the time she visibly fails to calve, an entire season is gone.

Check every served cow. Ultrasound works from around 30 days and tells you more; manual palpation from around 40 days is cheaper and widely available. Either beats waiting.

An early open diagnosis costs one visit and gives you a chance to re-serve within the same season. A late one costs a year.

Calving: The Part That Rewards Preparation

Most calving losses happen in a short window and most are preventable.

Before: move her to a clean, dry, sheltered area about two weeks out. Have colostrum on hand — frozen from another cow if possible — because a calf that does not feed within the first hours may not be able to absorb antibodies later at all.

During: most cows calve unassisted, and the common mistake is intervening too early rather than too late. But a first-time heifer straining hard for more than an hour or two without progress needs help. Know in advance who you call.

After: the calf should be up and sucking within an hour or two. Colostrum within six hours matters enormously; a calf's ability to absorb antibodies falls sharply through the first day and is largely gone by 24 hours. Check that the placenta is passed within about 12 hours — retained placenta needs attention and affects her chances of breeding back on time.

Record the calving date, whether it was assisted, and the calf's condition. Cows that need assistance twice tend to need it again, and that is a culling decision you can only make if it was written down.

Weaning and Getting Her Back in Calf

Weaning is usually between six and eight months. The important interaction is that a cow still feeding a calf while underfed will not cycle well — the body prioritises milk over reproduction.

If cows are not returning to heat by 60 days after calving, the answer is almost always nutrition rather than fertility. Body condition at calving predicts how quickly she breeds back better than nearly anything else. A thin cow at calving is a late cow the following year, and the year after that.

What to Actually Write Down

Per cow, per season, four things:

Every heat observed — including ones you do not act on
Service date and sire
Pregnancy check result and date
Calving date, assistance needed, calf outcome

From those four you get calving interval, conception rate, which sires produce easy calvings, and which cows are quietly costing you a season each year. Without them, every one of those questions is a guess.

Paper works if it survives the yard. If it does not, Livestock Manager records breeding events per animal — heat, insemination, pregnancy check, calving, weaning — and calculates due dates so the next check appears before it is late rather than after.

The Discipline, Not the Genetics

Herds with tight calving intervals rarely have better cows than their neighbours. They watch twice a day in the cool hours, serve on the right side of ovulation, pregnancy check everything, and cull the cows that repeatedly fail.

That is the whole method. It is unglamorous and it works.

Related reading: is livestock farming profitable for the economics behind culling decisions, and farm record keeping for keeping the four numbers above without losing them.