Getting all of your cows in calf as soon as possible is key to a profitable cattle operation.

With each missed heat costing dairy farmers €250 and suckler farmers €147, you can see how missing a few would add up.

However, one big obstacle many farmers face is when their cow, apparently, just doesn’t go into heat.

Are they infertile? Not necessarily. They may have just had a silent heat.

What is a silent heat?

A silent heat, or sub estrus, is defined as the lack of behavioral estrus symptoms although the genital organs undergo normal cyclical changes.

The incidence of silent heat varies from 10% to 40% between different herds.

A cow with a silent heat doesn’t display any of the obvious signs, like licking or sniffing other cows, mounting, standing to be mounted, or acting nervous and excitable.


However, she can still become pregnant, and the bull will know about it, even if they’re vasectomised. But you won’t.

This is why these vasectomised (or teaser) animals are used for heat detection.

They are the same as a stock bull essentially, but because the tubes that deliver semen have been cut, they can’t inseminate a cow.

If you get the procedure done, don’t let the bull in with the cows for a month because his sperm could still be viable.

A chin ball can be fitted to a teaser for adding paint to the cow as she is mounted. This device requires a lot of maintenance as you have to top up the pain every 15-20 mounts.

Additionally it can only tell you so much unless you go back and check how progress is going regularly and take lots of notes.

Young teaser bull with moocall heat collar and chin ball sniffing cows for heat

Enter Moocall HEAT

Moocall HEAT is our new heat detection system whose unique design uses the bull’s natural ability to your advantage.

It comes in two parts, a collar (for the bull) and Moocall RFID tags, one for each cow you’re breeding.

Moocall HEAT for heat detection in cattle

The system can tell you which cow is in heat, when the bull detected it, and how strong it is.

It doesn’t need to be monitored or adjusted, and sends the information straight to your phone which means you don’t have to spend hours every day checking for signs of heat.

Consider it like a chin ball for the modern farmer – with a miniscule margin of error.

Hereford bull wearing moocall heat collar for heat detection

How silent heats happen

Silent heats occur when not enough progesterone is being produced. Progesterone acts along with estrogen to manifest itself in visual signs of heat in a cow or heifer.

In heifers, the estrus associated with first ovulation is usually silent because not enough progesterone is being produced yet.

However during second ovulation, progesterone from regressing corpus luteum act synergistically with estrogen to produce estrus symptoms .

Causes of silent heats

Heat Stress

Environmental temperatures of over 32 degrees can lead to silent heats in cattle. This is more prominent in cattle with more black markings as they absorb more of the sun’s rays.

Heat Stress reduces the duration and intensity of oestrus, which in turn leads to lower mounting activity. Nobel et al. (1997) found that Holstein cows during the summer have 4.5 mounts per oestrus versus 8.6 per oestrus in winter.


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This is less of an issue in temperate climates like those of the UK and Ireland. However if you are based in a hot climate like Australia, this could be a big factor in how many heats you catch.

There are breeding programmes you can use to minimise the effect of heat stress on your herd’s fertility. However, implementing Moocall HEAT catches your silent heats, so it is like a silver bullet to a lot of these problems.


If iodine is limiting (it is generally quite deficient in New Zealand) it can also reduce the behavioral response of a cow in oestrus.

Other stress

Any type of stress can be a cause of silent heats. Some farmers have even claimed that their cows are more prone to silent heats during wet weather.

Cow is predisposed to having them

Every cow is put together a little differently, and some are more wont to silent heats than others.

One telltale symptom of this in a cow that doesn’t show any other signs of heat is mucous coming from her vulva every ~21 days. This typically signals that heat is over.


If you know what to look out for, you can run a bull with her. However this requires a lot of surveillance. Moocall HEAT allows you to use AI, and it gives you live updates on the cow and bull wherever you are.