The cost of a missed heat in a dairy cow in Ireland is €250/heat. This means a small increase in heat detection rates can get you a big return.

Many farmers depend on heat detection systems that require a lot of guesswork, however there’s no need to do that when you could just introduce an expert in his field – a bull.

Bulls – specifically vasectomised bulls for the purposes of this article – are the best heat detectors out there. They even catch silent heats that you would miss with systems without them.

Here we will talk about the merits of keeping a vasectomised bull on your operation.

Vasectomised bull and heifer wearing a moocall heat collar and moocall RFID tag

How it works

There is a myriad of heat detection methods including tail paint; scratch cards; Kamar heat detectors; pedometers

However, none can compare to a teaser bull, a bull that has been vasectomised.

When the bull is vasectomised the vet cuts and seals the ‘vas deferens’, the tube that transports semen from the testicles to the penis.

Vasectomies render the bull infertile as he cannot get females pregnant – he will still produce semen but he will be firing blanks.

However unlike castration, there is no change in the temperament, libido or size of the bull. The testicles are still intact and producing testosterone.

diagram of a bull's vas deferens being cut during a vasectomy

12 month use – Return of Investment

People tend to only keep a teaser bull for a year. Their temperament can change after that. This is why many farmers prefer to rear and vasectomise one of their own bull calves, and sell them on afterwards. Apart from feeding, and the relatively minuscule amount you pay for the vasectomy procedure, it’s pure profit.

A major advantage of vasectomised bulls is the expectation of a cash windfall at the end of the year from sending the bull to the factory.

If you’re buying in a) a stock bull and vasectomising him or b) a pre-vasectomised bull it’s not an expense, as you will see most of that again at the end of the year.

vasectomised hereford teaser bull wearing Moocall HEAT sensor

Age matters depending on your device

You will want to go for a younger one here too. Despite the fact they’re younger and more inexperienced, they can still sense heats coming on just as well. Because they are inexperienced they are less likely to be carrying a STD.

However, you do not want to use a bull that it too young – he needs to be a) sexually active and b) 60% of his mature size or a similar size to the cows he will be mounting.

Using a yearling bull for heat detection is particularly advantageous while using a chin ball, as their rather clumsy mounting leaves more paint leaving a more visible mark on the cows who are in heat.

However, you might be wary at the thought of spending copious amounts of time refilling the paint. During the breeding season, it is recommended the vasectomised bull must have his chin ball refilled at least once daily, as the paint will last for only 15-20 mounts.

vasectomised dairy bull wearing a Moocall HEAT for heat detection

This is not an issue with the Moocall HEAT however, as once you have the system set up, the cows tagged and the collar charged and hooked to the cow, you can leave him go for up to 60 days and not even need to monitor him yourself. You will receive alerts any time one of your cows enters heat.

Additionally, if you do opt to keep the teaser bull for another year, you can expect the hit rate to rise as he gets more experienced. This means bad news for the chin ball because it means less paint markings, but good news for the Moocall HEAT which accurately records all the bull’s movement.

Moocall HEAT collar, used with stock and teaser bulls for estrus detection in cattle


Using heat detection centered around a vasectomised bull means you can scale your spend by your needs. You won’t go spending big money on capacity and features you didn’t want or need.

Other systems of electronic heat detection can cost upwards of €8,000, and still be area restricted (they work off a base station).

Meanwhile Moocall HEAT gives you the same (if not better) hit rate, can work in pasture and costs a fraction of the price.

As well as that, you will still be getting top performance, unlike tail paint, scratch cards etc which can require a lot of guesswork.

Thinking of getting a vasectomised bull?

A herd of 100 cows needs at least 2 teaser bulls. A single bull working would be susceptible to exhaustion and injury from overworking.

Moocall HEAT or your Chin Ball should be fitted to the vasectomised bull at least one week before the planned start of breeding, to allow him to get used to it.

Don’t leave it too late – when you vasectomise a bull you need 6-8 weeks to let him recover from the surgery and to empty him out – some semen might still be left upstream.

Learn more about Moocall HEAT here: