When it comes to bulls, fertility is of upmost importance. Their job is securing the future of your herd, and if he can’t do that to his best ability then it can put a farmer out of pocket.

Sometimes you can help him, sometimes you can’t. Here are a number of things that affect a bull’s fertility.

Body Condition

Your bull should have a Body Condition Score (BCS) of 3 or more before being turned out to the cows.
As bulls can lose hundreds of pounds of weight during the breeding season it is a bad idea to have them in bad condition at the start of breeding season. This will likely compromise herd fertility and reduce the reproduction rate.
Dramatic weight loss leads to lower sperm quality and production.
However you need to watch out for overweight bulls too because they can become lazy.

Bull fertility


Heat stress can have a detrimental effect on sperm motility in Bulls. It also affects fertility in cows.
Excessive cold can affect bull fertility too, especially in cases of frostbite.

Scrotal frostbite can affect fertility. Usually the way to spot this is inflammation and swelling days after freezing.

This inflammation generates heat which affects development of the bull’s sperm and could temporarily – or permanently – sterilise the bull.

Disease and infection

Disease and parasite control in bulls is very important. Even if the disease doesn’t directly relate to fertility, it could affect his body condition. If the bull fails to maintain a good body score it could lead to reduced vigor.

Infections like foot rot can display itself with a fever. Fever is harmful to a bull’s performance, as the sperm that were forming whilst he was suffering from it will be abnormal, and afterwards, he will have an infertile period of about 60 days.

Disease prevention should be treated the same in a bull as with females. New animals should be screened by a vet for possible infectious agents, and only buy bulls from a reputable source with a healthy herd plan.

healthy bull bcs fertile body condition

Here are three rules you should follow to avoid disease in cattle.

  1. Don’t expose cows to bulls from other herds or vice versa.
  2. No leasing or borrowing bulls
  3. No grazing in common lands with other herds, good solid fences to keep neighbours out.

Annually test and vaccinate your cows for sexually transmitted diseases like leptospirosis and campylobacteriosis.

Vibriosis/Campylobacteriosis – This disease is transmitted by the bull to the cow and can cause abortion, poor conception rates, long calving intervals and uterine infection.

To stop the infection from taking hold, you need to vaccinate the bull annually. If you can vaccinate the cows too then all the better.

IBR / Bovine herpesvirus-1 This infection can cause abortion. It may be transmitted by the semen of infected bulls. As infection is much more common than disease, it is difficult to interpret blood tests.

Bovine Trichomoniasis – This is a venereal disease which leads to repeat breeders, low pregnancy rates and abortions beginning in early pregnancy and continuing right up to the time of calving.
There is no treatment for Trichomoniasis, although most cows will self-clear of the disease within 120 days.

Bulls spread the disease between cows and any bull found carrying it must be culled. Because of this you should test your bulls annually.




If a bull is lame he won’t be able to stand up to his task. If he is partly lame his performance will be impaired.


Different bulls – often particular to certain breeds – can have varying temperament when it comes to breeding.
Some bull breeds may appear to be ‘lazy’ in their breeding habits. One oft quoted example of this is Limousin bulls vs Belgian blue bulls. If a limousin bull is in a field with two cows in heat at once, he will bull them one after another without a break.
However in the same situation, the Belgian blue will mount and breed one first, lie down for a rest, and then service the other cow.

Structural problems

Injuries to the penis and sheath may also prevent the bull from serving. They may cause pain and swelling, and occasionally become infected, preventing the bull from extending the penis.

Prolapse of the prepuce in the bull is also a serious condition causing infertility. It is most common in the Bos indicus breeds (Brahman, Gyr, etc) but also in some British breeds.

Bulls with pendulous sheaths must be watched closely for this problem. Any form of deviation of the extended penis may affect the bull’s fertility by preventing a full service.

Premature spiral deviation (‘corkscrew’ penis) is one of the more common penile defects. It is believed to be an inherited problem mainly affecting polled breeds, and its severity increases as the bull gets older.

BULL fertility


Some bulls are prone to conditions like arthritis. Other bulls have genetic defects which leave them infertile or subfertile. While new syndromes and mutations crop up occasionally, most are silently eliminated.

Occasionally if a cow and bull both carry a mutated gene that is lethal to the progeny it can result in an abortion.

This can happen very often with purebred breeders as it is more likely that animals within a breed will share some co-ancestry.

However cross breeding often resolves this as mutated genes are almost always recessive.


This isn’t particularly tied to fertility per se, but it is important if you are running multiple stock bulls.

Large multiple-sired pastures often develop a social hierarchy where the oldest, maturest and most aggressive bull ends up having the most progeny.

This is obviously a very inefficient system and you’re not getting your money’s worth out of the additional bulls.

Dominant bull pasture fertility

More problems can arise if the dominant bull has a poor performance, or is subfertile, studies have shown.

If you have a very dominant but sub-fertile bull, there will be a lower rate of conception in your herd because it isn’t the smaller bulls’ place to breed.

In order to circumvent this bull dominance in a pasture mating system, bulls should be grouped by similar age, weight, and social ranking in the herd before going into pastures.


Moocall HEAT, our new heat detection device has the ability to tell you – and in good time – if your bull is infertile, subfertile, suffering from lameness or a lack of libido.

It sends you an SMS message with the details of your cow’s standing heat as it happens.

Hereford bull wearing moocall heat collar

Learn more about Moocall HEAT here: https://moocall.com/pages/moocall-heat-information

OR call us here: +353-1-969-6038