A seasonal reminder about dud bulls. We do see breakdowns with bulls and many of these problems aren’t obvious until pregnancy testing, and by then (pardon the pun) the bull has bolted!

Good bull fertility is essential to achieving a high breeding rate. Bull failure through disease, injury, infertility or lack of numbers can ruin an otherwise successful season. There is some truth to the old saying ‘a bull is half of the herd’. It is essential that your bulls be ready for a busy joining season ahead.

We recommend service testing of all bulls before they go in with cows, especially where there is only one bull in with a mob. If you are leasing bulls it is also worth enquiring if the bull has been service tested prior to his delivery.


Bull health and fertility


1 Make sure bulls can perform

We recommend examining and testing bulls before working the herd. The cost of examining bulls is easily offset by one extra cow being in calf.

Often it’s not the new, inexperienced bull that is infertile, but the older bull who has suffered a penile injury or is developing arthritis.


WVS offers bull testing

This incorporates examination of the many different attributes that make the breeding bull;

  • Examination of feet, legs, joints and gait – swollen joints & poor feet affect mobility & service rates
  • Examination of eyes, teeth and jaw – it should go without saying that the working bull needs to see well and eat!
  • Measurement of scrotal circumference – This is critical because bulls with testicles below a certain size will be less fertile.
  • Palpation of the penis and testicles – Often problems can be detected from the consistency of the testicles.
  • Semen Evaluation – A sample of ejaculate is examined to check quality and quantity of healthy sperm.


2 Make sure bulls perform during joining and that you have enough bulls

The InCalf rule of thumb for seasonal/split calving herds is:

1 bull / 40 cows

Check the bulls for signs of lameness, any swelling in the penis/scrotum or inability to serve.

If possible, rotate bulls to cover a problem bull and to keep them interested

Make sure you have bulls in reserve in case of breakdown


To reduce the risk of fighting in your bull group: organise the group early. Run the bulls together for at least six weeks before introducing them to the herd to give the bulls time to establish their social order. If time is tight, try sourcing all bulls from one farm or a breeder. Ideally the bulls will have been together before arriving on your farm.


Separate bulls into working groups and keep them together. Only introduce new bulls to the group if a bull needs to be replaced. Start the season with enough ‘bull power’ in each group, including replacements, to get through the mating season.

Run bulls of similar age and size. Use bulls between 18 months and 4 years of age.


3 All bulls should be vaccinated!

Several transmissible diseases can cause a drop in reproductive rates. Vibriosis is probably the most widely known. It is asymptomatic in bulls but causes a 30-60% drop in reproductive rate in cows and heifers. This is by conception delay, irregular oestrus, embryonic mortality and even the occasional abortion.

Diagnosis can be made from samples taken from the bull, dam or aborted calf. It is easily spread – one stray animal jumping a fence could cause a herd infection.


Pestivirus and Leptospirosis are both implicated in poor production, both reproductive and in general production terms. They may be present at low levels causing unexpectedly poor returns. The naïve or closed herd is most at risk – one portal of entry may lead to a significant breakdown – we advise vaccination with 7 in 1, Vibrovax and Pestigard. This will also confer immunity to the clostridial diseases. Upon completion of this vaccination protocol there is a self certification provided by the product manufacturer called the ‘Pfizer Star Bull Program’


Bulls not previously vaccinated should receive 2 injections 4 weeks apart, with the second injection being given more than 2 weeks before joining. An annual booster is then needed, this should be given at least 2 weeks before joining.


   If you have any questions about bull management or bull testing please give us a call