8th June 2021

Vet View: Bulling spring calving cows

Vet View: Bulling spring calving cows

By Mark Pearson, Director at Moray Coast Vet Group, Forres

Mark has 20 years’ experience working as farm animal vet.Trained to fertility test bulls to BCVA standard, his clients include commercial suckler herds and pedigree beef breeders and also works with Scottish Government Bull stud in inverness.

Summer has finally arrived and is the time of year when your bulls should be out working for you. There are plenty of things that will reduce the number of calves you produce, so getting a good pregnancy rate is a vital first step.

How many bulls should you keep?

There's a simple formula to work out the number of bulls you need.


X is the perfect number of bulls.

N is the number of bulls you currently have!

The truth behind that joke is that bulls always have problems at the worst time, just as you need them to be working, so in a perfect world you would always keep at least one spare.

A fertile bull is expected to achieve 95% pregnancy in 12 weeks with a group of 45 cows. These numbers are hard to achieve in the real world. So realistically, for every 100 cows, you need three bulls. This means the bulls are working with a female group size that is well within their serving capacity (33 and a bit cows each) but allows for spare bull capacity if one breaks down.

The insurance claims I am involved with for bulls split roughly like this:

45% sub-fertile

40% Accidental injury

10% sudden death

5% other

So just under half the issues could be managed, predicted or controlled in relation to fertility The other half is just bad luck. You can't control luck, so focus on what you CAN do.

Going back to basics, a bulls job is simple.

1) Detect and walk to a female that is in oestrus (bulling).

2) Serve her.

3) Achieve pregnancy.

Steps 1 and 2 require a healthy bull with good legs and feet.

Step 3 requires good semen quality.

Healthy bulls

Know your health status and buy bulls appropriate to it (BVD, Johnes, IBR, Lepto). Vaccinate, worm and fluke them according to your farm’s requirements and remember to include bulls in your veterinary health plan. It is easy for the big, expensive males to be overlooked when you are giving your females their routine treatments.  High body temperature reduces sperm quality. Always assume an unwell bull is not fit to work, until proved otherwise. Any interruption to sperm production can take up to 8 weeks to recover from. Unwell or lame bulls should be swapped out of the bulling group they are with and fertility tested before they return to work.

Feet and legs

All bulls should have their feet trimmed once a year. Even if they are not over-grown, it is a good chance to find problems before they develop into lameness.  Some foot problems are a result of management, for example laminitis and hoof weakness from over-feeding cereals, whereas some are genetic such as corkscrew claw. These can be passed on to offspring, so they are very bad news for those of you keeping or selling breeding heifers. Some are unfortunate such as infection like foul, or injuries.  Regardless of the cause, foot problems in bulls are always a BAD THING. Assume a lame bull is not fit to work. Treat him, rest him, and then fertility test him before he returns to work.


It is extremely rare that a bull which has suffered an injury to a hind limb joint, or to his penis, will return to work. Often, they will appear to recover if given enough time and rest, only to break down when they return to service. If your bull suffers an injury, let your vet know immediately but expect a gloomy prognosis and be prepared to make alternative arrangements.

Feeding and condition

Bulls bought through sales are always over-conditioned.  A good condition for work is 3.5/5 and if a bull is too fat he's unlikely to be fit enough to pursue the cows. Also, fat in the neck of the scrotum reduces sperm quality.  Being too thin (<2.5) reduces sperm quality and losing weight before the bulling period has a serious negative effect on fertility.  Ideally a new bull should be bought in good time, allowed to reduce his weight as he gets established on his new forage-based ration and then held at that weight (BCS 3.5) in the run up to bulling.  Bulls will lose weight when they are working. Feed them a moderate amount of concentrated feed to limit this weight loss and get them back to 3.5 after bulling is finished.

Fertility test (Pre-breeding exam)

Checking a bull's fertility with an electro-ejaculator is quick, reliable, and well-proven. It tells you if he is fertile on the day of testing. I would like everyone to check their bulls at least annually. All too often we only get involved with a problem bull after the damage has been done.  Statistically 1 in 5 bulls are sub-fertile so don't wait to find out at PDing or calving!  Test bulls pre or post-purchase and ideally before each breeding period.  Even after that though, you'll still need to observe the cows closely during bulling to spot returns to service.  Smartphone diaries are great for noting down cows and checking 3 weeks later.


  • Keep your bulls fit, not fat.
  • Vaccinate, and treat for worms and fluke according to your farm's requirements.
  • Look after their feet.
  • Check their fertility.
  • Any interruption to sperm production takes 8 weeks to recover.
  • Treat bulls that have been lame, or unwell with caution for this long.
  • Seriously consider insurance; or hope you're lucky!


View our infographic here -https://www.qmscotland.co.uk/sites/default/files/summer_bulling_a4_0.pdf

Sign up for the latest news and views