Bull Soundness

Franklin Vets 0040Are your bulls doing the job?

With more herds doing aged pregnancy testing, we now have a better handle on how herds are performing during AI and during the bull mating period, and the results during the bull period are not pretty!

A large number of herds  have poor repro performance after week six. For many herds this is the time when AB finishes and the bulls are put in with the herd. This can be due to both cow and bull factors, but there is no doubt that for many of you bull performance will be holding you back.

Inductions have now been banned, which will mean shorter mating lengths on some farms, and pressure to get more cows in calf earlier on all farms.
So, what are the key points?
  • Bull numbers- do you have enough bulls for the likely number of empty cows at the end of AB? Don’t just assume that the numbers you used last year are fine, check the chart below and see if you are on the right track. Changing AB length and changes in your three week submission rate can have a significant impact on the number of cows that are empty at the end of AB. If in doubt, be conservative and use more bulls!
  • Bull fertility- careful bull selection can reduce the risk of selecting sub fertile bulls (DairyNZ InCalf bull selection tool). However, why not be safe and test your bulls to make sure? It is easy to do and costs way less than the cost of one empty cow!
  • Bull management- if bulls are not correctly managed, just like cows that are poorly managed after calving, fertility can crash (see the link to the Dairy NZ In Calf bull management tool).
  • Bulls and BVD- Most people realise BVD can wreak havoc during mating time, and we are seeing more and more herds affected every year. As you can imagine, bulls are pretty effective at spreading BVD through a herd of cows, for obvious reasons. Ensure all bulls have been blood tested for BVD before they join the cows. Ask to see a certificate, don’t believe word of mouth- there is too much at risk. If in doubt, re-test them. Bulls should also receive two shots of BVD vaccine (four weeks apart) before they join the herd or heifers.
Fertility Testing Bulls
It’s easier than you think. We simply need a race that the bulls can fit down and somewhere to plug in the microscope. An electro-ejaculator is inserted into the bull’s rectum, which stimulates the prostate and semen is collected and at the same time the genitalia is examined.
The exam covers:
  • Palpation and measurement of testicles
  • Palpation of internal sex glands
  • Collection of semen and examination of the penis
  • Examination of semen on farm for motility
  • Examination of semen in the lab for morphology- checking sperm cells are normally formed and a live dead count
Every year we test suspect bulls on groups of poorly performing heifers or cows after the end of mating. This is like shutting the door after the horse has bolted. Be proactive, check all your bulls when they arrive, select the fertile bulls, and you may even be able to return the sub-fertile bulls.

Don’t carry passengers in your bull team- get them checked!

Bull numbers table:
The table below shows the number of bulls required based on herd/mob size and expected number pregnant at the end of AB. If you are unsure of likely number pregnant at the end of AB, give us a call and we can discuss based on AB length, submission rate, calving spread and cow condition.

The numbers stated are for bulls in with the herd on a daily basis. Dairy NZ suggests you should have the same number resting, with bulls doing two days on, two days off, to maintain body weight, feet and libido.
No. cows in Likely % of herd pregnant at start of bull mating
milking herd very low low moderate high
  <40% 40-50% 50-70% >70%
100 2 to 4 2 to 3 2 2
200 5 to 6 4 to 5 2 to 3 2
300 7 to 8 6 4 to 5 3
400 9 to 11 7 to 8 5 to 6 3 to 4
500 12 to 13 9 to 10 7 4 to 5

Reference : DairyNZ InCalf bull selection tool

Bull age

15 months to 4 years is ideal

Bull to cow ratio

1 bull to 25-30 cows.  You will need double the number to enable bull rotation.

Bull management

Observe bulls on a daily basis and:
  • Remove lame bulls immediately
  • Remove bulls that are not mounting and penetrating cows
  • Separate fighting bulls
  • Do not use overly-aggressive bulls
  • Replace bulls that are losing excessive condition
Ideally bulls should be left in the paddock when cows are bought in for milking. If this is not possible, at least limit the time bulls spend on the concrete.

Evaluate & monitor 

Evaluate and monitor serving ability while bulls are with the herd.  Every bull should be able to successfully mount and penetrate the cow

Disease test & vaccinate

  • Test for BVD and EBL and vaccinate for BVD.  Any booster vaccinations should be completed at least two weeks prior to joining the cows
  • Testing for venereal diseases like Trichomonas and Campylobacter are not routinely included in the soundness evaluation and are uncommon in virgin bulls

Bull soundness & fertility

We offer a bull fertility soundness assessment at Franklin Vets.
Testing for soundness and fertility includes the following:
Evaluation of overall appearance
  • Avoid overly-aggressive bulls
  • Should be no less than 2/3 the size of mature cows and no more than 1/3 bigger
  • Good legs and claws for walking
  • No deformities of the head and mouth
  • In good condition but not over-fat
Examination/palpation of the reproductive organs
  • Scrotum circumference is a good indicator of puberty and semen capacity
  • Testis should be elastic and an even size without any lumps
  • The penis should be free-moving in the sheath with no visible defects
  • The internal sex glands should be of normal consistence and size
Semen collection and evaluation
5-20% of bulls have semen quality issues.  If this is one of the dominant bulls it can severely impact on your herd's empty rate.
Semen is collected with an electro-ejaculator and evaluated for motility and morphology.

It is important to plan ahead and get enough sound breeding bulls on farm well ahead of mating.  Talk to your Franklin Vets team today for advice on bull management or to schedule a soundness and fertility exam.