Each year from late winter CVH vets are busy testing bulls as producers increasingly recognise the importance of undertaking bull testing and examination in the lead up to the joining season. Testing at this time gives flexibility should a replacement bull be required.
Why is this so important?
Beef producers should aim for a short and concentrated calving span and a high weaning percentage from all cow groups. Reduced fertility in bulls makes these goals unachievable.
It’s often difficult to identify infertile or lower fertility bulls. Observation in the paddock may not be enough to recognise the multiple causes of reduced bull fertility. Bulls can still show what appears to be normal mating behaviour and fertility problems may not be discovered until pregnancy diagnosis or calving reveal lower than expected percentages. Identification of fertility problems is compounded when more than one bull is used within a group of cows and heifers at the time of joining.
As a benchmark, the Australian Association of Cattle Veterinarians state that fertility is the ability of a bull to achieve, by natural service with 50 normally cycling females, a pregnancy rate of 60% within three weeks and 90% within nine weeks of mating.
What are the most common causes of reduced fertility?
- Disease of, or injury to, the genitalia – for example, infections of the testicles or prepuce (following injury or foreign body penetration), or contact injuries sustained from bull fights.
- Congenital conditions of the genitalia – corkscrew penis, retained testicles, persistent frenulum (causes a downward curving penis).
- Mobility – any injury to the limbs, pelvis or spine, foot infections or arthritis can significantly impede a bull’s capacity to serve.
- Poor libido – this can be a hereditary condition, the result of dominance behaviour of other bulls (joining bulls of different weights and ages is not recommended, bulls need to spend their time serving, not fighting), pain from arthritis or other conditions affecting mobility.
- Abnormalities of sperm cells – causes can include genetics or environmental impacts such as high temperatures (recovery from heat or a high temperature due to a fever can take up to eight weeks, the length of the sperm production cycle), and poor or inappropriate nutrition (both under and overfeeding can impact sperm quality).
- Other diseases – campylobacter (formerly vibriosis), trichomoniasis and papilloma virus (warts).
Left: note the swelling in the upper left scrotum – inguinal hernias are one of the potential causes of poor fertility in bulls.
What does bull examination entail?
There are several components to a comprehensive veterinary bull examination:
- Gathering information about the general health and vaccination status, and the previous performance history of each bull, is our starting point before on-farm clinical examination.
- Clinical examination starts with observation of the bull(s) in the yard for lameness or other poor mobility, any obvious abnormalities of the genitalia and the animal’s general condition.
- In the crush, the genitalia are palpated and checked for signs of injury or disease, the limbs and feet given a closer examination, teeth examined for wear and loss, and eyes checked for signs of cancer, pink eye or other conditions impacting on full sight.
- Testing is two-pronged:
- examination of semen involves collection via manual manipulation or, if required, electro-ejaculation. The fresh semen is immediately examined in the field under the microscope for density and motility of sperm cells. On occasion, samples will be sent for further laboratory examination – for example, to investigate suspected abnormalities in the morphology (shape and structure) of the sperm cells.
- testing of each bull’s serving ability. This is best done by observing a bull’s performance with in-season females.
Pre-joining examination of bulls goes a long way to preventing income loss due to poor conception rates. Talk to us about how we can help ensure your herd has the best opportunity for delivering satisfactory calving percentages.