Natural service is still the cornerstone for commercial and pedigree beef enterprises and while AI in dairy herds is by far the norm, many dairies still use a stock-bull.

Bull fertility is therefore fundamental to herd efficiency, the tightness of any calving period, and ultimately the number of calves born, and kilos of beef sold per year.

The most efficient beef farms are achieving target calving stats of 95% pregnancies in a nine-week period. To meet this target, a stock bull must be fertile and all cows ‘cycling’ at the start of the breeding season.

Conception rates of 65% each three-week cycle allow this to be achieved. A nine-week breeding season will ensure a good tight calving block and ensure all cows have calved and are cycling for the subsequent breeding season.

A nursing beef cow will start to cycle 60 days after calving, but nursing heifers will take 90 days before they start to ovulate. Ideally, calving heifers a month in front of the main herd gives these heifers more time to start cycling before they join the main herd.

Sub-fertile bulls are very common – 20% or one in five bulls are known to be sub-fertile and will not achieve conception rates of 65%. Having a sub-fertile bull in the herd means you will never achieve a 95% target of cows pregnant. Leaving sub-fertile bulls with the breeding herd for longer will only lengthen the calving period, decreasing herd efficiencies.

The Scottish Farmer: One in five bulls are sub-fertile. Testing the quality of a bull's semen is the only way to find outOne in five bulls are sub-fertile. Testing the quality of a bull's semen is the only way to find out

Semen quality varies greatly – the density and motility of the sperm will directly affect conception rates. Sometimes this is congenital, and the bulls are born sub-fertile. But often, sub-fertile bulls develop later in life. These effects maybe temporary or permanent, caused by infection or fever. Taking 12 weeks for sperm to mature, even temporary effects will take months to recover.

With the average age of stock bulls under five years old, this means such animals have less than three breeding seasons before they need to be replaced. Common reasons for replacement or early culling are mobility or lameness issues, injury, disease, and fertility. Looking after stock bulls is essential and cost-effective, to ensure they stay in the herd.

Care of stock bulls starts with biosecurity and immunity.

Ensure bulls are sourced from low disease herds and are fully vaccinated in accordance with the herd health plan – IBR, Lepto, and BVD are common diseases that can affect fertility.

The feeding and nutrition of stock bulls can be overlooked. Young bulls pushed for sale can be over conditioned and overworked. Young bulls should not be given more than 20 cows in their first season, whereas mature bulls shouldn’t be given more than 30-40. Young bulls that are still growing should receive supplementary feeding to maintain their condition.

Winter housing and the environment can also have an impact on bull conditions. Cubicle housing is never ideal and rarely large enough – bulls spend more time standing and this increases the risk of lameness. Bull pens, with a clean, dry bedded lying area, are ideal.

Lameness and mobility are very common causes of poor performance in bulls. Mostly preventable, white line disease, abscesses, soler bruising, and ulceration will prevent a bull from working. Hoof balance and overgrowth should be corrected with routine foot trimming – any lameness issues must be identified early for their best chance of cure and to limit long-term impact.

Visual inspection of a bull and previous breeding history is no guarantee of fertility. It is highly recommended to do a breeding soundness exam and fertility test at least one month before each intended breeding period.

This could be combined with a routine check of feet and hoof trimming to identify and prevent any potential lameness issues.

A breeding soundness exam is a three-stage process: a physical exam including testicles and sex organs; semen evaluation, including density, motility, and abnormalities; and finally, a bull’s libido and ability to serve. A bull needs to pass all three stages to pass his examination.

Semen collection may be done using several techniques but using an artificial vagina (AV) or electro-ejaculation is the most common. The AV technique requires a trained bull or a cow in season. The advantage of this technique is that the bull’s libido can be assessed with a true ejaculation. However, there are health and safety considerations. With a good temperament and halter-trained animals, this can be a straightforward procedure. But there are no guarantees of safe collection.

Electro-ejaculation has become the industry standard. Bulls are safely restrained, and several bulls can be tested at the same time. However, it is very important to observe the bull’s mating behaviour before he has passed a full breeding soundness exam.

Dairy farms may use stock bulls on parts of the milking herd and are a convenient way to serve groups of heifers. These bulls’ fertility is equally as important, whereas sub-fertile bulls can have a huge impact on heifer calving age, pregnancy rate, and calving index.

Check your calving figures this year – are you achieving 65% of calves born in the first three weeks?

For farm efficiency, stock-bull fertility is key. Ensure bulls are well looked after with good housing, nutrition, and preventative foot care. Pre-breeding soundness examinations will identify the most fertile bulls in the herd and ones that are not currently fit for use.