21/09/2026
Bluetongue (BTV) and Bull Fertility
Guidance for farm vets on bull breeding examinations during the BTV risk period
(With thanks to the Sheep Veterinary Society and the associated guidelines on the examination of rams for breeding)
• To achieve good conception rates within a compact breeding period, bull fertility must be optimal before he is turned out or used for AI.
• BTV causes pyrexia and general illness that can suppress fertility, and evidence suggests it may also directly damage s***m production. In bulls previously infected with BTV-8, Müller et al. (2009) found a higher proportion of s***m defects than in uninfected bulls, and post-thaw semen motility remained impaired well beyond the point the bull was still PCR-positive.
• BTV can be shed in semen from infected bulls, adding a further route of spread within a herd (Bowen and Howard, 1984). This is relevant to natural service and to semen collected for AI.
• Spermatogenesis takes around 61 days in the bull (Staub and Johnson, 2018). Any insult during s***m production – such as pyrexia caused by BTV – can therefore suppress fertility for up to two months while he recovers.
• Clinical signs of BTV in cattle can be vague, or infection may be entirely subclinical. A pre-breeding bull examination (‘bull MOT’) is the best way to confirm he is fit for purpose and avoid large losses across the breeding period.
• BTV vaccines have not been formally tested for efficacy in bulls, but this is not unusual and is not expected to be a barrier to protection. Best practice is to vaccinate bulls ahead of the breeding period so full immunity is established before they are required for work.
• Bull breeding examinations and electroejaculation should only be carried out by those trained and competent in the relevant techniques.
The full document has been sent via email to BCVA members and the PDF is available on our website.
https://tinyurl.com/3usu4m6v
