The ‘pre-season check-up’ for stags
The ability of sire stags to service and fertilize oestrous hinds is often overlooked in relation to reproductive performance of the herd, except in catastrophic situations of complete or near complete failure of a breeding group. This is generally only noticed for single-sire mating groups, where the primary sire has failed and no ‘chaser’ stags have been used.
With sire stags of high value, or in situations where there is increased risk that stag failure could be catastrophic (e.g. single sire mating over a large number of hinds), it is wise practice to get the vet to give the stags a ‘pre-season check-up’. This involves checking for testicular and penile injuries or abnormalities, and screening for a number of pathogens that can affect fertility.
Injuries and abnormalities
Stags are commonly injured during the rut; this may not only affect their performance at the time of the injury but may also have a major effect in the following rut. Such injuries may include testicular damage and tears to the prepucal (penile) sheath that inhibit libido or mating ability. However, other physical injuries that affect the stags general well-being may also have a debilitating effect on future mating ability.
Cryptorchidism (poorly descended testes) has been observed occasionally in red deer stags. This leads to reduced fertility but can easily be detected by a soundness examination.
Diseases affecting stag performance
Brucella ovis has been diagnosed in red deer and results in poor semen quality or aspermia (total lack of sperm).
Cervid herpesvirus-1 (CvHV-1) has been shown to produce severe pustular and ulcerative lesions of the penis and prepuce, which are likely to result in pain and loss of libido. The first identification of CvHV-1 in deer in NZ was in a stag semen sample which was abnormal, so semen quality may also be affected.
Any observation of stag infertility should also be investigated for a variety of other pathogens such as Campylobacter and Trichomonas.
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