Reproductive Disorders - Donkey
There are very few recent studies on the overall fertility of the asinine population. High pregnancy and foaling rates are often observed in feral donkeys when pasture conditions are optimal.
As in the horse, the most important venereal diseases are equine viral arteritis, EVA (Ramina et al, 1999), contagious equine metritis, CEM (Matsuda and Moore, 2003), and dourine (Turnbull et al, 2002). Infections with Pseudomonas aeruginosa and Klebsiella pneumoniae have also been suspected as possible causes of poor reproductive performances due to venereal transmission.
The asinine strain of equine arteritis virus (EAV) has been shown to behave similarly to the horse strain (Paweska et al, 1996; Ramina et al, 1999). The South African strain of EAV appears to be poorly transmissible to horses (Paweska et al, 1996; Paweska et al, 1997).
CEM organisms isolated from donkeys are different from Taylorella equigenitalis and a new nomenclature for the organism has been proposed, that is, T. asinigenitalis (Jang et al, 2001; Matsuda and Moore, 2003). These ‘atypical’ donkey Taylorella have been shown to cause the same syndrome as CEM in mares and remain in the urethral fossa for as long as 111 days (Katz et al, 2000).
Reproductive disorders in the male
Most conditions affecting horses can be found in donkeys and the diagnostic approach to infertility is similar to that used in stallions (Tibary, 2005). Testicular descent may be delayed until two or three years of age. In donkeys, the authors (Tibary, A., Sghiri, A. & Bakkoury, M.) have seen several cases of cryptorchidism, haemospermia and ejaculation failure.
Oestrone sulphate levels are not a good indicator of the presence of testicular tissue and CANNOT be used to differentiate between cryptorchid males and geldings displaying male behaviour (Arrighi and Bosu, 1989). A standard technique for the diagnosis of cryptorchidism is to determine testosterone levels before and at 2 hours and 24 hours after intravenous administration of human chorionic gonadotrophin (6,000-10,000 IUhCG). Males with testicular tissue should have a circulating testosterone level greater than 100 pg/ml or should register at least a twofold increase in testosterone concentration after hCG challenge.
Castration tends to result in a higher incidence of haemorrhage complications. This is not the case for mules. Ectopic testicles (Ragab and Mostafa, 1993), interstitial cell tumours (Panebianco, 1960) and infectious epididymitis (Schebitz and Hansen, 1959) have been reported. In the authors’ (Tibary, A., Sghiri, A. & Bakkoury, M.) experience, testicular degeneration is common and may be due to nutritional causes and heavy parasitism. Orchitis may be caused by strongyle larva migrans.
Reproductive disorders in the female
Fertility in jennies seems to be higher than in mares. Inbreeding may be an important factor of poor fertility in some isolated herds (Kadir, 1980; Darre et al, 1998). Reported anomalies of reproduction in jennies include persistent corpus luteum, ovarian teratomas, granulosa cell tumours (Norris et al, 1968), uterine infection and uterine fibrosis. Pyometra may be a consequence of severe dystocia.
Donkeys are prone to hyperlipaemia and hepatic lipidosis during pregnancy, often complicated by hepato-encephalopathy, hypocalcaemia, azotaemia, hyponatraemia, hypochloraemia and acidosis (Tarrant et al, 1998). Retained placenta and hypocalcaemia may be seen in stressed animals.
Abortion has been cited as a major problem in working equines (Pearson et al, 2003). Infectious causes of abortion in donkeys are similar to those reported in horses, the most commonly reported being EHV-1 (Tewari et al, 1994), Leptospira (Arora and Baxi, 1978), Streptococcus equi zooepidemicus (Giorgi et al, 1984) and Salmonella spp. (Hofer et al, 2004). Non-infectious abortion due to foetal abnormalities has been described in miniature donkeys (Miller, 1989). Twinning is a cause of non-infectious abortion in some breeds.
References
- Tibary, A., Sghiri, A. & Bakkoury, M. (2008) Reproduction In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) The Professional Handbook of the Donkey, 4th edition, Whittet Books, Chapter 17
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