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This article was published in 1969-70
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Ovine Posthitis - Present Understanding and Control Methods
By W. H. SOUTHCOTT, B.V.Sc. C.S.I.R.O., Pastoral Research Laboratory, Armidale, N.S.W. 2350
The etiology and epidemiology of ovine posthitis have been reported in detail in recent years and a control programme incorporating new information concerning the contagious nature of the external lesion has been proposed (Southcott, 1965: Keogh, 1968).
The main objectives of this paper are to draw attention to aspects of the disease needing further elucidation and to discuss control methods.
1. FACTORS ASSOCIATED WITH PATHOGENESIS OF THE DISEASE
The interaction of diet (high protein), infection (urea splitting diphtheroid) and hormone (testosterone) determine the development and progression of the disease. Experiments and observations of natural cases have established that the disease does not occur if either a predisposing diet or the diphtheroid are missing. Testosterone plays a lesser part in the disease; its most important role is to limit the incidence of internal ulceration (sheathrot).
Diet: The effect of diet is manifest through the urine and the main urinary constituent associated with the disease is urea. However, as perfusion of urea solution alone through a prepuce in the presence of the diphtheroid failed to establish a lesion, other excretory products may have an effect. The occurrence of posthitis is independent of systemic factors of dietary origin (Brook, Southcott and Stacy, 1966). Diet is probably less important for the development of internal than external ulceration. Manipulation of the diet is commonly employed in the treatment of established disease, but is usually of limited value for prophylaxis.
Infection: It has been suggested that the diphtheroid of posthitis initiates the early external lesion by releasing ammonia from urea in urine. Histologically the external ulcer resembles in some aspects the lesion that can be produced by perfusing ammonia solutions through the prepuce, but completely convincing evidence as to the mode of initiation of ulceration is still required. The bacteriology and histopathology of the internal lesion and the relationship of the external to the internal lesion is now under study at Armidale (McMillan, personal communication). The diphtheroid of posthitis is unnamed though attempts to classify it have been made (Skerman, personal communication).
Hormone: Field observations of a lower incidence of posthitis in rams than in wethers led to the use of testosterone propionate by Watson and Murnane (1958) and its subsequent evaluation in a control programme (Osborne and Widdows, 1961: Southcott, 1962).
No conclusive evidence is available as to how testosterone controls posthitis; changes in the size and shape of the external genitalia, increased retention of nitrogen and changes in the tissues surrounding the prepuce have all been suggested as possible mechanisms. Testosterone and its intermediates have been shown to possess antimicrobial activity (Yotis and Waner, 1968) and this is another aspect that requires investigation.
2. FACTORS AFFECTING CONTROL
Control measures should be adopted using the information available on the causative organism, the epidemiological and management factors involved, and the course of the disease.
Epidemiology: Seasonal conditions that lead to high protein intakes favour development of the disease. Affected wethers are a source of contagion for others in the flock and it has been presumed that transmission occurs by way of contaminated pasture and camping areas. Both bush flies and blowflies can carry the diphtheroid. The potential reservoir of infection in cattle, vulvitis (scabby-ulcer) in the ewe, and venereal transmission are other important features. There is no information on the survival time of the diphtheroid under field conditions, but laboratory studies indicate that the bacterium can survive many weeks in cool protected situations off the sheep: hot, dry conditions and sunlight are inimical to its survival.
Management: Scabs and wool surrounding the preputial opening become highly contaminated with the diphtheroid and shearing and ringing remove this source of infection. Shearing itself reduces the incidence of external ulceration although the reason for this is not known. At Armidale shearing and dipping were not important in transmission of the disease.
Course of the Disease: The external lesion which always precedes internal ulceration may regress or can persist for weeks or months without much change. Factors involved in further development are under study, and recent experiments suggest that retention of urine, associated in natural cases with scabbing of the external lesion, preputial erosion and stenosis assists in the progression to internal ulceration.
3. CONTROL PROGRAMMES
A general programme of control embracing a range of prophylactic and treatment procedures has been outlined (Southcott, 1965). However, there is need to clarify the roles of antiseptic preputial treatment and hygiene and the use of testosterone propionate implantation.
Whether or not a grazier elects any form of treatment will depend on his economic assessment of the problem. Some graziers will refrain from any action except to treat severe cases, while others will aim to achieve control through prevention, and it is the latter who may require some guidance.
An essential difference between a control programme based on antiseptic treatment and hygiene on the one hand, and testosterone implantation on the other is that the former is controlling the disease by limiting infection whereas the latter acts mainly to reduce the severity of the disease. There is no reason why one has to be used to the exclusion of the other.
Prophylactic treatment with antiseptics is aimed at preventing the external lesion, thereby forestalling development of the severe and economically important internal lesion. Effective prophylaxis by antiseptic treatment and hygiene has been demonstrated in experimental and commercial wether flocks at Chiswick. but further information as to the efficiency of this approach is required under a range of pastoral conditions. The basic programme consists of the application of antiseptic to the prepuce (5 ml of 0.8% Hibitane) after shearing, and after crutching-ringing in March and August. The wethers are not always rung before the third treatment. Affected wethers are isolated and given additional treatment. One cent per head per year covers the cost of antiseptic and with a tilting panel in the race and a suitable method of application, the labour cost is not high. Treatment can therefore be quick, easy and economical.
Implantation with testosterone propionate costs about 20c per head for the drug but the labour involved is less than for antiseptic treatment. Effective control may be achieved by using the hormone alone, but usually antiseptic treatment is recommended as well for animals observed to be affected at the time of implantation.
Testosterone treated wethers produce more wool (¼ to ½lb. greasy wool per head per year at Chiswick); this offsets some of the cost but does not produce a strong argument for overall treatment with the hormone when the incidence of posthitis in the flock is low.
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Keogh, J. (1968). N.S.W. Department of Agriculture, Animal Disease Bulletin No. 81
Southcott, W. H. (1962). Aust. vet. J., 38, 33
Southcott, W. H. (1965). Canterbury Chamber of Commerce Agricultural Bulletin No. 428
Osborne, W. B., and Widdows, F. A. (1961). Wool Tech. Sheep Breed, 8, 99
Watson, R. H., and Murnane, D. (1958). Aust. vet. J., 34, 125
Yotis, w, and Waner, J. (1968). Antonie van Leeuwenhoek, 34, 275