Paradontal Disease of Sheep in South Canterbury

New Zealand Journal of Agriculture, Volume 100, Issue 5, 16 May 1960, Page 429

Paradontal Disease of Sheep in South Canterbury

Preliminary Report on Investigations

By

M. C. ARMSTRONG.

Veterinarian, Department of Agriculture, Timaru

Paradontal Disease . . . ★ Will be a difficult problem to solve ★ Has seasonal incidence in South Canterbury ★ Gives no evidence of contagiousness or of having a specific infective agent ★ Is probably of hormonal, metabolic, or nutritional origin, possibly a mineral deficiency.

F\URING recent years veterinarians in the Department of Agriculture have investigated a dental disease of sheep commonly known as pyorrhoea and referred to as paradontosis or enzootic paradontal disease by the veterinary profession. The disease is of comparatively recent incidence and is identified at present in certain districts of South Canterbury and in the Bulls-Santoft district of Manawatu.

T)ARADONTOSIS is characterised by chronic inflammation in the periodontal membrane of one or more teeth, resulting in pain, looseness of teeth, reluctance' to graze, and consequent starvation. In some seasons it may be an important cause of wastage. Investigations have been largely confined to the Bulls-Santoft area of the Manawatu and to the Fairlie, Pleasant Point, and Morven areas of South Canterbury. Veterinarians in charge of the areas concerned have used research facilities available at the Department of Agriculture Wallace-

ville Animal Research Station and the Pathology Department of the Otago University Dental School to define the nature and causes. First Reports of Disease Paradontal disease was first investigated in New Zealand by the author and K. G. Gray near Fairlie in 1952. R. M. Salisbury did the laboratory work at Wallaceville and the disease was recorded in the “New Zealand Veterinary Journal” of March 1953 under the name “Ulcero-membranous Gingivitis in the Sheep”. At that time the disease was considered to resemble Vincent’s angina or trench mouth in humans. First cases were observed in the spring of 1945 when some unthrifty ewes were found diseased in the mouth when yarded for drenching. No more cases were observed until February 1952, when several ewes and some rams became affected. In the 1952 outbreak the disease appeared to arise at the gum tooth margin of molars and/or incisors. There was ulceration of the gum and penetration of the infection down into the alveolus with involvement of all the periodontal tissues and eventual expulsion of the tooth. No specific infective agent could be isolated and the disease could not be transmitted to healthy sheep by contact or by artificial inoculation.

Later Cases

In South Canterbury no more opportunities for investigations were available until autumn of 1958, when the disease was reported in several flocks near Fairlie. During autumn to spring of 1958 this disease was identified on 18 farms in the Fairlie district, one near Pleasant Point, and one near Morven. The incidence varied from 2 to 8 per cent, the highest being about 140 cases in 1,700 sheep. Most cases recover slowly, but affected animals seldom make good sheep. The death rate averages about one in every five affected. Since about 1954 the disease has been observed and investigated in

some flocks in the Bulls area of the Manawatu. The disease in the Manawatu differs in minor respects from that in South Canterbury but its basic nature is the same. For instance, in South Canterbury inflammation of the gum margin is observed frequently and the disease affects rams and ewes of various ages from hoggets onward. It is also seen in the different breeds of sheep peculiar to the farming areas involved. The breeds of sheep affected in South Canterbury have been Romney, Cheviot, Corriedale, Border Leicester, and various crossbreds. In the Manawatu the flocks concerned are all Romney, the affected sheep are four-tooth or older, and all cases were in ewes except for one ram. Soil Types The soil types affected vary greatly from fertile clay downs to low-lying silt loams, to very stony silt loams, and to some sandy soils. There is no apparent relation to soil type or carrying capacity or to the degree of de-

velopment of the property. Molars and incisors or either molars or incisors may be affected, but the animal declines more rapidly when the molars are affected. Pathology Pathological studies reveal localised degeneration and shrinkage of the tissues surrounding the tooth. A

crevice in the gum degenerates to form a deep pocket impacted with food which tends to surround and detach the tooth. In advanced stages inflammation of the jawbone may occur with resultant hard bony swellings which often distort the face. If 1 the tooth drops out, healing occurs, but there is less chance of this occurring with deep-rooted molars. Affected sheep can be recognised by irritation in the mouth causing unusual jaw movements (mouthing), reluctance to masticate, a foul-smelling mouth, missing, loose, or displaced teeth, and perhaps lesions on the gums. Pathological studies indicate the disease is primarily a bone disease which begins in the superficial tissues and then extends to bone at an early stage. It is essentially localised and does not spread to all teeth. It most commonly affects premolars and molars. No Infective Agent Found Bacteriological studies have been unable to find any specific infective agents that can transmit the disease to healthy sheep. Biochemical studies have revealed no significant findings in the nutritional and mineral field. Radiographical findings have supplemented and confirmed the pathological picture. In South Canterbury the disease is definitely extremely seasonal. The 1959 season was remarkable for the almost complete absence of the disease and this is all the more significant because the previous season was the worst ever recorded.