High Degree of Control of Infertility in Rams

New Zealand Journal of Agriculture, Volume 95, Issue 2, 15 August 1957, Page 117

High Degree of Control of Infertility in Rams

Wallaceville Double Vaccination Procedure Gives

A HIGH degree of protection against the disease causing infertility in rams has been conferred in field trials by a double vaccination procedure that has been worked out at the Department of Agriculture's Wallaceville Animal Research Station. The two vaccines used were Strain 19, used for ~the control of contagious abortion in cattle,, and a new vaccine prepared from killed organisms of the disease causing the infertility, which is closely allied to that causing abortion in cattle. The vaccines are being prepared commercially and are now available for use by veterinary surgeons. This article is adapted from a paper delivered at the Ruakura Farmers' Conference Week in June by M. B. Buddle, Senior Veterinary Research Officer at Wallaceville, who developed the new vaccine and evolved the double vaccination method.

THE importance of infertility in the sheep industry is well appreciated by farmers, veterinarians, and research workers. Infectious diseases contribute greatly to these losses. In New Zealand during the past few years intensive research has been concentrated on Brucella ovis infection in sheep. Infection of sheep with this bacterium, which is closely related to the organism causing brucellosis or contagious abortion in dairy or beef cattle, is widespread in New Zealand, Australia, and almost certainly in other major sheep raising countries.

The disease has most serious and lasting effects on the fertility of rams, a large proportion of affected animals being rendered permanently sterile. Infection is excreted in the semen of infected rams after localisation in the genital organs.

Detection by Palpation

Most farmers are familiar with the manual examination of the purses of rams by veterinary surgeons for the detection of abnormalities of the external genital organs. One of the commonest abnormalities detected by this method of examination is the condition referred to as “epididymitis”, or inflammation of the epididymis. A large percentage of rams infected with Br. ovis do show enlargements detectable by palpation of the epididymis, an organ located within the scrotum attached closely to the testicle. All infected rams do not show abnormalities of the genital organs which can be readily recognised by this form of clinical examination.

This disease constitutes an important cause of ram wastage. Ewes may also become infected with the disease and deliver dead lambs up to full term or weakly lambs which may die within a few days of birth.

Infection of sheep with Br. ovis may be described as a venereal disease, as infected rams have been shown experimentally to transmit infection to clean ewes at tupping. Tupping also provides the greatest opportunities for spread of infection from infected to

clean rams. However, clean rams may acquire infection from diseased rams even in the absence of ewes. The common habit of rams jumping one another is responsible for the dissemination of infective semen and the consequent infection of clean rams through mucous surfaces such as the rectum, prepuce, eye, nostril, or mouth. Experimental transmission trials at Wallaceville have shown that rams and pregnant ewes may become infected after the drenching of suspensions of Br. ovis organisms. In other experiments, where non-infected rams and pregnant ewes were grazed on pastures intentionally contaminated with diseased afterbirths, none of these animals developed infection. However, the possibility is not excluded that individual rams and ewes may become infected by grazing on contaminated pastures. Ram lambs, as young, as 8 weeks of age, have been shown to be susceptible to experimental infection. On the other hand active disease did not develop subsequently in a group of ram lambs which were delivered and reared by a number of actively infected ewes. Active infection is more persistent in rams than in ewes. In one experiment a group of ewes, all of which had diseased membranes at their first lambing, was observed over subsequent years. Only 4 of the original 26 infected ewes had diseased membranes at their second lambing and at their third lambing all ewes had normal membranes. Rams mated to these ewes subsequent to their first lambing failed to develop active infection. Attempts at Treatment Some attention has been directed at the treatment of affected rams. In view of the encouraging results from use of aureomycin, particularly when combined with streptomycin, in human Brucella infections this form of treatment was tested on a small group of experimentally infected rams at Wallaceville. Two other simpler and less expensive forms of treatment were applied to other groups. Aureomycin

plus streptomycin was the only procedure which eliminated infection in all the treated rams. Treatment of individual animals of special value would have greater appeal if more economical and convenient forms of treatment were available which, in addition to eliminating infection, resulted in the animal regaining unimpaired fertility. What methods of control are available in the light of present knowledge of the disease? It is known that a significant proportion of infected rams can be detected by palpation of the scrotum. These rams are of doubtful fertility and serve as reservoirs of infection for clean rams and ewes. Obviously these rams should be culled from the flock. A number of infected rams do not exhibit obvious abnormalities of the genital organs in spite of being capable of transmitting infection in the semen. It is possible for these rams to be identified by. laboratory examinations conducted on semen samples collected by an electrical stimulation method. For very practical reasons it is not possible • to apply this supplementary method of diagnosis on a wide scale. However, by the institution of annual or even more frequent veterinary

examination of the ram flock and culling of the rams with palpable abnormalities of the genitalia, the incidence and spread of the disease have been substantially reduced on many properties. Spread of infection may be further reduced by rigid isolation of the younger clean rams from the older rams. Infection can develop in ram hoggets and virgin 2-tooth rams after contact with older infected rams and every , effort should be made to avoid such contact. Also young rams have been protected from contact with heavy infection during the tupping season by ensuring their • segregation from the older rams or by confining their mating to ewes of their own age. As soon as the infective nature of this disease was established. research was undertaken to develop methods of conferring immunity or resistance on sheep against the disease to supplement other methods of control. Development of Vaccines In experiments at Wallaceville , extending over the past 4 years attention has been directed at the development of vaccination procedures which would confer a high degree of immunity against controlled experimental infection. In a preliminary trial rams and ewes were. inoculated with a variety of vaccines either singly or in various combinations. Vaccinated and nonvaccinated animals in the various groups were later exposed to severe infection by the intravenous inoculation of virulent Br. ovis organisms. The only procedure which consistently conferred significant protection was the simultaneous inoculation of Br. . abortus Strain 19 and a special vaccine prepared from killed Br. ovis organisms. Strain 19 is the vaccine used for the protection of cows against contagious abortion and is a suspension of living but non-virulent organisms. This vaccine was shown to be incapable of causing active disease in rams or ewes. The special Br. ovis vaccine contains chemically treated and killed organisms in an emulsion prepared from mineral oil. This method of preparation of the vaccine greatly improves its efficiency, so consequently, this type of product has been called an “adjuvant vaccine”. Subsequent work has involved the use of larger groups of rams immunised at different ages with a variety of procedures. Again in the later trials Strain 19 with the adjuvant vaccine conferred a high degree of protection on rams against experimental infection. Field Trials In the first field trial, initiated on two properties in 1955, approximately half the 2-tooth rams were immunised with Strain 19 and the adjuvant

vaccine and the remainder left untreated. The results after two examinations at the end of the 1956 tupping season are summarised in Table 1.

TABLE I—RAM VACCINATION FIELD TRIAL, 1956 Infection in rams after first tupping season 2-tooth rams Older rams Vaccinated Non-vaccinated Non-vaccinated per cent. per cent. 0/31 8/32 25 29/121 24

In this trial the vaccination procedure had obviously conferred a high degree of . protection on the 2-tooth rams against heavy infection during their first tupping season. The results from this trial and from more intensive experiments running concurrently at Wallaceville led to the decision in September last year to proceed immediately to a more extensive field trial. Through the collaboration of the Department of Lands and Survey the main part of the trial was located in the Rotorua district. Two different vaccination procedures were to be compared, Strain 19 plus the adjuvant vaccine and the adjuvant vaccine used alone. The latter procedure was included, as results from laboratory controlled experiments had indicated that an adjuvant vaccine used alone did confer some degree of protection. Vaccination was confined to the recently purchased 2-tooth rams and a number of these on every block were left untreated as controls. To ensure that the 2-tooth rams were exposed to severe infection during their first tupping season infected older rams were intentionally retained in the flocks and rams of all age groups were run together during tupping. Results are available from the first clinical examination conducted on the experimental 2-tooth rams after tupping.

Table 2 summarises the results from the blocks where groups of 2-tooth rams were vaccinated with Strain 19 plus adjuvant vaccine as well as with adjuvant vaccine alone. The results confirm the efficiency of the double vaccination procedure and demonstrate clearly that the adjuvant vaccine used alone did not confer adequate protection.

Table 3 summarises the available results from the flocks where the only treatment given was the adjuvant vaccine inoculated alone. Again on these blocks this procedure did not confer satisfactory protection.

TABLE 2—RAM VACCINATION FIELD TRIAL, , 1957 Department of Lands and Survey, Rotorua district Per 2-tooth rams Number Cases cent. Adjuvant vaccine . . . . 159 8 5 Strain 19 plus adjuvant vaccine .. .. .. 174 10.6 Non-vaccinated .. .. 210 21 10

TABLE 3—RAM VACCINATION FIELD TRIAL, 1957 Department of Lands and Survey, Rotorua district Per 2-tooth rams Number Cases cent. Adjuvant vaccine .. .. 282 18 6.4 Non-vaccinated .. . . 341 37 79 9

Vaccination studies . have, been primarily concentrated on rams in view of the importance of the male as regards susceptibility and transmission in ovine brucellosis. The economic importance of Br. ovis infection in ewes is not yet so clearly established. As infection in ewes might originate exclusively from the use of infected rams, lamb losses through infection of the ewe might be most conveniently and economically controlled by confining vaccination to rams. Experiments are still in progress to determine whether vaccination of the ewe will confer protection against infection presented by the use of infected rams for tupping.

Vaccination Procedures Vaccination procedures should be applied as follows for effective control of the disease: 1. Ram lambs after weaning should be kept in strict isolation from older sheep. 2. Young rams may be vaccinated at any age from 4 months until 2 months before their first tupping season. Vaccination as yearlings rather than at an earlier age will result in the development of better protection, and vaccination should therefore be left as late as possible. 3. Older rams should be examined by. a veterinary surgeon and rams with clinical lesions of the disease should be culled from the flock. The remainder of the rams may be vaccinated either immediately or at any time until 2 months before the next tupping season. 4. Vaccination of ewes is not recommended at present, as it is not known if this would be effective. The vaccines are now being prepared in a commercial laboratory and are available for use by veterinary surgeons. Farmers wishing to arrange for the vaccination of ram hoggets and older rams are advised to consult their veterinary surgeon. Though . the vaccination field trials are incomplete at present, the available results indicate that the double vaccination procedure confers a high degree of immunity in rams against experimental and natural infection and will provide a formidable weapon for more effective control of the disease in the near future.