BasedonlengWweight calculations (Webb andManoh 1989) the crocodile was estimated to be approximately 25 kg body weight. Thus the dose rate of oxytocin used was about 1 IU/kg. Variable dose rates of oxytocin to induce oviposition in reptiles have been suggested, with or without the concurrent use of calcium, and varying degrees of success have resulted (Huff 1976; Rosskopf andWoerpel1983; GrainandEvans 1984).Dose rates of oxytocin have varied between 1 and 10 IU/kg. Brown and Martin (1990) suggest that this variation may be due to differences in hormonal and receptor states of individuals rather than to a true species difference. It has been suggested that arginine vasotocin is the reptilian endogenous oxytocin analogue which may be up to 10 times more potent than oxytocin in inducing uterine contractions in reptiles (HE McCracken per- sonal communication). Further studies on this hormone are indi- cated.

The cause of dystocia in this crocodile may be multifactorial. There are numerous theories on the cause of egg retention in reptiles. Primary inertia of the uterus is a likely cause. Grain and Evans ( 1984) regard this as the main cause of egg retention in pet snakes. Inertia may occur due to a failure of myometrial contrac- tions as a result of an inability to respond to hormonal stimuli, or due to subnormal hormone levels. Prolonged labour may also result in inertia due to exhaustion. In the case described here this is unlikely since no true abdominal contractions were observed before oxytocin administration.

Calcium is often given to eggbound reptiles in the thought that hypocalcaemia may be involved. Unfortunately blood calcium levels are seldomly determined so it is not often known whether calcium is used only as a part of a ’shotgun’ approach to therapy. In fact low serum calcium levels are considered an unlikely cause of dystocia in reptiles that are fed correctly since ample calcium is supplied through ingested whole animals (Millichamp ef a1 1983; Barten 1985).

Husbandry factors may also contribute to dystocia in reptiles. Suitable nesting sites, temperature, humidity, photoperiod, ade- quate diet and availability of fresh water are all vital for captive reptile breeding @rye 1981). Disturbances or inadequacies in these environmental factors may result in dystocias. Stress is also likely to play a role due to the inability to provide a true natural environment in captivity. It has been suggested that overfeeding and lack of exercise resulting in poor muscular condition may be a contributing factor in reptilian dystocias (Grain and Evans 1984). This is a possible explanation for the dystocia described in this report. The animal involved was a well fed captive crocodile which had not been bred previously. It has been noted that captive saltwater crocodiles can be up to 20% heavier than their wild counterparts and females may reach maturity at around 2.1 m in total length (Webb and Manolis 1989).

Based on the clinical response it appears that oxytocin was effective in inducing oviposition in a dystocic saltwater crocodile using a dose rate of approximately 1 IU/kg. The subsequent successful incubation of a number of the eggs indicated that the hormonal induction was unlikely to be premature.

References Barten SL (1985)JZoo Anim Med 16: 141 Brown CW and Martin RA (1990) CompendContin EducPract Vet 12: 361 Frye L (1981) In Biomedical and Surgical Aspects of Captive Reptile

Husbandry, Veterinary Medical Publishing, Edwardsville, Kansas, p 296 Grain E and Evans E (1984) J Am Vet Med Assoc 185: 679 Huff TA (1976) Int Zoo Yearbook 16: 82 Millichamp NJ, Lawrence K. Jacobsen ER (1983) JAm Vet Med Assoc 183:

Patterson RW and Smith A (1979) Vet Rec 104 551 Reichling SB (1988) Comp Anim Pract 2: 42 Rosskopf WJ and Woerpd R (1983) Mod Vet Pract 6 4 644 Webb G and Manolis C (1989) In Crocodiles of Australia. Reed Books,

(Accepted for publication 29 January 1991)

1213

Frenches Forest, NSW, p 64

CORRESPONDENCE

Efficiency of inspection procedures for the detection of tuberculous lesions in cattle

Australian Quarantine and Inspection Service, Department of Primary Industries and Energy, PO Box 858, Canberra ACT 2601

G MURRAY R BIDDLE P MILLER

Corner et a1 (1990) reported that abattoir post-mortem inspection, using the 1976 inspection procedure (“76”)(Anon 1976), hadlow sensitivity for detecting tuberculous lesions. They inferred from their results that, even though the 1976 procedure was not that sensitive, a return to this more labour-intensive post-mortem inspectionsystem, as used in Australiabefore 1985, was needed, implying that the 1986 procedure (“86”) (Anon 1986) was comparatively inadequate for the monitoring phase of the Brucellosis and Tuberculosis Eradication Campaign (BTEC) programme. Their argument requires some comment.

It should be pointed out that cwrently under the “86” system, “reactor” animals are subjected to a more detailed post-mortem inspection than cattle that are from areas considered to be free of tuberculosis and that are being monitored for breakdown of disease freedom in these areas, so differences between the 2 systems are unlikely to be significant. It is during a monitoring programme, particularly after 1992 under BTEC, that any dif- ferences between the inspection systems could be important.

It is also worth mentioning that “86“ has been accepted by regulatory authorities of countries that import meat from Australia with their own tuberculosis eradication programmes. Thesy include the USA, the EC, Canada and New Zealand.

Noteworthy, also, is the recent report by Tolson and Jervois (1990) to the BTEC committee, in which they recommended that “86” be continued as the abattoir monitoring system after 1992. However, on the basis of the cost-benefit analysis presented in this report, it could be argued that a less intensive abattoir monitoring system, based on palpation only of lymph nodes, would be the most cost-effective abattoir inspection system of monitoring for tuberculosis after 1992.

Comer ef a1 (1990) did not include “86“ in their study and so there was no direct comparison between it and “76”. Their conclusions are based on the distribution of single lesions in infected cattle and the likely consequences this would have on the sensitivity of the 2 inspection procedures to detect these infectedcattle. Theirjustification forpreferring “76” over “86” assumes a worst-case-scenario, namely a failure of “86” to detect a lesion in every case that a lesion would have been detected using “76”. The rigid experimental conditions of the study, and the disease status of the cattle used in the study, would be likely to emphasize any potential differences in sensitivity between the inspection procedures. The true difference in sen- sitivity of the 2 inspection systems under field conditions is most likely to be smaller ( McMahon ef al1987), but such speculation can only be resolved by a trial to directly compare the 2 procedures.

Accepting that a more intensive inspection protocol should be more sensitive in finding cattle with tuberculous lesions, we feel that Comer et a1 (1990) have not properly addressed the issues of costs and the reassignment of risks relative to the marginal benefits of returning to the old system. Working with values quoted by the authors in their paper, “76” was likely to miss 47% of animals with tuberculous lesions (derivation of this value is unclear from the paper); and based on the distribution of single lesions, “76” would miss 0.8% of cases and “86” would miss 8.9% of cases. These values imply that the sensitivity of “86” was 92% relative to “76”. Using these values, it would require 5 infected animals using “76” to be 95% codident of detecting at least one of them, and 6 infected animals using “86”. Is this difference significant?

Australian Veterinary Journal, Vol68, No 6, June 1991 217

Weighed against the putative marginal gain in sensitivity of “76” compared to “86” would be the real large increase in inspection costs. This then becomes an issue of optimal allocation of frniteresources in the broader context of industry productivity, a smaller and more efficient public sector, and service costs to a very important export industry to Australia, particularly in a situation of expected low prevalence of tuberculosis in the monitoring phase after 1992.

In addition, there is the issue of reallocation of risks. A scientific approach to the assessment of risk in veterinary public health, so that resources are directed at dealing with real risks to public health and animal health, will become increasingly important in a persistent climate of constrained public sector funding (Murray 1986; Hathaway et a1 1987). The study by Moo et a1 (1985) has shown that routine incision of mesenteric lymph nodes would be likely to substantially increase the risk of contamination of edible meat with Salmonella strains, an organism of real and growing public health concern world-wide as a cause of food-borne disease (Todd 1990; Cooke 1990).

Therefore, we would argue that the small improvement in detection sensitivity (at best) associated with areturn to the 1976 inspection procedure to find isolated lesions in cattle at infre- quent sites would not be justified either on grounds of veterinary public health or in terms of costs.

References Anon (1976) Manual of Instruction for Meat Inspection and Meat Handling

Procedure, 3rd edn, vol 1: Inspection. Aust Gov Publ Sew, Canberra Anon (1986) Australian Exporl Meat Manual, vol 3: Administrative

Instructions to Meat Inspection Staff, Chapter 13, Aust Gov Publ Sew, Canbemi

Cooke EM (1990) The Lancet ii: 788 Comer LA, Melville L. McCubbin K. Small KJ, McCormack BS et a1 (1990)

Hathaway SC, McKenzie A1 and Royal WA (1987) Vet Rec 120 78 McMahon J, Kahn S, Batey R, Murray JG, Moo D and Sloan C (1987) Au t

Moo D, O’Boyle D. Mathers W and Frost AJ (1980)Aut VetJ56 181 MurrayG(1986)AustVetJ63:211 Todd E (1990) The Lancet ii: 790 Tolson JW and Jervois KYM (1990) A Study to Determine the MOnkOring

Requirements for the BruceIlosir andTuberculosis Campaign in Amtralia after 1992, A Report to the National Brucellosis and Tuberculosis Eradication Campaign Committee and Animal Health Committee

Aust Vet J61: 389

Vet J 64: 18‘3

CSIRO Division of Animal Health, LA CORNER Private Bag No 1, PR WOOD Parkville, Victoria 3052 JS ROTHEL

A defmitive evaluation of efficiency of the Australian meat inspection procedures to detect tuberculous lesions was necessary before questions on the future use of this prooedure in the bovine tuberculosis eradication campaign (BTEC) and questions of cost-benefit could be addressed. We obtained empirical data on the performance of the 1976 procedure by comparing it to a detailed post-mortem procedure (Comer et al1990).

We found the 1976post-morteminspectionprdure detected only 53% of tuberculous cattle. We foundnot only were the actual procedures insensitive, but an additional 0.8% (1976 procedure; Anon 1976) and 8.5% (1986 procedure; Anon 1986) of cattle with lesions were not detected because the tissues containing lesions were not on the list of tissues required to be examined. The importance of abattoir inspection lies in finding infected cattle from herds in which tuberculosis is not suspected. The detection of lesions in reactor cattle is less important as they are already suspect and the fmding of lesions only confirms the diagnosis and gives little additional information on herd status.

Tuberculin reactors were used in our study to ensure a reasonable level of tuberculosis in the cattle examined. We have no reason to believe that the distribution of lesions in reactor cattle is any different to that in infected cattle that have not been tuberculin tested

Post-mortem inspection of cattle carcases at slaughter has been a significant feature of BTEC since its inception in 1970. Its importance will become paramount during the monitoring phase after 1992, when it will be our only monitoring tool. Tolson and Jervois (1990) advocated an increased reliance on monitoring through abattoir surveillance, “monitoring for tuberculosis now can only be reasonably achieved by inspection of meat carcases at slaughter in abattoirs” (p 4). Murrayet a1 (1991) acknowledge this significance and the impact that any decrease in sensitivity of post-mortem inspection will have on disease detection when they state that, “accepting that a more intensive inspection protocol should be more sensitive in finding cattle with tuber- culous lesions..”.

The acceptance of the changed inspection procedures by countries importing our meat is only relevant to the question of meat hygiene, not to disease eradication monitoring.

Tolson and Jervois (1990) diJ not endorse the 1986 procedure but recommended, “that abattoir monitoring of bovine tuber- culosis should continue after 1992” and “the current system (post mortem inspection per se) should continue until 8 years after the last herd breakdown”. Freedom from tuberculosis will be declared only when all animals in contact with the last known case of tuberculosis are removed Any substantial delays in achieving this goal will be very costly. Tolson and Jervois (1990) concluded that any decrease in sensitivity of post-mortem inspec- tion could delay the achievement of tuberculosis freedom by up to 12 years (p 4). In a review of the requirements for monitoring procedures in the period after 1992 Tolson and Jervois (1990) agreed that the overall level of detection of tuberculous carcases was between 53% (Comer et a1 1990) and 60% (Kantor et a1 1987), “for the procedure adopted by the Commonwealth in 1986” (p 26). Why do Murray et al (1991) believe that the differences in

sensitivity of the two procedures will be smaller under field conditions? Their conclusion that differences between the 1976 and 1986 procedures, “can only be resolved by a trial to directly compare the two procedures” directly conflicts with the sig- nificance accorded the work of McMahon et a1 (1987). McMahon’s work was purported to have been just such a trial and it was on the basis of McMahon’s results that the changes in the inspection procedures were implemented Unfortunately it is now impossible to conduct any further trials of this type in Australia because the prevalence of tuberculosis is so low.

We disagree with Murray et a1 (1991) about the justification for our preference for the 1976 procedure. We believe our projections constitute a bestcase scenario. We are disappointed with their conclusion that the application of good rigorous scientific methodol- ogy would bias the results and that they should prefer subjective data from uncontrolled studies where no independent measures of suc- cess were used (Archer 1981; McMahon et al1987).

In conclusion we are willing to accept that the issue of cost- benefit is valid but let us not allow economic rationality to cloud the scientific basis of our judgments.

References Anon (1976) Manual of Instruction for Meat Inspection and Meat Handling

Procedures.Vo1 l:lnspection,3rdedn, AustralianGovemment Publishing Service, Canberra

Anon (1986) Autraiian Export Meat Manual, Vol 3: Administrative Instructions toMeat Inspection Staff, Chapter 13. Australian Government Publishing Service, Canberra

Archer JF (1981) In Advances in Veterinary Public Health, Vol 1, edited by Hein W, Australian College of Veterinary Scientists, Indooroopdly. p36

Comer LA, Melville L, McCubbin K, Small KJ, McCormick BS. Wood PR and Rothel JS (1990) Aust Vet J67 389

218 Autralian Veterinary Journal. Vol68, No 6, June 1991