D.K. Blackmore

The epidemiological interpretation of serological responses to leptospiral serovars in sheep.

Serum samples were examined for evidence of leptospiral agglutinins from 928 sheep from 45 lines and kidneys from 12 of these lines for evidence of leptospiral infection. All sheep had been submitted for slaughter at meat works in the Manawatu. Serological results were analysed using the results at a minimum serum dilution in the microscopic agglutination test (MAT) of 1:24 and at a minimum dilution of 1:48. It was shown that a minimum dilution of 1:24 resulted in many non-specific or cross-reactions. A minimum dilution of 1:48 was more accurate for detecting the serological prevalence of specific agglutinins to leptospires in ovine sera. Twenty percent of the sheep had titres of 1:48 or greater to hardjo, 3.8% to pomona, 2.6% to tarassovi, 2.3% to copenhageni and 2.7% to ballum. No titres of 1:48 or greater to australis were detected. Serovar hardjo was isolated from the kidneys of three animals in one line. Eighteen months later 291 serum samples and 95 urine samples were collected from live animals on the property from which the three hardjo infected animals originated. No titres to hardjo were detected in the sera of lambs, but a serological prevalence of 44% and 84% to this serovar was demonstrated in the hoggets and ewes respectively. No leptospires were demonstrated in any of the urine samples. These results show that sporadic infection of sheep with hardjo can occur but they also indicate that infection with this serovar is not endemic and that sheep are unlikely to act as maintenance hosts for hardjo in New Zealand.

Slaughter methods: Electroencephalographs (EEG) studies on spinal cord section, decapitation and gross trauma of the brain in lambs

By means of electroencephalograms (EEG), attempts were made to determine when insensibility could be presumed in five lambs, two subjected to immobilisation by the punctilla method, two decapitated and one shot by a captive bolt in the poll region. Section of approximately 80% of the spinal cord by the punctilla method had no apparent effect on sensibility and the technique was considered to be inhumane. The EEG obtained from a decapitated bead showed no obvious change in pattern for eight seconds and subsequent changes were similar to those associated with exsanguination only. Thus no evidence was obtained to indicate that decapitation causes immediate insensibility, neither was the belief substantiated that severance of the spinal cord, during the slaughter of sheep, hastens the onset of insensibility. These results also provide additional evidence on the inhumane nature of punctilla slaughter of cattle. The animal shot with a captive bolt in the poll region, as opposed to the frontal region, showed EEG activity for 78 seconds.

Stunning and slaughter of sheep and calves in New Zealand

Abstract The effects of various aspects of electrical stunning and slaughter were studied in more than 4,000 sheep and calves, the majority of which were being processed in different New Zealand meat export works. Electrical stunning must induce cardiac dysfunction to ensure that sheep and lambs do not regain sensibility during currently employed slaughter processes. Electrical stunning by both “head-to-back” and “head-to-leg” methods produces cardiac inhibition provided that electrodes are properly positioned and sufficient electrical current is applied. Electrocardiograms (ECG) of electrically stunned animals demonstrated that cardiac dysfunction can be readily detected by the use of stethoscope. The reactions of stunned and slaughtered animals to various nervous stimuli are unreliable determinants of insensibility. Slaughter of sheep, stunned by a “head only” method, by a lateral stab incision of the neck is unsatisfactory. In more than 14% of the animals the blood vessels were incised only on one side...

Insensibility during slaughter of pigs in comparison to other domestic stock

The onset of insensibility during slaughter was studied in five, 31-day-old pigs. The state of sensibility was determined from the study of electroencephalograms (EEC) which were of a bipolar transhemispheric derivation. In 3 pigs slaughtered by bilateral severance of both common carotid arteries and jugular veins, it was judged that insensibility occurred within 25 s and there was no resurgence of cerebrocortical activity following subsequent respiratory gasps. The EEGs became isoelectric within 115 s. These results are compared with previous findings by the authors that adult sheep and lambs slaughtered by similar techniques became insensible within 7 s whereas, in calves, the onset of insensibility was delayed for up to 85 s and there were resurgences of cerebrocortical activity, following a respiratory gasp, for more than 300 s. These differences in the apparent onset of insensibility in the 3 species of animal are discussed in relation to the anatomical features and possible dynamics of the blood supply to the brain during slaughter. It is concluded that for humane reasons, head-to-back electrical stunning of pigs is preferable to a head-only method.

The effect of different slaughter methods on the post mortem glycolysis of muscle in lambs.

Differences in muscular activity and rates of decline in the pH of the M. longissimus dorsi of lambs subjected to different methods of stunning and slaughter were observed. Lambs electrically stunned by a head-to-leg method had significantly lower initial pH values as compared to animals stunned by an electrical head-only method, or by captive bolt, or without any form of stunning prior to slaughter. When electrical stunning by a head-to-leg method was combined with low voltage (24 V) electrical stimulation during slaughter and bleeding, mean pH values declined at the highest rate and fell to approximately 6.0 within two hours of slaughter. This last procedure, therefore, has the potential to greatly reduce times between slaughter and freezing without increasing the risk of cold shortening and the associated toughness of meat.

Epidemiology of leptospirosis in dairy farm workers in the Manawatu Part I: A cross-sectional serological survey and associated occupational factors

Abstract A serological survey of 213 randomly chosen dairy farm residents in the Manawatu showed that 66 (34%) of the people who milked cows had leptospiral titres ≤ 1:24 by the Microscopic Agglutination Test. Forty-eight (72.7%) of these people had titres to hardjo, while 29 (43.9%) had titres to pomona. Dual hardjo/pomona titres occurred in 12 people. Ballum and Copenhageni accounted for 8% of the titres found. Women milkers and farm residents who did not milk were all serologically negative. A third of the seropositive milkers had a history of clinical leptospirosis. Other factors which significantly correlated with leptospiral titres included the time spent in the dairy shed during milking, the wearing of shorts, the keeping of pigs for sale, and the number of years the individual had been working on a dairy farm. The type of milking shed and the size of the herd were interrelated and both showed strong trends towards a correlation with serological prevalence.

The serological and cultural prevalence of leptospirosis in a sample of feral goats

Abstract Ninety-eight serum samples and 101 kidneys were examined from feral goats submitted for slaughter from Raglan county. It was found that 13•3% of the sera had agglutinating antibodies to serovars hardjo and balcanica. One hardjo and three balcanica isolates were made from the kidneys of the same group of goats. No Hebdomadis group titres were demonstrated from a further 18 blood samples of feral goats from the Taranaki and Taupo regions. Four of the total 116 sera examined had titres of between 1:24 to 1:196 to ballum. It is inferred from these results that the goat is not a natural maintenance host for leptospires in New Zealand. It is suggested that the balcanica infections were related to close association with possums. The hardjo infections, and the evidence of previous ballum infection are believed to have resulted from associations with cattle and wild rodents respectively.

Isolation of Leptospira interrogans serovars tarassovi and pomona from dogs

Abstract Extract This communication reports the isolation of Leptospira inter-rogans serovars tarassovi and pomona from dogs in New Zealand.

Failure to demonstrate the maintenance of leptospires by free-living carnivores.

Abstract Free-living members of the Mustelidae and feral cats (Felis catus) inhabiting farmland in the southern half of the North Island of New Zealand were examined for evidence of leptospiral infection. Nine stoats (Mustela erminea), 9 ferrets (Putorious putorious) and 4 weasels (Mustela nivalis) showed no serological or bacteriological evidence of infection. No leptospires were isolated from the kidneys of 11 feral cats but 2 animals had low titres to pomona and ballum respectively. All animals examined were from ecosystems where ballum infection was endemic in rodents; thus predator-chain transmission does not appear to be an important natural route of transmission for this serovar.

The detection of pigs carrying Streptococcus suis type 2.

An indirect fluorescent antibody test (I.F.A.T.) was performed on tonsillar swabs collected at slaughter and on nasal swabs from electrically stunned pigs prior to exsanguination. The identification of carriers of Streptococcus suis type 2 using the I.F.A.T. was compared with bacteriological isolation. If it is assumed that 100% of pigs were carrying the bacterium, 76% of 89 carriers were detected when the I.F.A.T. was performed on the bacterial growth from blood agar cultures of tonsillar swabs, compared with only 15% detected using cultural techniques. Similarly, I.F.A.T. on nasal swabs increased the sensitivity of the detection of carriers. Nasal swabbing, although of lower sensitivity than tonsillar swabbing, allows for the detection of S. suis type 2 carriers in the live animal.