Jf Weston

Efficacy of a Neospora caninum killed tachyzoite vaccine in preventing abortion and vertical transmission in dairy cattle.

A clinical trial was undertaken to assess the efficacy of Bovilis(®) Neoguard, a killed Neospora caninum tachyzoite vaccine on 5 commercial dairy farms in New Zealand with a history of Neospora-associated abortion. Cattle were enrolled in the trial at 30-60 days of gestation and randomly allocated to treatment or control groups. Treatment consisted of 5 mL doses of Bovilis Neoguard administered subcutaneously at enrolment then 4 weeks later. Isotonic saline was administered to the control group. Of 2246 cattle enrolled in the trial, 10.7% of cows and 12.6% of heifers were seropositive to N. caninum. Sampling of a randomly selected proportion of enrolled animals 6 weeks after the second treatment showed that 188/232 (81.0%) vaccinated with Bovilis(®) Neoguard had seroconverted, while 11/130 (8.5%) cows and 10/36 (27.8%) heifers in the control group had seroconverted. Forty-eight vaccinated and 63 control animals aborted. On one farm 12.5% of control animals and 6.1% of vaccinated animals aborted (vaccine efficacy 0.61; p=0.03). On another farm with a high level of abortion 8.4% of control animals and 8.7% of vaccinates aborted. On the remaining 3 farms fewer abortions occurred than expected. A modified Poisson regression approach was used to calculate relative risks for abortion and vertical transmission. Overall vaccine efficacy was 0.25 (p=0.12). Heifer replacement calves from the animals enrolled in the trial were sampled for antibodies to N. caninum at 6-9 months of age. Fourteen of 17 calves from vaccinated, seropositive cows were seropositive as were 13/23 calves from seropositive cows in the control group. The interaction between dam serostatus and treatment group was significant (p=0.05) with vaccination increasing the risk of vertical transmission. It was concluded that vaccination after conception prevented 61% abortions in one of five herds and that vaccination may have increased the risk of early embryonic death.

Foraging and denning patterns of brushtail possums, and their possible relationship to contact with cattle and the transmission of bovine tuberculosis

Radio-tracking and direct observation were used over 18 months in 1990-92 to investigate both the use of sleeping dens and foraging activity by possums (Trichosurus vulpecula) on a 21 ha site in the Wairarapa used for a longitudinal study of bovine tuberculosis. Males had larger home ranges than females, and both sexes had larger activity areas during the autumn mating season than at other times of the year. Possums typically foraged in only a small area of their home ranges (termed an activity area) on any one night, and the areas used by individuals were commonly very similar over a series of nights. Activity areas overlapped extensively among possums. Possums used a limited number of dens, commonly in a small and in most cases a circumscribed part of their home range. No simultaneous den-sharing was found, with the exception of mother-joey pairs. The mortality of juveniles after independence was 36%. Only two of 25 juveniles under surveillance to detect dispersal dispersed more than 500 m off the study site, and both subsequently died. Grazing patterns of cattle meant that almost all accessible areas of the paddock were covered by at least some grazing cattle, and so all activity areas of possums within the paddock were covered by areas where cattle foraged. However, possums avoided contact with cattle, and when some cattle were excluded from access to the part of the paddock principally used by both tuberculous and healthy possums for denning, transmission of Mycobacterium bovis from possums to these cattle ceased, although there was subsequent transmission to deer. Cattle which grazed the area used principally for possum denning continued to become infected, and these denning areas appeared to be of importance in the transmission of tuberculosis.

Assessment of the duration of the pain response associated with lameness in dairy cows, and the influence of treatment

Abstract AIM: To assess the welfare impact of lameness on dairy cattle in New Zealand by measuring the duration of allodynia (decreased nociceptive threshold) and increased locomotion score, and to evaluate the influence of treatment on that duration. METHODS: After lame cows were treated using corrective paring by a veterinarian, they were allocated to one of six treatment groups. If the veterinarian determined that additional elevation of the lesion was not required the cow was randomly allocated to receive one of four treatments, viz 2 mg/kg tolfenamic acid, a plastic shoe to elevate the lesion, both treatments, or no further treatment. Cows that required additional elevation were treated using a plastic shoe and then randomly allocated to two separate treatment groups, either 2 mg/kg tolfenamic acid or no further treatment. Assessments of locomotion score (based on posture and gait) and mechanical nociceptive threshold (using a pneumatically actuated blunt pin) were made prior to treatment, and 3, 8, 28 and 100 days later. RESULTS: Data were collected from 149 lame cows from nine dairy farms. There were significant improvements in mean locomotion score and nociceptive threshold in all treatment groups. At all time-points after treatment, locomotion score and nociceptive threshold were significantly improved when compared with the previous time-point. Thus, in these cows, the deleterious effects of lameness persisted for longer than 28 days, despite treatment, as the mean locomotion scores and nociceptive threshold on Day 100 were better than those on Day 28. No significant long-term benefit of using tolfenamic acid at the time of treatment was observed on either locomotion score or nociceptive threshold, nor was there any benefit in using a plastic shoe in cases where it had been determined that such treatment was not necessary. CONCLUSIONS: This study demonstrated that the welfare impact of lameness on dairy cattle in New Zealand is of long duration even when treated effectively. In contrast to previous studies, no significant long-term benefit of using non-steroidal anti-inflammatory drugs (NSAID) at the time of treatment was observed, probably because unlike those previous studies the nociceptive threshold improved in the cattle which did not receive an NSAID, perhaps because treated cattle were kept on pasture rather than housed. CLINICAL RELEVANCE: The long duration of increased allodynia after treatment demonstrates that prevention of lameness rather than therapeutic treatment is the key to reducing its impact on the welfare of dairy cows.

The potential extent of transmission of foot-and-mouth disease: A study of the movement of animals and materials in Southland, New Zealand

A survey of Southland farms was conducted to assess the potential for foot-and-mouth disease dissemination through normal movement patterns of farm animals and materials over a period similar to what would be expected from the time the virus arrived on a property to the time of diagnosis. Each farmer participating in the survey was required to complete a diary, recording all movements of people, animals and materials on to or off a farm during a 14-day period. The mean number of movements recorded per farm was 50. The distribution of movement distances showed the majority of movements occurred within the immediate neighbourhood of the origin, with 31.5% and 59.5% of all movements occurring within 5 km and 10 km respectively. In order to contain 95% of all movements, an area where movement was controlled would have to have a radius of 100 km. The data was then used to construct a spatial simulation model to study the movements off a hypothetical index farm. When secondary movements off primary destinations were included in the model, the mean number of movements to be traced to contain the disease was 100 (range 77-160) for a 14-day simulation period. The area required to contain 95% of all movements tended to increase slightly, depending on the length of simulation run. The mean number of high risk movements that occurred over the 100 km radius was 3.4.

Associations between pregnancy outcome and serological response to Neospora caninum among a group of dairy heifers

Abstract AIM: To monitor pregnancy in a group of rising 2-year-old dairy heifers on a farm on which abortion due to Neospora caninum was known to occur in previous years. METHODS: A prospective cohort study group of 164 rising 2-year-old heifers was pregnancy-tested and blood-sampled at 4–5-week intervals throughout gestation. Sera were tested for antibodies to N. caninum at 3–4-month intervals, using an enzyme-linked immunosorbent assay (ELISA). When loss of pregnancy was detected, an N. caninum indirect fluorescent antibody test (IFAT) was conducted retrospectively on stored sera collected the month before abortion, the month abortion was detected, and for the following 2 months, from heifers that aborted. All fetal and placental material detected following abortion was subjected to gross post-mortem and histopathological examination. RESULTS: Eleven of 18 (61%) heifers that were seropositive and 4/146 (3%) heifers that were seronegative to N. caninum by ELISA, aborted. The relative risk for abortion among ELISApositive heifers was 23.6. Abortion occurred predominantly between Days 120 and 152 gestation among the ELISA-positive heifers and throughout gestation among the ELISA-negative heifers. IFAT titres rose around the time of abortion in most of the heifers that were previously seropositive by ELISA, but dropped rapidly again in post-abortion samples. IFAT titres among 4/6 ELISA-positive heifers that did not abort increased, but later in gestation than the time other heifers aborted. IFAT titres remained negative in heifers that aborted that were ELISAnegative. CONCLUSIONS: Heifers that were seropositive to N. caninum by ELISA had a much greater risk of abortion than seronegative heifers. Most seropositive heifers showed evidence of a reactivation of infection during pregnancy. High (≥1:2,000) N. caninum IFAT titres also occurred in non-aborting heifers. CLINICAL RELEVANCE: Culling of replacement heifers seropositive to N. caninum may be a cost-effective strategy for minimising risk of abortion. Pregnancy testing heifers before 5 months gestation may overestimate the number that calve in N. caninum-infected herds, but would assist in documenting the occurrence of abortion. Reliance on a high (>1:2,000) IFAT titre to rule-in N. caninum as a cause of abortion is likely to produce false-positive results.

The occurrence of Cryptosporidium parvum, Campylobacter and Salmonella in newborn dairy calves in the Manawatu region of New Zealand.

Abstract AIM: To determine the occurrence of Cryptosporidium parvum oocysts, Campylobacter spp and Salmonella spp in faecal samples taken from newborn dairy calves on 24 dairy farms in the Manawatu region of New Zealand. METHODS: A cross-sectional study was conducted during the 2002 calving season. Faecal samples were collected from 185 newborn calves from a convenience sample of 24 dairy farms. The samples were tested microscopically for the presence of C. parvum oocysts, and bacteriologically for the presence of Campylobacter spp and Salmonella spp. RESULTS: Infections with C. parvum were identified in 33/156 (21.2%) calves from 10 farms. More than 106 oocysts/g (OPG) faeces were detected in calves from four farms. Campylobacter spp were isolated from 58/161 (36%) calves from 18 farms; in particular, C. jejuni subsp jejuni was isolated from 11/161 (6.8%) calves from seven farms. Salmonellae were not detected. CONCLUSIONS: Despite the short and concentrated calving pattern and the long interval between calving seasons characterising most dairy farms in New Zealand, C. parvum is widespread among calves. Campylobacter spp, especially C. jejuni, rapidly colonise the intestinal tract of newborn calves. RELEVANCE: This study provided an estimate of the ecological impact of newborn dairy calves with regard to the potentially zoonotic enteric pathogens most frequently isolated from human gastrointestinal infections in New Zealand.

Dose-titration challenge of young pregnant sheep with Neospora caninum tachyzoites.

Pregnant ewe lambs (7-8 months old at breeding) were inoculated intravenously at 90 days after joining with the ram with 50, 5 x 10(3), 10(6), or 10(8)Neospora caninum tachyzoites and outcomes were compared to a control group. Seroconversion was measured by indirect fluorescent antibody test (IFAT) at fortnightly intervals and by enzyme-linked immunosorbent assay (ELISA) at 28 days post-challenge. Seroconversion (by IFAT) occurred in all animals except for 2 sheep in the lowest dose group, including the 9 sheep in the control group. IFAT antibody titres rose and fell rapidly, peaking at 1:800 and in 8 animals was negative within 7 days of abortion. ELISA results more closely reflected infection dose and outcome of pregnancy than IFAT serology did. All 10 ewes in each of the 2 highest dose groups aborted, 5 of 10 ewes in the mid-dose group aborted and no ewes in the lowest dose or control groups aborted. Histological lesions consistent with N. caninum infection were seen in the brains of all 25 aborted lambs, as well as in 2 live-born premature lambs from the group receiving 5 x 10(3) tachyzoites and 2 clinically normal lambs (one from the control group). Polymerase chain reaction (PCR) detected N. caninum DNA in a variety of tissues from lambs, aborted foetuses and dams including 3 of 9 ewe-lamb pairs from the control group. The results from this study showed a strong relationship between challenge dose of N. caninum tachyzoites, the sample to positive (S/P) percentage in an ELISA test 28 days after challenge and pregnancy outcome. IFAT results did not correlate well with the level of challenge or the outcome of pregnancy and their relevance in studies of this kind should be questioned.

Causes of abortion on New Zealand dairy farms with a history of abortion associated with Neospora caninum

Abstract AIM: To investigate the cause of abortion in cows from farms with a history of abortion associated with Neospora caninum. METHODS: Cows and primiparous heifers (n = 2,246) that were enrolled in a clinical trial of a vaccine for N. caninum, and 403 cows and heifers that conceived >6 weeks after the planned start of mating (PSM), were monitored for abortion on five dairy farms with a history of abortion associated with N. caninum. When abortion was detected the fetus and/or placenta were submitted for histopathological examination and maternal paired sera were collected for the detection of antibodies to N. caninum using the indirect fluorescent antibody test (IFAT), bovine viral diarrhoea virus (BVDV) using ELISA, and Leptospira spp. using the microscopic agglutination test (MAT). RESULTS: At the start of the clinical trial, 189/1,760 (10.7%) of cows and 61/486 (12.6%) of heifers had IFAT titres ≥1:200 for N. caninum. Abortions were detected in 111 (4.9%) enrolled and 37 (9.2%) non-enrolled cows and heifers. The relative risk of abortion was 4.21 (95% CI 2.92–6.08) times greater in enrolled animals that were seropositive to N. caninum than seronegative animals (p < 0.01). Among all animals, histopathological lesions suggestive of protozoal abortion were seen in nine, and of bacterial infection in 15, of the 40 cases where the fetus and/or placenta were recovered. IFAT titres for N. caninum ≥1:1,000 were detected in 66 cows at abortion, including 7/9 cases where there were fetal lesions indicative of N. caninum infection. In nine cows that aborted, there was evidence of seroconversion to BVDV and eight cows had MAT titres for Leptospira spp. ≥1:200. Histopathology revealed dual infectious aetiologies in two cases and, in another 17 cases, there was serological evidence of recent exposure to a second infectious agent capable of causing abortion in conjunction with N. caninum lesions in the fetus or fetal bacteraemia. CONCLUSIONS: Multiple infectious aetiologies occur at herd-level and in individual cows on farms with a history of abortion associated with N. caninum. A diagnosis of abortion due to N. caninum infection was made in 9/34 (26.5%) cases where fetal histopathology was undertaken. CLINICAL RELEVANCE: Thorough and ongoing diagnostic investigations should be undertaken in herds with higher than expected abortion losses to identify all causative agents as control measures could be implemented that may also reduce the risk of abortion in cows infected with N. caninum.

Stressors and Protective Factors among Veterinary Students in New Zealand

A study was undertaken to investigate the stressors faced by veterinary students and the protective factors against those stressors. The study was conducted as a workshop during which students collaborated with their peers through an iterative process to identify personal and external factors that contributed to or protected against stress as a veterinary student, and then to suggest strategies that would protect their mental health and well-being. Workload and assessment were the most commonly reported stressors. Students reported a variety of effective coping strategies and avoidance behaviors, although most of the suggested solutions revolved around organizational change within the university. Students also recognized that their own perspectives, traits, and behavior could enhance their student experience or increase their perceived levels of stress. While it is important that educators monitor student feedback about the program and make changes when required, students must recognize that stress is an expected component of life and develop effective coping strategies. They should develop a balanced view of the positive and negative aspects of the student experience and, ultimately, of working as a veterinary professional.

Spina bifida with associated malformations of the central nervous system in Dorper-cross sheep

Abstract CASE HISTORY: In 2008, six lambs within a flock of Dorpercross sheep were born with musculoskeletal and neurological disease. Clinical signs included hindlimb weakness, and urinary incontinence. CLINICAL FINDINGS: All lambs had focal, inverted areas of alopecic skin over the caudal sacrum, and short, often kinked tails. Four affected lambs were subject to euthanasia, and necropsied. On gross examination, the arches of sacral vertebrae were absent, and spinal nerves and meninges were adherent to the overlying subcutis. Other gross lesions included narrow, elongated skulls, herniation of the occipital lobes into the caudal fossas, hydrocephalus, and syringomyelia. One lamb had coning of the cerebellar vermis, but cerebellar herniation through the foramen magnum was not identified. DIAGNOSIS: Spina bifida, with associated malformations of the central nervous system. CLINICAL RELEVANCE: Examination of breeding records suggested either an autosomal recessive or partially penetrant autosomal dominant pattern of inheritance. Because of the associated tail lesions it is proposed that the pathogenesis of this syndrome involves a defect in development of the tail bud (secondary neurulation), that tethering of the spinal cord resulted in the clinical signs, and abnormal pressure of the cerebral spinal fluid resulted in the defects in the skull and brain.