Reproductive performance of farmed red deer (Cervus elaphus) in New Zealand: II. Risk factors for adult hind conception

A 2-year longitudinal observational study of 15 red deer farms was carried out in New Zealand from March 1992. About 2600 adult hinds were individually monitored for reproductive success. After mating, hinds were pregnancy-tested by ultrasound and were classified as having conceived before 1 May, after 1 May or as being not pregnant. Risk factors potentially affecting the probability of conception before 1 May or of conception that year were investigated using path analysis. Final path diagrams were used to formulate a putative management strategy for farmers to achieve the desired reproductive performance from adult hinds. To achieve a high pregnancy rate early in the mating season, farmers should wean calves early, exclude hinds which failed to rear a calf to weaning and hinds with a body condition score < or = 2.0 at mating, join hinds early with one or more sire stags, use only experienced sires for mating, limit the hind: stag ratio, use at least one back-up sire after the peak of mating, keep mating mobs away from disturbance and avoid shifting or handling mating mobs. The farmer should choose paddocks with high green pasture allowance and grazed down to no less than 5 cm high.

A descriptive analysis of the potential association between migration patterns of bean and white-fronted geese and the occurrence of Newcastle disease outbreaks in domestic birds

The sightings and migration patterns of 65 bean (Anser fabalis) and 65 white-fronted geese (Anser albifrons) are reported. In the past, these geese were serologically screened for the occurrence of Newcastle disease virus (NDV) and other avian viral diseases by Hlinak et al. (3). Of the 130 birds originally tagged and serologically screened in 1991, 53 birds were resighted between 1991 and 1996. Most of the sightings were reported from main wintering and resting sites in Germany and The Netherlands. It is noteworthy that 19 of the 53 birds sighted had serologic evidence that they had been exposed to NDV before the time of marking in 1991. Although the origin of these infections in bean geese and white-fronted geese is still unknown, the sightings reported in this study indicate that, once infected, wild geese may be involved in the dissemination and spread of avian viral diseases, specifically Newcastle disease. The migration patterns of the wild geese provided further evidence that the main resting and wintering areas of migratory waterfowl are likely to be important for the inter- and intraspecies transmission of avian diseases, thereby representing risk areas for the poultry industry.

Field efficacy of a combined use of Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae vaccines in growing pigs

The effectiveness of simultaneous administration of commercial Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae vaccines was tested in an indoor commercial piggery which had experienced continuing respiratory-disease problems confirmed as due to both of these pathogens. Piglets were randomly assigned in equal numbers to vaccination and control groups, and each vaccine was administered at a separate site to assigned piglets at two and four weeks of age. Live weight of vaccinates immediately prior to slaughter was 2.49 kg higher (p = 0.04) than for controls at equal mean slaughter age of 132 days. Average daily gain (ADG) from 16 weeks to slaughter of vaccinates was also significantly higher (33 g/day) than in controls (p = 0.05). Daily gain was not significantly different in younger age groups. Active enzootic pneumonia lesions were more likely in control than in vaccinated pigs. There were no significant differences between vaccination groups with regard to severity of pleurisy or presence of pleuropneumonia lesions at slaughter. Log-linear modelling was used to test the statistical association between vaccination, enzootic pneumonia lesions, pleurisy lesions and pleuropneumonia lesions. It showed a reduction in the severity of enzootic pneumonia lesions for vaccinated pigs, and the presence of pleuropneumonia lesions increased the likelihood of pleurisy lesions. No other association was significant, and no evidence of synergy between the vaccines in influencing lesion severity for pleuropneumonia was detected (within the limitations set by the trial design).

An on-farm study of the epidemiology of Actinobacillus pleuropneumoniae infection in pigs as part of a vaccine efficacy trial

Thirty cohort pigs were followed from birth to slaughter to study epidemiological patterns of porcine pleuropneumonia caused by Actinobacillus pleuropneumoniae. The study was conducted within a larger 380-animal study of vaccination against Mycoplasma hyopneumoniae and A. pleuropneumoniae in a 340-sow farrow-to-finish piggery with 4-month weaning, operating a continuous system of intensive production in the North Island of New Zealand. The cohort pigs were randomly allocated into two equal groups: vaccinated and control. Pigs in the first group were vaccinated at 2 and 4 weeks of age with both M. hyopneumoniae vaccine and A. pleuropneumoniae vaccine at separate vaccination sites. A series of nasal swabs was taken at 4, 8, 10, 11, 12, 14, 16 and 18 weeks of age. Each swab was streaked onto the surface of a selective medium on the farm and the plates were immediately transported to a laboratory and incubated at 37 degrees C for 5 days. After the trial, pigs were slaughtered at an average of 132 days of age, lungs were examined and samples taken for bacteriological culture and isolation. Thirty-five out of 256 samples produced haemolytic colonies which were Gram-negative, V-factor-dependent and positive to the CAMP test. A. pleuropneumoniae was first isolated at 4 weeks of age from one vaccinated pig. This finding suggests that piglets became infected in the farrowing pen and the source of infection might be a carrier sow. The interval-specific cumulative incidence of A. pleuropneumoniae infection reached a maximum of 54% and 40% at 11 weeks of age in the vaccinated and control groups, respectively. Infection status of the litter is considered to be a factor influencing morbidity in infected herds during weaner and grower periods. Our results suggest that simultaneous vaccination with M. hyopneumoniae and A. pleuropneumoniae vaccines at 2 and 4 weeks of age might lessen the prevalence but cannot absolutely prevent A. pleuropneumoniae infection during the weaner or grower-finisher periods.

Naturally occurring osteoarthritis in the metacarpophalangeal joints of wild horses

This study identified changes consistent with osteoarthritis; articular cartilage damage, subchondral bone sclerosis and marginal osteophytes, in the metacarpophalangeal joints of wild New Zealand horses. The articular cartilage lesions were identified by Indian ink staining techniques and histology. The lesions occurred on the proximodorsal aspect of the first phalanx (P1) and were more severe on the medial compared to the lateral eminence of the bone, and their severity increased with age. The bone mineral density of the subchondral bone underlying the cartilage lesions, assessed using conventional radiography and dual energy absorptiometry, also increased with age and with severity of the overlying cartilage lesion. Subjective assessment of cabinet radiographs revealed that the subchondral bone sclerosis was greater in horses with severe articular cartilage damage. Ossicles, with a distinct trabecular bone pattern, were identified at the proximo-dorsal margin of P1 in 8 specimens from 5 horses from the older age groups (greater than age 5 years). The results of this study demonstrate age-related changes consistent with osteoarthritis in the metacarpophalangeal joints of wild horses. There appears to be a significant relationship between subchondral bone sclerosis and overlying cartilage degeneration in the proximodorsal aspect of P1. We have identified an age-related osteoarthritic process naturally present in horses; and postulate that the stresses of racing and training may accelerate this ageing process.

Production and reproductive responses to use of DairyMAN: a management information system for New Zealand dairy herds

To assess the benefits of on-farm use of a computerized management information system (DairyMAN, Department of Veterinary Clinical Science, Massey University, Palmerston North, New Zealand) on seasonally calving herds of New Zealand, data for 144 herds using this system were compared with a stratified random sample of 294 herds using only the centralized National Dairy Database system during the season 1993 to 1994. Demographic, reproductive performance, and milk yield indices were compared. Herds using DairyMAN had superior reproductive outcomes, measured as a higher percentage (+8.4%) of cows calving during the desired seasonal period (critical in this seasonal system) and a higher percentage of cows (+9.7%) mated at the optimal time to achieve a concentrated calving in the following year. Multiple analysis of covariance was used to differentiate effects. The superior performance was not associated with differences in some of the more commonly used reproductive indices (efficiency of estrus detection, first service nonreturn rate, and pregnancy rate), but the data used in the study do not accurately reflect true performance. Herds using DairyMAN had more information on breeding performance because pregnancy data were available and natural breedings were recorded for a longer period. With cows of equivalent genetic merit, herds using DairyMAN produced more milk (+1.2 L/d per cow) indicating that users achieved better management of the herd through improved attention to managerial details. This improved production was associated with the adoption of DairyMAN but is not shown by this study to be a direct consequence of it. DairyMAN user herds were larger (245 cows) than were herds not using the system (181 cows), but this difference did not significantly affect the various outcomes measured.

The accuracy and reliability of linear measurements of the ulna for anthropometrical studies in dogs

This study investigated the accuracy and reliability of measuring the distance between two surface landmarks (the point of the tuber olecrani and the proximal aspect of the stopper pad) as an indication of ulna length in the live dog. It was found that the chosen skin landmarks did correlate well with the length of the ulna bone. The reliability of such measurements was high when performed by a single person, however this fell to unacceptable levels when multiple people were used to make the measurements. It was concluded that if this technique was to be used in studies to serially record the bone length in live growing dogs, then the measurements should be taken by a single person.

Effects of calving induction on subsequent milk yield and reproductive performance of cows from seasonally mated New Zealand dairy herds

AIM

To identify some production and reproductive effects of calving induction in seasonally calving herds.

METHODS

Forty seasonally calving herds entered on the DairyMAN management information system and whose milk yield and reproductive data were recorded, including pregnancy diagnosis results, were included in the study. Cows with an induced parturition were compared with normally calving contemporaries that had the same lactation number and calved at the same time.

RESULTS

Milk yield was 1.2 +/- 0.2 litres/cow/day less over the entire lactation for cows induced to calve, with the greatest difference being 2.5 +/- 0.4 litres/cow/day measured in early lactation. The effects on milkfat and protein yield were similar, with 0.04 +/- 0.01 kg/cow/day less milkfat (p < 0.0001) and 0.03 +/- 0.01 kg/cow/day less protein (p < 0.0001). A higher milkfat percentage (+ 0.09 +/- 0.04 %) (p < 0.0001) and protein percentage (+ 0.10 +/- 0.02%) (p < 0.0001) for cows that were induced to calve reduced the effect of a lower milk yield on milkfat and protein production. The first service conception rate for cows induced to calve was 54.4 +/- 3.3%, which was significantly less (p = 0.03) than for cows that calved normally (59.5 +/- 3.3%). Cows induced to calve had a pregnancy rate at the end of mating of 91.4 +/- 2.1%, which was also significantly less (p <0.0001) than for cows that calved normally (93.6 +/- 1.7%). The 21-day submission rates were not significantly different between groups.

CONCLUSIONS

This study indicates that, under some New Zealand management conditions, the induction of calving is associated with reduced daily milk yield and inferior reproductive performance.

[Frequency and cost of health problems in Swiss dairy cows and their calves (1993-1994)]

Between July 1993 and July 1994 morbidity and management information related to dairy cows and their calves up to the age of 8 weeks were recorded in 113 randomly selected dairy herds. Also recorded were any costs incurred through disease and prevention. Blood and faeces were analysed with respect to selected pathogens. The health problems most frequently diagnosed in cows were reproductive and udder diseases. Calves suffered most often from diarrhea, omphalitis and pneumonia. The directly disease-related costs per cow-year on average amounted to CHF 139.44 and CHF 4.18 per calf. For prevention, farmers spent on average CHF 10.18 per cow-year. Results from the laboratory analyses indicate that in 68.1% of the farms antibodies against Leptospira hardjo and in 61.9% against Coxiella burnetii were detected. In 8.0% of the farms antibodies against Mycobacterium paratuberculosis were found. Antibodies against BVD virus was present in 99.4% of the farms. Cows from 63.7% farms were infected with gastrointestinal strongylids. Veterinary assistance was required on average 1.96 times per cow-year. In almost all reproductive and puerperal disease cases a veterinarian was consulted while lameness in the majority of cases was treated by the owner. The veterinary profession was hardly ever involved in disease prevention.

The production system and disease incidence in a national random longitudinal study of Swiss dairy herds

A prospective longitudinal observational study based on a stratified random sample of 113 Swiss dairy farms was conducted between April 1993 and July 1994 with the following objectives: (i) to provide statistically valid estimates of disease frequency in the Swiss dairy cow population, and (ii) to evaluate the feasibility and quality of an intensive farm-based data recording system. During the 15-month study period, farmers were asked to record every health and management event related to their cattle herd. This information was mailed back to the study centre at fortnightly intervals. Additionally, farms were visited regularly to verify received data and to discuss specific problems. During these farm visits, management data were recorded using questionnaires. A complete data set of individual animal events with a total observation time of about 1740 cow-years and 275 calf-years was collected and disease-incidence measures were calculated. The most frequent events were reproductive disorders and udder diseases, followed by lameness and metabolic disorders. Experience with the data collection technique used in this study suggests that a farm-based system is effective and reliable, as long as good contact with the farmers is maintained, and incentives to stimulate their motivation are provided.

Superficial digital flexor tendonitis in thoroughbred race horses: outcome following non-surgical treatment and superior check desmotomy

OBJECTIVE

This study documents the results of non-surgical treatment and treatment by superior check desmotomy in Thoroughbred racehorses with superficial digital flexor (SDF) tendonitis.

DESIGN

A prospective study was made of 124 thoroughbred racehorses with unilateral or bilateral SDF tendonitis.

PROCEDURE

The flexor tendons were assessed by physical and ultrasonographic examination before treatment, and the lesions detected in affected tendons were characterised according to lesion type, length and cross-sectional area. Ninety three horses were managed non-surgically and 31 by superior check desmotomy. Recurrent or new injuries were defined as injuries affecting a previously injured superficial digital flexor tendon, the contralateral SDF tendon, or the suspensory ligament (interosseous muscle) in either forelimb.

RESULTS

No statistically significant difference was found in ultrasonographic lesion severity between treatment groups. Horses managed by superior check desmotomy were 1.3 times more likely to complete five or more races than horses managed non-surgically (95% confidence limits 0.93-1.82). Horses treated surgically were 1.2 times more likely to develop recurrent or new injuries after returning to training than horses managed non-surgically (95% CL 0.95-1.55). Horses undergoing superior check desmotomy were 5.5 times more likely to develop suspensory desmitis than horses treated non-surgically (95% CL 1.13-26.4). There was no difference in the time to recurrent or new injury between treatment groups.

CONCLUSION

There was no statistically significant difference between treatment groups in the proportions of horses able to complete five or more races after an episode of superficial digital flexor tendonitis. Superior check desmotomy did not appear to offer an advantage over non-surgical treatment in preventing recurrent or new injuries in Thoroughbred racehorses. Horses undergoing superior check desmotomy appeared to be at greater risk of developing suspensory ligament injuries than horses managed non-surgically.

Re-insertion of a progesterone-containing intravaginal device to synchronise returns to oestrus in dairy heifers

Recommendations for oestrus synchronisation of dairy heifers using progesterone-containing intravaginal devices suggest re-insertion of used devices 16 days after first insemination for a period of 5 days to allow a second opportunity for artificial insemination. Controlled studies on the effectiveness of re-using intravaginal devices to synchronise returns to oestrus in non-pregnant dairy heifers are lacking. A clinical trial was conducted involving 750 Friesian heifers in 13 herds. After an initial synchronisation programme, the used intravaginal devices were re-inserted 14 or 16 days after first insemination into half of the heifers in each herd for a period of 5 days. After the first synchronisation programme, 47.5% of heifers remained non-pregnant. Re-insertion of used intravaginal devices for 5 days significantly increased the number of non-pregnant heifers detected in oestrus and inseminated by 48 hours after device removal compared to heifers in which devices were not re-inserted (45.2% v. 27.3%, p < 0.05, in herds where intravaginal devices were re-inserted on day 14; 48.8% v. 13.6%, p < 0.05, in herds where intravaginal devices were re-inserted on day 16). Re-insertion at 14 or 16 days after first insemination was equally effective in increasing visible returns to service. However, the number of non-pregnant heifers synchronised for a second round of artificial insemination was less than expected. Conception rate to the re-synchronised oestrus was unaffected by the treatment. It is concluded that the additional procedures of CIDR re-insertion, removal, tailpainting and insemination involved in there-synchrony programme, and the relatively low in-calf rate to the re-synchronised round of insemination, reduced the potential benefits of re-synchronisation.

Effect of intraruminal monensin capsules on reproductive performance and milk production of dairy cows fed pasture

Cows from three herds calving in spring that were fed on pasture were paired by herd, production index, predicted calving date, and age. One cow from each pair was allocated randomly to the treatment group and received a controlled-release capsule of monensin 1 mo prior to the start of AI. A random sample of 20 matched pairs of cows was selected within each herd to monitor BW and metabolic parameters. Treated cows produced more fat, protein, and liters of milk per day during the 2nd mo of monensin activity and produced a greater total milk volume than did control cows. Treated cows gained less BW during the 1st mo after treatment. No significant differences were identified in submission rates, overall pregnancy rates, or pregnancy rate to first or second AI. Blood urea nitrogen was elevated in the treatment group as a main effect, and NEFA were elevated in the 2nd and 3rd mo after treatment. There was no significant effect on blood concentrations of glucose, albumin, or BHBA.

The effect of estradiol benzoate administration on estrous response and synchronized pregnancy rate in dairy heifers after treatment with exogenous progesterone

The objectives of this trial were to determine the effects of 0.5 mg estradiol benzoate administered intramuscularly 24 h after the removal of progesterone-containing intravaginal devices on the occurrence and timing of estrus, synchronized pregnancy rate and synchronized conception rate in dairy heifers. A clinical trial was conducted involving 750 dairy heifers in 13 herds. Within each herd heifers were randomly allocated to 1 of 2 estrus synchronization treatments. All heifers received a CIDR-B progesterone-containing intravaginal device containing a 10 mg estradiol benzoate capsule for 12 d. Twenty-four hours after CIDR-B removal one group received 0.5 mg, im estradiol benzoate while the other group received an intramuscular injection of a placebo. Estrus detection was performed at 48 and 72 h after intravaginal device removal, and heifers detected in estrus at those times were inseminated. Administration of estradiol benzoate 24 h after removal of CIDR-B devices significantly increased the number of heifers exhibiting estrus within the observation period (96.1 vs 90.5%; P < 0.01). It also altered the onset of estrus so that significantly more heifers were in estrus (86.6 vs 72.3%; P < 0.01) and conceived (47.1 vs 37.5%; P < 0.05) by 48 h after CIDR-B device removal. The synchronized conception rate was unaffected by treatment. The distribution of estrus was such that fixed-time insemination after estrus synchronization with this treatment program may be recommended.

Directions and issues in bovine tuberculosis epidemiology and control in New Zealand

Current knowledge on the epidemiology of bovine tuberculosis in New Zealand is reviewed, with emphasis on recent findings. It would appear that the epidemiology of the disease is determined by the behaviour of both wildlife and domestic stock, and environmental influences on the development of the infectious state in wildlife. The central cause of persistent disease nationally remains the possum, although other species may play a subsidiary role locally. Current understanding provides much improved prospects for control, which will be based on implementing individual farm control strategies to complement current regional control, with additional later prospects of vaccination of wildlife and possibly reproductive control of possums.

The epidemiology ofMycobacterium bovisinfection in brushtail possums (Trichosurus vulpeculaKerr) in the Hauhungaroa Ranges, New Zealand

The prevalence of Mycobacterium bovis infection in the wild possum population around the perimeter of the Hauhungaroa Ranges, New Zealand, was determined by a cross-sectional study, and risk factors associated with tuberculosis were identified. Of 6083 possums necropsied, 128 (2.1%) showed gross lesions suggestive of tuberculosis infection, and 76 (1.25%) were subsequently confirmed as tuberculous on histopathological examination. Considering only traplines where tuberculosis was detected, adult possums were 1.9 times as likely to be infected as immature animals, and the total prevalence was 5.4% in males compared with 3.9% in females. Adult females were 3.64 times as likely to be infected as immature females, whereas there was no significant age difference for males (odds ratio = 1.46, p=O.29). Immature males were 3.12 times as likely to be infected as immature females. Possums in poor condition were more likely to be found infected than possums in good condition. Tuberculous possums were found in 27 local clusters of infection. The correlation between the prevalence of tuberculosis in possums in zones and the incidence of tuberculosis in cattle on adjoining properties was 0.4 (p<O.05).

Evaluation of three serological assays for the diagnosis ofMycobacterium bovisinfection in brushtail possums

Three serological tests for the diagnosis of Mycobacterium bovis infection were evaluated on 29 possums (Trichosurus vulpecula) with tuberculosis and on 100 possums from a tuberculosis-free area. An indirect ELISA using M. bovis culture filtrate as the antigen had a sensitivity of 45% and a specificity of 96%, while an indirect ELISA using a M. bovis specific antigen (MPB70) had a sensitivity of 21% and a specificity of 98%. A blocking ELISA which utilised a monoclonal antibody against MPB70 had a sensitivity of 28% and a specificity of 99%. Combination of the test results of the three ELISAs resulted in an increase in sensitivity to 51% and a decrease in specificity to 93%. A previous study has shown that possums experimentally infected with M. bovis produced cellular responses to M. bovis antigens relatively early in the infection, but these responses decreased in the terminal stages of the disease. In contrast, analysis of serological responses in the current study from sequentially collected sera of possums experimentally and naturally infected with M. bovis showed that antibody was first detected late in the disease.

The epidemiology of Mycobacterium bovis infections

Mycobacterium bovis has an exceptionally wide host range, but until recent years there was little concern about infection in species other than cattle and man. Diversification of farming enterprises has led to cognizance of the need for control in other domestic animals, notably deer. There has also been recognition that self-maintaining infection is present in wildlife hosts in some countries--notably the European badger in the United Kingdom and Ireland, the Australian brush-tailed possum in New Zealand, and various species of ungulates in limited areas of a number of countries. Although transmission of M. bovis can occur by a number of different routes, control measures imposed on cattle and to a lesser extent on other species have reduced a number of the routes to insignificance. Hence the vast preponderance of transmission within host species is now by the airborne route, and predominantly between species as well. Transmission of infection from badgers to cattle may be an exception, with evidence remaining equivocal about the relative importance of pasture contamination by excretion in badger urine and airborne transmission. In general, contamination of feed and pasture appears to be unimportant in transmission of the disease, because survival times of infective doses of organisms on fomites are relatively short under realistic conditions and because animals are not commonly exposed to a dose high enough to be infective by the alimentary route. Infection through the oro-pharyngeal mucous membrane may be significant, although the infective dose for this route is not known. While many species of animals can become infected with M. bovis, only a few act as maintenance hosts and the rest are spillover hosts in which infection is not self-maintaining. With the exception of cattle and deer, other species have become maintenance hosts only within part of their ecological range. For both badgers and possums, maintenance of infection within a local population is due to pseudo-vertical transmission from mother to young, and horizontal transmission linked to breeding activity. Transmission from possums to domestic animals appears to occur mainly during atypical behavioural interactions between the species, and this may well be important for badgers as well. Difficulties in controlling the disease adequately in domestic animals generally result from administrative problems since the necessary technical procedures are available and have been shown to be effective. Where there is interplay between infection in wildlife and domestic animals, eradication of the disease becomes impractical.(ABSTRACT TRUNCATED AT 400 WORDS)

Canine wobbler syndrome: A study of the Dobermann pinscher in New Zealand

The aim of this study was to investigate the prevalence of wobbler disease within a Dobermann pinscher population from three geographical locations in New Zealand. The study population consisted of 138 adults (aged 1-13 years) and 32 puppies (aged 6 weeks to 11 months). Data collected for each dog included age, sex, geographic location, if a choker chain was used or not and, in adults, the following body measurements: dimensions of head length, head circumference, width between shoulders, neck length, height at withers and withers to rump length. In addition, lateral radiographs were taken of the caudal cervical vertebrae of each dog and the radiological abnormalities associated with wobbler disease scored, so that each dog could be assigned to one of three radiological groupings. Based upon a neurological examination, each animal was also placed into one of three neurological groupings. The relationship between radiological and neurological groupings and the independent variables was initially compared using a univariate and subsequently a multivariate analysis. It was found that 48.8% of the dogs investigated had some abnormal radiological sign associated with wobbler disease, and 32.0% of them showed neurological signs. Dogs with radiological signs of the disease were 5.56 times more likely to have neurological signs. Statistical analysis of the data indicated that more severe radiological and neurological abnormalities occurred in the older dogs. In addition, dogs located in Hawke's Bay region had less chance of showing radiological changes than dogs from the other two regions, Hamilton and Wellington. Twelve of the 32 puppies were examined for radiological and neurological changes over the first year of their life. No abnormalities were detected in puppies under 12 weeks of age, but 28% (n=9) of the 32 puppies over 3 months of age did show some radiological changes. Only 9% (n=3) of puppies showed any neurological signs. Although several pedigree lines were investigated, the lineage data were incomplete, and therefore there was no conclusive evidence that wobbler disease was an inherited trait. This study showed that, although the radiological signs of wobbler disease were present throughout a wide age range, the associated neurological changes tended to appear at a later age. In both instances, the severity of these changes increased with age.

Geographic information systems: their application in animal disease control

Geographic information systems (GIS) are computerised information systems that allow for the capture, storage, manipulation, analysis, display and reporting of geographically referenced data. They have been used in recent years for a wide variety of purposes, including town planning and environmental resource management. The technology has many features which make it ideal for use in animal disease control, including the ability to store information relating to demographic and causal factors and disease incidence on a geographical background, and a variety of spatial analysis functions. A number of possible veterinary applications are suggested, and three examples of the use of GIS in New Zealand are discussed.

Environmental and behavioural factors affecting the prevalence of foot lameness in New Zealand dairy herds — a case-control study

A case-control study of environmental and behavioural factors influencing foot lameness was undertaken on 62 dairy herds comprising an average of 185 milking cows in Taranaki, New Zealand. Thirty two case herds were identified as having had at least 10 per cent of the cows lame during the milking season in which the herd was studied, and thirty control herds were selected on the basis that no more than 3 per cent of cows in these herds had been lame per year for at least two years immediately prior to investigation. Each herd was visited at both a morning and an afternoon milking, and 58 risk factors were measured between the time the farmer began to assemble the cows for milking and the completion of milking. Comparison of single variables between case and control herds identified 24 which showed differences (p<0.10). These variables were then subjected to stepwise multivariate logistic regression, and statistically significant variables in this analysis were used to create a tentative path diagram of possible causal web relationships between the various risk factors and the outcome variable, the lameness prevalence level. Information from a review of the published literature was used to include further variables to the 24 into the initial (or null hypothesis) path model. Logistic path analysis was then used to eliminate non-significant paths from the diagram, leaving 19 arrows joining 13 variables in the final path diagram, compared with 33 joining 20 variables in the initial version. The most influential variables in explaining variation between case and control herds were the average level of maintenance of the track and the degree of patience shown by the farmer in bringing the cows in for milking. Overall, factors associated with the movement of animals to the milking shed explained 40 per cent of the variation (deviance) with regard to the lameness prevalence level. Risk factors associated with characteristics of the milking process explain 24 per cent, and risk factors associated with characteristics of the cows in the herd explain 9.5 per cent. Recommendations are made on management changes which deserve further investigation as ways of reducing lameness problems in dairy herds.