Clinical findings of cows who originated from dairy herds with chronic wasting disease

Since Spring 1999, a number of dairy farms have reported problems with wasting in cattle. After calving, the physical condition of the cows deteriorated for reasons unknown. Chronic wasting is also associated with disorders such as lameness, abortion, endometritis, mastitis, and respiratory problems. Between April 1999 and March 2000, 19 cows were sent to the Faculty of Veterinary Medicine for further investigation of the chronic wasting. Clinical and pathological investigations resulted in a broad range of diagnoses such as mastitis, abomasal displacement, and claw disorders. The latter, characterised severe laminitis, were predominant and could explain a number of secondary symptoms (inflammation of the bursa, metastatic processes). There were no clear consistent changes compatible with a certain agent, with the exception of one case in which a virus was shown to be the causative agent. The results indicate that wasting disease is not a distinct entity but is characterized by a broad range of diseases in which acute laminitis may be the original problem. The disease profile of chronic wasting disease is very similar to that of 'concrete disease' described by Rebhun in 1995.     

Housing system and herd size interactions in Norwegian dairy herds; associations with performance and disease incidence

Background

According to the Norwegian animal welfare regulations, it has been forbidden to build new tie-stall barns since the end of 2004. Previous studies have shown that cow performance and health differ between housing systems. The interaction between housing system and herd size with respect to performance and disease incidence has not been evaluated.

Methods

Cow performance and health in 620 herds housed in free-stall barns were compared with in 192 herds housed in tie-stall barns based on a mail survey and data from the Norwegian Dairy Herd Recording and Cattle Health Systems. The housing systems herds were comparable with respect to herd size (15-55 cows). Associations between performance/disease incidence and housing system, herd size and year of building the cow barn were tested in general linear models, and values for fixed herd size of 20 and 50 cows were calculated. On the individual cow level mixed models were run to test the effect of among others housing system and herd size on test-day milk yield, and to evaluate lactation curves in different parities. All cows were of the Norwegian Red Breed.

Results

Average milk production per cow-year was 134 kg lower in free-stall herd than in tie-stall herds, but in the range 27-45 cows there was no significant difference in yields between the herd categories. In herds with less than 27 cows there were increasingly lower yields in free-stalls, particularly in first parity, whereas the yields were increasingly higher in free-stalls with more than 45 cows.In free-stalls fertility was better, calving interval shorter, and the incidence rate of teat injuries, ketosis, indigestions, anoestrus and cystic ovaries was lower than in tie-stalls. All of these factors were more favourable in estimated 50-cow herds as compared to 20-cow herds. In the larger herd category, bulk milk somatic cell counts were higher, and the incidence rate of mastitis (all cases) and all diseases was lower.

Conclusion

This study has shown that there is an interaction between housing system and herd size, and that performance and health is not universally better in small free-stalls than in tie-stalls.     

Management interventions in dairy herds: Exploring within herd uncertainty using an integrated Bayesian model

Knowledge of the efficacy of an intervention for disease control on an individual farm is essential to make good decisions on preventive healthcare, but the uncertainty in outcome associated with undertaking a specific control strategy has rarely been considered in veterinary medicine. The purpose of this research was to explore the uncertainty in change in disease incidence and financial benefit that could occur on different farms, when two effective farm management interventions are undertaken. Bovine mastitis was used as an example disease and the research was conducted using data from an intervention study as prior information within an integrated Bayesian simulation model. Predictions were made of the reduction in clinical mastitis within 30 days of calving on 52 farms, attributable to the application of two herd interventions previously reported as effective; rotation of dry cow pasture and differential dry cow therapy. Results indicated that there were important degrees of uncertainty in the predicted reduction in clinical mastitis for individual farms when either intervention was undertaken; the magnitude of the 95% credible intervals for reduced clinical mastitis incidence were substantial and of clinical relevance. The large uncertainty associated with the predicted reduction in clinical mastitis attributable to the interventions resulted in important variability in possible financial outcomes for each farm. The uncertainty in outcome associated with farm control measures illustrates the difficulty facing a veterinary clinician when making an on-farm decision and highlights the importance of iterative herd health procedures (continual evaluation, reassessment and adjusted interventions) to optimise health in an individual herd.     

Management of the dairy herd treated with bovine somatotropin

Cows that produce large quantities of milk require more management and higher quality of management than cows producing smaller quantities of milk. This is true whether improvements in milk production occur through genetic selection, increased milking frequency, or use of bovine somatotropin (bST). The milk response to use of bST is similar (10 to 15%) to that of three times a day (3x) milking and we expect that the management required to maintain the increased production through successive lactations with bST will be similar to that required for the 3x herd. Maximum economic benefit from use of bST will be achieved by dairy managers who (1) feed cows to maximize intake of diets with appropriate nutrient content and balance, (2) maintain proper body condition of their cows, and (3) have health and reproduction management programs that prevent rather than cure problems. Efficient use of record-keeping systems that enable the manager to monitor individual cow status will be advantageous. Economic forces will continue to bring change to the dairy industry. The manager that plans for change and ensures that the dairy's management programs allow for the most economically efficient production will be in position to adapt to these changes. The well-managed dairy will be able to adopt new, efficiency-enhancing technologies, such as bST, to ensure the continued opportunity to compete in the dairy industry.     

Immunohistochemical diagnosis of chronic wasting disease in preclinically affected elk from a captive herd.

An immunohistochemical (IHC) method was used to test brain tissues from 17 elk in a captive herd in which chronic wasting disease (CWD) had previously occurred. The IHC technique detects the protease-resistant prion protein (PrP-res), which is considered a disease-specific marker for transmissible spongiform encephalopathies (TSE), regardless of the species affected. Of the 17 elk tested, 10 were positive by IHC. Only 2 of these 10 animals had shown clinical signs and histologic lesions of CWD, and an additional animal had histologic lesions only. The most consistently IHC-positive tissue was medulla oblongata, especially the obex. These results show that the PrP-res IHC test on brain tissue, specifically medulla oblongata at the obex, should be considered an essential component of any surveillance study intended to determine the incidence of CWD in captive or free-ranging cervids.     

Database system for herd health management of dairy herds especially for udder health

Integrated herd health management is an effective method to improve animal health as mastitis and fertility disorders in dairy herds. For optimizing the costs and work load for the herd health management, it is necessary to have a data tool that enables a quick and comfortable data handling and provides practicable handouts for extension. The Research Institute of Organic Agriculture in Switzerland (FiBL) has developed such a database-system for the animal health management project "pro-Q". Objective of this database is to combine external available and on-farm collected data and to provide routine tools on herd and cow level (incl. udder quarter level) for farmers, veterinarians and advisers. These tools should give a comprehensive overview over the animal health situation of the herd and the single animal level. Furthermore, the database presented in this article, meets the requirements of a multi-user system with remote-access which enables different instances to gain the requested information.     

Comparative serologic and virologic study of commercial swine herds with and without postweaning multisystemic wasting syndrome

A comparative serologic and virologic study was performed in pigs from 5 herds with postweaning multisystemic wasting syndrome (PMWS) and 2 herds without PMWS in Quebec. In each herd, 60 blood samples were collected at 4-wk intervals from pigs from 3 to 23 wk of age. The serum was evaluated for the presence of antibodies to porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV), as well as for the presence of nucleic acid of PCV2, PRRSV, and porcine parvovirus (PPV), by means of the polymerase chain reaction (PCR). Serologic profiles for PCV2 were very similar in 6 of the 7 herds, including the 2 without PMWS, and were characterized by a gradual decrease in antibody titres from 3 until 11 wk of age, followed by seroconversion at 15 wk, and high PCV2 antibody titres thereafter in all pigs. Only starting at 11 to 15 wk of age could PCV2 viremia be detected, except in 1 herd, in which clinical signs were observed at 6 to 7 wk of age. A PCV2 viremia could be detected within the same pigs for a minimum of 8 wk, and the virus could still be detected in 41% of the serum samples obtained at 23 wk of age. The antibody level did not appear to influence the occurrence of disease, since titres were similar in pigs in the herds with or without PMWS. Infection with PRRSV, as demonstrated by PCR and seroconversion, preceded that of PCV2 by at least 1 mo in both types of herd. Both PRRSV and PCV2 were detected in some pigs in 5 of the 7 herds, including 1 herd without PMWS. Porcine parvovirus could be detected in serum by PCR in 2 herds with PMWS after the onset of clinical signs and also in 1 herd without PMWS. Genomic analysis of PCV2 strains identified in the herds without PMWS indicated complete or very high homology (99.4% to 100%) with the PCV2 strains identified in 4 herds with PMWS. In our field study, the triggering of PMWS in the herds could not be linked to coinfection with either PRRSV or PPV or to the use of a specific immunostimulant, such as vaccines, or to particular genomic differences between the PCV2 strains identified.     

Association of herd productivity and bulk-tank somatic cell counts in US dairy herds in 1996

OBJECTIVE: To assess the association of bulk-tank somatic cell counts (BTSCC) and the value of herd productivity (milk produced, calves born, and net costs for cow replacements) in US dairy herds in 1996. DESIGN: Randomized stratified national survey of dairy producers. SAMPLE POPULATION: Records from 1,219 dairy herds in the top 20 dairy states. PROCEDURE: Responses for 1,178 herds had complete information for economic analysis. Per-cow value of production was determined for each herd. Data for herds with high (> or = 400,000 cells/ml) and medium (200,000 to 399,999 cells/ml) BTSCC were compared with values for herds with low BTSCC (< 200,000 cells/ml), using a multivariable regression model. RESULTS: In 1996, milk was priced at $0.287/kg ($13/cwt). Herds with low BTSCC annually generated $103.90/cow more in herd productivity than herds with medium BTSCC and $292.39/cow more than herds with high BTSCC. CONCLUSIONS AND CLINICAL RELEVANCE: Increased BTSCC (> 200,000 cells/ml) were associated with a reduced value of productivity per cow. Thus, dairy producers have a financial incentive to seek out and implement cost-effective management practices that will enable them to decrease their BTSCC to < 200,000 cells/ml and maximize herd productivity.     

Effect of pathogen-specific clinical mastitis on herd life in two New York State dairy herds

The objective of this study was to estimate the effects of clinical mastitis (CM) (both with and without specific pathogen identification) occurring in different stages of lactation on length of herd life in two New York State dairy farms. The 2,697 cows in the study were followed for one lactation (the first-occurring one on or after 1 October 1999), until it ended because of a new lactation, culling, or end of study (31 March 2001 in one farm; 31 July 2001 in the other). A Cox proportional hazards model with time-dependent covariates, in SAS((R)), was used to measure, within a lactation, the effect of the first occurrence of CM (without specific pathogen identification) occurring 1--7, 8--66, 67--100, 101--225, or >or=226 days in milk (DIM), on how long cows remained in the herd. For the first occurrence of CM due to Streptococcus spp., Staphylococcus aureus, Staphylococcus spp., Escherichia coli, Klebsiella spp., and 'no pathogen isolated', the intervals were before and after the median DIM of first occurrence of each pathogen. There were too few cases due to Arcanobacterium pyogenes, and 'other pathogens grouped together' to split into intervals, so they were modeled as binary variables, i.e. as they occurred. CM was modeled using time-dependent covariates, to account for its differing effects throughout lactation on culling. Other variables controlled for were herd, parity, calving season, and other significant diseases. In the dataset, the lactational incidence risk of the first occurrence of CM was 18.2%; 20.0% of the cows did not survive the lactation that was studied. The overall annual culling percentage for both herds during the study period (including all cows, whether eligible for the study or not) was 35.6%. For cows with CM without pathogen identification, their highest hazard ratio (HR) of culling occurred from 67 to 100 DIM. All of the pathogens modeled markedly reduced herd life. On average over the entire lactation, cows with Staphylococcus spp. CM had the highest HRs for culling, although there were no significant differences among pathogens (at p=0.0018 (reflecting 28 pairwise comparisons)). For early-occurring (before median DIM of first occurrence) S. aureus CM, the daily rate of change of the HR of culling increased over time. The HRs for culling were particularly high for late-occurring (after median DIM of first occurrence) E. coli and Klebsiella spp. CM early in the interval, but the daily rate of change of the hazard of culling for these two pathogens decreased sharply over time. Treating CM as time-dependent therefore allowed us to measure in greater detail, its varying effects (of when it occurred) on herd life.     

Disposal and disease rates in 340 British dairy herds

Data derived from 340 dairy herds, mainly in southern England, between April 1998 and March 1999, showed that the average total culling rate was 22.1 per cent, with 5.6 per cent for infertility, 3.6 per cent for mastitis, 1.7 per cent for lameness, 2.0 per cent for poor milk yield, 3.7 per cent for age and 5.5 per cent for miscellaneous reasons which included death. The average annual rate of assisted calvings was 8.7 per cent, of injury 0.9 per cent, digestive disease 1.3 per cent ketosis 0.4 per cent, hypomagnesaemia 0.7 per cent, hypocalcaemia 5.3 per cent, mastitis 36.6 per cent, and lameness 23.7 per cent. There was a significant association (P<0.001) between higher rates of mastitis in cows housed in straw yards as opposed to cubicles and also between higher rates of lameness in cows housed in cubicles as opposed to yards (P<0.015). However, there were farms with low rates of mastitis in cows kept in straw yards and low rates of lameness in cows kept in cubicles. Larger herds tended to have more problems with lameness and higher bulk milk somatic cell counts (BMSCC). There was a positive association between BMSCC and mastitis rate.     

An outbreak of mucosal disease in a dairy herd

An outbreak of mucosal disease (MD) was studied in a dairy herd, comprising 12 cows, 9 heifers and 18 calves. During a period of 1 month, six 5 to 8 month-old calves showed typical signs of MD. They all died or were killed in extremis after 2-8 days with progressively worsening clinical signs. Post mortem lesions were examined in one calf. Non-cytopathogenic MD virus was isolated from serum or tissues from 3 clinically affected calves and from 1 healthy heifer. All cows and heifers except for the viremic one possessed neutralizing antibodies against bovine pestivirus. According to the current MD-pathogenesis concept, the affected calves were probably infected transplacentally during the first half of foetal life with pestivirus from the persistently infected heifer in the herd.     

Possibilities for further research of chronic wasting in dairy cows

In this study, we reviewed the research that has been conducted in relationship with the problem of 'chronic wasting' in dairy cows in the Netherlands as was experienced during 1998 and 1999. Emphasis was drawn towards three aspects of this 'chronic wasting'; the definition, the magnitude, and the possible cause or causes. It appeared that a clear, objective definition of 'chronic wasting' in cows, and of farms with a problem of 'chronic wasting' cows is still lacking. Furthermore, the incidence (of the problem) was restricted to approximately 150 dairy farms at most. Currently, no farms with 'chronic wasting' cows are known. Combined with the uncertainty in the definition, this will hamper future research. Many of the studies were related to the hypothesis that the vaccination with the BHV1 marker vaccine had caused 'chronic wasting' in the cows. None of the results, however, substantiated this hypothesis. Other possible causes have hardly been investigated and further research would be needed to evaluate the role of nutrition, infectious agents, and genetics. However, due to the waning of the phenomenon, the availability of data and controls will be limiting.     

Management of calving in Norwegian cubicle-housed dairy herds.

Sixty of the 65 dairy farms with cubicle houses in the Norwegian county of Oppland were included in a field study of the management of calving in 1990. The farmers recorded the location of the cow when giving birth, farmer presence and whether assistance was given during calving, occurrence of suckling, and time after birth when cow and calf were separated. Such data were recorded for a total of 1125 calvings. About 10% occurred on pasture, while 78% of the remaining calvings took place in the cubicle-equipped section. Thirteen percent calved in a calving pen, the remaining cows being tethered at the time of calving. Thirty-two percent of the calvings took place in houses lacking a calving pen altogether. Farmers were present during 41% of the calvings. Suckling most frequently occurred after pasture calvings, and was least frequent after calvings within the cubicle-equipped section of the cowhouse. Injuries to the calf caused by trampling or contact with fittings etc. were rare, and no more common in association with calving in the cubicle-equipped section than with calving taking place with the cow isolated from the rest of the herd. All calves were removed from their dams within 24 h after birth.     

Some aspects of reproductive performance in selected town-supply dairy herds

Breeding and production data were collected from 20 town-supply dairy herds in the Manawatu/Horowhenua region. Calving interval, calving to first service interval, first service to conception interval, inter-service interval, calving rate to first service and services per cow calving were 384, 85, 11, 43 days, 51% and 1.7, respectively, for the pooled population of 12, 056 calvings. The mean milk yield was 3730 litres per cow and the mean lactation length 291 days. Age, herd, season within year, and year, had statistically significant effects on reproductive performance, although the amount of variation due to these variables was small. The younger cows (2-year-olds) were relatively poor performers. Reproductive performance was best during the spring. Days from calving to first service, and from first service to conception, were of similar importance in determining differences in calving interval. A high incidence (25%)of return intervals of more than 49 days was found between first and second service. It was concluded from the data that a programme for breeding each cow as she comes into oestrus 46–66 days post-partum is a simple and appropriate procedure for achieving a 365-day calving interval. Such a programme is more likely to be successful if continued attention is paid to both heat-detection procedures and the nutritional requirements of animals during rearing, late pregnancy and early lactation, and if routine pregnancy testing 6 to 8 weeks after service is used to recognise the problems of post-service anoestrus.     

Eradication of paratuberculosis in dairy herds: determination of the initial herd prevalence and modelling of prevalence development

A prerequisite for the success of any eradication programme is the accurate determination of the initial herd prevalence as well as a herd-specific prediction of prevalence development. This prerequisite is not currently given for the eradication of paratuberculosis in infected herds. In the work presented a method to predict the initial paratuberculosis prevalence in infected herds is presented; it is based on the formation of two groups (ELISA-positive and negative) and the determination of generally applicable factors (positive predictive value [ppvn] of the ELISA and sensitivity of fecal culture in the ELISA-negative group [senF]). The ppvn of the ELISA was determined to be 0.6 based on the cultural examination of the ileocaecal lymph node of 64 ELISA-positive animals; the value for senF was set to be 0.64 based on the cultural examination of feces and ileocaecal lymph nodes of 40 ELISA-negative animals. To calculate the initial herd prevalence the number of animals in each of the groups was multiplied with the ppvn of the ELISA or with the reciprocal value of senF (1.5). The values were added and divided by the size of the herd. The practicability of this model was examined on nine herds with a total of 708 animals. The development of herd prevalence was modelled based on the examination scheme given in the paratuberculosis control programme of the "Nieders?chsische Tierseuchenkasse" (local board for infectious disease control in food animals in the state of Lower Saxony, Germany). For the calculation a yearly turnover-rate of 33% with restocking from within the herd and a possibility of paratuberculosis diagnosis only in animals two years and older were assumed. The development of herd prevalence is exemplarily presented for four herds with different initial prevalences.     

A prion disease of cervids: chronic wasting disease

Chronic wasting disease (CWD) is a prion disease of deer, elk, and moose, initially recognized in Colorado mule deer. The discovery of CWD beyond the borders of Colorado and Wyoming, in Canada and as far east as New York, has led to its emergence as a prion disease of international importance. Epidemiological studies indicate that CWD is horizontally transmitted among free-ranging animals, potentially indirectly by prion-containing secreta or excreta contaminating the environment. Experimental CWD transmission attempts to other wild and domestic mammals and to transgenic mice expressing the prion protein of cattle, sheep, and humans have shed light on CWD species barriers. Transgenic mice expressing the cervid prion protein have proven useful for assessing the genetic influences of Prnp polymorphisms on CWD susceptibility. Accumulating evidence of CWD pathogenesis indicates that the misfolded prion protein or prion infectivity seems to be widely disseminated in many nonneural organs and in blood. This review highlights contemporary research findings in this prion disease of free-ranging wildlife.     

Using on-farm records to evaluate the reproductive performance in dairy herds

The designated abolition of the European milk quota system on April 1st 2015 is expected to have tremendous effects on the business environment on most dairy farms. Meanwhile farmers should use weak-point analyses to identify "bottlenecks" within their production and herd management system. As experts in herd health and herd performance, veterinarians should give advice to their clients based on sound analyses of production data. Therefore, accurate and reliable on-farm records are needed. This paper will focus on data management, especially data collection, and will address the concepts of evaluation of reproduction records.     

Use of dairy herd improvement monthly summary data to monitor intervention strategies in a dairy herd experiencing suboptimal reproductive performance and reduced milk production

An 87-cow dairy herd with a history of high milk production was visited because of reduced reproductive performance and decreasing milk production. Cows that had recently delivered calves were thin, and many cows had evidence of previous episodes of laminitis. A ration that provided an unfavorable forage-to-concentrate ratio was being fed. In addition to various diagnostic efforts, management changes that were made included alteration of the ration and installation of a computer-operated feeder. After the initial visit, the herd was monitored for 30 months by the use of Dairy Herd Improvement monthly herd summary data. Several potential strengths and weaknesses of using selective production and reproduction monthly summary statistics were illustrated by this study. Milk production, as monitored by mature-equivalent production and average relative value-milk, continued to increase throughout the 30 months after intervention. Reproductive performance, as indicated by first-service conception rate, did not begin to improve until the final 6 months of the monitoring period. Overall, in addition to assisting in diagnostic efforts. Dairy Herd Improvement monthly herd summary data may be used to establish goals, provide comparisons, and maintain producer interest after practitioner intervention in herd management.