Ostertagia ostertagi antibodies in milk samples: Relationships with herd management and milk production parameters in two Mediterranean production systems of Spain

The present study analyzed Ostertagia ostertagi antibodies by indirect ELISA in milk samples in two cattle systems in Mediterranean Spain to indirectly monitor gastrointestinal nematode (GI) parasitism effects on production. Individual samples from 10 animals and the corresponding milk herd samples were collected from 133 herds in Girona (intensive management) and 123 herds in Minorca (extensive management). Both locations showed high and significant positive relationships between average optical density ratios (ODR) of individual animals and ODR in their milk tank. Although antibodies levels were low, there were significantly higher in Minorca. Negative correlations between ODR values and milk production were found in both systems. Importantly, in Minorca, average herd milk production was higher in the herds that treated their animals against GI nematodes compared to those that did not treat. The ELISA technique was valuable to indirectly assess differences in the level of GI nematode infection even in cattle production systems with low levels of infection.     

Milk antibodies against Ostertagia ostertagi: relationships with milk IgG and production parameters in lactating dairy cattle

The present study was carried out to evaluate the relationship between milk optical density ratios (ODRs) from an indirect Ostertagia ostertagi ELISA, total milk IgG levels and milk production and then establish a correction factor to adjust ODR. Five hundred and sixty composite milk samples collected from 358 cows on four dairy herds in June and August 2002 were used in this analysis. The average ODR was 0.34. A positive correlation was found between ODR and IgG values in milk, days in milk, age and log transformed somatic cell counts (SCC). However, ODR was negatively correlated with milk production. The IgG levels and ODR values were constant from 30 to 200 days in milk. However, ODRs increased from 200 days until the end of the lactation. After controlling for age, season, herd and SCC, an increase in milk production of 13 kg/day was associated with a reduction in ODR values of 0.052. The results of the present study suggest that ODR values are not greatly influenced by production factors. ODR follow the same pattern as the IgG variation across lactation and could be adjusted in order to compare ODR values obtained from high producing cows with those obtained from low producing animals.     

The use of an indirect Ostertagia ostertagi ELISA to predict milk production response after anthelmintic treatment in confined and semi-confined dairy herds

An indirect Ostertagia ostertagi ELISA was used in late lactation milk samples from cows in confined and semi-confined dairy herds to determine if it could predict milk production response after endectocide treatment at calving. Holstein cows from 9 dairy farms from Prince Edward Island (PEI), 5 from central Nova Scotia and 16 from southern Ontario that were participating in a clinical trial of endectocide treatment around calving were used in this study. The cows were randomly treated with either eprinomectin pour-on endectocide or a placebo solution. Milk samples were obtained from cows late in the lactation before treatment was applied. These samples were tested for antibodies to gastrointestinal nematodes (GIN) using the indirect ELISA with the results expressed as optical density ratios (ODR). Production records were obtained from a computerized database of dairy herd improvement data. Pre-calving ODR showed a seasonal pattern. They were higher in the summer and fall and lower during the winter months. Older animals had higher pre-calving ODR values compared with younger cows. Similarly, cows from semi-confined herds had higher parasite antibody levels compared with cows from confined herds. The endectocide treatment did not affect the milk production response in the overall study population. However, the interaction effect between treatment and pre-calving ODR on milk production response after endectocide treatment was significant (P = 0.02), with some evidence of positive treatment response in cows with an ODR > 0.4. The relationship between pre-calving ODR and production response appeared to be quadratic rather than linear.     

Association between anti-F. hepatica antibody levels in milk and production losses in dairy cows

This study was conducted to determine: (1) the associations between anti-Fasciola hepatica antibody levels in milk and some productive and reproductive parameters in dairy cattle, and (2) the threshold antibody level associated with loss of productivity, at both herd and individual level. Anti-F. hepatica antibodies were analysed by MM3-SERO ELISA in milk samples from the bulk tanks of 490 dairy farms and from 686 lactating cows. The results of general linear model analysis revealed a significant (P<0.05) negative association between the F. hepatica infection status at herd level, determined by analysis of specific antibodies in bulk tank milk, and the average herd milk production. Highly positive herds (MM3-SERO ELISA result>0.405) produced an average of 1.5 kg milk/cow per day less than the negative herds. At cow-level, the mixed model analysis also revealed a significant (P<0.05) association between anti-F. hepatica antibody levels and milk yield. A significant (P<0.05) average reduction of 2 kg milk/day was observed in cows with highly positive ELISA results (>0.762) in relation to cows with negative results. The results of the study led us to conclude that MM3-SERO ELISA is a powerful tool that can be successfully applied, if appropriate "economic thresholds" are established, to identify herds and cows suffering from milk production losses associated with natural infection by F. hepatica.     

A longitudinal survey of anti-Ostertagia ostertagi antibody levels in individual and bulk tank milk in two dairy herds in Normandy

The Ostertagia-specific antibody levels in milk were monitored in 2 dairy herds to investigate seasonal variations and the relationship between individual and bulk tank milk antibody levels. Bulk tank and individual milk samples from all lactating animals were collected over a 1-year period at weekly and monthly intervals, respectively. The Ostertagia-specific antibody levels were measured with an indirect ELISA and the test results were expressed as optical density ratios (ODR). A clear seasonal pattern that followed the expected intake of infectious larvae was observed in the individual and bulk tank milk antibody levels of both herds. Within each herd, there was a large variation in the individual ODRs. This variation remained large when the distribution of individual ODRs was plotted according to high and low bulk tank milk ODR categories. The results suggest that the effect of seasonal variations on cut-off levels that predict production responses after anthelmintic control, needs to be assessed.     

Effects of farm management practices and environmental factors on bulk tank milk antibodies against gastrointestinal nematodes in dairy farms across Canada

Enzyme-linked immunosorbent assays (ELISAs) have been used as a diagnostic tool to quantify levels of gastrointestinal nematodes in dairy cattle by measuring Ostertagia ostertagi antibodies in milk. Higher levels of O. ostertagi antibodies measured by ELISA methods, referred to as optical density ratios (ODRs), are associated with decreased milk production in dairy cattle. On-farm management practices (e.g. pasturing techniques and anthelmintic usage) can influence the exposure of cattle to nematode infections and the magnitude of acquired worm burdens. Additionally, environmental and climatic factors, such as land elevation and precipitation, may also influence the levels of gastrointestinal parasitism. This repeated cross-sectional study investigated the effect of farm management practices and surrounding environmental factors on bulk tank (BT) ODRs in herds from provinces across Canada, and further examined the potential effects of various anthelmintic treatment protocols on BT ODRs. A total of 195 herds contributed an average of 3.5 BT samples between December 2003 and April 2005. The farm management practices were recorded from a questionnaire asking producers about their pasturing methods (confined, pastured, etc.), pasture sharing practices (e.g. mixing heifers with milking cows) and anthelmintic treatments. Environmental data were downloaded online from various governmental databases (e.g. Natural Resources Canada, Statistics Canada, Environment Canada, etc.). Statistical models, accounting for repeated measures (multiple BT ODRs for each farm) and for clustering of farms within a region (province or ecoregion), were used to analyze environmental and farm management data. Overall, the greater the exposure that heifers and milking cows had to pasture, the higher the levels of anti-parasite antibodies detected in BT samples. Treating the entire herd or treating milking cows at calving reduced BT ODR values. Farms in areas with higher number of rainy days, higher normalized difference vegetation index (NDVI) values, and lower land surface temperatures (LSTs), were also likely to have higher BT ODRs. Seasonal variation was such that late summer and early fall, when parasite load was at its highest, yielded larger BT ODRs. Due to the high clustering effect at the herd level, factors at the herd level (e.g. pasturing methods, anthelmintic administration) had a higher potential impact on bulk-tank measurements than the herd's surrounding environmental factors.     

A survey to determine relationships between bulk tank milk antibodies against Ostertagia ostertagi and milk production parameters

In temperate climate regions, gastrointestinal nematodes are still widespread in adult dairy cows, but until now there exists no reliable diagnostic tool that can identify herds where the infection interferes with productivity. The objective of this study was to investigate the relationships between levels of antibodies against Ostertagia ostertagi in bulk tank milk and milk production. Bulk tank milk samples of 2553 dairy herds were obtained in spring and 2104 of these herds were sampled a second time in autumn. The antibody levels against O. ostertagi were determined with a milk ELISA and test results were expressed as an optical density ratio (ODR). The effect of bulk tank milk ODR on three different production parameters, kg milk, % and kg fat, % and kg protein was assessed by a multivariable linear regression model on the herds for which production data were available (n = 1063 and 867 in spring and autumn, respectively). The mean and standard deviation for ODRautumn (0.972+/-0.238) were higher than for ODRspring (0.825+/-0.201). Significant negative relationships were found between ODR and milk yield. An increase in ODRspring and ODRautumn from the 25th to the 75th percentile of the available ODR data was associated with a drop in the annual milk yield of 1.1 kg/cow/day, respectively 0.9 kg/cow/day. When a herd's ODR increased between spring and autumn with 0.142, it produced on average 0.4 kg/cow/day less in September than in April, in comparison with herds where the ODR did not increase. A significant negative association was found between ODRautumn and % protein averaged over the period of a year. No significant associations were found between ODR and % fat averaged over the year. When protein and fat production of September were expressed in kg an increase in ODRautumn from the 25th to the 75th percentile was associated with a decrease of 0.037 kg protein/cow/day and 0.042 kg fat/cow/day.     

The effect of repeated, four-weekly eprinomectin treatment on milk production in pasture-based, seasonally-calving dairy cattle

A randomised clinical trial from the North Island of New Zealand was conducted to assess the effect of repeated anthelmintic treatment on milk production, and to assess factors that affect treatment response. Nine hundred and twenty three multiparous, lactating dairy cattle from three pasture-based, spring-calving dairy herds were enrolled in this trial. Within each herd, cattle were stratified on age and calving date, and were randomly allocated to treatment (n=319) or control (n=604) groups. The treatment group received ≥0.05mg/kg of topical eprinomectin every 28 days for eight treatments during lactation. Pooled-milk from treated cows and bulk-milk samples were obtained at each treatment and analysed with an Ostertagia antibody ELISA, expressed as optical density ratios (ODR). Bi-monthly milk data were collected and expressed as energy-corrected milk (kg/day; ECM). A linear mixed model was used to analyse ECM, with cow as the random effect. The effect of anthelmintic treatment on days from calving, and start-of-mating, to conception were analysed with Cox-proportional hazard models. ODR values ranged from 0.6 to 1.3; there were no differences in ODR between herds (p=0.12), or between pooled-milk from treated cows and bulk-milk (p=0.26). Repeated treatments had no effect on daily ECM yields (p=0.74). However, there was a significant treatment×herd interaction (p=0.03); treatment increased ECM in one herd by 0.781kg/cow/day (p=0.015), but resulted in a non-significant decrease in the other two herds. A curvilinear interaction existed between days-in-milk and treatment response (p=0.039); the greatest treatment effect occurred during mid-lactation. Previous year milk production (p=0.46) and age (p=0.11) did not influence the effect of treatment on ECM. Treatment had no effect on any reproductive parameter. In conclusion, under New Zealand pastoral conditions, anthelmintic treatment increased milk production in one herd, but had no effect in two other herds. Further work is needed to identify why this variation in gastro-intestinal parasitism occurs.     

A survey of anti-Ostertagia ostertagii antibody levels in bulk tank milk samples (BTM) in dairy herds in Lower Silesia Region (Poland)

This work presents serological evidence of cattle ostertagiosis in the Lower Silesia Region (Poland), based on the measurement of antibodies in bulk tank milk (BTM) samples. It represents the first evidence of this parasite examined with the use of the ELISA test and milk samples in Poland. The prevalence of Ostertagia ostertagii antibodies was determined in BTM from 32 dairy cattle herds. Antibodies to O. ostertagii were demonstrated in all herds. The optical density ratio (ODR) varied from -0.088 to 1.024. The mean ODR value in the examined region was 0.53.     

Association between milk production, somatic cell count and bacterial dermatoses in three dairy cattle herds

OBJECTIVE: To determine the correlations between three bacterial dermatoses in cattle, milk production and bulk-milk somatic cell count (BMSCC). DESIGN: Field observations in three dairy cattle herds. METHODS: Milk production, BMSCC, fertility and all herd diseases were recorded by computerised dairy management systems. Each herd was visited twice weekly and the clinical signs, course of diseases and morbidity and culling rates were noted. Bulk-tank milk was sampled twice monthly and analysed for somatic cell count. Bacteriological and histological examinations were carried out from samples collected from affected animals in the respective herds. RESULTS: The acute exudative form of dermatophilosis was diagnosed only in first-calving cows. The morbidity rate was 53% and the culling rate was 16% of the affected animals. The BMSCC increased by a factor of 2.4 times, and there was an average loss of milk production of 30%/cow/day in affected animals. Ulcerative lymphangitis was diagnosed in first-calving cows (22%) and older cows (15%). The culling rate was 28%. The BMSCC increased by a factor of 17.3 times, and the average loss of milk production was 5.5%/affected animal/day. Papillomatous digital dermatitis (PDD) was diagnosed in first-calving cows (25%) and in older cows (18%). The culling rate was 8%. The BMSCC increased by a factor of two times, and the average loss of milk production was 1.7%/affected animal/day. CONCLUSIONS: The correlations between three skin diseases (ulcerative lymphangitis, dermatophilosis, papillomatous digital dermatitis), milk production and BMSCC have been found to be unfavourable.     

Anti-Neospora caninum antibodies in milk in relation to production losses in dairy cattle

A comprehensive field study was carried out with the following objectives: (a) to assess the usefulness of individual and bulk tank milk analysis for determining Neospora caninum serostatus in individual cows and herds, and (b) to study the associations between N. caninum infection status (based on milk testing), and several productive and reproductive parameters in the animals. Antibodies were detected with a commercially available ELISA test (Bio K 192/5). Analysis of paired serum and milk samples from 1134 lactating cows on 38 farms revealed that 97.6% of the ELISA results were coincident, irrespective of whether serum or milk samples were used. Moreover, multiple linear regression analysis revealed that 86.0% of the variations in ELISA values in milk were due to variations in the serum. The measurement of antibodies in bulk tank milk was a good estimator of the herd level status of N. caninum infection, and enabled detection of infection in 94.7% herds with ≥10.0% seropositive cows and/or in all herds with >4% highly seropositive cows. The odds ratio for abortion in seropositive animals was 9.1 times higher than in seronegative animals. The infection serostatus was also a significant risk factor, as the odds ratio for abortion was even higher (12.0 times) in cows categorized as highly seropositive. ELISA values for the bulk milk from 387 randomly selected herds were negatively associated with average milk production. Moreover, milk production losses mainly occurred on farms categorized as highly positive (i.e. herds with ≥20.0% seropositive cows).     

Neospora caninum serostatus and milk production of Holstein cattle

OBJECTIVE: To determine whether Neospora caninum serostatus was associated with milk production among Holstein cattle in Ontario. DESIGN: Case-control study and cross-sectional observational study. ANIMALS: 3,702 Holstein cows in 83 herds (case-control study) and 3,162 Holstein cows in 57 herds. PROCEDURE: Herds in the case-control study were grouped on the basis of N. caninum abortion status. Herds in the observational study were considered representative of Ontario dairy herds. The N. caninum serostatus of individual cows was determined with a kinetic ELISA. Milk production was modeled to compare seropositive with seronegative animals while controlling for parity, days since parturition, and herd clustering. RESULTS: In the case-control study, 305-day milk production of seropositive cows was significantly less than milk production of seronegative cows in herds with abortions attributable to N. caninum infection and in herds with abortions attributable to pathogens other than N. caninum, but not in herds without abortion problems. In the observational study, 305-day milk production for seropositive cows was not significantly different from milk production of seronegative cows. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the association between N. caninum serostatus and milk production in Ontario Holstein dairy cattle may depend on abortion status of the herd. In herds with abortion problems, regardless of cause, N. caninum-seropositive cattle produced less milk, whereas in herds without abortion problems, N. caninum-seropositive cattle produced the same amount of milk as seronegative cattle.     

A longitudinal study of gastrointestinal parasites in Canadian dairy farms. The value of an indirect Ostertagia ostertagi ELISA as a monitoring tool

The general objective of this study was to evaluate a crude Ostertagia ostertagi antigen enzyme-linked immunosorbent assay (ELISA) for monitoring gastrointestinal parasites in lactating dairy cattle. A longitudinal study of gastrointestinal parasites in lactating dairy cows was carried out in 38 herds in four provinces of Canada (Prince Edward Island, Quebec, Ontario and Saskatchewan) from September 1999 to October 2000. Bulk tank milk, cow milk, serum and fecal samples were collected monthly or quarterly from all these farms. Information on herd management factors was collected by a standard questionnaire and individual cow production data were obtained from an electronic database. The overall mean optical density ratio (ODR) was 0.30 and ranged from -0.05 to 1.55. Although a clear seasonal pattern was not observed, the ODR values tended to decrease during the housing period and start increasing in the spring before the cows went out to pasture. The second and third or greater lactation cows had significantly higher ODR values compared with first lactation animals. The individual cow ODR had a very low correlation with individual squared root fecal egg counts but showed a reasonably high correlation when herd averages values were computed (r=0.73). A moderate correlation (r approximately 0.50) between the bulk tank and herd average ODR was observed. Milk yield was negatively associated with individual cow milk ODR and a quadratic effect on ODR was observed for days in milk. Twenty-eight of the herds participated in a clinical trial of eprinomectin (Ivomec Eprinex) treatment at calving. The cow level ODR values determined late in the previous lactation had a marginally significant effect (P=0.07) on treatment response, suggesting that high OD cows responded better to the anthelmintic treatment. However, because of the small sample size available in this model, more research is needed to better understand this relationship. In conclusion, the indirect ELISA using an O. ostertagi crude antigen appears useful as a technique for monitoring gastrointestinal parasite burdens in adult dairy cows and holds promise as a potential predictor of response to anthelmintic treatment.     

Evaluation of an O antigen enzyme-linked immunosorbent assay for screening of milk samples for Salmonella dublin infection in dairy herds.

Levels of antibodies to the O antigens (O:1,9,12) of Salmonella dublin were tested in 1355 serum, 1143 cow milk and 160 bulk milk samples from dairy herds using an enzyme-linked immunosorbent assay (ELISA). In order to define the background reaction, milk samples from all lactating cows and serum samples from 9 animals were collected in each of 20 salmonellosis-free herds located on the island of Bornholm, where cattle salmonellosis has not been reported. Similar samples were collected from all stalled animals in 10 herds with recent (< 6 months) outbreaks of salmonellosis located in Jutland, where salmonella infection is enzootic. Using herd history of salmonellosis, herd location and clinical status of the herds as criteria, the optimal cutoff in the milk ELISA was determined as being at least 5% of the samples having optical density > 0.5, resulting in herd sensitivity of 1.0 and herd specificity of 0.95. While none of the sera in the herds from Bornholm was ELISA positive, 2 herds had a few reactors in the milk ELISA. Using the same cutoff, all but 1 bulk milk sample from 150 herds on Bornholm was ELISA-negative, and all 10 salmonellosis-positive herds from Jutland were ELISA-positive. A significant correlation was found between ELISA reactions in milk and in serum of cows (34% and 32% respectively, rs = 0.69, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Challenges for bovine viral diarrhoea virus antibody detection in bulk milk by antibody enzyme-linked immunosorbent assays due to changes in milk production levels

Background

Bovine viral diarrhoea (BVD) is considered eradicated from Denmark. Currently, very few (if any) Danish cattle herds could be infected with BVD virus (BVDV). The Danish antibody blocking enzyme-linked immunosorbent assay (ELISA) has been successfully used during the Danish BVD eradication program, initiated in 1994. During the last decade, the cattle herd size has increased while the prevalence of BVDV has decreased. In this study, we investigated how these changes could affect the performance of the Danish blocking ELISA and of the SVANOVIR^®BVDV-Ab indirect ELISA. The latter has successfully been used to eradicate BVD in Sweden.Data (2003–2010) on changes in median herd size and milk production levels, occurrence of viremic animals and bulk milk surveillance were analysed. Additionally, the Danish blocking ELISA and the SVANOVIR ELISA were compared analyzing milk and serum samples. The prevalence of antibody positive milking cows that could be detected by each test was estimated, by diluting positive individual milk samples and making artificial milk pools.

Results

During the study period, the median herd size increased from 74 (2003) to 127 cows (2010), while the prevalence of BVDV infected herds decreased from 0.51 to 0.02 %. The daily milk yield contribution of a single seropositive cow to the entire daily bulk milk was reduced from 1.61 % in 2003 to 0.95 % in 2010 due to the increased herd size. It was observed that antibody levels in bulk milk decreased at national level. Moreover, we found that when testing bulk milk, the SVANOVIR^®BVDV-Ab can detect a lower prevalence of seropositive lactating cows, compared to the Danish blocking ELISA (0.78 % vs. 50 %). Values in the SVANOVIR^®BVDV-Ab better relate to low concentrations of antibody positive milk (R² = 94-98 %), than values in the blocking ELISA (R² = 23–75 %). For sera, the two ELISAs performed equally well.

Conclusions

The SVANOVIR ELISA is recommended for analysis of bulk milk samples in the current Danish situation, since infected dairy herds e.g. due to import of infected cattle can be detected shortly after BVDV introduction, when only few lactating cows have seroconverted. In sera, the two ELISAs can be used interchangeably.     

Feasibility of serological bulk milk testing as a method for BVD surveillance

A commercial ELISA detecting antibodies against bovine viral diarrhoea Virus (BVDV) was analysed for its applicability for bulk-milk screening. Detection limits were analysed using native and concentrated milk samples (milk treated with rennet and ammonium sulfate precipitated) from 10 cows whose sera showed different reactivity levels in the ELISA and from two cows which gave birth to persistently infected calves during the last year. Further this and a second commercial ELISA were used to screen 591 randomly selected bulk-milk samples. To clarify discrepancies thirty-nine herds were included in a follow-up study. A second bulk-milk sample and serum samples from 10 young cattle of 6 to 28 month of age per herd were analysed for antibodies against BVDV. The results of this second testing and the detection of viremic animals in 4 herds confirmed the results from initial bulk-milk testing with both tests. The analysed test is suitable for bulk-milk testing although its application is limited by vaccination.     

Paratuberculosis sero-status and milk production,SCC and calving interval in Irish dairy herds

The objective of this study was to investigate the impact of paratuberculosis sero-status on milk yield, fat, protein, somatic cell count and calving interval in Irish dairy herds. Serum from all animals over 12 months of age (n = 2,602) in 34 dairy herds was tested for antibodies to Mycobacterium avium subsp. paratuberculosis using an ELISA. Herds were categorised by sero-status into positive, non-negative and negative, where a positive herd contained two or more positive cows, a non-negative herd contained only one positive cow and a negative herd contained no positive cows. Data at animal, parity and herd-level were analysed by multiple regression using general linear models. Positive herds (mean herd size = 129 cows) and non-negative herds (81 cows) were larger than negative herds (72 cows) (P < 0.01). Negative herds had the highest economic breeding index (EBI), while positive herds had the highest estimated breeding value (EBV) for milk yield. There was no significant effect of paratuberculosis sero-status at animal, parity or herd-level on milk yield, milk fat or protein production, somatic cell count score (SCCS) or calving interval. Negative herds tended to have a lower SCCS than positive and nonnegative herds (P = 0.087). This study only examined the effects of paratuberculosis sero-status but did not examine the clinical effects of Johne's disease at the farm or dairy industry levels.     

A bulk tank milk survey of Ostertagia ostertagi antibodies in dairy herds in Prince Edward Island and their relationship with herd management factors and milk yield

The objective of this study was to quantify the relationship of the levels of antibodies to Ostertagia ostertagi in bulk-tank milk samples from Prince Edward Island (PEI) dairy farms to milk production and to herd-management practices potentially related to gastrointestinal nematode infections. The milk samples were obtained from 289 to 322 dairy farms during 2000; production and management data were available from 197 and 200 farms, respectively. Cow exposure to pasture and whole-herd anthelmintic treatment were the only herd management variables significantly associated with antibody levels in the fall of 2000. An increase in antibody levels from the observed 25th percentile to the 75th percentile (interquartile range) was associated with a drop in milk production of 1.2 kg/cow/day. The results of this study indicate that the enzyme-linked immunosorbent assay for O. ostertagi antibody is a potentially useful technique to measure parasite exposure in adult dairy cows and that parasite burdens in lactating cattle in PEI have an important impact on milk production.     

Risk of removal and effects on milk production associated with paratuberculosis status in dairy cows

OBJECTIVE: To determine effects on production and risk of removal related to Mycobacterium avium subsp paratuberculosis (MAP) infection at the individual animal level in dairy cattle. DESIGN: Longitudinal study. ANIMALS: 7,879 dairy cows from 38 herds in 16 states. PROCEDURE: A subset of dairy cattle operations that participated in the National Animal Health Monitoring System Dairy 2002 study was evaluated via a serum ELISA for antibodies against MAP and categorized according to ELISA score. Dairy Herd Improvement Association records were obtained to collect current and historical lactation data and removal (ie, culling) information. Production variables were evaluated on the basis of serum ELISA category. RESULTS: Cows with strong positive results had mature equivalent (ME) 305-day milk production, ME 305-day maximum milk production, and total lifetime milk production that were significantly lower than cows in other categories. No differences were observed for ME 305-day fat and protein percentages, age, lactation, and lactation mean linear somatic cell count score between cows with strong positive results and those with negative results. After accounting for lactation number and relative herd-level milk production, cows with strong positive results were significantly more likely to have been removed by 1 year after testing. CONCLUSIONS AND CLINICAL RELEVANCE: Without management changes designed to reduce the farm-level prevalence of MAP infection, paratuberculosis will continue to reduce farm income by decreasing milk production and potentially increasing premature removal from the herd.     

Risk factors for herds to test positive for Mycobacterium avium ssp. paratuberculosis-antibodies with a commercial milk enzyme-linked immunosorbent assay (ELISA) in Ontario and western Canada

The objectives of this study were to identify risk factors associated with i) a Mycobacterium avium subsp. paratuberculosis (MAP)-antibody milk enzyme-linked immunosorbent assay (MAP milk ELISA)-positive herd status, and ii) the within-herd MAP milk ELISA-positive prevalence in Canadian dairy herds. This prospective cohort study was conducted between 2005 and 2009 on 226 herds in Ontario and western Canada, which participated in a voluntary risk assessment (RA)-based Johne’s disease control program. Two MAP milk ELISA and risk assessments and a previsit survey were available per herd. The overall farm RA scores alone could not be used to predict whether a herd would test positive for MAP antibodies. However, the results of this study indicated that increasing the likelihood of exposing calves to MAP through certain management practices, as assessed with the RA, increased the likelihood of a herd being test-positive for MAP antibodies.