Dairy management practices associated with multi-drug resistant fecal commensals and Salmonella in cull cows: a machine learning approach.

BACKGROUND: Understanding the effects of herd management practices on the prevalence of multidrug-resistant pathogenic Salmonella and commensals Enterococcus spp. and Escherichia coli in dairy cattle is key in reducing antibacterial resistant infections in humans originating from food animals. Our objective was to explore the herd and cow level features associated with the multi-drug resistant, and resistance phenotypes shared between Salmonella, E. coli and Enterococcus spp. using machine learning algorithms. METHODS: Randomly collected fecal samples from cull dairy cows from six dairy farms in central California were tested for multi-drug resistance phenotypes of Salmonella, E. coli and Enterococcus spp. Using data on herd management practices collected from a questionnaire, we built three machine learning algorithms (decision tree classifier, random forest, and gradient boosting decision trees) to predict the cows shedding multidrug-resistant Salmonella and commensal bacteria. RESULTS: The decision tree classifier identified rolling herd average milk production as an important feature for predicting fecal shedding of multi-drug resistance in Salmonella or commensal bacteria. The number of culled animals, monthly culling frequency and percentage, herd size, and proportion of Holstein cows in the herd were found to be influential herd characteristics predicting fecal shedding of multidrug-resistant phenotypes based on random forest models for Salmonella and commensal bacteria. Gradient boosting models showed that higher culling frequency and monthly culling percentages were associated with fecal shedding of multidrug resistant Salmonella or commensal bacteria. In contrast, an overall increase in the number of culled animals on a culling day showed a negative trend with classifying a cow as shedding multidrug-resistant bacteria. Increasing rolling herd average milk production and spring season were positively associated with fecal shedding of multidrug- resistant Salmonella. Only six individual cows were detected sharing tetracycline resistance phenotypes between Salmonella and either of the commensal bacteria. DISCUSSION: Percent culled and culling rate reflect the increase in culling over time adjusting for herd size and were associated with shedding multidrug resistant bacteria. In contrast, number culled was negatively associated with shedding multidrug resistant bacteria which may reflect producer decisions to prioritize the culling of otherwise healthy but low-producing cows based on milk or beef prices (with respect to dairy beef), amongst other factors. Using a data-driven suite of machine learning algorithms we identified generalizable and distant associations between antimicrobial resistance in Salmonella and fecal commensal bacteria, that can help develop a producer-friendly and data-informed risk assessment tool to reduce shedding of multidrug-resistant bacteria in cull dairy cows.

Understanding the transmission dynamics of Escherichia coli O157:H7 super-shedding infections in feedlot cattle.

BACKGROUND: The presence of Escherichia coli O157:H7 (E. coli O157:H7) super-shedding cattle in feedlots has the potential to increase the overall number (bio-burden) of E. coli O157:H7 in the environment. It is important to identify factors to reduce the bio-burden of E. coli O157 in feedlots by clarifying practices associated with the occurrence of super-shedders in feedlot cattle. METHODS: The objective of this study is to (1) identify host, pathogen, and management risk factors associated with naturally infected feedlot cattle excreting high concentrations of E. coli O157:H7 in their feces and (2) to determine whether the ingested dose or the specific strain of E. coli O157:H7 influences a super-shedder infection within experimentally inoculated feedlot cattle. To address this, (1) pen floor fecal samples and herd parameters were collected from four feedlots over a 9-month period, then (2) 6 strains of E. coli O157:H7, 3 strains isolated from normal shedder steers and 3 strains isolated from super-shedder steers, were inoculated into 30 one-year-old feedlot steers. Five steers were assigned to each E. coli O157:H7 strain group and inoculated with targeted numbers of 102, 104, 106, 108, and 1010 CFU of bacteria respectively. RESULTS: In the feedlots, prevalence of infection with E. coli O157:H7 for the 890 fecal samples collected was 22.4%, with individual pen prevalence ranging from 0% to 90% and individual feedlot prevalence ranging from 8.4% to 30.2%. Three samples had E. coli O157:H7 levels greater than 104 MPN/g feces, thereby meeting the definition of super-shedder. Lower body weight at entry to the feedlot and higher daily maximum ambient temperature were associated with increased odds of a sample testing positive for E. coli O157:H7. In the experimental inoculation trial, the duration and total environmental shedding load of E. coli O157:H7 suggests that the time post-inoculation and the dose of inoculated E. coli O157:H7 are important while the E. coli O157:H7 strain and shedding characteristic (normal or super-shedder) are not. DISCUSSION: Under the conditions of this experiment, super-shedding appears to be the result of cattle ingesting a high dose of any strain of E. coli O157:H7. Therefore strategies that minimize exposure to large numbers of E. coli O157:H7 should be beneficial against the super-shedding of E. coli O157:H7 in feedlots.

Bayesian estimation of diagnostic accuracy of fecal culture and PCR-based tests for the detection of Salmonella enterica in California cull dairy cattle.

Epidemiological studies of low prevalence disease problems are often hindered by the high cost of diagnostic testing. The objective of this study was to evaluate PCR screening of both individual and pooled fecal samples from culled dairy cows for the invA gene of Salmonella followed by culture to determine if the sensitivity and specificity were comparable to the results from traditional culture methods applied to individual samples. Cows from six different dairies were sampled in all four seasons. A total of 240 individual cow fecal samples, 24 fecal pools and 24 pools of 24-hour tetrathionate enrichment broth were tested. Diagnostic sensitivity of PCR screening followed by culture of PCR positive or indeterminate samples (i.e PCR-CUL method) was lower than that of culture (CUL) when applied to individual fecal samples (94.8%, 99.5%), however the specificity was comparable (99.6% and 97.7% respectively). For pools of five fecal samples and pools of five, 24 h tetrathionate broth samples, the specificity of both tests were comparable (∼98%); however, their sensitivity was only comparable in pooled fecal samples (∼93%) but greater for culture compared to PCR-CUL in pooled broth samples (∼99% versus ∼93%). Compared to culture results from testing of individual fecal samples, testing pooled fecal samples by culture had a relative sensitivity of 74% and relative specificity of 96%, testing pooled fecal samples by PCR-CUL resulted in relative sensitivity of 90% and relative specificity of 96%. Testing of pooled 24-hour enrichment broth by PCR-CUL increased the relative sensitivity and specificity to 100%. PCR testing followed by culture of positive or indeterminate samples is a time saving alternative to traditional methods. In addition, pooling of samples may be a useful method for decreasing cost if study aims can accommodate a moderate loss of relative sensitivity.

Bovine cardiac mesothelial hyperplasia: a common incidental finding in adult cattle.

Cardiac mesothelial hyperplasia forming pale plaque lesions on the epicardial surface is a common incidental finding in the hearts of aged humans. A similar phenomenon with a more papillary appearance has also been reported as an incidental finding in dogs and mice. These lesions are believed to occur in response to friction between the epicardium and overlying pericardium. We investigated this lesion in adult cattle, a phenomenon that has been associated with bovine leukemia virus infection and epicardial lymphoma. We examined 73 hearts from adult cattle, predominantly of dairy breeds: 53 from a rendering facility and 20 from a state diagnostic laboratory. Cardiac mesothelial hyperplasia was much more prevalent in cattle than in other reported species (97% of examined hearts). The most common distribution was overlying the great vessels in a dark red papillary pattern. Cardiac mesothelial hyperplasia was also variably observed on all 4 cardiac chambers and the pericardium. Occasionally these lesions took on a smooth plaque-like appearance resembling those observed in humans. The lesions varied from 0.25 cm2 to covering 90% of the epicardial surface. No association was observed between cardiac mesothelial hyperplasia and bovine leukemia virus infection or cardiac lymphoma. Cardiac mesothelial hyperplasia was a common incidental finding in bovine hearts that must be distinguished from neoplasia and acute or chronic inflammation.

Environmental sampling to assess the bioburden of Mycobacterium avium subspecies paratuberculosis in drylot pens on California dairies.

Mycobacterium avium subspecies paratuberculosis (MAP) is a bacterium that can cause substantial economic losses in infected dairy herds due to reduced milk production and increased cow-replacement costs. In order to control MAP in dairies with drylot pens, a standardized environmental sampling protocol to quantify MAP in fecal slurry was developed based on an existing protocol for freestall pens. Specifically, following a 24 h hold of the flush, a grab sample of approximately 10 ml of fecal slurry was collected every 1 m along the flush lane of the drylot pens, avoiding individual cow fecal pats. To determine the reliability and repatability of the new environmental sampling protocol for estimation of MAP bioburden at the pen level, two collectors simultaneously collected fecal slurry samples every day for 3 days from six drylot cow pens on two Central California dairies. During the study period no cow movement between pens was allowed with the exception of sick cows. The study herds had MAP seroprevalence of 5.8% and 3.2%, respectively, based on whole pen serum ELISA results. Variance components models for quantitative real-time PCR (qPCR) results showed samples collected from different pens on different dairies accounted for greater variablitiy in MAP concentration (65%), while samples collected by different collectors had the least variability (0.1%). In contrast, variability in MAP concentration in environmental samples collected on different days had 25% variability. The intraclass correlation coefficient showed high reliability (93%) of environmental sampling simultaneously by different collectors. In contrast, the reliability of environmental sampling at different days was 65%, which was similar to the reliability for sampling by different collectors on different days. Investigators can expect high reliability when employing the new environmental sampling protocol along with qPCR testing of environmental samples from drylot pens.

Association between herd management practices and antimicrobial resistance in Salmonella spp. from cull dairy cattle in Central California.

BACKGROUND: In this study cull dairy cows from six California dairy herds were sampled seasonally over the course of a year. The objectives were to determine the prevalence of antimicrobial resistant (AMR) Salmonella spp. shed in cull cow feces, and the factors associated with fecal shedding of AMR and multidrug resistant (MDR) Salmonella. METHODS: Six dairy farms located in the San Joaquin Valley of California were identified and enrolled as a convenience sample. On each dairy, and once during each of the four seasons, 10 cull cows were randomly selected for fecal sampling on the day of their removal from the herd. In addition, study personnel completed a survey based on responses of the herd manager to questions related to the previous 4 month's herd management and the specific cattle sampled. Fecal samples were submitted to the California Animal Health and Food Safety laboratory for Salmonella isolation. Antimicrobial resistance was evaluated using broth microdilution method and a gram-negative assay plate following Clinical Laboratory Standards Institute (CLSI) guidelines and breakpoint references. All statistical models were survey adjusted for number of animals on sampling day. RESULTS: A total of 62 Salmonella were isolated from 60 of the 239 fecal samples collected. For 12% (95% confidence interval (CI) [3-20]) of fecal samples a multidrug resistant Salmonella was isolated. The survey-weighted results for the two most common drug classes for which isolates were resistant were tetracycline (39%; 95% CI [27-51]) and ampicillin (18%; 95% CI [9-27]). An important finding was the identification of cephalosporin as the third most common drug class for which isolates were resistant, with ceftriaxone (10%; 95% CI [2-17]) being the most common drug associated with resistance in that class. At the cow-level, reason for culling, prior treatment with antimicrobial drugs as the reason for culling was associated with higher odds of isolating an AMR Salmonella isolate. At the herd-level, percent of animals monthly culled on the farm as well as number of milking cows in the herd were associated with isolation of antimicrobial resistant Salmonella in cull cows. DISCUSSION: Salmonella isolated from fecal samples from cull cows were resistant to important antimicrobials, such as ceftriaxone. The most common drug classes for which isolates were resistant were tetracyclines and beta-lactams, with ampicillin, ceftriaxone and ceftiofur being the three most common drugs within the latter. Cow and herd level factors were associated with isolating antimicrobial resistant Salmonella that should be further investigated for their potential role in promoting occurrence of AMR Salmonella. Our results also highlight the importance of monitoring dairy cattle sent to slaughter for shedding of Salmonella resistant to medically important antimicrobial drugs.

Avian pulmonary proteinosis: six cases and a review of the literature.

Pulmonary alveolar proteinosis (PAP) is a disease of surfactant clearance in which functional abnormalities in alveolar macrophages lead to accumulation of surfactant within alveoli in mammals. Histologic examination of 6 avian autopsies, including 4 chickens, a turkey, and a cockatiel, revealed accumulation of hypereosinophilic densely arrayed lamellar material in the lungs that was magenta by periodic acid-Schiff stain and diastase resistant. Transmission electron microscopy of the proteinaceous material in 2 cases demonstrated alternating electron-dense and electron-lucent lamellae that formed whorls and had a regular periodicity of 6-14 nm, consistent with pulmonary surfactant. Given the anatomic differences between avian and mammalian lungs, we designated the presented condition "pulmonary proteinosis," which can be observed as both an incidental finding or, when severe, may be a contributing factor to death through respiratory failure.

Polycystic liver in two adult llamas.

Polycystic liver is usually considered an incidental finding in human and veterinary medicine. Two unrelated adult llamas ( Lama glama) with a history of marked anorexia and weight loss were received for autopsy and diagnostic workup. The main gross change in the liver of both animals was multiple variably sized cysts randomly distributed throughout the parenchyma. Histologically, the cysts compressed the adjacent parenchyma and were lined by a single layer of cuboidal-to-columnar epithelium, surrounded by a fibrous collagen capsule. The lumen of the cysts contained finely granular-to-homogeneous basophilic material. The lining epithelium displayed strong immunoreactivity for pancytokeratin AE1/AE3 and cytokeratins 7, 8, 8/18, and 19, and was negative for vimentin, confirming the biliary epithelial origin of the cysts. No parasitic or infectious agents, or neoplastic changes, were detected. All other laboratory tests performed in both llamas were negative or non-diagnostic, suggesting that the congenital hepatic cysts described may have been at least partly responsible for clinical disease in both animals.

Pathology of blackleg in cattle in California, 1991-2015.

Blackleg is an infectious disease of cattle and rarely other ruminants, produced by Clostridium chauvoei and characterized by necrotizing myositis. In most cases of blackleg, the large muscles of the pectoral and pelvic girdles are affected, with other skeletal muscles and the heart involved less frequently. We studied 29 blackleg cases selected from the archives of the California Animal Health and Food Safety Laboratory, 1991-2015. Immunohistochemistry was also evaluated to detect C. chauvoei in formalin-fixed, paraffin-embedded (FFPE) tissues of cattle. Nineteen animals had gross and/or microscopic lesions in both skeletal muscle and heart, 9 had lesions in the skeletal musculature alone, and 1 in the heart alone. Gross lesions in the skeletal musculature involved the following muscle groups: hindquarters ( n = 8), forequarters ( n = 5), neck ( n = 5), lumbar area ( n = 3), brisket ( n = 2), diaphragm ( n = 2), abdominal wall ( n = 1), thoracic wall ( n = 1), and tongue ( n = 1). Of the 20 animals that had lesions in the heart, 11 had pericarditis and myocarditis; 7 had pericarditis, myocarditis, and endocarditis; and 1 each had pericarditis and myocarditis. Immunohistochemistry was 100% sensitive to detect C. chauvoei in FFPE skeletal muscle and/or heart of cattle with blackleg. Simultaneous lesions in skeletal musculature and heart were relatively common in blackleg cases in California; the most affected skeletal muscles were those of the hindlimbs.

Multiple episodes of 1080 (sodium monofluoroacetate) intoxication in a California calf-raising operation.

Over a 1-y period, a California calf-raising operation experienced 4 separate episodes of sudden death in 4-6-mo-old steers. Each episode occurred in 1-3 contiguous pens on 1 of 3 properties owned by the operation, but eventually all 3 properties were involved. In each episode, animals appeared normal at the evening feeding but at the subsequent morning feeding were found dead or dying. Remaining live calves had a stiff gait and were often dribbling urine, but did not show respiratory signs until they were down and agonal. At postmortem examination, calves consistently had moderate-to-large numbers of ecchymotic and suffusive hemorrhages on the epicardial surface and moderate-to-large amounts of fluid in the pericardial sac. Pulmonary edema and/or moderate amounts of watery fluid in the thoracic and abdominal cavities were present in a smaller percentage. On histologic examination, the myocardium had variable myofiber degeneration characterized by hypereosinophilia and fragmentation with mild interstitial infiltrates. Testing of heart and liver samples for monensin found levels lower than in previous cases of monensin toxicity. Rumen content was negative for oleandrin and grayanotoxins. Sodium monofluoroacetate (trade name: 1080) was consistently detected at ⩾10 ppb in kidney and liver, and was concluded to be the cause of the intoxication.

Parapoxviral vulvovaginitis in Holstein cows.

A group of Holstein first-calved heifers developed small pustules and ulcers on the vulva and in the vagina during the first 1-4 wk postpartum. The lesions varied from small red pinpoint foci to pustules and ulcers, 3-5 mm diameter. Some ulcers coalesced to form large ulcerated areas up to 15 mm diameter. In some animals, these ulcers progressed to become deep ulceration of the vaginal and vulvar mucosa with >50% of the mucosa involved. Vaginal biopsies from 4 heifers and vaginal individual swabs from 8 heifers for a combined sampling of 9 heifers were taken for clinical assessment. Six of the 9 heifers had parapoxvirus based on histopathology and/or PCR. Histologic examination of the biopsies of the pustules identified ballooning degeneration of the epithelium with degenerate epithelium containing eosinophilic intracytoplasmic inclusions consistent with a parapoxvirus in 3 of 4 biopsies. Testing for bovine herpesvirus 1, 2, and 4, bovine viral diarrhea virus, bovine papular stomatitis virus, and orf virus remained negative.

Cecal infarction in neonatal calves.

Cecal infarction is an uncommon lesion in calves that results in localized peritonitis and, on occasion, perforation with secondary diffuse peritonitis and death. This lesion in calves has not been described previously. We reviewed the postmortem cases of cecal infarction in dairy calves ≤30 d of age that had been submitted over the course of 5 y to the Tulare branch of the California Animal Health and Food Safety Laboratory System. The area of cecal infarction and the associated lesion margins were examined histologically. Ischemic necrosis of the mucosal side of the cecal wall with various degrees of neutrophilic inflammation of subjacent tissues was found consistently, and thrombosis and vascular occlusion within the areas of necrosis and inflammation was found in 21 of 34 cases. Cecal infarction cases were then compared to controls using a retrospective matched case-control study design. Cases ( n = 34) and controls ( n = 86) were compared with respect to bacteremia (as defined by pure culture of a single bacterial agent from lung and/or liver), species of bacteria isolated, and for the presence of K99 Escherichia coli (calves ≤5 d), attaching and effacing E. coli, Cryptosporidium (calves ≥5 d of age), Salmonella isolation from the intestine, rotavirus, Bovine coronavirus, and Bovine viral diarrhea virus. In addition, the presence of rumenitis or abomasitis, and omphalitis were compared between cases and controls. There were no significant differences in ruminal, abomasal, or umbilical cord tissue inflammation, or pathogen test-positive status between cases and controls.

Epidemiology of Salmonella sp. in California cull dairy cattle: prevalence of fecal shedding and diagnostic accuracy of pooled enriched broth culture of fecal samples.

BACKGROUND: The primary objective of this cross-sectional study was to estimate the crude, seasonal and cull-reason stratified prevalence of Salmonella fecal shedding in cull dairy cattle on seven California dairies. A secondary objective was to estimate and compare the relative sensitivity (Se) and specificity (Sp) for pools of 5 and 10 enriched broth cultures of fecal samples for Salmonella sp. detection. METHODS: Seven dairy farms located in the San Joaquin Valley of California were identified and enrolled in the study as a convenience sample. Cull cows were identified for fecal sampling once during each season between 2014 and 2015, specifically during spring, summer, fall, and winter, and 10 cows were randomly selected for fecal sampling at the day of their sale. In addition, study personnel completed a survey based on responses of the herd manager to questions related to the previous four month's herd management. Fecal samples were frozen until testing for Salmonella. After overnight enrichment in liquid broth, pools of enrichment broth (EBP) were created for 5 and 10 samples. All individual and pooled broths were cultured on selective media with putative Salmonella colonies confirmed by biochemical testing before being serogrouped and serotyped. RESULTS: A total of 249 cull cows were enrolled into the study and their fecal samples tested for Salmonella. The survey-weighted period prevalence of fecal shedding of all Salmonella sp. in the cull cow samples across all study herds and the entire study period was 3.42% (N = 249; SE 1.07). The within herd prevalence of Salmonella shed in feces did not differ over the four study seasons (P = 0.074). The Se of culture of EBP of five samples was 62.5% (SE = 17.12), which was not statistically different from the Se of culture of EBP of 10 (37.5%, SE = 17.12, P = 0.48). The Sp of culture of EBP of five samples was 95.24% (SE = 3.29) and for pools of 10 samples was 100.00% (SE = 0). There was no statistical difference between the culture relative specificities of EBP of 5 and 10 (P > 0.99). DISCUSSION: Our study showed a numerically higher prevalence of Salmonella shedding in the summer, although the results were not significant, most likely due to a lack of power from the small sample size. A higher prevalence in summer months may be related to heat stress. To detect Salmonella, investigators may expect a 62.5% sensitivity for culture of EBP of five, relative to individual fecal sample enrichment and culture. In contrast, culture of EBP of 10 samples resulted in a numerically lower Se. Culture of EBP of size 5 or 10 samples, given similar prevalence and limit of detection, can be expected to yield specificities of 95 and 100%, respectively.

Off-site rearing of heifers reduces the risk of Mycobacterium avium ssp. paratuberculosis ELISA seroconversion and fecal shedding in a California dairy herd.

The objective of this cohort study was to evaluate whether rearing dairy heifers at different premises than the dairy of origin (off-site) reduced the risk of Mycobacterium avium ssp. paratuberculosis (MAP) infection more effectively than rearing on the dairy of origin (on-site). From 2003 to 2005, 3 cohorts of Jersey heifers were born on a single California dairy, with heifers in the first cohort raised on-site until first calving (n=797); heifers in the second cohort raised on-site until approximately 5 mo of age and off-site until about 1 to 2 mo precalving (n=791); and heifers in the third cohort raised off-site from d 1 until about 1 to 2 mo before first calving (n=797). Cohorts were sequentially enrolled, and heifers were followed until death, culling, or up to 6 yr of age. Heifers were tested annually for MAP infection by serum ELISA and bacterial culture of feces, from lactation 1 until they were 6 yr old, and all mortality and culling events were recorded. Compared with cohort 1, cohort 3 had lower hazards of seroconverting and shedding of MAP in feces, approximately 70 and 38%, respectively. Cohort 2 was not significantly different from cohort 1 for the same outcomes. Mortality hazards were only significantly different between cohorts before first calving, with calves raised completely off-site at lower risk than the remaining 2 cohorts. Additionally, the hazards for culling in cohorts 2 and 3 were only significantly different from cohort 1 after the first calving. To our knowledge, the current study is the first cohort study to evaluate the association between off-site heifer rearing and risk of MAP infection, mortality, and culling. Rearing heifer calves off-site, away from infected adult dairy cows, may have allowed for reduced exposure to MAP in the environment of the calves and, hence, served as a control strategy for Johne's disease.

Jejunal hematoma in cattle: a retrospective case analysis.

Sixteen years of adult cattle submissions to the California Animal Health and Food Safety Laboratory System were examined and data captured from cases with anaerobic cultures of intestinal content. Analysis was performed to determine if there were statistical differences between case submission types (nonbloody intestinal content [129 cases], bloody intestinal content [134 cases], and jejunal hematoma [JH; 51 cases]) for the presence of Clostridium perfringens (314 cases), C. perfringens toxinotypes (35 cases), and C. perfringens toxins (51 cases) in the content. Across submission types, significant differences were found in the isolation of C. perfringens between different specimen types (live cow, dead cow, or tissue from a field necropsy) with field samples being the most likely to have C. perfringens detected and live animals the least likely (P = 0.001). In cases of JH, detection of C. perfringens by enzyme-linked immunosorbent assay was more likely when a live or dead animal was submitted (P = 0.023) or when a live animal was submitted (P = 0.019) compared with submission of field necropsy tissues. These differences were not observed when cultures were performed to detect C. perfringens in cases of JH. There were no statistical differences between submission types with regard to any other variables evaluated. Detailed histologic examination of 21 cases of JH suggested disturbance of normal vascular or lymphatic function as the underlying problem in this entity.

Congenital portosystemic shunts and hepatic encephalopathy in goat kids in California: 11 cases (1999-2012).

Between 1999 and 2012, 11 cases of congenital portosystemic shunts (cPSS) resulting in hepatic encephalopathy were diagnosed in goat kids necropsied at the California Animal Health and Food Safety Laboratory System and at the Department of Pathology, Immunology & Microbiology, School of Veterinary Medicine, University of California-Davis. Affected animals included 6 females and 5 males of various breeds including Boer (5/11), Nigerian Dwarf (1/11), Saanen (1/11), Toggenburg (1/11), and mixed-breed (3/11) aged between 1.5 months and 11 months, submitted live (2/11) or dead (9/11) for necropsy. The most frequent clinical signs in these goats were ataxia, blindness, tremors, head bobbing, head pressing, seizures, circling, weakness, and ill thrift. Bile acids were measured in 2 animals, and were elevated in both cases (134 and 209 µmol/l, reference interval = 0-50 µmol/l). Necropsy findings were poor to fair body condition. Grossly, the livers of 4 animals were subjectively small. Microscopic lesions included portal spaces with increased numbers of arteriolar profiles and hypoplastic or absent portal veins, diffuse atrophy of the hepatic parenchyma with the presence of small hepatocytes and, in some cases, multifocal hepatocellular macrovesicular vacuolation. In the brain and spinal cord of all animals, there was bilateral and symmetric spongy degeneration affecting the cerebrum, mesencephalon, cerebellum, brainstem, and cervical spinal cord. In all cases, the brain lesions were consistent with hepatic encephalopathy. Congenital portosystemic shunts should be considered in the differential diagnosis of young goats with a history of ill thrift, and nonspecific neurological signs.

Systemic Bovine herpesvirus 1 infections in neonatal dairy calves.

During a 6-year period, 62 out of 2,980 calves examined (2.08%) between 1-30 days of age had lesions consistent with Bovine herpesvirus 1 infection. The mean and median age of affected calves was 14 days of age. Most cases of infection were in calves 12 and 15 days of age, with 34 calves (54.8%) affected; 14 calves (22.6%) were between 16-21 days of age; 11 calves (17.8%) were between 7-11 days of age; and 3 calves (4.8%) were between 22-30 days of age. In 29 of the calves, the adrenal gland was the only organ affected. In 25 calves, the adrenal gland and at least 1 other tissue had lesions consistent with herpes viral infection. Five animals had no adrenal lesions but had 1 or more additional tissue with lesions consistent with herpesvirus. Three animals had no adrenal gland present for examination but had lesions in other tissues. Organs and number of animals affected by Bovine herpesvirus 1 infection were adrenal gland (54), liver (18), lungs (15), kidney (8), small intestines (7), large intestines (7), rumen/omasum (7), trachea/larynx (3), abomasum (2), heart (1), esophagus (1), thymus (1), and lymph node (1).

Cost-effectiveness of diagnostic strategies to identify Mycobacterium avium subspecies paratuberculosis super-shedder cows in a large dairy herd using antibody enzyme-linked immunosorbent assays, quantitative real-time polymerase chain reaction, and bacterial culture.

Diagnostic strategies to detect Mycobacterium avium subsp. paratuberculosis (MAP) super-shedder cows in dairy herds have been minimally studied. The objective of the current study was to compare the cost-effectiveness of strategies for identification of MAP super-shedders on a California dairy herd of 3,577 cows housed in free-stall pens. Eleven strategies that included serum or milk enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qPCR) or culture of environmental samples, pooled or individual cow fecal samples, or combinations thereof were compared. Nineteen super-shedders (0.5%) were identified by qPCR and confirmed by culture as cows shedding ≥ 10,000 colony forming units (CFU)/g feces (median of 30,000 CFU/g feces). A stratified random sample of the study herd based on qPCR results of fecal pools was the most sensitive (74%) strategy and had the highest cost ($5,398/super-shedder). The reference strategy with the lowest cost ($1,230/super-shedder) and sensitivity (47%) included qPCR testing of fecal samples from ELISA-positive lactating (milk) and nonlactating (serum) cows housed in pens with the highest MAP bioburden. The most cost-effective alternative to the reference was to perform qPCR testing of fecal samples from ELISA-positive cows (milk and serum for milking and dry cows, respectively) for a sensitivity of 68% and cost of $2,226/super-shedder. In conclusion, diagnostic strategies varied in their cost-effectiveness depending on the tests, specimen type, and labor costs. Initial qPCR testing of environmental samples from free-stall pens to target cows in pens with the highest MAP bioburden for further testing can improve the cost-effectiveness of strategies for super-shedder identification.

Low rate of detectable in utero transmission of Mycobacterium avium subspecies paratuberculosis in a dairy herd with a low prevalence of Johne's disease.

In an effort to correlate the likelihood of in utero transmission of Mycobacterium avium subsp. paratuberculosis (MAP), the causal organism of Johne's disease, with the test status of the dam, tissues from neonatal calves borne to known test status cows were cultured for the presence of MAP. Tissues from a single calf borne to a test-positive cow shedding large numbers of organisms in the feces were positive for MAP. The detected overall transmission rate was approximately 2% (1/49), and the detected transmission rate in cows that were fecal culture positive and serum enzyme-linked immunosorbent assay suspect or positive was approximately 4.3% (1/23).