Anthelmintic efficacy against equine strongyles in the United States.

Equine strongyle parasites are ubiquitous in grazing equids across the world. Anthelmintic resistance is widely developed in cyathostomin populations, but very few surveys have evaluated anthelmintic efficacy in equine populations in the United States, and most of these are over 15 years old. The present study was carried out as part of the National Animal Health Monitoring Systems (NAHMS) Equine 2015-2016 study. The aims were to investigate anthelmintic treatment efficacy by means of the fecal egg count reduction test (FECRT) and identify parameters associated with decreased efficacy. Data were collected from equine operations in 28 states via questionnaires and fecal samples submitted for fecal egg count analysis. Participants were instructed to collect samples from six equids at the day of anthelmintic treatments and 14 days later, and they were asked to include an empty syringe with a legible label of the anthelmintic product used in the shipment. Overall, dewormer treatment was effective for 76.3% of operations (84.6% of animals). Macrocyclic lactone use was effective for 88.7% of operations (95.0% of animals) while pyrimidine/benzimidazole use was effective for 21.4% of operations (43.5% of animals). Univariate analysis revealed that overall, macrocyclic lactones exhibited significantly higher efficacy than the pyrimidine and benzimidazole drug classes (p < 0.0001). There were no statistically significant differences observed between geographic regions (West, South Central, North East, and Southeast). Body weight (p = 0.0355), amount of anthelmintic administered (p = 0.0119), and operation size (p = 0.0162) were statistically associated with anthelmintic efficacy, while anthelmintic treatment frequency in the previous 12 months was not (p = 0.7081). Multiple, mixed-effect logistic regression revealed that anthelmintic drug class (p < 0.0001) was the most impactful factor in predicting anthelmintic efficacy, after accounting for operation size, region and clustering of equids at the operation level. Pasture rotation (p = 0.0129) also demonstrated a significant effect using this model. These data document widespread occurrence of reduced anthelmintic efficacy of benzimidazole and pyrimidine products against strongyle infections in equids in the United States. Anthelmintic efficacy patterns were relatively uniform between the four studied regions, and some epidemiological factors were identified to be associated with anthelmintic efficacy against strongyle infections. This information can be useful in devising sustainable parasite control strategies in the future.

Preweaned heifer management on US dairy operations: Part V. Factors associated with morbidity and mortality in preweaned dairy heifer calves.

The objective of this study was to evaluate morbidity and mortality in preweaned dairy heifer calves based on different health, feeding, and management practices, as well as environmental factors. This study was conducted as part of the calf component of the National Animal Health Monitoring System's Dairy 2014 study, which included 104 dairy operations in 13 states. The calf component was an 18-mo longitudinal study focused on dairy heifer calves from birth to weaning; data were collected on 2,545 calves. The percentage morbidity for all calves enrolled in the study was 33.9%. Backward elimination model selection was used after univariate screening to determine which management practices and environmental factors significantly affected morbidity and mortality. The final morbidity model included birth weight, serum IgG concentration, ventilation type, and average temperature-humidity index (THI) during the preweaning period. After controlling for other independent variables in the model, calves born at a higher birth weight had a lower predicted risk of morbidity than calves with a lower birth weight. An increase in serum IgG concentration was associated with decreased morbidity. Calves housed in positive- or cross-ventilated systems had a 2.2 times higher odds of developing disease compared with calves housed in natural ventilation systems. Average THI during the preweaning period was inversely correlated with morbidity; as THI increased, the predicted morbidity risk decreased. The percent mortality for all calves enrolled in the study was 5.0%. The final mortality model included birth weight, serum IgG concentration, amount of fat/day in the liquid diet, and morbidity. After controlling for other independent variables in the model, calves born at a higher birth weight had a lower risk of mortality. An increase in serum IgG concentration decreased the risk of mortality. The odds of mortality were 3.1 times higher in calves fed ≤0.15 kg of fat/d in the liquid diet compared with calves fed ≥0.22 kg of fat/d. The odds of mortality were 4.7 times higher in calves that experienced any disease throughout the preweaning period than in calves with no disease. In summary, morbidity and mortality were both associated with birth weight and serum IgG concentration. Additionally, morbidity was associated with ventilation type and average monthly THI, and mortality was associated with amount of fat per day in the liquid diet and morbidity.

Risk factors associated with clinical signs of vesicular stomatitis and seroconversion without clinical disease in Colorado horses during the 2014 outbreak.

Vesicular stomatitis (VS) is caused by a contagious rhabdovirus that affects horses, cattle, and swine. Clinical signs of vesicular stomatitis virus (VSV) infection in pigs and cattle are indistinguishable from foot-and-mouth disease (FMD), a foreign animal disease and reportable disease in the United States (Rodriguez et al., 2000). A VS epidemic occurred in the Rocky Mountain region in 2014-15. A study was conducted in Colorado to evaluate horse- and management-level factors associated with VS. For a horse to be considered a clinical VS horse, there were two requirements. First, clinical VS horses had to have clinical signs consistent with VS, including one or more of the following: vesicles, ulcers, erosions or crusting on the muzzle, nares, lips, oral or nasal mucosa, ears, ventrum, udder or penile sheath, or coronary band lesions. Second, clinical VS horses had to have laboratory confirmation of VSV exposure via virus isolation from lesions or a positive complement fixation test performed on sera. All non-clinical horses residing on VSV-affected premises enrolled in the study were evaluated for exposure (i.e., seroconversion) to VSV. Overall, management and housing data were collected from 334 horses on 48 premises in Colorado. Approximately one-third (31.4%) of enrolled horses were clinical cases and two-thirds (68.6%) were controls. Three premises-matched logistic regression models were constructed in SAS using backward elimination (P-value < 0.05) after univariate screening of a priori-selected variables (P-value < 0.20). Model outcomes included differences in characteristics and management of 1) clinical and nonclinical horses, 2) exposed and unexposed horses, and 3) exposed nonclinical and unexposed nonclinical horses. Overall, factors most strongly associated with risk of being a VS clinical horse were access to pasture (P-value = 0.002), and pregnancy status (P-value = 0.001). Factors most strongly associated with VSV exposure among horses were access to pasture (P-value = 0.003) and lack of any insect control (P-value = 0.001). The only factor associated with VSV-exposed nonclinical horses compared with unexposed VSV horses was contact with clinical horses (P-value = 0.013). There were no associations identified regarding clinical horses compared with exposed nonclinical horses. With regard to severity of lesions (severe vs. moderate or mild), no variables met the criteria for inclusion in the multivariable model. Results of this study provide evidence that pasture access and fly control are important factors associated with VSV exposure.

Preweaned heifer management on US dairy operations: Part II. Factors associated with colostrum quality and passive transfer status of dairy heifer calves.

Passive transfer of immunity is essential for the short- and long-term health of dairy calves. The objective of this study was to evaluate factors associated with colostrum quality and passive transfer status of US heifer calves. This study included 104 operations in 13 states that participated in the calf component of the National Animal Health Monitoring System's Dairy 2014 study. This 18-mo longitudinal study included 1,972 Holstein heifer calves from birth to weaning. Multivariable mixed linear regression models were selected using backward elimination model selection after univariate screening to determine which factors were associated with colostrum IgG and serum IgG concentrations. The mean colostrum IgG concentration was 74.4 g/L with 77.4% of colostrum samples having IgG concentrations >50 g/L. The final model for colostrum IgG included colostrum source and a categorized temperature-humidity index value (cTHI) for the month before calving. Mean colostrum IgG concentrations were highest for dams in third and higher lactations (84.7 g/L) and lowest for commercial colostrum replacers (40.3 g/L). Colostrum IgG concentrations were highest for cTHI ≥70 (72.6 g/L) and lowest for cTHI <40 (64.2 g/L). The mean serum IgG concentration was 21.6 g/L, with 73.3% of calves having serum IgG concentrations >15 g/L. The final model for serum IgG concentration included region, heat treatment of colostrum, colostrum source, timing to first feeding, volume of colostrum fed in the first 24 h, age of the calf at blood sampling, and colostrum IgG concentration. Mean serum IgG concentrations were highest for calves that received colostrum from first-lactation dams (25.7 g/L) and lowest for calves fed commercial colostrum replacer (16.6 g/L). Serum IgG concentrations were higher for calves fed heat-treated colostrum (24.4 g/L) than for calves fed untreated colostrum (20.5 g/L). Serum IgG concentration was positively associated with the volume of colostrum fed in the first 24 h and colostrum IgG concentration, and negatively associated with the number of hours from birth to colostrum feeding and age (days) at blood collection. Dairy producers should be encouraged to measure the quality of colostrum before administering it to calves and to measure serum IgG or a proxy such as serum total protein or Brix to evaluate passive immunity and colostrum management programs.

Preweaned heifer management on US dairy operations: Part I. Descriptive characteristics of preweaned heifer raising practices.

The objective of this study was to describe preweaned dairy heifer calf management practices on dairy operations across the United States that were used to analyze factors associated with colostrum quality and passive transfer, Cryptosporidium and Giardia, morbidity and mortality, and average daily gain. This study included 104 dairy operations in 13 states that participated in the National Animal Health Monitoring System's Dairy 2014 calf component study. This 18-mo longitudinal study focused on dairy heifer calves from birth to weaning, and data were collected on 2,545 heifer calves. Descriptive statistics were generated regarding colostrum feeding, preweaning housing, milk feeding and consumption, growth, morbidity and mortality, and weaning practices. The majority of calves enrolled were Holsteins (89.4%). Over half the calves (63.2%) enrolled in the study received the majority of their colostrum via bottle; however, 22.1% of calves from 51.0% of operations received colostrum via suckling from their dams. For all calves, the mean time to the first colostrum feeding was 2.8 h, and the average amount of colostrum at the first feeding was 2.9 L, with 4.5 L provided in the first 24 h. The mean serum IgG of all calves was 21.7 g/L; however, 76.0% of operations had at least 1 calf with failure of passive transfer of immunity with a serum IgG below 10 g/L. The majority of calves in the study were housed individually (86.6%). Nonetheless, 20.2% of operations housed some calves in groups, representing 13.4% of all calves. Approximately one-half of the calves in the study (52.3%) were dehorned or disbudded during the preweaning period, with only 27.8% of these calves receiving analgesics or anesthetics during the procedure. Whole or waste milk was the liquid diet type fed to 40.1% of calves, and milk replacer was fed to 34.8% of calves. A combination of milk and milk replacer was fed to 25.1% of calves. Calves, on average, were fed 2.6 L per feeding and fed 2.6 times/d, resulting in a total of 5.6 L of liquid diet fed per day. The mean average daily gain for all calves enrolled in the study was 0.7 kg/d. Fecal samples were collected and almost all operations had at least 1 calf positive for Cryptosporidium (94.2%) or Giardia (99.0%), and 84.6% of operations had calves that tested positive for both Cryptosporidium and Giardia. Over one-third of calves (38.1%) had at least one morbidity event during the preweaning period and the mortality rate was 5.0%. The mean age at weaning was 65.7 d. This study provides an update on dairy heifer raising practices in the United States.

Preweaned heifer management on US dairy operations: Part III. Factors associated with Cryptosporidium and Giardia in preweaned dairy heifer calves.

The objective of this study was to evaluate management practices and environmental factors associated with cryptosporidiosis and giardiasis in preweaned heifer calves on US dairy operations. This study was conducted as part of the calf component of the National Animal Health Monitoring System's Dairy 2014 study. The calf component included 104 dairy operations in 13 states and was an 18-mo longitudinal study focused on dairy heifer calves from birth to weaning. Fecal samples were collected from 2,249 calves: 839 calves in the West region (California, Colorado, and Washington) and 1,410 calves in the East region (Iowa, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, Vermont, Virginia, and Wisconsin). Fecal samples were collected only once from calves during the preweaning period. Samples were collected from calves 3 to 66 d of age, with a mean of 22 d. Overall, Cryptosporidium and Giardia were detected in 43.1 and 30.5% of fecal samples, respectively. Backward elimination logistic model selection was used after univariate screening to determine which management practices and environmental factors significantly affected the presence of Cryptosporidium or Giardia. The final Cryptosporidium model included herd size, days of age at fecal collection, and average temperature-humidity index for the month of fecal collection (fTHI). Cryptosporidium was found on a higher percentage of large operations (≥500 cows) than small operations (30 to 99 cows). Younger calves were more likely to have a fecal sample positive for Cryptosporidium than samples from older calves. Fecal samples from calves during the warmer parts of the year (fTHI >70) were more likely to be positive for Cryptosporidium than samples collected in colder months (fTHI <20). The final Giardia model included herd size, days of age at fecal collection, average fTHI, failure of passive transfer status, and average daily gain (kg/d) during the preweaning period. Giardia was isolated more frequently from calves on small operations than on large operations and from calves that were older compared with younger calves. Giardia was more frequently isolated in warmer months. Samples from calves with failure of passive transfer were more likely to have Giardia than calves with adequate passive transfer (>10 g/L IgG). Average daily gain during the preweaning period was lower in calves from which Giardia was isolated. These results highlight the factors associated with the presence of Cryptosporidium and Giardia in preweaned dairy heifer calves.

Risk factors associated with strongylid egg count prevalence and abundance in the United States equine population.

Equine strongyle parasites are considered ubiquitous in grazing equids across the world, and cyathostomin parasites are known pathogens causing well-described disease complexes in horses. Decades of intensive anthelmintic treatments have led to anthelmintic resistance in cyathostomins, and current recommendations are to lower treatment intensity and base control strategies on fecal egg count surveillance. Little is known about risk factors associated with strongyle parasite egg shedding patterns in the United States equine population, as the most recent national survey was conducted 20 years ago. The present study was carried out as part of the National Animal Health Monitoring Systems (NAHMS) Equine 2015-2016 study. The aims were to describe strongyle parasite egg shedding patterns in the United States equine population and identify risk factors associated with prevalence and egg count magnitude. Data were collected from equine operations in 28 states via questionnaires and fecal samples submitted to a parasitology research laboratory for fecal egg count analysis and the data gathered underwent comprehensive statistical analyses. Though region and season were related, overall, the summer months and the fall in the southeast tended to have the greatest odds of presence of strongyles eggs on a FEC. Generally, equids resident in the Western region (Arizona, California, Colorado, Montana, Oregon, and Wyoming) had significantly lower strongyle prevalence, no matter the season, as well as a markedly different distribution between strongyle egg shedding levels (p = 0.0005). Overall, egg counts were over-dispersed with about 27% of equids (95% Confidence Interval (CI): 20-34%) contributing 80% of the egg output. Pasture history was significantly associated with strongyle egg prevalence (p = 0.0003) and egg shedding levels (p = 0.0063) with daily access in the previous 30 days being associated with higher odds of presence and greater median egg count levels. Equid gender was significantly associated with strongylid presence (p = 0.0081) and egg count level (p = 0.0008), with male equids having significantly lower odds and median egg counts than female equids, and age was significantly negatively associated with strongylid prevalence (p < 0.0001). Time since last deworming was significantly positively associated with prevalence of strongyle eggs, and this was dependent on the class of dewormer used (p = 0.0086), with equids treated with macrocyclic lactone class of drugs having lower odds of strongyle egg presence at 120 days since the last deworming. These data provide useful insights into strongylid egg shedding patterns in the United States equine population, and they can help refine parasite control recommendations depending on region, pasture access, and age distribution.

Preweaned heifer management on US dairy operations: Part VI. Factors associated with average daily gain in preweaned dairy heifer calves.

The study objective was to evaluate average daily gain (ADG) in dairy heifer calves based on health, feeding, management practices, and environmental factors. This study included 102 operations in 13 states that participated in the calf component of the National Animal Health Monitoring System's Dairy 2014 study. This 18-mo longitudinal study included 1,410 Holstein heifer calves monitored from birth to weaning. The mean ADG from birth to final weight was 0.74 kg/d. Backward elimination model selection in Proc Mixed after univariate screening determined factors that significantly affected ADG. The final model included dam lactation number, singleton versus twin birth, bedding type, Giardia and Cryptosporidium fecal shedding, disease events, a categorized average temperature-humidity index for the preweaning period (pTHI), amount of protein in the liquid diet (kg/d), milk pasteurization, direct-fed microbials, and the interaction between milk pasteurization and direct-fed microbials. After controlling for other independent variables in the model, calves born to first-lactation dams gained less (0.60 kg/d) than calves from second- (0.65 kg/d) or third- or greater-lactation (0.64 kg/d) dams. Singleton calves gained 0.07 kg/d more than twins. Calves bedded with sand or no bedding gained less (0.49 kg/d) than calves on all other bedding types. Calves negative for Cryptosporidium or Giardia at the time of sampling gained 0.03 or 0.02 kg/d more, respectively, than calves that were positive for Cryptosporidium or Giardia. Calves with no disease events gained 0.07 kg/d more than calves with one or more disease events. Calves experiencing an average pTHI <50 gained more (0.67 kg/d) than calves experiencing an average pTHI from 50 to 69 (0.62 kg/d), or ≥70 (0.59 kg/d). Within the range of observed kilograms of protein fed per day in the liquid diet, every additional 0.1 kg of protein fed per day equated to 0.02 kg/d of gain. Calves fed milk replacer with a direct-fed microbial gained less (0.44 kg/d) than calves fed milk replacer without a direct-fed microbial (0.60 kg/d) and calves fed pasteurized or unpasteurized milk regardless of direct-fed microbial use. These results highlight the importance of feeding a quantity and quality of a liquid diet to achieve optimal growth, keeping calves free of disease, the type or status of bedding, and mitigating the effects of temperature and humidity on preweaning ADG.

Parasite control strategies used by equine owners in the United States: A national survey.

The widespread occurrence of anthelmintic resistance in equine parasites across the world has led to recommendations of fecal egg count-based parasite programs to reduce treatment intensity and thereby delay further development of resistance as much as possible. The most recent study describing equine parasite control in the United States was conducted 20 years ago, and little is known about current strategies employed. This study was part of the National Animal Health Monitoring Systems (NAHMS) Equine 2015 Study, and aimed to describe equine parasite control strategies in the U.S. and evaluate to which extent respondents were in compliance with current guidelines. The study was carried out in 28 states, representing 70.9% of all equine operations with at least five equids present. Two questionnaires were administered, either by mail or delivered in person by veterinary medical officers. Participants provided specific details of their operation and were asked questions about strategies for anthelmintic therapy and diagnostic testing. A total of 380 operations provided data regarding their parasite control practices. Most respondents dewormed 2-3 times a year with ivermectin being the most commonly used anthelmintic. About 22% of respondents used fecal egg counts (FEC) in some form, with less than 10% using them on a regular basis. Less than 5% made use of fecal egg count reduction tests (FECRT). These results suggest little change since the last nationwide survey was conducted in 1998, as the majority of respondents did not report using FECs. This is in stark contrast to recent European surveys, where 50-60% of respondents were using FECs routinely. However, the anthelmintic treatment intensity appears to have been lowered compared to 1998. Taken together, these results suggest a continuing need for education and outreach regarding sustainable parasite control.

Associations between housing and management practices and the prevalence of lameness, hock lesions, and thin cows on US dairy operations.

The objective of this study was to determine the association among different housing and management practices on the prevalence of lameness, hock lesions, and thin cows on US dairy operations. This study was conducted as part of the National Animal Health Monitoring System's Dairy 2014 study, which included dairy operations in 17 states. Size categories were assigned as follows: small (30-99 cows), medium (100-499 cows), and large (≥500 cows). Trained assessors visited 191 dairy operations from March through July 2014 and recorded locomotion and hock scores (on a 3-point scale), and the number of thin cows (body condition score ≤2.25) from a total of 22,622 cows (average 118 cows per farm). The majority of cows (90.4%) were considered to be sound (locomotion score = 1), 6.9% were mild/moderately lame (locomotion score = 2), and 2.7% were severely lame (locomotion score = 3). Similarly, most cows (87.3%) had no hock lesions (hock score = 1), 10.1% had mild lesions (hock score = 2), and 2.6% had severe hock lesions (hock score = 3). A low percentage of cows (4.2%) were thin. Univariate comparisons were performed using PROC LOGLINK, which accounts for study design and weighting. Variables meeting the univariate screening criterion of P < 0.20 were eligible for entry into multivariable models. Statistical significance in the multivariable models was declared at P < 0.05. Large operations had a lower within-herd prevalence of cows with locomotion score ≥2 and locomotion score = 3 compared with small or medium-sized operations. Operations on which cows were kept primarily on pasture had a lower percentage of locomotion score = 3 than those housed in freestall or open/dry lot operations. The use of sand bedding was associated with a lower within-herd prevalence of locomotion score ≥2 than straw/hay or dry/composted manure as the primary bedding material. Sand bedding was also associated with a lower within-herd prevalence of locomotion score = 3 than other bedding types except for rubber mats or mattresses. Operations that housed cows in an open/dry lot had a lower percentage of hock score ≥2 and hock score = 3 than other housing types. Providing sprinklers for heat abatement and having a nutritionist balance rations for cows was associated with a lower percentage of thin cows. Results from this study highlight management practices that may reduce the prevalence of lameness, hock lesions, and thin cows on dairy operations in the United States.

Comparison of mixed effects models of antimicrobial resistance metrics of livestock and poultry Salmonella isolates from a national monitoring system.

Antimicrobial use in agriculture is considered a pathway for the selection and dissemination of resistance determinants among animal and human populations. From 1997 through 2003 the U.S. National Antimicrobial Resistance Monitoring System (NARMS) tested clinical Salmonella isolates from multiple animal and environmental sources throughout the United States for resistance to panels of 16-19 antimicrobials. In this study we applied two mixed effects models, the generalized linear mixed model (GLMM) and accelerated failure time frailty (AFT-frailty) model, to susceptible/resistant and interval-censored minimum inhibitory concentration (MIC) metrics, respectively, from Salmonella enterica subspecies enterica serovar Typhimurium isolates from livestock and poultry. Objectives were to compare characteristics of the two models and to examine the effects of time, species, and multidrug resistance (MDR) on the resistance of isolates to individual antimicrobials, as revealed by the models. Fixed effects were year of sample collection, isolate source species and MDR indicators; laboratory study site was included as a random effect. MDR indicators were significant for every antimicrobial and were dominant effects in multivariable models. Temporal trends and source species influences varied by antimicrobial. In GLMMs, the intra-class correlation coefficient ranged up to 0.8, indicating that the proportion of variance accounted for by laboratory study site could be high. AFT models tended to be more sensitive, detecting more curvilinear temporal trends and species differences; however, high levels of left- or right-censoring made some models unstable and results uninterpretable. Results from GLMMs may be biased by cutoff criteria used to collapse MIC data into binary categories, and may miss signaling important trends or shifts if the series of antibiotic dilutions tested does not span a resistance threshold. Our findings demonstrate the challenges of measuring the AMR ecosystem and the complexity of interacting factors, and have implications for future monitoring. We include suggestions for future data collection and analyses, including alternative modeling approaches.

Comparison of individual, pooled, and composite fecal sampling methods for detection of Salmonella on U.S. dairy operations.

The objectives of this study were to estimate the prevalence of Salmonella for individual, pooled, and composite fecal samples and to compare culture results from each sample type for determining herd Salmonella infection status and identifying Salmonella serovar(s). During the U.S. Department of Agriculture National Animal Health Monitoring System Dairy 2007 study, data and samples were collected from dairy operations in 17 major dairy states. As part of the study, composite fecal samples (six per operation) were collected from cow areas, such as holding pens, alleyways, and lagoons, where manure accumulates. Fecal samples also were collected from individual cows (35 per operation), and fecal sample pools were created by combining samples from 5 cows (7 per operation). A total of 1,541 composite fecal samples were collected from 260 operations in 17 states, and 406 (26.3%) of these samples were culture positive for Salmonella. Among the 116 operations for which all three sample types were obtained, 41.4% (48 operations) were Salmonella culture positive based on individual samples, 39.7% (46 operations) were positive based on pooled samples, and 49.1% (57 operations) were positive based on composite fecal samples. Relative to individual samples, the sensitivity of composite fecal samples for determining herd infection status was 85.4% and the sensitivity of pooled fecal samples was 91.7%. On 33.6% of operations (39 of 116), Salmonella was cultured from all three fecal sample types (individual, pooled, and composite), and 20 (51.3%) of these operations had exactly the same serovar in all three sample types. Use of composite fecal samples is less costly and time-consuming than use of individual or pooled samples and provides similar results for detecting the presence and identifying serovars of Salmonella in dairy herds. Therefore, composite sampling may be an appropriate alternative to culture of individual samples when assessing Salmonella status in dairy herds.

Consequence of alternative standards for bulk tank somatic cell count of dairy herds in the United States.

Noncompliance with current US and European Union (EU) standards for bulk-tank somatic cell count (BTSCC) as well as BTSCC standards recently proposed by 3 US organizations was evaluated using US Dairy Herd Improvement Association (DHI) herds and herds supplying milk to 4 Federal Milk Marketing Orders (FMO). Herds with 15 to 26 tests (frequently monthly) from January 2009 through October 2010 were included. Somatic cell scores (SCS) from 14,854 herds and 164,794 herd-tests were analyzed for DHI herds with ≥10 cows for all tests. Herd test-day SCC was derived as a proxy for BTSCC and was the basis for determining noncompliance and percentage of the milk it represented. For FMO herds, actual milk marketed and BTSCC were available from 27,759 herds and 325,690 herd-tests. A herd was noncompliant for the current EU BTSCC standard after 4 consecutive rolling 3-test geometric means (geometric method) were >400,000 cells/mL. A herd was noncompliant for the current US BTSCC standard after 3 of 5 consecutive monthly BTSCC shipments (frequency method) were >750,000 cells/mL. Alternative proposed standards (600,000, 500,000, or 400,000 cells/mL) also were examined. A third method designated noncompliance when a single 3-mo geometric mean of >550,000 or >400,000 cells/mL and a subsequent test exceeded the same level. Results were examined based on herd size or milk shipped by month. Noncompliance for the current US standard for the 12 mo ending October 2010 in DHI and FMO herds was 0.9 and 1.0%, respectively, compared with 7.8 and 16.1% for the current EU standard. Noncompliance was always greater for the frequency method than for the geometric method and was inversely related to herd size or milk shipped. Using the frequency method at 400,000 cells/mL, noncompliance was 19.1% for DHI herd-tests in herds with <50 cows compared with 1.1% for herds with ≥ 1,000 cows. For FMO herds shipping <900 t, noncompliance was 44.5% using the frequency method at 400,000 cells/mL compared with 8.0% for herds marketing >9,000 t. All methods proposed increased the percentages of herds and shipped milk that exceeded the regulatory limit. Producers will need to place more emphasis on reducing the incidence and prevalence of subclinical mastitis through known management practices such as proper milking techniques, well-functioning milking machines, postmilking teat disinfectant, dry cow treatment, and culling of problem cows to meet any of the proposed new standards.

Associations between cow hygiene, hock injuries, and free stall usage on US dairy farms.

This cross-sectional study evaluated cow comfort measures in free stall dairies across the United States as part of the National Animal Health Monitoring System's Dairy 2007 study. The study was conducted in 17 states and evaluations were completed between March 5 and September 5, 2007. Assessors recorded hygiene and hock scores, number of cows housed in the pen, the number of cows standing with only the front feet in a stall, standing fully in a stall, and lying in a stall. Facility design measures included bedding type, bedding quantity, stall length and width, presence of a neck rail or brisket locator, and relevant distances from the rear and bed of the stall. Of the 491 operations that completed the cow comfort assessment, 297 had Holstein cows housed in free stalls and were included in this analysis. Negative binomial models were constructed to evaluate the following outcomes: the number of cows that were very dirty, had severe hock injuries, stood with front feet in the stall, stood with all feet in the stall, and were lying in the stall. Hygiene was better on farms that did not tail dock cows compared with those that did (5.7 vs. 8.8% were dirty) and on farms located in the study's west region compared with those located in the east region (5.2 vs. 9.7% were dirty). Severe hock injuries were less common on farms in the west than those in the east (0.5 vs. 4.1%). In addition, severe hock injuries were less common on farms that used dirt as a stall base or sand as bedding compared with farms that did not. A higher percentage of cows was standing with front feet in the stall at higher ambient temperatures (incidence rate ratio=1.016) and as time since feeding increased (incidence rate ratio=1.030). A lower percentage of cows were standing with front feet in the stall when the stalls were shorter and when there were fewer cows per stall. Standing fully in a stall was performed by a higher percentage of cows during the summer than during the spring (13.6 vs. 8.1%), when cows were provided free stalls with rubber mats or mattresses, and as the distance from the rear curb to neck rail increased. A higher percentage of cows were lying in a stall when sand bedding was used, when bedding was added more frequently, and during the spring months. Results of this national survey indicate that tail docking provides no benefit to cow hygiene and that stall base and bedding are key factors influencing hock injuries and stall usage on US free stall dairy farms.

Prevalence of failure of passive transfer of immunity in newborn heifer calves and associated management practices on US dairy operations.

Failure of passive transfer of immunity (FPT) in dairy replacement calves has been linked to increased neonatal morbidity and mortality and long-term decreases in productivity. The purpose of this study was to estimate the prevalence of FPT in US dairy heifer calves in 2007 and to use nationally representative data to investigate associations of FPT with colostrum and calf management practices. A cross-sectional study was conducted by the USDA's National Animal Health Monitoring System between January and August 2007. Producers from 394 operations in 17 states completed survey questions about colostrum and calf management practices, and serum samples were collected from 1,816 healthy heifer calves on those operations. Serum immunoglobulin G (IgG) levels were determined by radial immunodiffusion, and calves were classified as having FPT if the IgG concentration was less than 10 mg/mL. To investigate associations between FPT and management practices, a multivariable analysis was completed using a weighted logistic regression model. The estimated prevalence of FPT in US dairy heifer calves was 19.2%. The odds of FPT were higher for calves on operations that pooled colostrum [odds ratio (OR = 2.2)], allowed nursing (OR = 2.4), or hand fed colostrum more than 4 h after birth (OR = 2.7). The odds of FPT were also higher for calves on operations that did not provide a source of heat during cold weather for calves experiencing a dystocia (OR = 1.6), would not seek veterinary assistance when unable to correctly position a calf for delivery (OR = 2.6), or did not routinely monitor serum proteins in calves as a measure of passive transfer (OR = 13.8). The prevalence of FPT in dairy heifer calves has decreased in the last 15 yr, so progress has been made in this important area of calf management. This study identified several management practices associated with FPT that could be targeted for educational campaigns or further research.

Prevalence and antimicrobial susceptibility of Salmonella spp. isolates from US cattle in feedlots in 1999 and 2000.

AIMS: Faecal samples from cattle in US feedlots were evaluated for the presence of Salmonella. When Salmonella isolates were recovered the antimicrobial resistance patterns were determined. METHODS AND RESULTS: Faecal samples were collected from pen floors in 73 feedlots in 12 states during the period from October 1999 to September 2000. Pens of cattle selected for sampling were those that had been in the feedlot for the shortest period of time, the longest period of time and a randomly selected pen from the remaining pens. Faecal samples were cultured for Salmonella spp. and all Salmonella isolates were categorized by serotype. The susceptibilities of all isolates were determined using a panel of 17 antimicrobials. Overall, 6.3% (654/10,417) of the samples cultured positive for Salmonella spp. and 22.2% (94/422) of pens and 50.7% (37/73) of feedlots had one or more positive samples. There was little difference in the proportion of positive samples from short-fed (6.1%, 212/3482), random (6.4%, 217/3400) and long-fed (6.4%, 224/3485) pens of cattle. One of two pens of cattle that could not be attributed to a pen type had a single positive sample (2.0%, 1/50). Samples collected during the period of April to June (6.8%, 209/3054) and July to September (11.4%, 286/2500) were more likely to be positive than those collected during October to December (4.0%, 73/1838) and January to March (2.8%, 86/3025). The most common serotypes of Salmonella were dissimilar from those that are typically seen in human illness and cattle illness. The majority of isolates (62.8%, 441/702) were sensitive to all of the antimicrobials tested. Resistance was most frequently observed to tetracycline (35.9%, 252/702) followed by streptomycin (11.1%, 78/702), ampicillin (10.4%, 73/702) and chloramphenicol (10.4%, 73/702). Multiple resistance (resistance to > or =2 antimicrobials) was observed for 11.7% (82/702) of the isolates. CONCLUSIONS: Salmonella was isolated at low frequency from faeces of feedlot cattle and the serotypes were not those commonly associated with human illness. In addition most of the Salmonella isolates were sensitive to all the antimicrobials tested. SIGNIFICANCE AND IMPACT OF THE STUDY: This study contributes to understanding the ecology of Salmonella in cattle feedlots and the prevalence of resistance among potential food-borne pathogens.

Prevalence of antibodies against Mycobacterium avium subsp paratuberculosis among beef cow-calf herds.

OBJECTIVE: To estimate the prevalence of Mycobacterium avium subsp paratuberculosis infection among cows on beef operations in the United States. DESIGN: Cross-sectional seroprevalence study. Sample Population-A convenience sample of 380 herds in 21 states. PROCEDURES: Serum samples were obtained from 10,371 cows and tested for antibodies to M avium subsp paratuberculosis with a commercial ELISA. Producers were interviewed to collect data on herd management practices. RESULTS: 30 (7.9%) herds had 1 or more animals for which results of the ELISA were positive; 40 (0.4%) of the individual cow samples yielded positive results. None of the herd management practices studied were found to be associated with whether any animals in the herd would be positive for antibodies to M avium subsp paratuberculosis. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the prevalence of antibodies to M avium subsp paratuberculosis among beef cows in the United States is low. Herds with seropositive animals were widely distributed geographically.

Estimate of the national incidence of and operation-level risk factors for colic among horses in the United States, spring 1998 to spring 1999.

OBJECTIVE: To estimate the national incidence of, operation-level risk factors for, and annual economic impact of colic among horses in the United States during 1998 and 1999. DESIGN: Epidemiologic survey. ANIMALS: 21,820 horses on 1,026 horse operations in 28 states. PROCEDURES: Horses were monitored for colic for 1 year, and results were recorded in a log that was collected quarterly. Operation-level data were collected via 4 on-site personal interviews. Associations between colic and independent variables adjusted for size of operation were determined. RESULTS: Annual national incidence of colic in the US horse population was estimated to be 4.2 colic events/100 horses per year. Case fatality rate was 11%, and 1.4% of colic events resulted in surgery. Annual cost of colic in the United States was estimated to be $115,300,000. CONCLUSIONS AND CLINICAL RELEVANCE: The national impact of equine colic is substantial because of the high case fatality rate.

Developmental effects and mineral interactions in rats fed textured vegetable protein.

The teratogenic effects of feeding a diet based on textured vegetable protein to Long-Evans rats were studied along with maternal and fetal mineral interactions and their relationship to diet composition. Pregnant rats were fed purified diets containing 18% protein as casein (CAS), textured vegetable protein (TVP, from defatted soy flour) with 18 mg Zn/kg, or TVP diet with 100 mg Zn/kg. A fourth group was fed diet NIH-31. The animals received their diets throughout pregnancy and were sacrificed on day 20 of gestation. Fetuses were examined for developmental effects, and mineral levels were determined in maternal and fetal tissues by inductively coupled argon plasma-atomic emission spectrometry. Females fed the casein diet or diet NIH-31 had normal weight gains throughout pregnancy and their progeny exhibited normal development. The animals on the TVP-containing diet with 18 mg Zn/kg had decreased food consumption and body weights, and their fetuses exhibited developmental anomalies as well as reductions in size and weight. These developmental alterations may be the result of decreased zinc levels in the fetal tissues, caused by reduced bioavailability of the trace element in the maternal diet. Significant increases in tissue iron accompanied the low zinc levels. No developmental effects were found in animals receiving the high Zn-TVP diet, and mineral data from these animals were not significantly different from the casein group.