National Animal Health Monitoring System Research Articles

Opportunities for Cow-calf Practice

Production efficiency has become the watch word for cow-calf producers. Over the years the concept of initially integrated reproductive management and later integrated resource management has been adopted as a means to improve production efficiency on operations. Over time there has been a realization that maximum production is not always compatible with profitability or long-term sustainability. In addition, there has been a realization that one must focus on both components of the profit equation, revenues and costs, in order to achieve profitability in the enterprise. Many factors contribute to the potential for increased efficiency and profitability. Improved genetics, control of animal pathogens, nutrition research, and the development of reproductive technology all contribute to the potential for efficiency. However, data from the National Animal Health Monitoring System's (NAHMS) Beef '97 study suggest that relatively few producers are implementing some of the techniques that could contribute to production efficiency. The veterinarian is a key provider of information to producers and is in a position to help producers adopt technologies or improve management where appropriate. These sorts of decisions should always be based on the anticipated economic benefit to the producer.

Rangeland Cattle and the Risk of Waterborne Cryptosporidium parvum Infection in Humans

Cryptosporidium parvum (C. parvum) is a tiny protozoal parasite that can cause gastrointestinal illness in a wide variety of mammals, including humans, cattle, sheep, goats, pigs, and horses. It also occurs in various wildlife species such as deer, raccoons, opossums, and rabbits (Fayer et al. and Ungar 1990). In cattle, clinical disease and shedding of the parasite is usually limited to calves under a few months of age (National Animal Health Monitoring System 1994, Kirkpatrick 1985, Anderson and Hall 1982). Although not confirmed by studies done in the U.S., researchers in England and in Spain have reported the shedding of C. parvum in adult beef cattle (Scott et al. 1994, Lorenzo Lorenzo et al. 1993). In humans, clinical disease and shedding can appear at all ages, but is typically more common among children (Ungar 1990). The predominant clinical sign is profuse, watery diarrhea lasting from a few days to several weeks in normal (immunocompetent) calves (Kirkpatrick 1985) and humans (Jokipii and Jokipii 1986). While this disease is usually self-limiting in immunocompetent calves and humans, it can be prolonged and life-threatening among immunocompromised people such as AIDS patients. An effective treatment for eliminating this parasite from the gastrointestinal track still does not exist (White et al. 1994, Goodgame et al. 1993). A few antibiotics may show some promise in reducing the amount of oocyst shedding in AIDS patients, but further clinical trials are needed to fully evaluate their efficacy (White et al. 1994, Goodgame et al. 1993). The severity of this disease for the immunosuppressed and the fact that this parasite was implicated in recent large scale water-borne outbreaks of gastroenteritis in humans (MacKenzie et al. 1994, Hayes et al. 1989) has prompted the U.S. Environmental Protection Agency (U.S. EPA), Centers for Disease Control and Prevention, state and local public health agencies and regional water districts to seek ways to reduce surface water contamination of this parasite. Some of this attention has focused on identifying the primary sources of C. parvum in surface water. Cattle are often perceived to be a leading environmental source of water-borne C. parvum. For example, the U.S. EPA has explicitly warned that inclusion of C. parvum into the proposed Enhanced Surface Water Treatment Rule will likely result in new restrictions being placed on the location and management of livestock operations situated within watershed regions (U.S. EPA 1994). Presented below is a brief summary of the medical ecology of C. parvum in calves and in humans and the existing scientific evidence that addresses the claim that grazing of cattle on watershed regions puts humans at significant risk for water-borne infection of C. parvum.

The National Animal Health Monitoring System: A Source of On-Farm Information

The National Animal Health Monitoring System is a program of the USDA:APHIS:Veterinary Services designed to collect, analyze, interpret, and disseminate data on the management and health of US livestock, poultry, and aquaculture populations. The system is comprised of a national program staff, the National Veterinary Services Laboratories, and a field component that includes state and federal animal health officials distributed throughout the United States. The system uses a variety of approaches (large national studies, on-going monitoring, and target short-term studies) to address high priority objectives for US animal agriculture defined through a far-reaching information-needs assessment process.

Design and implementation of the United States National Animal Health Monitoring System 1995 National Swine Study

The United States Department of Agriculture's National Animal Health Monitoring System 1995 National Swine Study was designed to estimate management, health and productivity parameters on pig operations in the United States. Sixteen major swine-producing states that accounted for nearly 91% of June 1, 1995 swine inventory and nearly three-fourths of United States swine producers were included in the study. In the initial phase of the study, National Agricultural Statistics Service enumerators collected information from 1477 producers involved in all phases of swine production (farrowing, nursery, and grower/finisher). Of these, 405 operations with ≥300 finisher pigs (with at least one finisher pig ≥54 kg) participated in the subsequent component of the study, which involved on-farm visits by state and federal veterinary medical officers and animal health technicians, and which concentrated on the grower/finisher phase of production. Of those eligible to take part in the second phase of the study, participation was higher among independent producers (48.3%) than among contract producers (15.3%). Participation was also higher among operations that used advanced record-keeping systems (such as record cards for individual breeding hogs or a computer-based record-keeping system). Thus, study results could have been influenced by response biases. As a biosecurity measure, 40.5±2.1% of operations restricted entry to employees only. For operations that permitted non-employees to enter the premises, relatively few enforced other biosecurity measures on visitors (0.4±0.1% required feed-delivery personnel and livestock handlers to shower before entering the premises; 3.3±0.9% required a footbath; and 7.0±1.5% required feed-delivery personnel and livestock handlers not to have visited another operation with pigs on that day). The most common method of waste storage (used by 49.9±3.8% of operations with ≥300 finisher pigs) was below-floor slurry or deep pit.

An analysis of mortality in the grower/finisher phase of swine production in the United States

Over a 6-month period, the mean mortality risk (based on 393 operations participating in the United States National Animal Health Monitoring System 1995 National Swine Study, and representing operations with ≥ 300 market hogs in 16 states), was 2.3 ± 0.2% in the grower/finisher production phase (where figures after the ± represent the standard error of the estimate). Mortality ≥ 4% was experienced by 13.5 ∓ 2.9% of grower/finisher operations, while 63.6 ± 5.3% had ≤ 2% mortality. To identify factors associated with ≥ 4% mortality, stepwise logistic regression [Statistical Analysis Systems, (1989). SAS/STAT ® User's Guide, Version 6, 4th edn, Vol. 2. SAS Institute, Cary, NC, 794 pp.]was performed twice: once using operations with all mortality rates, and again excluding operations with between 2% and 4% mortality. Final models were run with SUDAAN [Shah, B.V., Barnwell, B.G., Bieler, G.S., (1996). SUDAAN User's Manual, Version 6.40, 2nd edn. Research Triangle Institute, Research Triangle Park, NC, 492 pp.] to take the sample design into account. In addition, SAS and SUDAAN logistic regression models were developed to analyze factors associated with > 2.3% mortality among grower/finisher pigs. Mean weaning age ≤ 28 days entered all models as being associated with increased mortality in the grower/finisher unit. Not obtaining all grower/finisher pigs from farrowing units belonging to the operation was associated with ≥ 4% mortality among grower/finisher swine. Not typically giving grower/finisher pigs antibiotics or other agents as disease-preventives or growth-promotants in the feed or water, and ranking producer organizations as very or extremely important sources of antibiotic information were associated with ≤ 2.3% mortality in the grower/finisher phase.

Issues concerning Mexican cattle on feedlots in the United States as reported in the United States National Animal Health Monitoring System 1994–1995 Cattle on Feed Evaluation

Producers participating in the United States National Animal Health Monitoring System 1994–1995 Cattle on Feed Evaluation provided information on cattle of Mexican origin in their feedlot operations. Cattle of Mexican origin accounted for 8.1% of cattle placed on United States feedlots from 1 July 1993 through 30 June 1994. Of operations with a one-time capacity of 1000 or more cattle, 12.8% placed cattle of Mexican origin on their feedlots over this time frame. Very few operations (about 1%) reported cattle of Mexican origin at the same time as cattle to be used for breeding in the United States.

Associations between off-label feed additives and farm size, veterinary consultant use, and animal age

Data from the United States National Swine Survey collected by the National Animal Health Monitoring System were used to describe the use of feed additives in swine feeds. Data were collected from 710 farms. The concentration of feed additives expressed in grams per ton of complete feed was described by stage of production, and the use of feed additives above the labeled treatment levels (i.e. off-label) was identified. Of the 3328 feeds, about 79% contained feed additives used in the labeled manner. For all classes of pigs, the prevalence of labeled feed additive use was greater than 75%. Penicillin was used according to its label most often, followed by apramycin, bacitracin, tetracyclines, lincomycin, and tylosin. Carbadox had the highest prevalence of off-label use. Of the 699 feeds that included feed additives in an off-label manner, about 57% included additives at greater than the recommended concentrations or were fed to an incorrect class of pig. About 56% of the feeds had off-label combinations of additives. Small farms were more likely to use rations with no feed additives than intermediate or large farms ( P < 0.001). Of those farms using feed additives, the odds of a small farm using all feed additives in the labeled manner was 7.7 times that of an intermediate or large farm ( P < 0.0001). After controlling for herd size, producers who used a veterinary consultant were 2.1 times more likely to use feeds with feed additives ( P < 0.0001).

Design and implementation of the United States National Animal Health Monitoring System 1994–1995 Cattle on Feed Evaluation, and an evaluation of the impact of response biases

The 1994–1995 Cattle on Feed Evaluation was a cooperative project (sponsored by the United States Department of Agriculture) involving Washington State University, state agricultural departments, and several agencies of the United States Department of Agriculture). The project focused on cattle-on-feed operations in 13 states that accounted for over 85% of the United States cattle on feed inventory. Participants were selected from National Agricultural Statistics Service list frames. Questionnaires were administered by telephone to operations with a one-time capacity of fewer than 1000 cattle; larger operations were visited twice to administer questionnaires. The participation rate for the first phase of the study was 56.7%. Ninety-one percent of eligible operations completed the second phase of the study. Data summarized from this national study can be used to profile management practices on cattle-feeding operations in the United States. Differences between participants and non-participants did not appear to be great. However, one does need to be mindful of the fact that a small percentage of the producers accounted for the vast majority of feedlot cattle marketed when interpreting the results.

Virulence attributes of Escherichia coli isolated from dairy heifer feces

Escherichia coli isolates from 1,305 (of 6,894) fecal samples collected during the 1991–1992 USDA, Animal and Plant Health Inspection Service, National Animal Health Monitoring System, Dairy Heifer Evaluation Project were tested for virulence attributes associated with human enterohaemorrhagic E. coli (EHEC) and the enterotoxin commonly associated with diarrhoea in newborn calves. Single, random isolates from each heifer were hybridized to probes derived from the 60 mDa EHEC plasmid (CVD 419), E. coli attaching and effacing gene ( eae), Shiga-like toxin ( slt) genes I and II, and E. coli heat-stable enterotoxin a (STaP). Seventy-seven of the 1305 isolates (5.9%) were slt-positive. Most (81.8%) slt-positive E. coli were also CVD 419 and eae-positive. Only 2 of the slt-positive E. coli isolates were STaP-positive.

Seroprevalence of Toxoplasma gondii in hogs in the National Animal Health Monitoring System (NAHMS).

Seroprevalence of Toxoplasma gondii in hogs in the National Animal Health Monitoring System (NAHMS).

Evaluation of attitudes of participating groups in the Colorado Beef National Animal Health Monitoring System pilot program

The National Animal Health Monitoring System (NAHMS) was established due to the need for information concerning the incidence of animal disease and the associated costs of disease. Three basic components were proposed in the pilot phase of NAHMS. They were the epidemiologic component, the economic component, and the evaluation component. The epidemiologic component was concerned with collection of data about disease incidence, including information related to identification of risk factors for disease. The economic component attached monetary significance to health occurrences. It also associated cost/benefit ratios with various management decisions and characteristics of individual operations. Food animal veterinary practitioners increasingly deal with animals on a population basis and can use this information in their animal health programming efforts. The third major component of the NAHMS pilot program in Colorado was the evaluation. Evaluation of the pilot project was essential to improve the program, to provide public accountability, to increase knowledge about it, and to provide assessment criteria for future development. There were two primary areas of focus in the evaluation process. They were the methodology of the study, which included the data collection methods and the procedures used to validate and analyze the data, and NAHMS itself, including input from participants.

California National Animal Health Monitoring System for Meat Turkey Flocks: 1988-89 Pilot Study: Management Practices, Flock Health, and Production

A pilot project for a meat turkey National Animal Health Monitoring System was undertaken in California in 1988-89 to explore data gathering techniques and to estimate the frequency, magnitude, and variability of management, flock health (including administration of pharmaceuticals for prevention and treatment of disease), and production variables in order to facilitate planning for future food animal monitoring systems. Enteritis, which occurred in over one-third of the flocks, and colibacillosis, which occurred in nearly one-quarter of flocks, were the most common diseases reported. Mycoplasma synoviae was reported in two flocks and Mycoplasma gallisepticum and Mycoplasma meleagridis each were reported in one flock. Total mortality rate in the sample flocks was 9.0% (95% confidence interval [CI] 8.2%-9.8%). The tom-specific mortality rate was 10.9% (95% CI 9.8%-12.1%) and the hen-specific mortality rate was 6.6% (95% CI 5.7%-7.4%).

Test-retest repeatability of the National Animal Health monitoring system dairy heifer health report in New York and Pennsylvania, USA

We did a test-retest study on 21 farms to assess the repeatability of the Dairy Heifer Health Report of the National Dairy Heifer Evaluation Project. The median retest interval was 42 days (range 14–63 days), retest interviewers were blinded as to responses on the first visits, and all date-specific questions were anchored to the dates of the first tests. The overall discrepancy percentage was 8.5% (95% CI 8.0–9.0). Individual farms had discrepancy percentages of 3.0–15.2%; 240 out of the 539 questions had no discrepancies at all, but 81 questions had more than four (out of 21 possible) discrepancies (lowest percentages among the 81: 24%; 95% lower confidence limit on 24%: 6%). Combining ‘no’ and ‘not applicable’ responses for six similarly worded questions in the Biosecurity section would reduce the overall questionnaire discrepancy percentage to 7.8% and would bring that section's discrepancy percentage down to 8.6%. The other discrepancy percentages by section were: Maternity Hygiene, 14.1 %; Preweaning Hygiene, 4.8%; Disease Agents, 3.6%; Vaccination Practices, 12.1%; Preventive Practices, 16.8%. Discrepancy percentages did not differ importantly by type of question (independent, filter, or subordinate) or by type of response required (categorical, count, or measurement). Discrepancy percentages were independent of retest interviewer, test-retest interval and order of test within state (a proxy for time since training of the interviewers) but were correlated with herd size ( r sp = 0.59).

Application of a stochastic distributed delay simulation model to the epidemiology of clinical respiratory disease in a dairy cattle population

A stochastic distributed delay simulation model was applied in studying the epidemiology of clinical respiratory disease in a dairy cattle population. The predictive ability of the model was tested against data from the National Animal Health Monitoring System (NAHMS) in Michigan. Using the annual incidence density (aID) as outcome, model predicted aIDs were compared with those observed from the actual data. The model results did not significantly differ from the observed 66% of the time. Observations of model behavior and applications of this modeling approach are discussed.

Preweaning losses of piglets on a state farm in Bosnia and Herzegovina

The objective of a 3 year pilot survey of preweaning mortality on a large swine farm in Bosnia and Herzegovina was to provide producers and/or veterinarians with information about causes of piglet losses, their occurrence and frequency at the herd (regional) level. This may also serve as a model for an assessment at the national level. The SNOVET system, a part of the National Animal Health Monitoring System (launched in the USA in 1985), was applied for the classification of causes of deaths among suckling piglets based on postmortem findings. To assess the incidences of causes of preweaning losses, 354094 piglets born in 34 648 litters were monitored daily from June 1985 to May 1988. Respective information from 20 682 (or 5.8%) stillborns and those piglets that died from birth to weaning (49 058 or 14.7%) was given. Among piglets born alive, overlaying was the most frequent cause of death (6%), followed by mortality due to gastrointestinal syndrome (3.9%), cachexia/inanitio neonatorum (2.2%), and losses of small or deformed piglets (1.6%). The incidence of pneumonia was very low (0.02%). A relatively high proportion of causes of mortality remained unknown (0.9%) partly owing to savaging or losing piglet corpses in the sewers. The use of recorded information on type, extent, and incidence of piglet mortality (gathered on the sample of appropriate size) on a long-term basis may help in the development of effective strategies to reduce/control losses until weaning.

Risk factors for metritis in Michigan dairy cattle using herd- and cow-based modelling approaches

A prospective study, using the Michigan portion of the National Animal Health Monitoring System, was conducted to determine disease and management factors that affect the incidence of metritis in Michigan dairy herds. A stratified random sample representing 1% of all Michigan dairy herds was observed. Data related to herd, feeding, and reproduction management, disease and environmental risk factors, and cow-based disease and reproductive data were collected monthly for a 12 month period. Cows with complete management records that were observed for at least 3 months postpartum were included in the study (85 herds, 5278 cows). A multivariate linear regression model was developed for lactational incidence of metritis by herd, and a multivariate random-effects logistic model was developed for the occurrence of metritis by cows. Significant factors associated with increased occurrence of metritis included larger herds, problem calvings, overconditioning, underconditioning, and more active reproductive management. Factors associated with reductions in metritis involved good nutritional management, and working relationships with veterinarians for disease management. Implications for the significance of these factors are discussed, with emphasis on differences in interpretation and use of results from herd and cow-based analyses.

A case-control study of Washington dairy herds experiencing drug residue violations in market calves

The purpose of this case-control study was to examine the association between management practices and the occurrence of violative drug residues in calves originating from Washington dairies. In 1992, 74 dairies were identified as first-time offenders sending to abattoirs calves less than 1 week of age that had violative residue levels. Of these, 56 answered a subset of previously validated management questions from the 1991–1992 US National Animal Health Monitoring System National Dairy Heifer Evaluation Program (NDHEP) study during a violation investigation and comprised the case group. The controls were the 51 randomly selected Washington dairies that participated in the NDHEP, completed the four NDHEP questionnaires, and had not been identified as having residue violations. Management factors investigated were those associated with maternity and pre-weaning hygiene, vaccination and preventive practices, type and management of liquid calf feed, and general management. Other factors included herd somatic cell count (SCC), the presence of clinical signs associated with diseases of body systems, and herd size. Significant associations were detected between violation occurrence and the management of calving cows, colostrum volume and management, and the person responsible for calf care. Significant associations but of the wrong direction were found between violation occurrence and type and management of liquid calf feed. No significant associations were detected between violation occurrence and the remaining management factors, herd size, animals entering the herd, or SCC.

Evaluation of non-sampling errors in the US National Swine Survey

On-farm data collection consists of a dynamic interaction between the interviewer and respondent via a questionnaire. Non-sampling errors introduced by these sources during the measurement process often account for a greater proportion of the total survey error than sampling error alone. A two pronged approach was used to evaluate non-sampling errors in the National Animal Health Monitoring System's National Swine Survey. First, results from two supplemental questionnaires, administered to field coordinators and interviewers of the National Swine Survey, were used to assess correlates of non-sampling errors. Second, since questionnaires contained multiple indicators of the same underlying concept, an index of inconsistency was used to quantify the level of response error for several variables. Bias due to the ecologic fallacy was shown by elevated estimates of response error for several indicators of preventive practices. Correlates of respondent error included the presence of multiple respondents for at least one interview for more than half of the interviewers. Correlates of interviewer error included demographic characteristics of interviewers and variations in question administration. Evidence corroborates the idea that survey questions should be unambiguous in wording and simple in structure. Results led to specific recommendations for future questionnaire design and interviewer training. The manifestation of many correlates of non-sampling error support the need for assessment of total survey error in large surveys.

Empirical similarity of responses of two random samples of North Carolina swine producers to a management questionnaire used in the US National Swine Survey

The United States Department of Agriculture's (USDA) National Animal Health Monitoring System (NAHMS) National Swine Survey (NSS), implemented in 1990, represents the first national effort to collect on-farm data using a statistically valid method. The purpose of the North Carolina Swine Survey (NCSS) was to evaluate the reliability of the NSS by assessing the similarity of responses between the North Carolina portion of the NSS and the NCSS using identical questions. Responses from the North Carolina portion of the NSS ( n = 40 farms) and from the NCSS ( n = 139 farms) were compared for a subset of the first three questionnaires used in the NSS. Chi-square analysis was used to test for significant differences between estimated proportions from the two studies. Plots of component chi-square values and frequency distribution of differences between point estimates were used to evaluate the similarity between sections of the questionnaires. Approximately 75% of the 446 point estimates were within 15% of each other. The majority of significant discrepancies occurred for the biosecurity section of the second questionnaire, specifically for response categories of ‘No’ and ‘ N A ’ (not applicable). Percent of farms responding ‘Yes’ showed greater comparability between the two studies. While most questions from the first and third questionnaires (General Swine Farm Report and the Facilities and Feed Report) proved to be similar, questions regarding disease problems, vaccination and preventive practices were less similar between the two studies.

Theoretical financial benefit of internal parasite control for Michigan dairy farms using National Animal Health Monitoring System data

A study was undertaken to assess the capability of the National Animal Health Monitoring System (NAHMS) to collect necessary and sufficient data for financial analysis of internal parasitism in Michigan dairy herds. This problem was chosen because of increasing interest in animal health monitoring systems in developing countries, where internal parasites are a major health concern. Partial budgeting was used to determine the financial effect of controlling internal parasites in a ‘typical’ dairy herd. Herd and health management parameters were defined using Michigan NAHMS data from 1987/1988 and 1988/1989. Financial parameters were determined from the 1989 Telfarm database. The effects of parasitism on production were defined from the literature. Selected sensitivity analyses were performed. If a ‘typical’ Michigan dairy herd was infected with internal parasites, and if a treatment was implemented where all animals responded positively, the dairy farmer could expect to gain over $ 15 per head in 1988/1989. These results were most sensitive to milk price, expected improvement in performance, and feed costs. Moderate sensitivity also was evident for production per cow and wage rate. The stratified random sampling procedure of NAHMS facilitated description of physical attributes for the ‘typical’ farm. However, several limitations in the database were defined during this exercise, including lack of definitive diagnosis of parasitism, feed cost data, weight gains of young stock, and livestock prices. Implications of these limitations are discussed.