Antibiotic residue prevention methods, farm management, and occurrence of antibiotic residues in milk

EFEITO DO TIPO DE ORDENHA E DO AMBIENTE SOBRE A QUALIDADE DO LEITE CRU COM BASE NA CONTAGEM DE CÉLULAS SOMÁTICAS

Resumo Objetivou-se avaliar o efeito do tipo de ordenha e de ambiente na qualidade do leite cru por meio da identificação da Contagem de Células Somáticas - CCS nas amostras obtidas das propriedades rurais da mesorregião do sul goiano e correlacioná-la com diferentes tipos de ordenha, bem como com os componentes do leite e o período do ano. A pesquisa desenvolveu-se em 229 fazendas associadas à Cooperativa de Catalão, divididas por tipo de ordenha: manual e mecânica. Em cada propriedade foi coletada amostra mensal no tanque de expansão, no total de 8244 amostras. A ordenha mecânica obteve maior número de amostras com CCS > 500.000 células/mL. Existiu correlação positiva entre CCS e teor de gordura e sólidos totais - ST, porém houve uma correlação negativa entre CCS e teores de proteína e lactose. No período da chuva tem-se uma elevação de CCS se comparado ao período da seca, e com a elevação do Índice de Temperatura e Umidade - ITU ocorreu uma redução nos teores de gordura e ST. Pode-se concluir que a ordenha manual mostrou-se mais viável para obtenção do leite com parâmetros de CCS exigidos pela legislação e que CCS e componentes do leite sofrem interferência da época do ano.

A genetically engineered Escherichia coli that senses and degrades tetracycline antibiotic residue

Due to the abuse of antibiotics, antibiotic residues can be detected in both natural environment and various industrial products, posing threat to the environment and human health. Here we describe the design and implementation of an engineered Escherichia coli capable of degrading tetracycline (Tc)-one of the commonly used antibiotics once on humans and now on poultry, cattle and fisheries. A Tc-degrading enzyme, TetX, from the obligate anaerobe Bacteroides fragilis was cloned and recombinantly expressed in E. coli and fully characterized, including its K m and k cat value. We quantitatively evaluated its activity both in vitro and in vivo by UV-Vis spectrometer and LC-MS. Moreover, we used a tetracycline inducible amplification circuit including T7 RNA polymerase and its specific promoter PT7 to enhance the expression level of TetX, and studied the dose-response of TetX under different inducer concentrations. Since the deployment of genetically modified organisms (GMOs) outside laboratory brings about safety concerns, it is necessary to explore the possibility of integrating a kill-switch. Toxin-Antitoxin (TA) systems were used to construct a mutually dependent host-plasmid platform and biocontainment systems in various academic and industrious situations. We selected nine TA systems from various bacteria strains and measured the toxicity of toxins (T) and the detoxifying activity of cognate antitoxins (A) to validate their potential to be used to build a kill-switch. These results prove the possibility of using engineered microorganisms to tackle antibiotic residues in environment efficiently and safely.

A 100-Year Review: Cheese production and quality

In the beginning, cheese making in the United States was all art, but embracing science and technology was necessary to make progress in producing a higher quality cheese. Traditional cheese making could not keep up with the demand for cheese, and the development of the factory system was necessary. Cheese quality suffered because of poor-quality milk, but 3 major innovations changed that: refrigeration, commercial starters, and the use of pasteurized milk for cheese making. Although by all accounts cold storage improved cheese quality, it was the improvement of milk quality, pasteurization of milk, and the use of reliable cultures for fermentation that had the biggest effect. Together with use of purified commercial cultures, pasteurization enabled cheese production to be conducted on a fixed time schedule. Fundamental research on the genetics of starter bacteria greatly increased the reliability of fermentation, which in turn made automation feasible. Demand for functionality, machinability, application in baking, and more emphasis on nutritional aspects (low fat and low sodium) of cheese took us back to the fundamental principles of cheese making and resulted in renewed vigor for scientific investigations into the chemical, microbiological, and enzymatic changes that occur during cheese making and ripening. As milk production increased, cheese factories needed to become more efficient. Membrane concentration and separation of milk offered a solution and greatly enhanced plant capacity. Full implementation of membrane processing and use of its full potential have yet to be achieved. Implementation of new technologies, the science of cheese making, and the development of further advances will require highly trained personnel at both the academic and industrial levels. This will be a great challenge to address and overcome.

Detection of tetracycline and other antimicrobial residues in milk from cows with clinical mastitis treated by combination therapy

The purpose of this study was to determine tetracycline and other antimicrobial residues in milk from dairy cows treated for clinical mastitis. Data on cow health and drugs used were obtained from the farm veterinarians. A milk sample from each affected udder quarter of each cow was taken for bacterial identification before treatment. All 35 cows in the study were treated with an intramammary product containing tetracycline, neomycin, bacitracin, and prednisolone (tetracycline injector) and also simultaneously with other drugs via the intramammary or parenteral route. The withhold period of the 'tetracycline product' was eight milkings but, in all cases, longer withhold periods were prescribed due to off-label application of additional combinations of drugs. Milk samples from treated udder quarters, taken two milkings before and two after the prescribed withhold period, were analysed for antimicrobial residues. Additionally, milk samples were taken from untreated healthy udder quarters to check if any crossover of drugs had occurred. Three screening tests were used for antimicrobial detection. In 15 (42·9%) cows the milk samples from the treated infected quarters contained tetracycline residues above the maximum residue limit (MRL) after the prescribed withhold period and, in two cases (5·7%) the same was true for neomycin and cefquinome residues. Cephalexin above the MRL was detected in only one case (2·9%). Beta-lactams did not exceed the MRL after the prescribed withhold period. Antimicrobial residues were not detected in milk samples from untreated quarters. Cow condition including parity, decreased milk production and severity of mastitis significantly influenced the excretion of antimicrobials in milk (P ≤ 0·05). No significant differences were found between the tetracycline positive and tetracycline negative cows regarding the bacteria involved, combination antimicrobial therapy, or treatment interval and duration.

Antibiofilm and antibacterial effects of specific chitosan molecules on Staphylococcus aureus isolates associated with bovine mastitis

Staphylococcus aureus is one of the major pathogens causing bovine intramammary infections (IMIs) and mastitis. Mastitis is the primary cause for the use of antibiotics in dairy farms but therapeutic failure is often observed. One of the reasons for the lack of effectiveness of antibiotic therapy despite the observed susceptibility of bacterial isolates in vitro are bacterial biofilms. In this study, we used chitosan of well-defined molecular weight (0.4–0.6, 1.3, 2.6 and 4.0 kDa) and investigated their antibiofilm and antibacterial activities in in vitro and in vivo models related to S. aureus IMIs. A chitosan of at least 6 units of glucosamine was necessary for maximum antibacterial activity. The 2.6 and 4.0 kDa forms were able to prevent biofilm production by the biofilm hyperproducer strain S. aureus 2117 and a bovine MRSA (methicillin-resistant S. aureus). The intramammary administration of the 2.6 kDa chitosan showed no adverse effects in mice or in cows, as opposed to the slight inflammatory effect observed in mammary glands with the 4.0 kDa derivative. The 2.6 kDa chitosan killed bacteria embedded in pre-established biofilms in a dose-dependent manner with a >3 log10 reduction in CFU at 4 mg/ml. Also, the 2.6 kDa chitosan could prevent the persistence of the internalized MRSA into the mammary epithelial cell line MAC-T. An in vitro checkerboard assay showed that the 2.6 kDa chitosan produced a synergy with the macrolide class of antibiotics (e.g., tilmicosin) and reduced the MIC of both molecules by 2–8 times. Finally, the intramammary administration of the 2.6 kDa chitosan alone (P<0.01) or in combination with tilmicosin (P<0.0001) reduced the colonization of mammary glands in a murine IMI model. Our results suggest that the use of chitosan alone or in combination with a low dose of a macrolide could help reduce antibiotic use in dairy farms.

Antibiotic residues in milk from small dairy farms in rural Peru

The use of antibiotics in livestock can pose a public health threat, especially if antibiotic residues remain in the food product. Understanding how often and why farmers sell products with antibiotic residues is critical to improving the quality of these products. To understand how often milk with antibiotic residues is sold on small farms in a major dairy-producing region of Peru and identify factors associated with selling milk with antibiotic residues, we tested milk samples for antibiotic residues from every provider on three routes of commercial milk companies and from bulk tanks of farmers currently treating cows with antibiotics. We also asked farmers if they sold milk from treated cows and examined factors associated with the tendency to do so. The prevalence of milk contamination with antibiotic residues on commercial routes was low (0-4.2%); however, 33/36 farmers treating their animals with antibiotics sold milk that tested positive for antibiotic residues. The self-reported sale of milk from treated cows had a sensitivity, specificity, and positive and negative predictive values of 75.8%, 100%, 100% and 27.2%, respectively (with testing of milk for residues as the gold standard). Finally, 69/156 randomly selected farmers reported selling milk from treated cows, and farmers' knowledge of antibiotics and the milk purchaser were significantly associated with a farmer's tendency to report doing so. Educating farmers on the risks associated with antibiotics and enforcement of penalties for selling contaminated milk by milk companies are needed to improve milk quality.

Comparison of two methods for collecting antibiotic use data on small dairy farms

Antibiotics are commonly used in animal agriculture; they can improve animal health and productivity, but their use may also represent a public health threat. Very little is known about antibiotic use on small farms in lower/middle income countries. To understand antibiotic use on these farms and promote the judicious use of these drugs, pharmacoepidemiologic data are necessary. However, acquiring such data can be difficult, as farmers are often illiterate (and therefore cannot participate in written surveys or keep treatment records), antibiotics can be obtained over-the-counter (in which case no prescriptions are generated) and monitoring and surveillance systems for drug use are often non-existent. The goal of this study was to compare two methods of acquiring pharmacoepidemiologic data pertaining to antibiotics that are well-adapted to farms in lower-middle income countries: self-report and the collection of discarded drug packaging. A convenience sample of 20 farmers in Cajamarca, Peru, participated in the study. Farmers placed discarded antibiotic packaging in bins for six months. At the end of the six-month period, farmers were interviewed and asked to recall the antibiotic usage that occurred on their farm over the past month and past six months; these self-reported data were quantitatively and qualitatively compared to the bin contents collected in the last month and previous six months. We found that the agreement between the bins and self-report was relatively poor for both the quantity and types of antibiotics used. The bins appeared to perform better than self-report when bottles and mLs of antibiotics were measured, while self-report appeared to perform better for intra-mammary infusions. The bins also appeared to perform better when data pertaining to an extended time period (six months) were collected. The results of this study will provide guidance to investigators seeking to collect pharmacoepidemiologic data in similar environments.

Prevalence of antimicrobial residues in pork meat in Madagascar

Residual antimicrobials in food constitute a risk to human health, but poor knowledge is available about the significance of contaminated meat in developing countries. The purpose of the study was to determine the occurrence of antimicrobial drug residues in pork products in Madagascar. The occurrence of antimicrobial drug residues in pork meat were investigated by the Premi® test (DSM(©)) technique. There was a high incidence rate of drug residues, with 360 (37.2 %) meat samples being contaminated. A significant increase was observed between 2010 and 2011, with 32 and 39%, respectively. Pork meat samples are less contaminated by drug residues when animals are slaughtered in urban abattoirs (34.4%) vs in provincial abattoirs (42.2%), suggesting that animals under treatment (or sick) are sold preferentially in local abattoir. Drug residue levels in pork meats purchased in Madagascar appear to be serious public health problem at the moment.

Occurrence of flunixin residues in bovine milk samples from the USA

5-Hydroxy-flunixin concentrations in milk samples were quantified by two commercially available screening assays--CHARM® and enzyme-linked immunoabsorbant assay (ELISA)--to determine whether any concentrations could be detected above the tolerance limit of 2 ng g⁻¹ from different regions in the United States. Milk samples came from large tanker trucks hauling milk to processing plants, and had already been screened for antibiotics. Positive results for flunixin residues based on a screening assay were confirmed by ultra-HPLC with mass spectrometric detection. Of the 500 milk samples analysed in this study, one sample was found to have a 5-hydroxy-flunixin concentration greater than the tolerance limit. The results of this study indicate that flunixin residues in milk are possible. Regulatory agencies should be aware that such residues can occur, and should consider incorporating or expanding flunixin screening tests as part of routine drug monitoring in milk. Larger studies are needed to determine the true prevalence of flunixin residues in milk from other regions in the United States as well as different countries.

Validation and comparison of the Copan Milk Test and Delvotest SP-NT for the detection of antimicrobials in milk

The Delvotest SP-NT and Copan Milk Test, two microbiological tests designed for screening antimicrobial substances in milk were compared and validated. The performance criteria described by the European Decision 2002/657/EC were used for the study. Both tests were evaluated with visual and automated reading (scanner) and the validation was performed on 10 different antibiotics (penicillin-G, cloxacillin, sulfamethazine, sulfadiazine, oxytetracycline, gentamicin, cephalexin, cefquinome, dihydrostreptomycin and trimethoprim). Both tests were found to detect penicillin, cloxacillin, sulfamethazine, sulfadiazine, cephalexin and gentamicin at or below the EU maximum residue limits (MRLs). Some other antibiotics such as oxytetracycline, dihydrostreptomycin, trimethoprim and cefquinome were not detected or only with a low sensitivity. Both tests were found easy to use, robust and fulfilled EU requirements.

Clinical herd health, farm management and antimicrobial resistance in Campylobacter coli on finishing pig farms in Switzerland

The world-wide increase of antimicrobial resistance in micro-organisms complicates medical treatment of infected humans. We did a risk-factor analysis for the prevalence of antimicrobial resistant Campylobacter coli on 64 Swiss pig finishing farms. Between May and November 2001, 20 faecal samples per farm were collected from the floor of pens holding finishing pigs shortly before slaughter. Samples were pooled and cultured for Campylobacter species. Isolated Campylobacter strains were tested for resistance against selected antimicrobials. Additionally, information on herd health and management aspects was available from another study. Because data quality on the history of antimicrobial use on the farms was poor, only non-antimicrobial risk factors could be analysed. Statistical analyses were performed for resistance against ciprofloxacin, erythromycin, streptomycin, tetracycline, and for multiple resistance, which was defined as resistance to three or more antimicrobials. Risk factors for these outcomes--corrected for dependency of samples at herd level--were analysed in five generalised estimation-equation models. Prevalence of antimicrobial resistance among Campylobacter isolates was ciprofloxacin 26.1%, erythromycin 19.2%, streptomycin 78.0%, tetracycline 9.4%, and multiple resistance 6.5%. Important risk factors contributing to the prevalence of resistant strains were shortened tails, lameness, skin lesions, feed without whey, and ad libitum feeding. Multiple resistance was more likely in farms which only partially used an all-in-all-out system (OR = 37), or a continuous-flow system (OR = 3) compared to a strict all-in-all-out animal-flow. Presence of lameness (OR = 25), ill-thrift (OR = 15), and scratches at the shoulder (OR = 5) in the herd also increased the odds for multiple resistance. This study showed that on finishing farms which maintained a good herd health status and optimal farm management, the prevalence of antimicrobial resistance was also more favourable.

Management of the dry cow in control of peripartum disease and mastitis

The dry period has great implications on overall health and productivity in the subsequent lactation. Many anatomic, physiologic, and immunolgic changes are occurring for both the cow and the mammary gland during this time. These changes need to be understood and taken into consideration when assessing and implementing health management programs that involve this crucial time period. Specifically, nutritional and immunologic requirements of the individual cow need to be considered. The occurrence of many peripartum diseases is significantly influenced through nutritional and metabolic parameters that can be strongly influenced, controlled, and monitored in the dry period. From an udder-health perspective, the goal of the dry period can be met by recommending administration of DCT to all quarters of all cows at the end of lactation. As research continues to explore and define shortcomings of this approach and as scrutiny of the prophylactic use of antibiotics increases, however, novel approaches to preventing and eliminating IMI may become more readily available. These approaches offer new methods to improve upon and redefine what should be realistic goals of the dry period and afford an opportunity for continued improvement of udder health in today's dairy herds.

Trends in somatic cell counts, bacterial counts, and antibiotic residue violations in New York State during 1999-2000

Milk quality data on a month-by-month basis from March 1999 to December 2000 were studied from five of the largest milk plants operating in New York State. The analyses focused on bulk tank somatic cell count (SCC), bacterial counts in the form of plate loop count (PLC), and antibiotic residue violations in the pool of milk of New York State, their mutual relation, and the influence of farm size. The average SCC was 363,000 cells/ml, the average PLC was 24,400 bacteria/ml, and the average number of antibiotic residue violations in the pool of milk was 3.9 per 1000 producers. Each month between 72 and 88% of the milk pool had SCC levels in compliance with the European Union (EU) requirements (SCC < 400,000 cells/ml). The findings in this study suggest that larger farms had lower SCC and PLC but more antibiotic violations. However, the larger farms contribute most to the SCC and PLC of the total pool of milk. Farms with high SCC also had higher PLC and more antibiotic violations. Measurable improvements in overall quality of the pool of milk in New York state would most likely occur by targeting incentives, education, and training programs for any farms with very high SCC and for larger farms with SCC between 400,000 and 750,000 cells/ml.

Occurrence of false-positive results of inhibitor on milk samples using the Delvotest SP assay

Three hundred twenty-one quarter, 207 whole udder, 310 bulk tank, and 93 tank-lorry milk samples were examined for confirmation of the presence of inhibitor by Delvotest SP assay. Four hundred twenty-six Holstein cows of no drug treatment for at least 30 days from January 1998 to September 1999 were used. Reading time was 2.50, 2.75, and 3.00 h, and results of sampling were recorded by four types according to comparison with the color of the well containing the control milk sample. False-positive outcome was identified by Delvotest SP assay in quarter (13 of 321), whole udder (9 of 207), and bulk tank milk samples (4 of 310), but was not shown on tank-lorry milk samples (0 of 93) at the reading time of 2.50 h. All of the 26 false-positive samples were negative from the examination after heat treatment at 82 degrees C for 5 min. But, two bulk tank milk samples that appeared to have positive results in LacTek and Charm II tests were positive from the test following heat treatment. Somatic cell counts (SCC) were related to the probability of a false-positive result. The more SCC increased, the more the occurrence of a false-positive result increased. In our investigations, 4 of 310 bulk tank milk samples at the reading time of 2.50 h produced false-positive results, and no false-positive results were apparent at a reading time of 2.75 h. Also, the occurrence of false-positive results in quarter and whole udder milk samples decreased when agar was cultured for 2.75 to 3.00 h. There were no false-positive results from tank-lorry milk samples. These results indicate that the Delvotest SP assay may provide a suitable means for the detection of drug residues in not only quarter and whole udder milk of cows but also in bulk tank and tank-lorry milk following reading times of 2.75 to 3.00 h.

Effect of composition of colostrum and transition milk from Holstein heifers on specificity rates of antibiotic residue tests

The objective of this study was to evaluate the effects of colostrum and transition milk composition on specificity rates of antibiotic residue screening tests. Milk from 25 primigravid Holstein heifers was collected from either first, second, or third milking (colostrum) and from either fifth, sixth, or seventh milking (transition milk) following parturition. Milk sampled was visibly normal and heifers were not treated with an antibiotic within 30 d before parturition. Quarter foremilk samples were collected aseptically and analyzed for mastitis pathogens. A sample from the total composite milk was analyzed for somatic cell counts (SCC), milk protein and fat, immunoglobulin concentrations and for antibiotics using four antibiotic residue screening tests. Mastitis pathogens were present in colostrum from 36% of heifers (n = 9) and from 16% of heifers (n = 4) in the subsequent transition milk. Mean SCC were 2,458,000 and 866,000 counts/ml and IgG1 concentrations were 22.7 and 3.07 mg/ml for colostrum and transition milk, respectively. Specificity rates of the screening tests ranged from 0.16 to 0.88 for colostrum and 0.60 to 1.0 for transition milk. Increased milk protein and IgG1 concentrations in milk were associated with an increase in the probability of a false positive outcome for the Charm Cowside (Charm Sciences, Inc., Malden, MA), CITE Snap (IDEXX Laboratories, Westbrook, ME), and Penzyme (Cultor Food Science, Milwaukee, WI) tests. Fat content of milk was positively related to an increase in false positive rates for the CITE Snap test. Milk should not be tested for antibiotic residues before the sixth milking after parturition to avoid high rates of false positive outcomes.

Effect of fat and protein content of milk from individual cows on the specificity rates of antibiotic residue screening tests

The effect of high concentrations of milk protein and milk fat on the specificity rates of several antibiotic residue screening tests was evaluated in this study. Milk was sampled from 60 Jersey and 30 Holstein cows at one milking and analyzed for beta-lactam residues using four antibiotic residue screening tests. Cows selected were not treated with an antibiotic for at least 30 d prior to sample collection, and milk was visibly normal. Before milk collection, quarter foremilk was aseptically sampled for mastitis pathogen analysis. Milk subsamples were analyzed for fat and protein contents, and somatic cell counts (SCC). Ten Jersey and four Holstein cows were infected with one or more mastitis pathogens. Concentrations of milk fat (4.78 vs. 3.39%) and protein (3.81 vs. 3.00%) were greater for Jersey cows compared with Holstein cows. Milk SCC averaged 148,000/ml and did not differ by breed. The specificity rates were greater than 0.9 for three of the four screening tests. Across breeds, there was an increased probability of a false-positive outcome for the Penzyme test (Coulter Food Science, Milwaukee, WI)), with increased milk protein content and decreased SCC. Increased milk fat content was associated with an increased probability of false-positive outcomes for the CITE Snap test (IDEXX Laboratories, Inc., Westbrook, ME). High concentrations of milk protein and milk fat can adversely affect antibiotic residue test performance, but the degree of the effect is dependent upon the analytical method of the screening test.

Association between measures of milk quality and risk of violative antimicrobial residues in grade-A raw milk

OBJECTIVE

To determine whether bulk-tank standard plate counts or plate loop counts and bulk-tank somatic cell counts (SCC) were associated with detection of violative antimicrobial residues in milk from dairy cattle.

DESIGN

Longitudinal study.

PROCEDURE

Information for 1994 through 1997 was obtained from a large milk marketing cooperative that operated in multiple states throughout the northeastern and midwestern United States (16,831 herd-years of information from 6,546 farms) and from the Ohio Department of Agriculture Grade-A Milk Certification Program (12,042 herd-years of information from 4,022 farms). Data were analyzed by use of multivariate logistic regression.

RESULTS

For both data sets, odds that a violative antibiotic residue would be detected increased as mean SCC for the herd-year increased. Standard plate counts and plate loop counts were not associated with odds that a violative antibiotic residue would be detected.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this study suggested that the odds that a violative antibiotic residue would be found in bulk-tank milk increased as mean SCC for the herd-year increased. This suggests that management practices that would be expected to influence SCC may also influence the risk of antibiotic residue violations.

Influence of the Milk and Dairy Beef Quality Assurance Program on dairy farm drug management practices

OBJECTIVE

To test the hypothesis that dairy farms certified in the Milk and Dairy Beef Quality Assurance Program (QAP) were more likely to use prudent drug management practices than farms that were not certified.

DESIGN

Cross-sectional study.

SAMPLE POPULATION

141 Michigan dairy farms of which 74 were not certified in the QAP, 30 were involuntarily certified, and 37 were voluntarily certified.

PROCEDURE

Dairy producers completed a self-administered questionnaire that focused on herd health management, drug use, record keeping, personnel management, and descriptive characteristics of their farm during 1993. Separate multivariable logistic regression models were developed to determine the association of QAP certification with each of the management practices.

RESULTS

Results suggested that farms adopted specific management practices irrespective of certification. Many farms used visible identification and non-emergency veterinary services and discussed residue prevention with employees. Involuntary certification was associated with maintenance of good written treatment records and performance of on-farm drug residue testing. Voluntary certification was weakly associated with use of refrigerated drug storage.

CONCLUSIONS AND CLINICAL RELEVANCE

QAP certification appeared to have been associated with the adoption of only a few prudent drug use practices, although QAP materials and framework were developed to assist veterinarians in the promotion of disease prevention, client communication, and residue prevention practices on farms. Veterinary care would benefit from the development and encouragement of better record keeping on farms.

Ontario bulk milk somatic cell count reduction program: progress and outlook

The objective of this study was to describe the results of the ongoing somatic cell count (SCC) reduction program in Ontario, Canada and to provide an outlook regarding the possible scenarios beyond the final stages of the current reduction program. The data were from all of the approximately 9500 farms in the province of Ontario during the last 10 yr and included monthly data for kilograms of milk sold, mean milk component measurements, and milk quality measurements (bulk milk SCC, plate loop count, and inhibitor presence). Four of five steps in the control program had a significant impact on the mean monthly bulk milk SCC. The total decrease in mean SCC that was attributable to the program was approximately 80 x 10(3) cells/ml. The monthly occurrence of inhibitor violations increased significantly. Cross-classification of the annual mean bulk milk SCC and the incidence of inhibitor violations indicated that the incidence specifically increased for farms with a relatively high bulk milk SCC. In 1994, bulk milk SCC increased, primarily because of farms that had a mean bulk milk SCC between 150 x 10(3) and 450 x 10(3)/ml. The small relative contribution of farms with higher bulk milk SCC was due to their relatively low production and the small number of farms in those classes. The Ontario SCC reduction program was initially successful in the reduction of mean bulk milk SCC. Further reduction will require the active participation of farms with a relatively low bulk milk SCC. Not only is it necessary to penalize farms that exceed thresholds, but also an incentive to prevent farms with good udder health management from increasing bulk milk SCC is of great importance. The increase in inhibitor violations is of concern and requires further attention.

Evaluation of selected antibiotic residue screening tests for milk from individual cows and examination of factors that affect the probability of false-positive outcomes

Total composite milk samples from 131 cows in one herd were analyzed. Eight beta-lactam residue screening tests were evaluated for performance using milk from individual cows and factors that affect the rate of false-positive outcomes were determined. Cows were not treated with an antibiotic for at least 30 d prior to sampling. Tests evaluated were Delvotest P, Charm Cowside, Charm Farm, Penzyme, Valio T101, LacTek, CITE Probe, and Charm Bacillus stearothermophilus disk assay. Cows averaged 155 d of lactation. Milk production at the time of sampling ranged from 3.6 to 26.3 kg per milking per cow. The somatic cell count of milk averaged 243 x 10(3)/ml and ranged from 8.5 x 10(3)/ml to 3437 x 10(3)/ml. Total viable bacteria counts averaged 197.8 x 10(3)/ml. Total coliform counts ranged from 0 to 205/ml. Selectivity rates (rate of truly negative samples that were found to be negative by the assay) were greater than 90% for all tests except the CITE Probe test. Use of logistic regression showed that an increase in colony-forming units was associated with a decrease in the probability of a false-positive outcome for the CITE Probe test. Milk production, coliform counts, and parity each affected the probabilities of positive outcomes for different tests. Except for one test, selectivity rates of the beta-lactam residue screening tests for milk from individual cows was greater than 0.9.

Implementing a quality assurance program using a risk assessment tool on dairy operations

Concerns and perceptions about antibiotic residues in milk prompted the dairy industry to develop a voluntary program to support rational antibiotic use on dairy farms. One deficiency of this program is the inability of producers to identify easily the weaknesses in antibiotic management in order to develop control plans. To overcome this deficiency, an educational approach was designed. The program centered on an on-farm risk assessment tool used by the producer and an industry educator to determine the current risk for residue violation. The risk assessment tool was tested by 25 field personnel working with northeastern milk receivers and 250 producers in seven states. The participants in the study identified a lack of adequate treatment records as being the highest risk factor for antibiotic residues, followed by deficiencies in understanding how to use antibiotics and poor relationships between veterinarians and their clients. When field representatives utilized the risk assessment tool, for most producers, risk of antibiotic residue decreased by approximately 19%. In particular, more farms kept written records or more complete records. Finally, producers with reported histories of antibiotic residues were less likely to implement management changes to reduce the risk of antibiotic residue.