A retrospective cohort study comparing dairy calf treatment decisions by farm personnel with veterinary observations of clinical signs.

Antimicrobials are frequently administered to calves with diarrhea, despite evidence suggesting questionable efficacy. Even if efficacious, providing the appropriate therapy to an animal requires accurate disease detection. The objective of this study was to use previously collected data and compare clinical scoring by a veterinarian to treatment decisions by on-farm personnel. Data describing daily clinical scores and farm treatments were previously collected from 4 farms for calves from birth to age 28 d. In this data set, a total of 460 calves were enrolled. Daily observations and clinical assessments were made on each farm by the same veterinarian, for a total of 12,101 calf observation days. Farm personnel made all treatment decisions based on their own observations, and these treatments were recorded by study personnel. Overall, the cumulative incidence of a calf exhibiting at least one abnormal clinical sign over the 28-d observation period was 0.93, with cumulative incidences of 0.85 and 0.33 for diarrhea and dehydration, respectively. The cumulative incidence of any treatment (including antibiotics and electrolytes) was 0.85, although the majority of treatments used an antimicrobial. The farm-specific probabilities that a calf with clinical signs of dehydration or diarrhea, respectively, received fluid or electrolyte therapy ranged from 0.08 to 0.27 and 0.03 to 0.12. These probabilities were greater for the day a clinical sign was first observed. The farm-specific probabilities that a calf with clinical signs of diarrhea received an antimicrobial was 0.23 to 0.65, and the probability that a calf exhibiting clinical signs of respiratory disease received an antimicrobial was 0.33 to 0.76. The first observation of diarrhea had similar probabilities to those for all observations of diarrhea. There was greater probability of treatment for calves with their first observed abnormal respiratory signs. Probabilities that treatment with antimicrobials, or fluids or electrolytes, was associated with an abnormal clinical sign were low-that is, calves received treatments in the absence of any abnormal clinical signs. This study illustrates incongruity between treatment decisions by calf treaters (the designated personnel on each farm responsible for calf health assessment and treatment decisions) and those of an observer using a clinical scoring system to identify calves with abnormal clinical signs. These findings indicate opportunities and the need for dairy farmers and advisors to evaluate calf treatment protocols, reasons for treatment, and training programs for calf health and disease detection, as well as to develop monitoring programs for treatment protocol compliance and health outcomes following therapy.

Risk factors for subclinical and clinical ketosis and association with production parameters in dairy cows in the Netherlands.

Ketosis is associated with many transition cow diseases and the subclinical form has been found to be a common condition in high-producing dairy cows. The objectives of this field study in the Netherlands were (1) to determine risk factors for subclinical ketosis [SCK; 1.2-2.9mmol of ß-hydroxybutyrate (BHBA)/L of serum] and clinical ketosis (CK: ≥3.0mmol of BHBA/L of serum) at 7 to 14 d in milk and (2) to assess the association of SCK and CK with production parameters at the first dairy herd improvement (DHI) testing. Twenty-three dairies were enrolled by a local veterinary practice from 2009 to 2010, and 1,715 cows were screened for ketosis by measuring serum BHBA concentrations at 7 to 14 d in milk. Overall, 47.2% of cows had SCK and 11.6% had CK. Mixed generalized logit models with a random effect of herd were used to evaluate cow level factors associated with SCK and CK. The associations of SCK and CK with milk production parameters were tested using mixed linear models with a random effect of herd. Cows at a moderate (3.25-3.75) or fat (≥4) body condition score before calving were more likely to develop SCK and CK than thin (body condition score≤3.0) cows. The risk for developing SCK was higher in parity 2 and older cows compared with heifers, whereas for CK only, parity ≥3 cows had a higher risk. The quarter of the year in which a cow calved was associated with the risk for SCK and CK. For SCK quarter 1 (January-March) and quarter 2 (April-June), and for CK quarter 1, quarter 2, and quarter 3 (July-September) all increased the risk of development of the condition compared with quarter 4 (October-December). An increased yield of colostrum at first milking was associated with increasing risk for SCK and CK. Prolonged previous lactation length and dry period length were both associated with increased odds for SCK and CK. Subclinical ketosis and CK were associated with a higher milk yield, a higher milk fat percentage, and a lower milk protein percentage at first DHI test day. Overall the study reinforces previous findings that the major risk factors for both SCK and CK are increasing parity, overconditioning of animals prepartum, season of calving, and dry period length. In addition, previous lactation length and liters of colostrum have been identified as additional risk factors for the development of ketosis.

The role of animal movement, including off-farm rearing of heifers, in the interherd transmission of multidrug-resistant Salmonella.

Fifty-nine commercial dairy farms were sampled 7 times over 15 to 21 mo to determine the role of animal movement, including off-farm rearing of heifers, in the interherd transmission of multidrug-resistant (MDR) Salmonella spp. Farm management data were collected by on-site inspections and questionnaires on herd management practices before and after the study. Forty-four percent (26/59) of herds did not acquire any new MDR Salmonella strains. The number of newly introduced MDR Salmonella strains acquired by the remaining 56% (33/59) of herds ranged from 1 to 8. Logistic regression models indicated that off-farm heifer raising, including contract heifer raising where heifers commingle with cattle from other farms [commingled heifers, odds ratio (OR) = 8.9, 95% confidence interval (CI): 2.4, 32.80], and herd size per 100-animal increment (herd size, OR = 1.04, 95% CI, 1.01, 1.05) were significantly associated with the introduction of new MDR Salmonella strains. The negative binomial regression similarly revealed that commingled heifers [relative risk (RR) = 2.3, 95% CI: 1.1, 4.7], herd size per 100 animals (RR = 1.02, 95% CI, 1.01, 1.03), and a history of clinical salmonellosis diagnosed before the study (RR = 2.5, 95% CI, 1.3, 5.0) were significantly associated with the number of new MDR Salmonella strains that were introduced. Factors not associated with the introduction of new MDR Salmonella strains were housing of heifers and cows in the same close-up pen, a common hospital-maternity pen, and the number of purchased cattle. This study highlights the role of animal movement in the interherd transmission of MDR Salmonella spp.

Targeting therapy to minimize antimicrobial use in preweaned calves: effects on health, growth, and treatment costs.

Prophylactic and therapeutic antimicrobial use in food animals is questioned because of the potential for development of resistant bacteria and future inability to use some antimicrobials for human or animal disease. The objectives of this study were to determine the effect of raising preweaned dairy calves without antimicrobials in the milk and minimizing therapeutic antimicrobial treatment on morbidity, mortality, weight gain, and treatment costs. Newborn calves (n = 358) were allocated to 1 of 4 groups, housed outdoors in individual hutches, and monitored for 28 d. Calves in the conventional therapy (CT) group were treated as per dairy protocol with sulfamethoxazole/trimethoprim, spectinomycin, penicillin, and bismuth-pectin for diarrhea. The targeted therapy (TT) group included bismuth-pectin for diarrhea and antimicrobial treatment only in cases of fever or depressed attitude. Within CT and TT groups, calves were equally assigned to receive neomycin and tetracycline in their milk for the first 2 wk of life (AB-milk) or no antimicrobials (NoAB-milk). Daily health evaluations included fecal consistency, respiratory disease, attitude, and hydration status as well as milk and grain consumption. A negative binomial model evaluated the total number of days with diarrhea days in each group. General linear models were used to assess average daily weight gain and grain consumption. Conventionally treated calves had 70% more days with diarrhea than TT calves, and AB-milk calves had 31% more days with diarrhea compared with NoAB-milk calves. The TT calves tended to have a higher average daily gain by 28 d and consumed more grain compared with CT calves. If antimicrobials were used only for diarrhea cases with fever, inappetence, or depression and no in-milk antimicrobials were used, a $10 per calf savings could be realized. Targeting antimicrobial therapy of calf diarrhea cases is prudent not only to save the drugs for future use but also to prevent the potential for antibiotic-associated diarrhea and reduce calf-rearing costs.

Evaluation of the effects of oral colostrum supplementation during the first fourteen days on the health and performance of preweaned calves.

Increasing concerns about antimicrobial resistance have led to the development and implementation of alternatives to antimicrobial use in animal production. The objective of this clinical trial was to determine the effect of colostrum supplementation of the milk replacer ration on morbidity, mortality, feed intake, and weight gain of preweaned calves. Ninety 1-d-old calves on each of 3 commercial calf ranches were randomly allocated to 1 of 3 groups. Treatment-group calves received 10 g of supplemental immunoglobulin G (IgG) in the form of 70 g of colostrum powder in the milk replacer twice daily for 14 d. The placebo-group calves received a nutritionally equivalent supplement lacking IgG in the milk replacer twice daily for 14 d. Control calves received milk replacer without supplements twice daily. Calves were housed in individual hutches and were weighed on d 1, 28, and 60. Serum was collected on d 2 for serum IgG determination. Daily health evaluations for the first 28 d of life were performed by study personnel blinded to treatment group assignment. Observed illness was treated based on health assessment, rectal temperature, and specific calf ranch protocols. Feed consumption (milk and grain) was recorded. Calves receiving supplemental colostrum had less diarrhea and received fewer antimicrobial treatments than control and placebo calves. The results indicated that calf diarrhea was associated with low serum IgG levels and low-weight calves. Grain consumption and weight gain over the first 28 d of life were significantly greater in colostrum-supplemented calves compared with control calves. No differences in mortality or respiratory disease incidence among groups were detected. Supplemental colostrum during the first 2 wk of life can reduce diarrheal disease in preweaned calves on calf ranches and thereby reduce the amount of antimicrobial treatments needed.

Comparison of Salmonella enterica serovar distribution and antibiotic resistance patterns in wastewater at municipal water treatment plants in two California cities.

AIM: To determine Salmonella enterica serovars and antibiotic resistance (ABR) in the human waste stream. METHODS AND RESULTS: Sampling of influent wastewater at municipal treatment plants in two California cities was performed by collecting composite samples, over a 24-h period, from the treatment plants on five to six occasions. Serial water quantities were filtered and cultured with a Salmonella selective method and an oxytetracycline-supplemented Salmonella selective method. Antibiotic susceptibilities to 12 antibiotics were determined and the isolates were grouped based on ABR patterns. From 983 S. enterica isolated, 102 represented unique sampling-serovar-ABR patterns. Thirty-five different serovars were identified to be distributed over 17 different ABR patterns. The serovar distribution differed between the sampling sites, whereas there was no significant trend in levels of multiple ABR. CONCLUSIONS: Salmonella enterica was recovered with ease from small sample volumes of wastewater received by municipal water treatment plants. A large variety of serovars and ABR profiles were represented in the recovered Salmonella. SIGNIFICANCE AND IMPACT OF THE STUDY: The ease of sampling and recovery of Salmonella from municipal wastewater from treatment plants makes it a valuable sampling approach for monitoring the presence of Salmonella in the human population.

Genetic and phenotypic variability among Salmonella enterica serovar Typhimurium isolates from California dairy cattle and humans.

Fifty-six human and 24 adult dairy cattle isolates of Salmonella enterica serovar Typhimurium from a single county in California were compared using ribotyping, insertion sequence typing (IS200), pulsed-field gel electrophoresis, plasmid typing, phage typing, and antimicrobial resistance testing. The majority of the isolates fell into one of two groups which were phage types DT104 and DT193. Combining the information from all typing methods, a total of 45 different "clusters" were defined, with 35 of those including only a single isolate. The library of isolates had a high degree of variability, but antibiotic resistance and plasmid typing each defined single clusters in which human or bovine isolates predominated (chi2, P < 0.05).

Animal and farm influences on the dynamics of antibiotic resistance in faecal Escherichia coli in young dairy calves.

It is believed that the intensive use of antibiotics in the management of disease in pre-weaned calves contributes to high levels of antibiotic resistance in commensal and pathogenic bacteria. We described the temporal dynamics of antibiotic-susceptibility patterns seen in bovine enteric Escherichia coli in pre-weaned calves on dairy farms and dedicated calf-rearing facilities. Cohorts of 30 calves at each of six farms were sampled at 2-week intervals during the pre-weaning period. Faecal E. coli isolates were analyzed for antibiotic susceptibility to 12 antibiotics with the disk-diffusion method and grouped using cluster analysis of inhibition-zone patterns. The influences of calf age, farm-type, and individual-calf antibiotic therapy on the clusterings were assessed using stratified analyses and cumulative multinomial logistic regression using generalized estimating equation with antibiotic-resistance cluster as an ordinal-dependent variable. The model controlled for farm and cohort by a nested design and included a repeated measure on calf at each sampling occasion. E. coli from calves 2 weeks of age were more likely to be increasingly multiply resistant than E. coli from day-old calves (OR = 53.6), as were 4- and 6-week-old calves (OR = 29.8 and 16.4, respectively). E. coli from calves on dedicated calf-rearing facilities were more likely to be increasingly multiply resistant than E. coli from dairy-reared calves (OR = 2.4). E. coli from calves treated with antibiotics within 5 days prior to sampling were also more likely to be increasingly multiply resistant than E. coli from calves not exposed to individual antibiotic therapy (OR = 2.0).

A clinical trial evaluating prophylactic and therapeutic antibiotic use on health and performance of preweaned calves.

The objective of this clinical trial was to evaluate the influence of prophylactic and therapeutic antibiotics on health and performance in preweaned dairy calves on a calf ranch. One hundred twenty 1-d-old calves were enrolled into 3 management systems for antibiotic use and raised until 4 wk of age. Sixty calves were not eligible to receive prophylactic or therapeutic antibiotics. Thirty calves were eligible to receive individual antibiotic treatment for disease, but no prophylactic antibiotics in milk replacer. The remaining 30 calves received milk replacer medicated with neomycin and tetracycline HCl, and could be treated with antibiotics. Health status and treatments were monitored and recorded daily. The primary study outcomes were weight gain, morbidity, and mortality. The most important factor associated with morbidity and mortality was passive immune transfer through colostrum. In-feed antibiotics delayed onset of morbidity, decreased overall morbidity, and increased weight gain. Nonantibiotic therapies for clinical disease were associated with increased mortality and morbidity compared with antibiotic treatments. The study has shown that minimizing or eliminating the use of antibiotics in the feed requires measures to ensure adequate passive transfer of immunity, but that in the face of inadequate passive transfer of immunity, animal welfare may be endangered by replacing medicated milk replacer with nonmedicated milk replacer, and therapeutic antibiotics with nonantibiotic alternatives.

Assessing antibiotic resistance in fecal Escherichia coli in young calves using cluster analysis techniques.

This study uses cluster analysis techniques to describe the antibiotic susceptibility patterns seen in calf fecal Escherichia coli (E. coli). Cohorts of 30 dairy calves at six farms were sampled at 2-week intervals during the pre-weaning period. At each sampling occasion five fecal E. coli isolates per calf were analyzed for antibiotic susceptibility to 12 antibiotics using the disk diffusion method. All isolates had a profile consisting of the aggregate measured inhibition zone size for each of the evaluated antibiotics. Several cluster analytic algorithms were assessed to partition the E. coli isolates. For our data, Ward's minimum variance method met the objectives of the study. Relative to the number of possible combinations of resistance clusters, a parsimonious set of 14 patterns was developed. This set of E. coli isolates exhibited a limited set of resistance patterns to the different antibiotics indicating that certain resistance genes may be linked.