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To evaluate the decision to test for milk antimicrobial residues in milk from dairy cows treated with procaine penicillin G (PPG).


Economic-decision analysis after stochastic simulation.

Sample Population—

1,000 computer-simulated cows/model.


Meta-analysis of the Food Animal Residue Avoidance Databank was used to generate PPG disappearance curves for cows given single PPG treatments, IM, of 6,600 U/kg (3,000 U/Ib) of body weight or 26,400 U/kg (12,000 U/lb), and multiple treatments at 26,400 U/kg (12,000 U/lb), IM. These curves were entered into 1,000-replication stochastic pharmacokinetic models, generating population-level milk PPG profiles for each treatment group for each day after treatment, which were subjected to economic-decision analyses of feasibility of residue testing. The model was evaluated for changes in herd size, proportion of herd available for testing, milk production, test price, test sensitivity/specificity, and withdrawal periods.


For both single-treatment groups, a 2-day withdrawal period avoided violative residues. However, nearly two thirds of the cows risked false identification for violative residues. For the multiple-treated group, nearly 40% had violative residues after a 5-day withdrawal period, and an additional 10 to 15% risked false identification for violative residues. Economic analysis yielded a decision against testing; mean cost was $2 (ie, 5% more than the mean cost of not testing).

Clinical Implications—

Complex dynamics of current milk residue tests discourage practitioners from recommending procedures to clients. In general, increases in herd size, milk production, proportion of a herd available for testing, or milk price will increase the value of testing. Increasing test sensitivity decreases its desirability to producers. (J Am Vet Med Assoc 1997;211:419–427)

Free access
in Journal of the American Veterinary Medical Association


Factors associated with foot abscess were evaluated in a cohort of 3,322 suckling pigs reared on a woven-wire floor (wire diameter, 0.5 cm; size of openings, 1 × 3.8 cm). In bivariate analysis, foot abscess was significantly (P < 0.05) associated with post-partum sow illness, number of pigs born alive, and parity, but not with birthweight (P = 0.31) or time spent on wire flooring (P = 0.89). One oxytetracycline treatment (100 mg, im) at birth or 1 treatment at birth and a second 5 to 7 days later reduced (P < 0.05) the risk of lesions by about half. Multivariate analyses indicated that pigs in large litters (> 10 pigs at birth) born to sows with postpartum illnesses had an increased risk (relative risk [rr], 3.77) of developing foot abscess, compared with pigs in small litters (≤ 10 pigs) born to unaffected sows. For sows without evidence of postpartum illness, pigs in large litters had a slightly increased risk (rr, 1.32) of developing foot abscess, compared with pigs in small litters. Pigs born to multiparous sows also had an increased risk (rr, 1.69) of developing foot abscess, compared with pigs born to primiparous sows. Similar risk estimates were obtained when logistic regression models included location farrowed (crate number) as fixed effect, and when litter was a random effect in a logistic-binomial regression.

Free access
in Journal of the American Veterinary Medical Association


A prospective cohort study was undertaken in a farrow-to-farrow swine herd to describe patterns of pneumonia, and to identify host risk factors associated with the extent of pneumonic lesions in 2 weight groups of slaughter swine.

The risk of coughing and pneumonic lesions increased with increasing age of pigs within the herd (P < 0.0001). The age-specific prevalence of pneumonic lesions was low (2.7%) in pigs < 16 weeks old at slaughter, but increased rapidly when pigs were were between 16 and 22 weeks old (8.6 to 67.9%). After 22 weeks, the prevalence remained relatively constant at about 80%.

Associations between possible risk factors and pneumonia were investigated by use of multiple-regression models. Age at weaning (< 24 days) and birth weight (< 1 kg) exerted small, but significant (P < 0.002), effects on the extent of pneumonic lesions in pigs slaughtered at 30 to 50 kg live weight. For pigs slaughtered at 90 to 110 kg, pneumonic lesions were more extensive (P = 0.007) in pigs sired by Yorkshire boars than pigs sired by non-Yorkshire sires (Duroc, Hampshire, Chester White, or American Spotted). Other host factor variables including weaning weight and clinical diseases (atrophic rhinitis, diarrhea, and arthritis) were not associated with pneumonia extent in either weight group. Higher pneumonia percentages were also associated with reduced growth rates in the grower/finisher phase. Pigs sired by Yorkshire boars grew significantly (P < 0.0001) more slowly from entry into shed 2 (mean, 38 kg) until about the time of exit (mean, 92 kg) than pigs sired by other breeds (747 g/d and 795 g/d, respectively).

Free access
in American Journal of Veterinary Research


Objective—To assess individual and combined associations of high-speed exercise and horseshoe characteristics with risk of forelimb proximal sesamoid bone fractures and proximal sesamoid bone midbody fractures in Thoroughbred racehorses.

Animals—269 deceased Thoroughbred racehorses.

Procedures—A case-control study design was used to compare 121 horses with a fracture of at least 1 of 4 forelimb proximal sesamoid bones (75 horses had a midbody fracture) and 148 horses without a forelimb proximal sesamoid bone fracture. Univariable and multivariable logistic regression analyses were used to evaluate potential risk factors for association with proximal sesamoid bone fracture.

Results—Compared with horses that died without proximal sesamoid bone fractures, horses that died with proximal sesamoid bone fractures were more likely to be sexually intact males, spend more time in active trainingand racing, complete more events, train and race longer since their last layup, have higher exercise intensities during the 12 months prior to death, and have greater cumulative distances for their career. Horses with proximal sesamoid bone midbody fractures were more likely to be sexually intact males, train and race longer since their last layup, and have higher exercise intensities during the 12 months prior to death.

Conclusions and Clinical Relevance—Limitingexercise intensity and the continuous time spent in activity duringa horse's career may decrease the frequency of forelimb proximal sesamoid bone fractures in Thoroughbred horses.

Full access
in American Journal of Veterinary Research


Objective—To evaluate flow cytometric analysis for sex identification in 3 psittacine species, establish reference values for blood cell DNA content for each species, and determine effects of sample storage on DNA content.

Animals—36 orange-winged Amazon parrots, 41 budgerigars, and 39 cockatiels.

Procedure—Blood samples were stained and analyzed by use of flow cytometry to measure cellular DNA content. Samples were analyzed immediately after collection and after being stored at 4 C for 48 and 72 hours.

Results—Mean DNA content (picograms per cell) was 3.248 for Amazon parrots, 2.702 for budgerigars, and 2.946 for cockatiels; DNA concentrations in samples analyzed immediately overlapped in a male and a female Amazon parrot and among 19 cockatiels. For budgerigars, DNA overlap between sexes was not detected in samples analyzed immediately or after storage for 72 hours. Sex was identified correctly in 94.4% of Amazon parrots, 100% of budgerigars, and 51.3% of cockatiels. For both sexes, DNA content in samples analyzed immediately was significantly different from that of stored samples.

Conclusions and Clinical Relevance—Flow cytometric analysis was accurate for sex identification of Amazon parrots and budgerigars. Sample storage at 4 C for 48 or 72 hours caused variability in DNA content. (Am J Vet Res 2000;61:847–850)

Full access
in American Journal of Veterinary Research


Objective—To investigate herd characteristics and management practices associated with a high seroprevalence of Mycobacterium avium subsp paratuberculosis (MAP) in dairy herds in central California.

Sample Population—60 randomly selected cows from each of 21 dairy herds.

Procedures—Sera of selected cows were tested for antibodies against MAP by use of an ELISA test kit. Cows with a test sample-to-positive control sample (S:P) ratio of ≥ 0.25 were considered seropositive, and herds with ≥ 4% seropositive cows were considered high-seroprevalence herds. Data on herd characteristics and management practices were collected via interviews with owners. Bayesian logistic regression was used to model the predictive probability of a herd having a high seroprevalence on the basis of various herd characteristics and management practices.

Results—9 of 21 (43%) herds were classified as high-seroprevalence herds. Five variables (history of previous signs of paratuberculosis in the herd, herd size, exposing cattle to water from manure storage lagoons, feeding unsalable milk to calves, and exposing heifers ≤ 6 months old to manure of adult cows) were included in the predictive model on the basis of statistical and biological considerations. In large herds, the predictive probability of a high seroprevalence of MAP infection decreased from 0.74 to 0.39 when management changed from poor to good practices. In small herds, a similar decrease from 0.64 to 0.29 was predicted.

Conclusions and Clinical Relevance—The seroprevalence of MAP infection in California dairies may be reduced by improvements in herd management practices.

Full access
in American Journal of Veterinary Research


Objective—To evaluate a Markov-chain model for the development of forelimb injuries in Thoroughbreds and to use the model to determine effects of reducing sprint distance on incidence of metacarpal condylar fracture (CDY) and severe suspensory apparatus injury (SSAI).

Sample Population—Weekly exercise and injury data for 122 Thoroughbreds during racing or training.

Procedure—Weekly data were used to construct a Markov-chain model with 5 states (uninjured [UNINJ], palpable suspensory apparatus injury [PSAI], SSAI, CDY, and lost to follow-up [LOST]). Transition probabilities between UNINJ and PSAI were estimated as a function of weekly sprint distance by use of linear regression analysis. The model was used to predict distributions of annual CDY and SSAI incidences in southern California racehorses and was validated by using CDY incidence reported by racetrack practitioners. The model was modified by reducing the number of sprint distances that were > 6 furlongs (> 1.20 km) by 20%, and CDY and SSAI incidences were compared with those generated by the baseline model.

Results—The model accurately fit development of injuries in the sample population but overestimated development of injuries in the southern California racehorse population. Development of and recovery from PSAI were correlated with distance run at high speeds. Reducing by 20% the number of sprints run at distances > 6 furlongs significantly reduced modeled annual CDY and SSAI incidence by 9%.

Conclusions and Clinical Relevance—Reducing the number of sprints at distances > 6 furlongs, particularly among horses with PSAI, reduces risk of CDY and SSAI. (Am J Vet Res 2003;64:328–337)

Full access
in American Journal of Veterinary Research


Objective—To create a stochastic model to quantify the risk that shipments of cattle from regions within the United States would contain animals seropositive for bluetongue virus and to determine shipment-level accuracy of serologic testing by use of a competitive ELISA (c-ELISA).

Sample Population—19,216 shipments containing 528,918 cattle and calves.

Procedure—Data were obtained on number of animals and state of origin of cattle in export shipments originating within the United States between January 1994 and March 2002. Probability distributions for size of export shipments were determined for all states within the United States, and distributions for agar gel immunodiffusion and c-ELISA accuracy (sensitivity and specificity) were determined from expert opinion and review of the literature. The model simulated selection of a shipment and then determined the probability that a threshold number or percentage of cattle within that shipment would have a positive c-ELISA result. Shipment-level sensitivity, specificity, positive-predictive value, and negative-predictive value were calculated.

Results—Substantial differences were evident in the regional probability of a shipment being declared positive, with shipments from northeastern states having the lowest probability and shipments from southwestern states having the highest probability. The c- ELISA had variable predictive values at the shipment level, depending on the threshold used and the prevalence of antibody-positive cattle within the region.

Conclusions and Clinical Relevance—Results from this study will aid importers in making scientifically based decisions regarding risk of importing antibodypositive cattle. ( Am J Vet Res 2003;64:520–529)

Full access
in American Journal of Veterinary Research


Objective—To determine whether foals with pneumonia that were treated with erythromycin, alone or in combination with rifampin or gentamicin, had a higher risk of developing adverse effects, compared with foals treated with trimethoprim-sulfamethoxazole (TMS), penicillin G procaine (PGP), or a combination of TMS and PGP (control foals).

Design—Retrospective study.

Animals—143 foals < 240 days old.

Procedure—Information on age, sex, breed, primary drug treatment, total days of treatment with the primary drug, and whether the foal developed diarrhea, hyperthermia, or respiratory distress was obtained from the medical records. Relative risk (RR) and attributable risk (AR) were calculated to compare risk of adverse reactions between foals treated with erythromycin and control foals.

Results—Only 3 (4.3%) control foals developed diarrhea; none developed hyperthermia or respiratory distress. Foals treated with erythromycin had an 8-fold risk (RR, 8.3) of developing diarrhea, compared with control foals, and increased risks of hyperthermia (AR, 25%) and respiratory distress (AR, 15%).

Conclusion and Clinical Relevance—Results suggest that use of erythromycin to treat foals with pneumonia was associated with an increased risk of diarrhea, hyperthermia, and respiratory distress, compared with use of TMS or PGP. (J Am Vet Med Assoc 2000;217:68–73)

Full access
in Journal of the American Veterinary Medical Association


To identify the preferable testing and vaccination strategy for control of porcine parvovirus (PPV) during a 6-month period.


Decision-tree analysis and computer simulations.

Sample Population

Computer modeling of 300-sow farrow-to-finish herd.


Serologic testing of 30 females to estimate herd PPV prevalence versus not testing any females was the initial decision alternative. On the basis of serologic test results, herds were classified into 1 of 3 PPV-risk categories: low (≥ 80% seropositive females), moderate (40 to < 80% seropositive females), or high (< 40% seropositive females). Vaccinating all females, only gilts, or not vaccinating was the second decision alternative.


For initial model assumptions (test sensitivity and specificity = 0.95; test cost = $5/female; vaccination cost = $0.30/dose; vaccination efficacy = 0.95; and foregone gross margin = $10.85/pig), vaccination of all females (with or without serologic testing) was preferable, but the financially preferable option was to omit serologic testing. Most profitable vaccination option varied with foregone gross margin, vaccination cost, and efficacy. For herds in which all sows were known to be immune, vaccinating only gilts was financially preferable, and serologic testing was not warranted. Variation in expected monetary losses was less in vaccination options than with nonvaccination.

Clinical Implications

For most herds in the United States, serologic screening for PPV prior to selection of a vaccination program is unlikely to be cost-effective, because vaccination is inexpensive ($0.30/dose) and effective (95%). At current profit margins ($10.85/pig), vaccination of all females has the least-risk and is the preferred option.

Free access
in Journal of the American Veterinary Medical Association