Disease,production and culling in Holstein-Friesian cows III. Disease and production as determinants of disease     

Ian R. Dohoo  S.Wayne Martin 《Preventive veterinary medicine》1984,2(5):671-690

The effects of the level of milk production and previous disease occurrence (both within the same lactation and in the previous lactation) on the risk of disease occurrence in Holstein-Friesian cows were investigated. The data were from 2875 lactation records from 2008 cows in 32 commercial dairy herds within a 50 mile radius of Guelph, Ontario.Discriminant analysis was applied to data from a subset of 817 cows which completed 2 lactations during the study. This was done in order to simultaneously evaluate the effects of the level of milk production and disease occurrence in 1 lactation, on the risk of disease in a subsequent lactation. Many diseases tended to recur in the second lactation, but the level of milk production was not related significantly to the risk of any of the common disease conditions. A path model, with previous lactation production entered as an exogenous variable, was constructed in order to further evaluate the role of the level of milk production as a determinant of disease. Only milk fever was significantly associated with the level of milk production.Relationships amongst diseases within a lactation were identified by a modified case-control procedure and were used to construct several path models. Relationships amongst diseases in heifers, mature cows and all cows combined are discussed.  相似文献   

A comparison of five serological tests for bovine brucellosis.   总被引：5，自引：0，他引：5       下载免费PDF全文

I R Dohoo  P F Wright  G M Ruckerbauer  B S Samagh  F J Robertson    L B Forbes 《Canadian journal of veterinary research》1986,50(4):485-493

Five serological assays: the buffered plate antigen test, the standard tube agglutination test, the complement fixation test, the hemolysis-in-gel test and the indirect enzyme immunoassay were diagnostically evaluated. Test data consisted of results from 1208 cattle in brucellosis-free herds, 1578 cattle in reactor herds of unknown infection status and 174 cattle from which Brucella abortus had been cultured. The complement fixation test had the highest specificity in both nonvaccinated and vaccinated cattle. The indirect enzyme immunoassay, if interpreted at a high threshold, also exhibited a high specificity in both groups of cattle. The hemolysis-in-gel test had a very high specificity when used in nonvaccinated cattle but quite a low specificity among vaccinates. With the exception of the complement fixation test, all tests had high sensitivities if interpreted at the minimum threshold. However, the sensitivities of the standard tube agglutination test and indirect enzyme immunoassay, when interpreted at high thresholds were comparable to that of the complement fixation test. A kappa statistic was used to measure the agreement between the various tests. In general the kappa statistics were quite low, suggesting that the various tests may detect different antibody isotypes. There was however, good agreement between the buffered plate antigen test and standard tube agglutination test (the two agglutination tests evaluated) and between the complement fixation test and the indirect enzyme immunoassay when interpreted at a high threshold. With the exception of the buffered plate antigen test, all tests were evaluated as confirmatory tests by estimating their specificity and sensitivity on screening-test positive samples.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

Model to predict septicemia in diarrheic calves     

Lofstedt J  Dohoo IR  Duizer G 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1999,13(2):81-88

The difficulty in distinguishing between septicemic and nonsepticemic diarrheic calves prompted a study of variables to predict septicemia in diarrheic calves <28 days old that were presented to a referral institution. The prevalence of septicemia in the study population was 31%. Variables whose values were significantly different (P < .10) between septicemic and nonsepticemic diarrheic calves were selected using stepwise, forward, and backward logistic regression. Variables identified as potentially useful predictors were used in the final model-building process. Two final models were selected: 1 based on all possible types of predictors (laboratory model) and 1 based only on demographic data and physical examination results (clinical model). In the laboratory model, 5 variables retained significance: serum creatinine > 5.66 mg/dL (>500 micromol/L) (odds ratio [OR] = 8.63, P = .021), toxic changes in neutrophils > or = 2+ (OR = 2.88, P = .026), failure of passive transfer (OR = 2.72, P = .023), presence of focal infection (OR = 2.68. P = .024), and poor suckle reflex (OR = 4.10, P = .019). Four variables retained significance in the clinical model: age < 5 days (OR = 2.58, P = .006), presence of focal infection (OR = 2.45, P = .006), recumbency (OR = 2.98, P = .011), and absence of a suckling reflex (OR = 3.03, P = .031). The Hosmer-Lemeshow goodness-of-fit chi-square statistics for the laboratory and clinical models had P-values of .72 and .37, respectively, indicating that the models fit the observed data reasonably well. The laboratory model outperformed the clinical model by a small margin at a predictabilty cutoff of 0.5, however, the predictive abilities of the 2 models were quite similar. The low sensitivities (39% and 40%) of both models at a predicted probability cutoff of 0.5 meant many septicemic calves were not being detected by the models. The specificity of both models at a predicted probability cutoff of 0.5 was >90%, indicating that >90% of nonsepticemic calves would be predicted to be nonsepticemic by the 2 models. The positive and negative predictive values of the models were 66-82%, which indicated the proportion of cases for which a predictive result would be correct in a population with a prevalence of septicemia of 31%.  相似文献   

Increase in milk yield following eprinomectin treatment at calving in pastured dairy cattle     

Nødtvedt A  Dohoo I  Sanchez J  Conboy G  DesCôteaux L  Keefe G 《Veterinary parasitology》2002,105(3):191-206

Gastrointestinal nematodes rarely cause signs of clinical disease in adult cattle. However, they have been shown to exert a negative impact on production in lactating animals, as seen by improved production following elimination of the worms using anthelmintics. A double blind, randomized clinical trial was performed in 28 dairy herds in Canada. The objective of the study was to evaluate the effect of treatment with eprinomectin pour-on solution (IVOMEC EPRINEX) at calving on production, in cattle that have had some exposure to pasture. Cows were randomly allocated to treatment or placebo in blocks of 10, based on calving date, and treated with eprinomectin or placebo on the day of calving.Information on milk production was obtained from all animals, as well as recorded cases of selected diseases. Milk production results from the Canadian dairy herd management system database were analysed using a mixed model with herd as a random effect and test within-cow as a repeated measurement. Test day milk yields from the first six tests after treatment were included in the model, representing a period of between 180 and 200 days in milk (dim). Treated cows produced an additional 0.94 kg of milk per day when compared to the controls over this period. The production effect was independent of calving season, age of the animal and geographical location. No effect of treatment was seen on milk composition, somatic cell count (scc) or on the selected health parameters that were recorded for all included animals.Monthly fecal egg counts (FEC) were performed for eight randomly selected animals in each herd. The observed FEC were low in this study, with a range from 0 to 419 trichostrongyle type eggs per 5g (ep5g) of feces in animals not yet treated with the anthelmintic. The average count was 9.8 and the median was 1.0. FECs dropped immediately after calving and stayed lower for at least 100 days in treated animals when compared to controls.In conclusion, gastrointestinal nematodes appear to have an effect on milk production in Canadian dairy cows that have had some degree of pasture exposure. Eliminating the present subclinical parasite burdens produced a consistent increase in milk production that can yield economic benefits for the dairy producer.  相似文献   

Estimates of within-herd incidence rates of Mycobacterium bovis in Canadian cattle and cervids between 1985 and 1994     

Munroe FA  Dohoo IR  McNab WB 《Preventive veterinary medicine》2000,45(3-4):247-256

We analysed the individual-animal data from six of the nine outbreaks of tuberculosis in Canadian cattle and cervids from 1985 to 1994. A “positive/reactor” animal was one which had either a positive culture or a positive or suspicious reaction on a mid-cervical, comparative cervical, or gross or histopathological test for tuberculosis. Individual-animal data were collected only for herds which had one or more positive/reactor animals. Data were collected from the outbreak records in the Regional or District offices of Agriculture and Agri-food Canada’s Animal and Plant Health Directorate. The within-herd spread of Mycobacterium bovis was studied by determining the most-likely date at which the herd was first exposed to M. bovis and the number of reactions which had developed by the time the herd was investigated. The animal-time units at risk in the herd were probably overestimated, resulting in conservative estimates of the within-herd incidence rates. Negative-binomial regression was used to investigate factors which might have influenced the within-herd spread of tuberculosis. Increasing age appeared to be a risk factor for being a positive/reactor animal. When compared to animals 0–12 months old, animals 13–24 months old had an incidence rate ratio (IRR) of 7.6, while animals >24 months old had an IRR of 10.4 (p=0.009). Actual and predicted incidence rates for tuberculosis in mature (>24 months old) animals were calculated. Actual and predicted incidence rates were similar for cervids, within an outbreak. There was more variability between actual and predicted rates in the dairy and beef animals. In the one outbreak (Ontario) where there were positive/reactor cervid, dairy and beef herds, the actual incidence rate for cervids (IR=9.3 cases per 100 animal-years) was almost twice that of dairy cattle (IR=5.0) and three times that of beef cattle (IR=3.1).  相似文献   

Evaluation of underlying risk as a source of heterogeneity in meta-analyses: a simulation study of Bayesian and frequentist implementations of three models     

Dohoo I  Stryhn H  Sanchez J 《Preventive veterinary medicine》2007,81(1-3):38-55

Evaluation of important causes of heterogeneity among study results is an important component of any meta-analysis. For factors which can be measured (e.g. population characteristics, indicators of study quality), standard methods such as meta-regression can be used for this evaluation. The underlying risk (i.e. risk of outcome in the control population) can be viewed as a summary of the effects of unmeasured population characteristics so it is a logical candidate for evaluation as a source of heterogeneity. Unfortunately, because of its relationship with the study outcome (odds ratio or relative risk), standard methods should not be used for evaluating underlying risk as a cause of heterogeneity. Three models with different sets of underlying assumptions were evaluated in a simulation study to determine how well they performed in assessing the role of underlying risk as a source of heterogeneity. All models were fit using both Bayesian and frequentist (maximum likelihood random slopes models) estimation procedures and the results compared. Two of the models produced good results (i.e. minimal evidence of bias in parameter estimates), while the third clearly produced biased estimates of some parameters. In general, the Bayesian and frequentist approaches produced similar results. In situations in which the number of studies in a meta-analysis is small ( approximately 10), the maximum likelihood (frequentist) approach was preferable. While the bias induced by heterogeneity associated with underlying risk was generally not large, use of one of the approaches described in this paper will produce better estimates of treatment effect in situations where there is substantial heterogeneity between studies. A model based on the assumption that the number of positive events in each of the treatment and control groups are binomially distributed (Model 1) is the recommended approach.  相似文献   

The design of randomized controlled trials of veterinary vaccines     

Dohoo IR 《Animal health research reviews / Conference of Research Workers in Animal Diseases》2004,5(2):235-238

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Risk factors for milk off-flavours in dairy herds from Prince Edward Island, Canada     

Mounchili A  Wichtel JJ  Dohoo IR  Keefe GP  Halliday LJ 《Preventive veterinary medicine》2004,64(2-4):133-145

A sudden increase in the incidence of milk off-flavours in bulk tank milk from Prince Edward Island (Canada) dairy farms in the late 1990s prompted an investigation of potential herd-level risk factors. A prospective case-control study was conducted from 2000 to 2002. Data on herd management were obtained by questionnaire and field investigation from all the 62 identified off-flavour positive farms (cases) and 62 loosely matched (for data-collection convenience) off-flavour negative farms (controls). Forty-three of the 62 cases (69%) of milk off-flavours identified during the study period were classified as “transmitted” (feed) off-flavours, and 9 (15%), 6 (10%), and 4 (6%) as “rancid”, “oxidized” and “malty” off-flavours, respectively. Given this evidence and the relatively low incidence of other flavour defects in milk, only transmitted-flavour cases were considered in the analyses of risk factors. Poor air quality in the lactating cows’ barn (OR = 40.8), using baled silage as the main forage (OR = 10.6), as well as feeding roughage before milking (OR = 253.3) or as a free choice (OR = 3.2) all were significantly (P < 0.05) associated with the incidence of transmitted flavours in bulk-tank milk. Clipping the hair on the cows’ udder (OR = 0.07) and changing the bedding material more than once a day (OR = 0.12) were protective. The finding about feeding baled silage before milking has raised hypotheses about silage composition (in particular the off-flavour compounds or their precursors) and also about the process of silage making itself.  相似文献   

Demographics, management, and welfare of nonracing horses in Prince Edward Island          下载免费PDF全文

Christie JL  Hewson CJ  Riley CB  Mcniven MA  Dohoo IR  Bate LA 《The Canadian veterinary journal. La revue veterinaire canadienne》2004,45(12):1004-1011

There are no detailed, representative, horse-level data about equine management practices in different parts of Canada. To help address this, the demographics, management, and welfare of 312 nonracing horses in Prince Edward Island were examined in a randomized, horse-level survey during summer 2002. Owners completed a pretested questionnaire, and a veterinarian examined each horse. Owners were experienced caregivers and the horses were generally in good condition. Areas for improvement included parasite control, dental and hoof care, and tail docking. The mean fecal egg count was 428 eggs per gram; 76% of owners never removed manure from the pasture. Sixty-two percent of horses had never had a veterinary dental examination. Many horses had hoof defects (excessively long hooves, 26.8%; hoof wall breaks, 32.0%; and white line disease, 8.5%). Many (54.9%) draft horses had docked tails. These results suggest owners might benefit their horses by receiving education in aspects of equine care.  相似文献   

Quantitative epidemiology: progress and challenges     

Dohoo IR 《Preventive veterinary medicine》2008,86(3-4):260-269

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