Alan H. Meek

Dairy calf management, morbidity and mortality in Ontario Holstein herds. III. Association of management with morbidity

Abstract Associations between heifer calf management and morbidity, particularly scours and pneumonia, were studied on 104 randomly selected Holstein dairy farms in southwestern Ontario between October 1980 and July 1983. At the farm level, data were stratified by season, with two six-month seasons (winter and summer) per year. The odds of farms with particular management strategies having above median morbidity were calculated. At the individual calf level, the odds of a calf being treated, controlling for farm of origin and month of birth, were calculated for different management practices. Farm size, and policies related to anti-scour vaccination, offering free-choice water and minerals to calves, methods of feeding, and the use of medicated feeds significantly altered the odds of a farm experiencing above-median pneumonia rates. Farm policies with regard to anti-scour vaccination, offering free-choice salt to calves, age at teat removal, type of calf housing, and use of preventive antimicrobials significantly altered the odds of a farm experiencing above-median scours rates. Scours and pneumonia were significantly associated with each other at both the farm and the calf level. No significant associations were found between individual calf management practices and the odds of being treated for scours. Sire used, method of first colostrum feeding, navel treatment, use of anti-scour vaccine in the dam, and the administration of preventive antimicrobials significantly altered the odds of a calf being treated for pneumonia.

Associations among antimicrobial drug treatments and antimicrobial resistance of fecal Escherichia coli of swine on 34 farrow-to-finish farms in Ontario, Canada

Logistic regression was used to model associations between antimicrobial treatment and resistance among fecal Escherichia coli of finisher pigs at the farm level. Four sets of potential risk factors representing different levels of refinement of antimicrobial use on farms were modelled on resistance to antimicrobials. Final models for each antimicrobial were constructed from treatment and management variables significant on initial screening, and corrections for overdispersion were made. In general, in-feed antimicrobial treatment of pigs was more consistently associated with an increased risk of resistance than individual-animal treatment. Antimicrobial treatment in starter rations was significant in final models of resistance to ampicillin, carbadox, nitrofurantoin, sulfisoxizole, and tetracycline. Treatment in grower-finisher rations was significantly associated with resistance to ampicillin, spectinomycin, sulfisoxizole, and tetracycline. There was little evidence that in-feed antimicrobials increased the risk of resistance to gentamicin, which is a drug used only for individual-pig treatment in this study population. These results suggest that antimicrobial medication of rations of post-weaning pigs selects for and maintains antimicrobial resistance among E. coli of finisher pigs. Although resistance was common on farms that did not medicate rations of post-weaning pigs, the results indicate that antimicrobial use does increase the risk of resistance to the antimicrobials studied.

INDIVIDUAL AND GROUP ANTIMICROBIAL USAGE RATES ON 34 FARROW-TO-FINISH SWINE FARMS IN ONTARIO, CANADA

Antimicrobial drug-use was assessed on 34 farrow-to-finish operations that marketed at least 500 hogs/yr. These operations either did not use any antimicrobials or used narrow-spectrum or broad-spectrum antimicrobials in rations of post-weaning pigs. Total antimicrobial use was measured for two months after obtaining inventories and records of all antimicrobials used. The collection of empty medication bottles and inventories of drugs on hand was convenient for producers and useful for estimating or validating recorded treatment rates, particularly for antimicrobials that were used only in one class of pig. Treatment records, however, underestimated by approximately 35% the amounts used for 27/29 farm-antimicrobial combinations. Rates of individual-pig treatment varied from 0-24.1 pigs treated/1000 pig-days, with a median of 5.29. Most individual animal treatments were given to piglets and sows at parturition and penicillin was the most commonly used antimicrobial. Gentamicin was administered to suckling piglets on 19 of the farms.

Dairy calf management, morbidity and mortality in Ontario Holstein herds. I. The data

Abstract Heifer calf management practices and clinical outcomes were studied on 104 randomly selected Holstein dairy farms in southwestern Ontario between October 1980 and July 1983. Data were collected at both the farm level (all farms) and the individual calf level (1968 calves, 35 farms). Farm-level management data were collected by means of questionnaires and farm visits. Calf-level management data were recorded by farmers on forms provided. Treatments for disease and mortality data were recorded by the farmers on the calves up to the age of weaning, the age at which calves were no longer fed milk or milk substitutes on a regular basis. Farm size ranged from 23 to 154 calvings per year. Farm-level mortality rates per six-month season (winter/summer) were skewed, with a mean of about 6%, a median of zero, and a range of 67%. Morbidity rates were similarly skewed. Four percent of liveborn heifer calves died, 20% were treated for scours, and 15% were treated for pneumonia before the age of weaning. Stated farm policies on calf rearing were implemented to varying degrees on different farms, as estimated from individual calf data. This posed particular problems for interpreting farm-level data, since the danger of committing an ecologic fallacy was high. The data set described in this paper formed the basis for an observational study of the interlationships of heifer calf management and clinical outcomes.

Dairy calf management, morbidity and mortality in Ontario Holstein herds. II. Age and seasonal patterns

Abstract Heifer calf management practices and clinical outcomes were studied on 104 randomly selected Holstein dairy farms in southwestern Ontario between October 1980 and July 1983. Data were collected at both the farm level (all farms) and the individual calf level (1968 calves, 35 farms). Age at death, and at first treatment for disease, during the first 20 weeks of life were described by life table methods and depicted graphically. Variations over calendar time in morbidity and mortality were described graphically. The percentage of calves at risk first treated for scours peaked during the second week of life, at 8.1% per week, then declined sharply, approaching zero by about six weeks. Pneumonia treatment rates peaked at about the sixth week of life, at 2.3% per week, but were more persistent than the rates for scours. Calves were at greater risk of dying during the first week of life than at any time thereafter; however, calf mortality in this population never exceeded 4% of the total. Treatment rates for scours and pneumonia were generally lower in spring and summer than during the autumn and winter. The mortality rates remained at

A dairy farm survey of antibiotic treatment practices, residue control methods and associations with inhibitors in milk

A mail survey was conducted of dairy producers who had received a positive bulk milk antibiotic residue test result in a two-year period (1987-88) of government monitoring (case farms) and farms that were negative for all tests conducted in the same period (control farms). Farmers were asked to complete questionnaires designed to determine dairy management practices, as well as, antibiotic handling and residue prevention methods. Using multiple logistic regression analysis, and adjusting for the size of the milking herd, the following factors were associated with increased risk of antibiotic residues in milk: the use of part-time assistance in milking, use of a milking parlor and increased estimated frequency of intramammary antibiotic treatments. Unconditionally, significantly more control farmers used separate equipment to milk treated cows rather than simply attempting to divert milk from the bulk tank. Controls were also more likely to vary the withholding time of milk for different drugs. Other significant differences between cases and controls with respect to residue prevention methods were observed, however, some of these may have been due to changes instituted on case farms after the antibiotic residue violations occurred. For example, significantly more case than control farmers reported using on-farm residue test kits and marking of treated animals as residue prevention methods and more case farmers believed that failure to keep good records of treatment was an important factor in residue occurrence. No significant differences were observed in the proportions of case and control farms that used medicated feed, in the number of people employed on the farm, or in the general knowledge of antibiotic residue prevention.

Prevalences of resistance to seven antimicrobials among fecal Escherichia coli of swine on thirty-four farrow-to-finish farms in Ontario, Canada.

Fecal specimens were composited and a hydrophobic-grid membrane-filter method was used to measure antimicrobial resistance to ampicillin 16 micrograms/ml, carbadox 30 micrograms/ml, gentamicin 4 mu/ml, nitrofurantoin 32 micrograms/ml, spectinomycin 16 micrograms/ml, sulfisoxazole 32 micrograms/ml and tetracycline 8 micrograms/ml among 8119 Escherichia coli isolates from 68 fecal samples collected on 34 farrow-to-finish swine farms marketing over 500 hogs/yr. The overall prevalences of resistance to antimicrobials among these isolates were: ampicillin 29%, carbadox 3.5%, gentamicin 0.6%, nitrofurantoin 27%, spectinomycin 28%, sulfasoxizole 38% and tetracycline 71%. Thirty to seventy-six per cent of the variations in prevalences were explained by between-farm differences.

Reproductive performance of Ontario beef breeding herds

Abstract Herd reproductive performance was assessed in 180 Ontario cow-calf herds on 170 randomly selected farms. Reproductive performance was measured by pregnancy rate and mean calving interval. The mean pregnancy rate was 92.8% and 75% of herds had pregnancy rates greater than 90%. The mean calving interval was 365 ± 1.4 days. Herd pregnancy rate was highest in late-summer and fall-winter breeding herds and was decreased by bull diseases. Pregnancy rates were also associated with a number of pasture and nutrition variables; but, their effects were not easily interpreted. Decreased mean calving interval was associated with: a decreased interval between first calving dates in 1986 and 1987 (used to control for delayed bull introduction), other than fall-winter breeding, natural service, pasture weed control, closed barn winter housing and manager ownership; increased calving interval was associated with bull chronic disease. There are two main conclusions. The first is that, regardless of management goals, approximately 20% of producers realistically could improve their herd pregnancy rate. The second is that, in Ontario, a short breeding season will be easiest to maintain by having spring and early summer breeding seasons, by natural service, by the timely introduction of herd sire(s), and by monitoring bull health carefully.

Clustering of fatal fibrinous pneumonia (shipping fever) in feedlot calves within transport truck and feedlot pen groups

Abstract Feedlot owners often state that shipping fever mortality does not affect calves in a random fashion across the feedlot; instead, mortality can be abnormally high in certain truckloads of calves or in certain pens. However, these apparent “clusters” of disease might be no more than coincidental concentrations of fatal shipping fever cases selected from a truly random distribution of cases throughout the feedlot. The purpose of this study was to distinguish between these two possibilities by critically examining the pattern of fatal shipping fever affecting calves placed in a large beef feedlot. Management and mortality data from 36 339 spring-born calves entering a large commercial beef feedlot in SW Alberta, Canada from 1985 to 1988 were used for the analysis in this study. Once at the feedlot, calves were placed in pens of approximately 300 animals. Truck manifests (which include freight or cargo documentation) and feedlot processing records were used to determine the truck and auction market origin of all incoming calves. Because the prevalence of shipping fever mortality varied dramatically among years, an analysis was performed on each of the 4 years separately. To determine whether clustering occurred within the transport truck, tests of homogeneity of binomial samples were run on the truckloads of calves making up each individual pen. To determine whether clustering occurred within a pen, a test for homogeneity of binomial samples was run within each year using the proportion of mortality due to fibrinous pneumonia in each pen; the intracluster correlation coefficient was used to correct for the nested effect of truck within pen. When the incidence of fatal shipping fever was high (greater than 2%), the disease clustered within truckload groups of calves and also, one year, within pens. Further work is necessary to determine whether contagious or non-contagious factors are responsible for the clustering that was documented.