Biosecurity practices in western Canadian cow-calf herds and their association with animal health

Abstract

Biosecurity practices of beef cow-calf herds in western Canada have not been studied extensively nor is there a good understanding of their association with herd health. A survey was sent to 103 cow-calf producers of the Western Canadian Cow-Calf Surveillance Network. Eighty completed questionnaires were returned. Bulls were purchased for all herds during the 2014 to 2017 study period; 54% of herds purchased heifers and 42% purchased cows. The use of standard biosecurity practices was generally low with 30% of producers keeping purchased animals separate and 30% vaccinating new additions. None of the evaluated biosecurity practices were associated with reporting Johne’s disease. The purchase of > 10 bulls, the purchase of cows, not vaccinating animals bought into the herd, and use of community pasture were associated with a bovine respiratory disease outbreak. Outbreaks of calf diarrhea were associated with the purchase of 10 or more bulls, the use of a community pasture, and leasing or sharing bulls.

Introduction

Globally there is a recognized need to reduce antimicrobial drug usage, making prevention of disease by other means a top priority, particularly as the worldwide demand for beef continues to increase. The objective of biosecurity is to prevent new pathogens from entering a livestock operation and to reduce the spread of existing pathogens within premises (1).

The beef industry in Canada presents some unique challenges to implementing and maintaining adequate biosecurity protocols. As of January 2020 there were 72 700 operations with cows and calves in Canada, with the majority concentrated in western Canada (2). Production in these operations is funneled into a small number of feedlots; in Alberta and Saskatchewan there are 165 feedlots with average annual capacity of 1000 head or higher, and together, they have a one-time capacity of 1.59 million head of cattle (3). This “funneling” results in extensive mixing of cattle from various farms as animals are sold through auction markets. This challenge of the industry structure is coupled with uncertainty regarding the level of knowledge about basic biosecurity practices among beef producers, consistent with that reported in other countries (4–8). In Canada, the Canadian Food Inspection Agency has published the Canadian Beef Cattle On-Farm Biosecurity Standard, which has recommendations for best practices in biosecurity for beef producers (9). It is uncertain to what extent these practices are followed. There is limited information about biosecurity practices in beef cow-calf farms in Canada (10–13). Previous research relevant to the current study reported that cows bred on community pastures were more likely to be pregnant and less likely to have an abortion if they had been vaccinated for bovine viral diarrhea virus (BVDV) and bovine herpesvirus type 1 (BHV-1) (10,12).

In the United States, the National Animal Health Monitoring System (NAHMS) reported > 2/3 of cow-calf ranches added new cattle to the herd within the previous 3 y (14). As well, 2/3 of producers did not quarantine new additions to the herd and < 5% tested new cattle for diseases such as bovine viral diarrhea (BVD) and Johne’s (14).

Several studies have shown that biosecurity can impact animal health. Cardwell et al (15) reported that cattle in beef herds in which the producer was given biosecurity advice tailored to them by their herd veterinarian were less likely to be seropositive to BVDV and Leptospira hardjo. Presi et al (16) determined that farms that bring in new livestock and use communal summer grazing are more likely to introduce BVDV infection into the herd. Dias et al (17) reported that buying cattle and renting pasture from other farmers were risk factors for bovine herpesvirus infection. Bringing new cattle into the herd is a significant risk factor associated with the presence of bovine tuberculosis (18–20). In 1 western Canadian study, purchased beef cattle had a 2.3 times higher odds of being Mycobacterium avium ssp. paratuberculosis (MAP) positive (21). Another study from the same area of Canada determined that the risk of death was higher in calves from herds in which cattle had been purchased in the months before or during calving (22).

Similar results have been reported in other areas of animal agriculture. In a study of Dutch dairy farms, farms in which cattle were not purchased incurred lower costs for veterinary services, had a lower average age at first calving, and a higher birth rate per 100 dairy cows (23). Laanen et al (24) reported that increased biosecurity in Belgian pig farms resulted in improvements in daily weight gain and feed conversion and that as biosecurity improved there was a decreased use of antibiotics for prophylaxis.

The objectives of this study were to describe current biosecurity practices in cow-calf herds in western Canada and to examine the potential association of those practices with animal health. Specifically, the association between biosecurity and the incidence of Johne’s disease, bovine respiratory disease (BRD), and calf diarrhea in those herds were examined.

Materials and methods

This study was approved by the University of Saskatchewan’s Animal Research Ethics Board (#20140003) and the Human Behavioural Research Ethics Board (#14-07).

Herd recruitment

A biosecurity questionnaire was distributed to 103 cow-calf producers in western Canada participating in the Western Canadian Cow-Calf Surveillance Network (WCCCSN) in July 2017. At the time of this study, the WCCCSN consisted of a convenience sample of 103 cow-calf producers in the Canadian provinces of Alberta, Saskatchewan, and Manitoba. The 2011 Census of Agriculture (25) was used to determine recruitment targets for herd numbers in various geographic regions representative of reported herd density. The distribution was targeted at moderately sized herds (100 to 300 cow-calf pairs) and larger herds (> 300 cow-calf pairs) from these data, although at the time of the survey, some herds had decreased to < 100 cows. Local veterinary clinics were asked to assist in the recruitment of herds from their clientele. Criteria for recruitment included those clients that were interested in participating, herds that had routine pregnancy testing, and producers who kept basic production records. Interested producers were paid a yearly honorarium to be part of the WCCCSN and were asked to complete approximately 3 surveys per year over a 5-year period.

Survey content

Questions relating to biosecurity included: current beef cattle inventory, other animals on the farm (dairy cattle and other species), number of cattle purchased, source of cattle purchased, where cattle were sold, intake procedures applied to cattle purchased (i.e., disease testing, quarantining, and vaccinations), commingling with other herds, potential risks from exposure to humans and equipment, animal health practices, and general biosecurity within the herd. Questions pertaining to diseases within the herd were also included. A copy of the survey is available from the corresponding author upon request.

Before full distribution, the questionnaire was sent to 5 cow-calf producers who were not study participants for pretesting and to gather feedback about the questions and suggestions for improvements in wording and clarity. The questionnaires were distributed in June 2017 to the WCCCSN participants who could either fill out a paper copy and return it by mail or complete the identical questionnaire online.

Data management and statistical analysis

Data from the biosecurity survey were collected and entered into a commercial spreadsheet program (Excel 2017; Microsoft, Redmond, Washington, USA). Data were then imported into a statistical software package (Stata/IC version 15.1; Stata, College Station, Texas, USA) for analysis. The study population was described using descriptive statistics. Herd size was categorized as large (having ≥ 300 or more cows when completing the survey in 2017) or moderate (< 300 cows).

Three health-related outcomes were examined to identify any associated biosecurity factors: the producer answered yes to “Have you had Johne’s disease diagnosed in your herd?”; the producer answered yes to “Have you had an outbreak (treated more than 10%) of animals for shipping fever/pneumonia in the last 5 years?”; and the producer answered yes to “Have you had an outbreak (treated more than 10%) of animals for calf diarrhea and/or coccidiosis in the last 5 years?” Each outcome was examined separately using logistic regression, and results are reported as odds ratios (OR) with 95% confidence intervals (95% CI). All potential risk factors were screened using unconditional analysis; factors with P < 0.2 were considered for inclusion in the final multivariable models. Manual stepwise backward selection was used to develop a main effects model, retaining only variables with P < 0.05. The final model was checked for confounding by the variable herd size.

Results

Herd demographics

Eighty questionnaires were completed, with the last one being returned in May 2018, resulting in a response rate of 78%. Herds ranged in size from 34 cows to 2500, with a median of 312 cows [interquartile range (IQR): 161 to 331]. Participants reported a median of 11 breeding bulls (IQR: 7 to 21), 49 replacement heifers (IQR: 29 to 83), 193 calves (IQR: 131 to 312), and 22 feeder calves (IQR: 3 to 111). Thirty-one herds were large (≥ 300 cows) and 49 were moderate in size (< 300 cows). A total of 95% of respondents reported having commercial cows, 22% had purebred cattle, 37% had calves that were being backgrounded (i.e., fed on a lower energy ration over the winter before entering the feedlot or summer grazing), and 9% also had a feedlot. Of the respondents, 38 herds were in Alberta, 25 herds were in Saskatchewan, and 17 herds were in Manitoba.

Cattle purchases made by producers

All producers reported buying at least 1 bull between 2014 and 2017 (Table 1). The next most common cattle purchased were heifers (54% of herds), cows (42% of herds), foster calves (22% of herds), and feeder calves (17% of herds). Over that same period, the median number of animals purchased was bulls–10, heifers–32, cows–15, foster calves–1, and feeder calves–200.

Table 1.

Cattle purchases made by producers between 2014 and 2017, reported by 80 cow-calf producers in western Canada.

	2017		2016		2015		2014		Overall
	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle purchased, median (5th to 95th percentile)	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle purchased, median (5th to 95th percentile)	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle purchased, median (5th to 95th percentile)	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle purchased, median (5th to 95th percentile)	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle purchased, median (5th to 95th percentile)
Bulls	91	3 (1 to 12)	89	3 (1 to 10)	90	2 (1 to 10)	91	2 (1 to 10)	100	10 (3 to 40)
Cows	8	37 (1 to 136)	17	11 (1 to 138)	22	36 (3 to 200)	18	18 (1 to 400)	42	32 (1 to 543)
Heifers	28	18 (1 to 200)	43	10 (1 to 121)	33	11 (1 to 118)	28	11 (1 to 73)	54	15 (2 to 387)
Foster calves	10	1 (1 to 4)	6	2 (1 to 5)	8	2 (1 to 3)	6	1 (1 to 3)	22	1 (1 to 14)
Feeder calves	9	42 (3 to 10 000)	11	210 (1 to 10 000)	15	200 (2 to 10 000)	9	900 (2 to 10 000)	17	200 (8 to 40 000)

Cattle movements

Producers were asked for the sources from which they purchased cattle and the site to which they sold cattle in the previous 12 mo (Tables 2, 3). Three options were given: auction market, another farm (cattle purchased or sold directly from or to a different farm), and private sale [a sale with a limited number of sellers but could be at any location (i.e., a bull sale)]. Again, the most common cattle type purchased was bulls, with 74% of herds purchasing bulls from private sales and almost half (43%) of herds purchasing bulls directly from other farms. Heifers were most often purchased from other farms, with 25% of participating herds buying heifers from farms. Fifteen percent of producers purchased a foster calf from another farm in the last 12 mo. The highest percentage of feeder calves were purchased from auction markets, with 10% of producers purchasing them there.

Table 2.

Locations from which cattle were purchased in the 12 mo before the survey reported by 80 cow-calf producers in western Canada.

	Auction market		Another farm		Private sale
	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle types purchased, median (5th to 95th percentile)	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle type purchased, median (5th to 95th percentile)	Percentage of producers who purchased cattle type (n = 80) (%)	For those producers purchasing, number of cattle types purchased, median (5th to 95th percentile)
Bulls	0	0	43	2 (1 to 20)	74	3 (1 to 11)
Cows	5	20 (11 to 43)	8	29 (1 to 94)	6	2 (1 to 46)
Heifers	14	20 (3 to 300)	25	8 (1 to 73)	19	3 (1 to 69)
Foster calves	0	0	15	1 (1 to 4)	0	0
Feeder calves	10	121 (1 to 1800)	4	200 (1 to 3066)	0	0

Table 3.

Locations to which cattle were sold in the 12 mo before the survey reported by 80 cow-calf producers in western Canada.

	Auction market		Another farm		Private sale
	Percentage of producers who sold cattle type (n = 80) (%)	For those producers selling, number of cattle types sold, median (5th to 95th percentile)	Percentage of producers who sold cattle type (n = 80) (%)	For those producers selling, number of cattle types sold, median (5th to 95th percentile)	Percentage of producers who sold cattle type (n = 80) (%)	For those producers selling, number of cattle types sold, median (5th to 95th percentile)
Bulls	86	3 (1 to 10)	29	6 (1 to 36)	12	42 (1 to 82)
Cows	91	24 (6 to 89)	14	21 (1 to 1200)	4	40 (33 to 50)
Heifers	35	11 (2 to 67)	27	25 (2 to 70)	12	7 (1 to 57)
Foster calves	2.5	3 (1 to 4)	16	3 (1 to 5)	0.0	0
Feeder heifer	70	50 (5 to 175)	12	64 (4 to 1500)	2.5	53 (6 to 100)
Feeder steer	72	74 (8 to 300)	19	105 (1 to 600)	2.5	163 (135 to 190)

Most cattle were sold through auction markets; 91% of producers sold cows at the auction market, 86% sold bulls, and 72 and 70% sold feeder steers and heifers, respectively. The next most common location for selling cattle was directly to another farm; 29% of producers sold bulls to another farm, whereas 27% sold heifers to another farm. Sixteen percent of producers sold foster calves to another farm.

Biosecurity practices of cow-calf herds in western Canada

Only 30% of producers kept purchased animals separate from the herd for some time, and only 30% vaccinated newly purchased animals (Table 4). Few producers asked about disease history when purchasing new cattle (16%), but most did ask about vaccination history (78%) before purchase decisions. Custom feeding (feeding cattle for a fee) and custom calving (feeding and calving cows for a fee), practices which would potentially bring new animals into the herd on a yearly basis, were not common, with only 12 and 6% of producers participating in these activities, respectively. Community pastures, which mix herds for summer grazing, were used commonly (30%), whereas 21% of producers took cattle to livestock shows. As well, 19% of producers in the study restricted access of visitors to their farm, although 27% of farms had hosted visitors from another country in the last 3 y, a potential source of foreign animal diseases (Table 4). Most producers used the same equipment for handling manure and feeding cattle (79%), and only 22% reported that they cleaned equipment after handling manure.

Table 4.

Responses of cow-calf producers in western Canada regarding survey questions about general biosecurity.

Survey questions	Yes (%)	No (%)	Under certain circumstances (%)
New animals purchased kept separate for a period of time.	30	46	24
New animals are vaccinated prior to adding them to the herd.	30	68
Producer asks about disease history prior to purchasing new animals.	16	64	17
Producer asks about vaccination history prior to purchasing new animals.	78	20	1
Producer has custom fed calves on their farm in the last 3 years.	12	85
Producer has custom calved cows on their farm in the last 3 years.	6	93
Producer uses community pasture for summer grazing.	30	69
Producer has taken cattle to a show in the last year.	21	78
Producer had a bull sale on their farm in the last year.	6	93
Producer has leased bulls for use on their farm in the last 3 years.	31	67
Producer restricts access of people from other farms to their cattle.	19	63	16
People from other countries had visited the producers farm in the last 3 years.	27	70
Producer uses the same equipment for manure handling and feeding cattle.	79	19
Producer cleans and disinfects loader after handling manure.	22	57

Health-related outcomes

Interdigital phlegmon of cattle, more commonly known as footrot, was the most common disease in this study, with 86% of producers reporting that they had treated at least 1 case in the last 5 y. Almost 1/3 of producers (31%) reported that there had been a case of Johne’s disease diagnosed in their herd. A total of 72% of producers had treated at least 1 case of BRD (i.e., pneumonia or shipping fever) and 83% of producers had treated at least 1 case of calf diarrhea (Table 5). Outbreaks were defined as a situation in which a producer treated ≥ 10% of their cattle for a particular disease in a single year; BRD outbreaks were reported in 19% of herds, 22% of cow-calf producers reported having an outbreak of calf diarrhea in the past 5 y, and coccidiosis outbreaks were reported in 16% of herds. Abortion outbreaks in which > 5% of the cow herd aborted in a single year over the last 5 y were only reported in 4% of herds.

Table 5.

Health-related outcomes based on the answers producers gave to questions about diseases that they observed in their herds.

Health related outcome (n = 80)	Percentage of herds that treated an animal for the disease	Percentage of herds that had an outbreaka of the disease
Shipping fever/pneumonia	72	19
Calf diarrhea/scours	83	22
Coccidiosis	58	16
Infectious bovine rhinotracheitis	6	0
Bovine viral diarrhea	6	0
Pinkeye	69	16
Footrot	86	12
Trichomoniasis	1	0
Vibriosis	3	1

^aOutbreak defined as treating ≥ 10% of animals in the herd for the specified disease.

Factors associated with having Johne’s disease diagnosed in a herd

Producers were asked, “Have you had Johne’s disease diagnosed in your herd?” There is a possibility that some herds may have had cows with Johne’s disease but may not have been aware as it had not been diagnosed. There were several factors unconditionally associated (P < 0.20) with reporting that a herd had a previous Johne’s disease diagnosis. They included herd size ≥ 300 cows, the purchase of ≥ 10 bulls from 2014 to 2017, new animals purchased are not kept separate for a period of time, new animals are not vaccinated before adding them to the herd, producer does not ask if Johne’s disease is present in the source herd, producer has taken cattle to a show in the last year, and the producer had a bull sale on the farm in the last year. The only variable significant (P < 0.05) in the final model was new animals not being vaccinated before adding them to the herd. However, when herd size was added to the model to check for confounding, it had a > 20% effect on the exposure variable. When accounting for the effect of herd size, none of the variables were associated with a herd having a diagnosis of Johne’s disease.

Factors associated with bovine respiratory disease outbreaks in a herd

Approximately 1 in 5 producers (20%) reported having had an outbreak of BRD in the previous 5 y. Unconditional associations (P < 0.20) with various biosecurity management factors were examined individually with the herd outcome of having a BRD outbreak in the past 5 y. A model was developed in which herd size was offered as a potential confounder, but it did not change important effect estimates by > 20% so was not retained in the final model. In the final model, producers who purchased > 10 bulls from 2014 to 2017 (OR: 9.70; 95% CI: 1.68 to 56.0, P = 0.011), bought cows in a private sale in the last 12 mo (OR: 20.7; 95% CI: 1.25 to 342, P = 0.034), bought cows from another farm in the last 12 mo (OR: 12.2; 95% CI: 1.11 to 133, P = 0.041), did not vaccinate purchased animals (OR: 10.8; 95% CI: 1.22 to 95.0, P = 0.032), and used community pasture grazing in 2017 (OR: 6.2; 95% CI: 1.26 to 30.5, P = 0.025), had greater odds of reporting a BRD outbreak in the last 5 y than producers who did not report these factors.

Factors associated with an outbreak of calf diarrhea

Several herds had either an outbreak of calf diarrhea (22%) or coccidiosis (16%) (Table 5). A final model was developed upon examining factors unconditionally associated (P < 0.20) with a producer reporting a calf diarrhea and/or coccidiosis outbreak. Herd size did not change important effect estimates by > 20%, so it was not retained in the final model as a confounder. In the final model, producers who purchased > 10 bulls from 2014 to 2017 (OR: 3.27; 95% CI: 1.16 to 9.21; P = 0.025), used community pasture for grazing in 2017 (OR: 2.86; 95% CI: 0.98 to 8.32; P = 0.054), or leased or shared bulls in the last 3 y (OR: 2.86; 95% CI: 0.98 to 8.32; P = 0.054) had greater odds of reporting an outbreak of calf diarrhea and/or coccidiosis in the last 5 y.

Discussion

Beef cow-calf herds in western Canada are typically extensively managed (i.e., cattle predominantly spend their time grazing on pasture) and this type of management does not easily allow for exclusion biosecurity practices that may be practiced in other livestock systems. There is little information in the literature regarding the typical biosecurity practices in cow-calf herds in North America. Much of the available information for western Canada is from a series of studies by Waldner et al (10,12,26). This research provided insights into biosecurity practices such as the impacts of community pasture and vaccination status on the incidence of abortions and non-pregnancy in these herds. The current study demonstrated the potential negative health effects of practices such as adding new adult cattle into the herd and communal grazing.

Introducing new animals into a herd presents 1 of the highest risks for introducing disease (27). In this study, all herds purchased bulls during 2014 to 2017 and over half of the herds also purchased heifers, indicating that introduction of new animals into the herd was a common practice. Most bulls and heifers were purchased from either private sales or other farms. This is potentially less risky from a biosecurity perspective than purchases made from an auction market where there is considerable mixing of cattle from multiple farms. Chi et al (28) investigated disease transmission in dairy cattle and reported that because auctions handle cattle from many farms, there is greater contact with cattle from multiple sources, and therefore more exposure to various infectious diseases.

Biosecurity precautions that would be considered standard practice in other areas of animal agriculture were not common in this study. Less than a third of producers kept new additions separate and vaccinated new animals. The survey did not specify the level of separation (i.e., separated by a significant distance versus nose-to-nose contact possible), so the level of contact may have been higher than reported. Additionally, many producers used community pasture, thereby mixing their cows with other herds in the summer grazing period. There was substantial mixing of cattle in other ways as well, such as custom feeding of calves and taking cattle to livestock shows. Finally, only 19% of herds had restricted access for visitors. Interestingly, these results are similar to those from studies in England (4), Australia (5), Finland (6), and Belgium (7). This suggests that exclusion biosecurity for cattle farms worldwide is not a priority. Partly, this can be attributed to the fact that beef cattle are more commonly raised extensively (on pasture), rather than intensively (in a confined space). Beef cattle in the North American production system often move from the cow-calf farm where they were born to a backgrounding operation for post-weaning growth to a finishing feedlot to be fed to slaughter weight, thereby encouraging buying, selling, and mixing of cattle along the production chain. Ribble et al (29) in a large Canadian study determined that increased mixing or commingling of calves from different ranches increased the risk of fatal pneumonia in those calves.

Previous studies have shown that the 2 most significant calf-hood diseases are BRD and calf diarrhea (11,13). In the current study, purchase of cows into the herd had a significant impact on the odds of having a BRD outbreak. Purchasing bulls and leasing or sharing bulls also had a significant effect on the odds of an outbreak of calf diarrhea. This demonstrates that bringing in adult cattle has an impact on diseases that are of primary concern in calves, BRD and calf diarrhea. Increasing herd size and commingling of adults increases the risk of preweaning BRD and calf diarrhea in cow-calf herds (11,30,31). The cows and bulls themselves could be carrying pathogens as commensal organisms in their respiratory or gastrointestinal tracts. Careful cow and bull selection based on known disease history and vaccination status of the source herd (i.e., not sourcing new additions through unknown sources such as auction markets) would be 1 means of reducing disease transmission. How BRD and calf diarrhea pathogens are transmitted from adult cattle to calves is not well-understood and further research in this area is needed. For example, are some cows and bulls “super shedders” of these pathogens and could these animals be culled to reduce disease?

Using community pasture was the other factor that increased the risk of both BRD and calf diarrhea. Community pasture, involving mixing multiple cow-calf herds together in the same pasture during the summer grazing period was used by 30% of producers in western Canada in the years of study. Cows sent to community pasture are more likely to mix with herds of different biosecurity status. Two Canadian studies reported that cows grazed on community pastures and not vaccinated for BVDV or BHV-1 were more likely to abort and less likely to be pregnant (10,12). A Brazilian study reported that communal grazing increased the risk of BHV-1 infection (17), and a Swiss study determined that the risk of BVDV introduction was higher in herds that grazed communally (16). Typically, there is a substantial lag between when cows are in community pasture and the time when BRD in calves (at weaning) or calf diarrhea (following calving season) is a problem. This would seem to indicate that the cows harbor the pathogens and subsequently pass them onto the calves later; an area for future research. One potential mitigation measure could be splitting up community pastures into smaller areas that have cattle from only 2 to 3 producers in each area. A step further would be to not allow mixing of herds that have current issues with calf diarrhea and BRD with herds that do not.

The last factor associated with increased risk of BRD, although not an increased risk of calf diarrhea, was not vaccinating purchased animals upon arrival. The survey did question what vaccines were used, but due to many types of vaccines being used, results were not included in the analysis. Most producers vaccinated for BVDV Types 1 and 2, BHV-1, bovine respiratory syncytial virus (BRSV), and parainfluenza virus 3 (PI3) (32). The efficacy of vaccinating calves to prevent BRD is well-established (31,33,34). The questionnaire did not distinguish between vaccination of adult new arrivals or calves. However, because this study did show that purchase of adult animals increases BRD risk in calves, vaccination of adult new arrivals would seem to be a prudent BRD prevention practice. Recent work on vaccination practices from herds in the WCCCSN showed that 91% of cows and 96% of replacement heifers are vaccinated at least once for BVDV and BHV-1(32), so this practice is already commonplace in western Canada.

There is potential in this study, as in all survey-based research, for recall bias. It may have been difficult for a producer to recall all purchases made and the data on sales of animals over the previous 4-year period. This could result in underreporting of cattle movements within the herds.

Another potential limitation is that the study does not represent a random sample. The WCCCSN has herds recruited through local veterinary practices in western Canada. This could result in selection of herds that are more likely to be involved with their local veterinarian, and subsequently represent producers more likely to implement improvements in biosecurity such as vaccinations. The odds ratios in these models had wide confidence intervals and should be interpreted with caution as many of the categorical management factors were somewhat open to producer interpretation (i.e., did animals that were kept separate still have fence line contact?) which could affect our estimates within the models.

In conclusion, it is interesting that the introduction of adult animals into a herd has such a significant association with diseases that are primarily a concern in young calves, namely BRD and calf diarrhea. The mechanism of how these pathogens spread from the newly introduced cattle into calves is an area that requires further study. Community pasture grazing was the other factor that was associated with both BRD and calf diarrhea outbreaks. Multiple studies from other areas of the world had similar results (10,12,16,17,23). The purchase of new animals and community pasture grazing are 2 aspects of cow-calf production that may compromise biosecurity and affect animal health. CVJ