Factors associated with rodent infestation on livestock farms in Japan

doi:10.21203/rs.3.rs-3342951/v1

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Factors associated with rodent infestation on livestock farms in Japan

https://doi.org/10.21203/rs.3.rs-3342951/v1

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One of the obstacles to controlling rodents on livestock farms in Japan is the lack of information about characteristics that lead to infestations. To address this knowledge gap, we performed a nationwide survey that collected information from livestock farmers, including the types and number of livestock present, severity of rodent infestation, rodent management approaches utilized, and details about the most- and least-infested barns. More than 80% of respondents reported rodent infestation on their farms, especially rodents observed on overhead beams and girders. A multiple ordinal logistic regression analysis revealed that the odds ratio of rodent infestation was higher on farms housing pigs and lower on farms with chickens, as compared to farms with cattle. We also found that medium-sized farms, but not large-sized farms, showed a higher odds ratio than small-sized farms. Furthermore, the odds ratio was similarly higher on farms that implemented rodent control measures by themselves or with the assistance of pest control operators, compared to farms with no rodent management. Within a farm, barn age contributed to infestation status, such that the most-infested barns were older than the least-infested barns, regardless of livestock species. Furthermore, the proportion of ad libitum feeding was higher in the most-infested barns than in the least-infested barns on pig farms. Taken together, our results provide valuable information for understanding rodent infestations on livestock farms in Japan, which can contribute to the development of better management approaches.

Black rats

brown rats

questionnaires

ship rats.

We performed a nationwide survey on rodent infestations on livestock farms in Japan.
More than 80% of respondents saw rodents on their farms.
The odds ratio of rodent infestation was higher on pig farms and lower on chicken farms.
The age of barns and ad libitum feeding by pigs were associated with rodent infestation.
The present study provided valuable information on rodent infestation on livestock farms.

Brown rats (Rattus norvegicus), roof rats (Rattus rattus), and house mice (Mus musculus) are some of the most common mammals worldwide. As commensal pests, they have followed human migration from different regions around the world and have adapted to each place. It is well-accepted that these three species of rodents are major pests in urban centers (Himsworth et al. 2013). Similarly, these rodents are considered important pests on livestock farms for several reasons. First, they can be a source of foodborne zoonoses to humans, including campylobacteriosis, salmonellosis, yersiniosis, listeriosis, and toxoplasmosis (Chlebicz and Slizewska 2018; Jones and Dubey 2012). Second, rodent infestation increases the risk of disease infection in livestock. This occurs because livestock cannot avoid feed contaminated with rodent excreta (Daniels and Hutchings 2001) and can result in salmonellosis, cryptosporidiosis, and tapeworms. Third, these rodents cause physical damage to buildings on farms by gnawing on electrical cables and burrowing under construction. Fourth, economic damage is also caused by rodents because they are attracted to, consume, and thrive on animal foods. Therefore, controlling rodents in livestock farms would contribute not only to our health but also to increasing the welfare of livestock.

One of the primary obstacles to controlling rodents on livestock farms in Japan is the lack of information about infestations. Without information on where and how often infestations occur or the factors that contribute to infestations, it is difficult to form effective strategies for rodent control. For example, if rodent infestations on livestock farms are rare, an emphasis should be placed on prevention, monitoring, and swift eradication. Alternatively, if rodent infestations on farms are common, management plans should focus more on maintaining the rodent population below an acceptable level. The lack of information about the predominant rodent pest species also prevents government policymakers and practitioners from effectively planning control programs. The proportion of the three commensal rodents is known to vary according to region. For example, in Denmark, brown rats and house mice were regularly observed on 39% and 69% of the participating farms, respectively (Leirs et al. 2004), suggesting that the house mouse is the predominant species in this region. In contrast, 56% and 17% of small mammals trapped in 10 pig farms and eight dairy farms in Argentina were brown rats and house mice, respectively, indicating that the predominant species in this region is the brown rat (Rosario et al. 2015). In Japan, although the Japanese pest control operators (PCOs) anecdotally believe that roof rats are the predominant species, no data are currently available. Finally, in order to advise farm owners on rodent management, there is a need to know the relevant factors that help predict whether a rodent infestation is likely to occur.

To better understand rodent infestations on livestock farms in Japan, we conducted a nationwide survey. In the first half of the questionnaire, we asked farm owners for basic information about their farms, rodents observed, and the implementation of rodent control. The second half of the questionnaire was aimed at elucidating the possible relevant factors for rodent infestation. We asked farm owners to identify factors related to the most- and least-infested barns on their farms.

Questionnaire

We developed an original questionnaire based on our experience with the management and analyses of rodent infestations in Japan (Supplemental information). In accordance with the approval by the Ethics Review Committee of the Faculty of Agriculture at The University of Tokyo, in the online questionnaire, we first requested the respondents to press the “Next” button if they had read the instruction and voluntarily agreed to participate in the survey. These requirements were also clearly indicated at the top of the printed questionnaire.

The first half of the questionnaire was designed to obtain basic information about farms, rodents observed, and the implementation of rodent control in the previous year (2021). Respondents were asked to provide the name of the farm’s prefecture, identify the species and number of livestock present, the total number of barns, the ratio of infested barns, whether and which rodent control measures were implemented in 2021, and the associated costs of rodent management.

In order to elucidate the possible relevant factors for rodent infestation, the second half of the questionnaire was designed to obtain information about the most- and least-infested barns on a farm. The respondents were asked about the number of rodents they saw at any one time, the location of rodent sightings, the presence of a wall on four sides of the barn, the age of the barn, the species, breed, and number of livestock, whether livestock went outside the barn within a day, the feed for livestock, and the feeding methods used in each barn.

Finally, the respondents were asked to document troubles with other wild animals to identify which species were prevalent among livestock farms.

Questionnaire distribution

A Microsoft Forms-based Japanese questionnaire was distributed on 5 August 2022 to 167 Livestock Hygiene Service Centers located in 47 prefectures in Japan by the Ministry of Agriculture, Forestry and Fisheries. Upon receipt, each Livestock Hygiene Service Center distributed the questionnaire to farm owners in their responsible area. We did not receive responses from several prefectures; therefore, the Ministry of Agriculture, Forestry and Fisheries distributed the questionnaire a second time to those prefectures on 14 October 2022. The responses and timestamps were automatically recorded on a server immediately after the respondents pressed the “submit” button at the end of the questionnaire. However, some Livestock Hygiene Service Centers did not have a mailing list and/or wanted to distribute a printed sheet to farm owners unfamiliar with the web-based survey. In such cases, when requested, an author emailed a PDF of the questionnaire sheet to the appropriate Livestock Hygiene Service Centers. The responses were sent to the Laboratory of Veterinary Ethology, The University of Tokyo, by email, fax, or post.

Data analyses

All data are expressed as mean ± standard error of the mean. All statistical analyses were performed using JMP Pro 17 (JMP Statistical Discovery, North Carolina, USA). The significance criterion for all statistical tests was set at P < 0.05.

The responses in the first half of the questionnaire were analyzed by ordinal logistic regression analysis. The degree of infestation was classified into 5 degrees depending on the ratio of infested barns (1 = “I have not seen any rodents, nor have I seen any signs of rodents (feces and gnaw marks),” 2 = “1% − 25% of barns,” 3 = “26% − 50% of barns,” 4 = “51% − 75% of barns,” or 5 = “76% − 100% of barns”) and used as an objective variable. The livestock species (“cows,” “pigs,” “chickens,” or “multiple species”) and implementation of rodent control last year (“no,” “by themselves,” or “with the assistance of PCOs”) were classified into 4 and 3 categories, respectively. The farm size was classified into three categories to obtain comparable numbers of respondents in each category (“small (≤ 30 cows, 4200 chickens, or 1100 pigs),” “medium (31–90 cows, 4201–75000 chickens, or 1100–3500 pigs),” or “large (> 90 cows, 75000 chickens, or 3500 pigs)"). In addition to these factors, the number of barns, average yearly temperature, and annual precipitation in each prefectural capital were used as explanatory variables. The weather data was obtained from the Japan Meteorological Agency website. In contrast, we excluded the cost spent on rodent control measures from the analyses because approximately 20.0% of respondents did not answer this question.

In the analyses on the second half of the questionnaire, the responses were classified into four categories depending on the livestock species kept in the two barns (cows, chickens, pigs, multiple species). Then, the differences in answers for the number of rodent individuals they saw at any one time (“no rodents and no signs of rodents (feces and gnaw marks),” “I see signs of rodents (feces and gnaw marks), but no rodents,” “about 1–9 rodents,” or “more than 10 rodents”), the locations where the respondents saw rodents (“primarily moving across the ground,” “primarily moving on beams and girders,” or “both types of movement”), the presence of a wall on four sides of the barn (“yes” or “no”), the age of the barn, the breed (cow: “dairy cows,” “beef cattle,” “both,” or “others,” chicken: “egg-laying hens,” “broiler,” “both,” or “others,” pig: “meat pigs,” “breeding pigs,” “both,” or “others”) and number of livestock in the barn, whether livestock went outside the barn within a day (“yes” or “no”), and the feeding methods (“restricted feeding” or “ad libitum feeding”) were analyzed by McNemar-Bowker test or Wilcoxon signed-rank test in each category. It should be noted that we did not compare the breed and number of livestock in the barn and the feed used in each barn in the multiple species category. The differences in the livestock species between the most- and least-infested barns prevent us from analyzing the effects of these factors on rodent infestation.

In addition, the percentage of respondents who answered that the same feed, or the same feed but with fewer items, was used in the most-infested barn as compared to the least-infested barn was calculated. We also listed wild animals other than rodents that caused problems in respondents’ farms.

Questionnaire distribution in the USA

We asked 78 universities on 29 June 2022 to distribute the English version of the questionnaire to livestock farms. We also asked IPM Coordinators in each state and to the Regional IPM Centers throughout the USA on 1 September 2022. In addition, the questionnaire was distributed through personal connections (sporadically), during farm outreach events, and on Twitter (26 August 2022). Unfortunately, we obtained a limited number of responses. Therefore, only the responses in the first half of the questionnaire were reported narratively.

In the present study, 468 respondents participated in the survey, but 67 responses were incomplete. Therefore, to analyze the first half of the questionnaire, we focused on 401 responses that answered all questions. Although we did not receive responses from the Hokkaido region, the respondents participated from all the other regions of Japan (Fig. 1A). The respondents participated evenly from farms keeping cows, chickens, pigs, and multiple species (Fig. 1B) and from small-, medium-, and large-sized farms (Fig. 1C). More than 80% of the respondents recognized rodent infestation on their farms (Fig. 1D). However, more than two-thirds of respondents did not associate rodent infestations with specific locations on their farms (Fig. 1E). More than 80% of the respondents saw rodents moving on beams and girders of the barn (Fig. 1E). When the respondents implemented rodent control measures in the previous year (2021), only a limited proportion of respondents requested assistance PCOs (Fig. 1G). The respondents used a variety of methods to manage rodents, and some used multiple methods. Of a total of 534 measures implemented by the respondents, two popular measures were using methods to kill rodents (rodenticides, etc.) and methods to catch rodents (traps, etc.) (Fig. 1H).

An ordinal logistic regression analysis revealed that the odds ratio of rodent infestation was higher in farms keeping pigs (P < 0.01) and lower in farms keeping chickens (P < 0.01), as compared to farms keeping cows (Table 1). Farms keeping multiple livestock species showed a similar odds ratio with farms keeping cows. We also found that medium-sized farms (P < 0.01), but not large-sized farms (P = 0.88), showed a higher odds ratio of rodent infestation than small-sized farms (Table 1). Furthermore, the odds ratio of rodent infestation was higher on farms where the respondents implemented rodent control measures by themselves (P < 0.01) or with the assistance of PCOs (P < 0.05), as compared to farms where no measures were implemented (Table 1). The number of barns (P = 0.50), average yearly temperature (P = 0.62), and annual precipitation (P = 0.25) were not associated with rodent infestation. We also confirmed that a Lack of Fit test supported the appropriateness of this model (P = 0.96).

Table 1

Summary of ordinal logistic analysis for rodent infestation
	c²	OR	95% CI	P
Livestock species
Cows (reference)
Chickens	11.4	0.59	0.43–0.80	P < 0.01
Pigs	9.34	1.70	1.22–2.37	P < 0.01
Multiple species	0.27	0.89	0.57–1.37	P = 0.60
Farm size
Small (reference)
Medium	7.70	1.44	1.11–1.88	P < 0.01
Large	0.02	1.02	0.78–1.34	P = 0.88
Implementation of rodent control measures
No (reference)
By the responders	22.5	1.95	1.48–2.57	P < 0.01
With the assistance of PCOs	6.13	1.68	1.11–2.55	P < 0.05
Number of barns	0.46	0.99	0.98–1.01	P = 0.50
Average yearly temperature	0.25	0.98	0.90–1.06	P = 0.62
Annual precipitation	1.31	1.00	1.00–1.00	P = 0.25
OR: odds ratio.
CI: confidence interval.

To analyze the second half of the questionnaire, we focused on 237 of 401 respondents who answered all questions. First, we confirmed that these respondents were not a biased population. Specifically, the respondents similarly represented all regions of Japan except Hokkaido (Tohoku: 18.4%, Kanto: 13.4%, Chubu: 23.0%, Kansai: 13.0%, Chugoku: 12.1%, Shikoku: 7.5%, and Kyushu-Okinawa: 11.7%), all livestock species (cows: 27.6%, chickens: 32.2%, pigs: 28.0%, and multiple species: 11.3%), and all farms sizes (small: 24.3%, medium: 38.5%, and large: 36.4%).

Statistical analyses confirmed that the respondents from all categories of farms saw more rodents at one time in the most-infested barn than in the least-infested barn (Ps < 0.01) (Fig. 2A). The most-infested barn was older than the least-infested barn on farms with cows, chickens, and pigs (Ps < 0.01), whereas barn age was similar on farms keeping multiple species (P = 0.56) (Fig. 2B). The most-infested barns had a larger number of cows than the least-infested barns (P < 0.01) (Fig. 2C). In contrast, the number of pigs was smaller in the most-infested barn than in the least-infested barn (P < 0.01) (Fig. 2C). There was no difference between the number of chickens in the most- and least-infested barns (P = 0.47) (Fig. 2C). The proportion of ad libitum feeding was higher in the most-infested barn than in the least-infested barn on farms keeping pigs (P < 0.01) (Fig. 2D). However, the proportion was similar on farms keeping cows (P = 0.78), chickens (P = 1), or multiple species (P = 0.48) (Fig. 2D). The location where the respondents saw rodents (cows: P = 0.95, chickens: P = 1, pigs: P = 0.42, multiple species: P = 0.80), the presence of a wall on four sides of the barn (cows: P = 0.76, chickens: P = 0.41, pigs: P = 0.78, multiple species: P = 0.10), the breed of livestock in the barn (cows: P = 0.54, chickens: P = 0.80, pigs: P = 0.13), and whether the livestock went outside the barn within a day (cows: P = 1, chickens: P = 0.16, pigs: P = 0.32, multiple species: P = 0.16) was similar between the barns on all categories of farms (Table S1).

In addition, the feed used in the most- and least-infested barns did not seem to differ greatly. Specifically, 65.2%, 87.0%, and 50.7% of respondents answered that the feed used in the most-infested barn was the same, or the same but had fewer items than that used in the least-infested barn on farms keeping cows, chickens, and pigs, respectively.

Finally, 249 of 401 respondents indicated multiple wild animal species that caused problems on their farms (345 species in total), including crows (26.9%), common raccoon dogs (24.5%), boars (26.9%), cats (12.4%), weasels (10.0%), foxes (7.6%), masked palm civets (6.0%), pigeons (6.0%), badgers (5.6%), deer (5.6%), bears (3.6%), raccoons (3.6%), old world sparrows (2.8%), dogs (1.6%), nutrias (1.6%), snakes (1.6%), marten (1.2%), monkeys (1.2%), hawks (0.4%), mongooses (0.4%), pheasants (0.4%), and wagtails (0.4%).

The survey in the USA

Among 15 respondents, only eight answered all questions in the first half of the questionnaire. The respondents participated from Texas (n = 3), Utah (n = 1), New Hampshire (n = 1), New York (n = 1), Nevada (n = 1), and Vermont (n = 1). The respondents participated from farms keeping cows (n = 3), chickens (n = 1), and multiple species (n = 4), and from medium- (n = 2) and small-sized farms (n = 6). While two respondents did not implement rodent control measures in 2021, five and one respondents implemented rodent control measures by themselves and with the assistance of PCOs, respectively.

All respondents saw rodents or their signs on farms. While two respondents answered that the infested barn was built in a specific location, six respondents found no commonalities between the locations of infested barns. In addition, when we focused on six respondents who saw rodents, half of the respondents saw rodents moving on the ground. The remaining half saw rodents both on the ground and on beams and girders.

In this study, we performed a nationwide survey to obtain information about rodent infestations on livestock farms in Japan. We found that more than 80% of the respondents saw rodents on their farms, suggesting that the presence of rodents is not a rare incident. Most of these rodents appear to be roof rats because the respondents mainly saw rodents on beams and girders. In addition, the ordinal logistic analysis on the first half of the questionnaire revealed that the livestock species, farm size, and implementation of rodent control measures were associated with rodent infestation. We also found in the analyses of the second half of the questionnaire that the most-infested barns were older than the least-infested barns in pig, chicken, and cow farms. In addition, the proportion of ad libitum feeding was higher in the most-infested barns than in the least-infested barns on pig farms. These results suggest that the age of the barn and ad libitum feeding by pigs are important factors for rodent infestation. Taken together, the present study provides valuable information for understanding rodent infestation on livestock farms in Japan.

In the present study, more than 80% of the respondents indicated that they saw rodents moving on beams and girders of barns. These results suggest that the roof rat is the predominant species on livestock farms in Japan. Accurate identification of rodents is difficult for farmers, especially if rodents are observed at a distance. Therefore, to estimate the percentage of roof rats among the other commensal rodents, we asked whether the rodents were moving on beams and girders since roof rats commonly occupy the upper parts of a building. The predominance of roof rats is consistent with the findings from urban centers. Specifically, in our previous work, Japanese PCOs indicated that 80% and 20% of rodents in Tokyo, Japan were roof rats and brown rats, respectively (Kiyokawa et al. 2022). Based on the present and previous studies, we suggest that the roof rat is the predominant rodent in Japan.

We found in the ordinal logistic analysis that the odds ratio of rodent infestation differed according to the primary livestock species on farms. Currently, little information is available to determine the reason for this. However, we can propose that pig farmers need to devote more resources to controlling rodents than other livestock producers. It is well known that brown rats and house mice on pig farms are carriers of a variety of zoonotic pathogens, as well as pathogens that affect pigs (Backhans and Fellstrom 2012). In addition, rodents are considered potential carriers of classical swine fever virus and African swine fever virus because there are still many contradictions about the transmission of these viruses (Olesen et al. 2020; Ribbens et al. 2004). For example, a previous experiment demonstrated that the classical swine fever virus could be physically transmitted by humans (Ribbens et al. 2007). Therefore, if there is frequent movement of large numbers of rodents between barns or farms, rodents can also physically transmit the classical swine fever virus and African swine fever virus, even if rodents themselves are not sensitive to the viruses (Dewulf et al. 2001). What is known is that the implementation of appropriate measures can improve the situation, as demonstrated by a longitudinal study that eradicated Toxoplasma gondii from Dutch farms (Kijlstra et al. 2008). It is therefore recommended that owners of pig farms pay special attention to rodent control.

The ordinal logistic analysis also revealed that medium-sized farms, but not large-sized farms, have a higher odds ratio of rodent infestation than small-sized farms. We also obtained a similar result when analyzing the second half of the questionnaire. In pig farms, the number of pigs was smaller in the most-infested barn than in the least-infested barn. These results are inconsistent with our intuition that rodent infestation will increase as the number of livestock increases. Indeed, a previous study has indicated that the number of sows was associated with the presence of rats in outdoor pig farms in Denmark (Leirs et al. 2004). One possible reason for this discrepancy would be whether the farms in the analyses are outdoor or indoor farms. As 81 to 99% of barns house livestock all day (Table S1), livestock farms in Japan are mostly indoor farms. Unlike a small proportion of farms established by large companies, indoor farms are increasing the number of livestock by replacing old barns with new barns for intensive livestock farming. Because the new barns are usually designed with the latest knowledge to prevent rodent infestation, these new barns tend to house a larger number of livestock with less rodent infestation. To support this interpretation, seven (10.6%), seven (9.1%), and nine respondents (13.4%) from cow, chicken, and pig farms, respectively, answered in this way. In an extreme case in pig farms, one respondent answered that the most-infested barn was aged 15 years old and kept 7,580 pigs, whereas the least-infested barn was aged five years old and kept 36,000 pigs. When we exclude this responder, statistical analysis indicates that most-infested barns house a significantly larger number of pigs than least-infested barns. Given that the age of the barn also affects rodent infestation, as discussed below, the number of livestock seems not to be a good factor in predicting rodent infestation on indoor farms.

In the present study, the ordinal logistic analysis indicated that the odds ratio of rodent infestation was similar between farms where the respondents implemented rodent control measures by themselves or with the assistance of PCOs. Given that there are no tools licensed only to PCOs in Japan, one interpretation would be that the two major methods (methods to kill rodents and methods to catch rodents) have several limitations. First, because wild rodents, in general, show neophobia and avoid novel objects (Kiyokawa et al. 2017; Koizumi et al. 2018; Koizumi et al. 2021; Koizumi et al. 2019; Stryjek and Modlinska 2016), tools used for rodent control (rodenticide and trap) are avoided by rodents. Given that an appeasing pheromone that ameliorates neophobia in the wild brown rat was recently identified (Kiyokawa et al. 2023), an application of the appeasing pheromone to these tools has the potential to improve the efficacy of rodent control. Second, due to the lack of information regarding the ecology of rodents in livestock farms, it is possible that these tools are not deployed in the most effective places. Therefore, it would be worth testing whether the computer program that estimates the effective locations of these tools to control brown rats on Dutch farms (Endepols and Klemann 2004; Endepols et al. 2003) would also work for roof rats on Japanese farms. However, we cannot deny the alternative interpretation that the odds ratio might be much higher if the respondents did not ask for assistance from PCOs. Furthermore, it is also possible that the PCOs did not perform at their full potential because they had to price out to obtain business. Further research is needed to clarify these points.

The analysis of the second half of the questionnaire suggested that the age of the barn and the presence of ad libitum feeding of pigs are the relevant factors for rodent infestation. As the majority of respondents recognized no commonalities between the locations of infested barns, rodents seemed to infiltrate barns randomly. Therefore, older barns may have experienced more rodent invasions cumulatively. In addition, older barns may also have a lot of gaps in the walls and places for rodents to hide and/or nest. For example, in urban areas, an 80-year-old market in Tokyo had many nests in the building (Kiyokawa et al. 2021). Therefore, rodents are expected to infest older barns easily. Similarly, rodents can easily find food when livestock is fed ad libitum. Given that a similar proportion of the least-infested barn in chicken farms performed ad libitum feeding, the feed for pigs appears to be attractive to rodents. Taken together, farm owners are advised to rebuild older barns and perform restricted feeding on pig farms.

The present study revealed that respondents also had problems with wild animals other than rodents. Although some respondents kept cats as one of the rodent control measures, cats were ranked as the fourth most problematic wild animal on respondents’ farms. Based on these results, we do not recommend that farm owners keep cats as one of the rodent control measures. It was reported that cats traveled an average of 3.8 km, with a maximum of 6.3 km, from the inhabited farm (Ferreira et al. 2011), although the home range can vary depending on many factors (Nottingham et al. 2022). Therefore, when farm owners keep cats, the cats can cause problems on livestock farms within this range. In contrast, the findings in the previous studies suggest that the value of cats in rodent control is limited. For example, because cats mostly hunted individuals weighing less than 100 g (Childs 1986), prey is likely limited to mice, young roof rats, and juvenile brown rats. In fact, predation attempts were recorded in only three of 306 videos that recorded cats and/or wild brown rats sharing the same spaces in New York City for 79 days (Parsons et al. 2018). Therefore, although farm owners may see fewer rodents after keeping cats, it may simply be that rodents have changed their activity patterns. In addition, even if cat odor alone can evoke strong defensive behavior, both laboratory rats (Staples et al. 2008) and wild brown rats (Bedoya-Perez et al. 2021) quickly showed habituation, suggesting that cat odor is likely to repel rodents from livestock farms for only a short period. Taken together, the disadvantages of cat ownership seem to outweigh the benefits.

The prevalence of rodents in livestock farms appears not to be a specific case in Japan. Although the sample size was too small to draw a general conclusion, all respondents from the USA saw rodents on their farms. However, the proportion of roof rats seems to be lower in the USA than in Japan because the number of respondents who saw rodents moving on beams and girders was half in the USA. These results are consistent with the widely accepted notion that brown rats are the predominant species in North America (Bonnefory et al. 2008), although no data are currently available. In order to further understand the similarities and differences between Japan and the USA, as well as among the countries, it is necessary to perform a nationwide survey of rodent infestation on livestock farms in various countries.

In summary, we obtained information about rodent infestation on livestock farms in Japan. Based on the present study, we recommend the following to farm owners. First, it is important to accept the assumption that rodents, mostly roof rats, are present on all farms. Therefore, it would be more reasonable to aim to keep the rodent population below an acceptable level as the first step in rodent control. Second, owners of pig farms are advised to devote more resources to controlling rodents. If possible, restricted feeding is recommended. Third, it is recommended that old barns be rebuilt as much as possible. Fourth, cat ownership is not suggested as a rodent control measure. In parallel, there is a need to develop new tools to more effectively kill or catch rodents. It is also necessary to obtain more information about the ecology of rodents on livestock farms in Japan. For example, it is currently unclear whether and how often rodents move between barns or farms. These activities would help us control rodents on livestock farms, which would contribute to our health and to increasing the welfare of livestock.

Funding: This study was conducted under the research project on “Regulatory research projects for food safety, animal health, and plant protection (JPJ008617.22682159),” funded by the Ministry of Agriculture, Forestry, and Fisheries of Japan.

Conflicts of interest: The authors declare that they have no conflicts of interest.

Availability of data and material: The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Code availability: Not applicable.

Authors’ contributions: Conceptualization: Yasushi Kiyokawa and Ryoko Koizumi; Data curation: Yasushi Kiyokawa; Formal analysis: Yasushi Kiyokawa and Ryoko Yamada; Funding acquisition: Yasushi Kiyokawa, Ryoko Koizumi, Shigeru Hirata, and Tsutomu Tanikawa; Investigation: Yasushi Kiyokawa, Ryoko Koizumi, Matthew Frye, Michael H. Parsons, and Tsutomu Tanikawa; Methodology: Yasushi Kiyokawa and Ryoko Yamada; Project administration: Yasushi Kiyokawa; Resources: Yasushi Kiyokawa; Supervision: Yasushi Kiyokawa; Validation: Yasushi Kiyokawa and Ryoko Yamada; Writing-original draft: Yasushi Kiyokawa; Writing-review & editing: Ryoko Koizumi, Ryoko Yamada, Matthew Frye, and Michael H. Parsons.

Consent to participate: We did not collect personally identifiable information in the survey. Nonetheless, informed consent was obtained from all individual participants included in the study.

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Factors associated with rodent infestation on livestock farms in Japan

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