Socially engaged calves are more likely to be colonised by VTEC O157:H7 than individuals showing signs of poor welfare

Untangling the role of environmental and host-related determinants for on-farm transmission of verotoxin-producing Escherichia coli O157

Background: Cattle colonised by the zoonotic pathogen verotoxin-producing Escherichia coli of serotype O157 (VTEC O157) can shed high levels of the pathogen in their faeces. A suggested key for controlling VTEC O157 is preventing colonisation of individuals. Aim: In this study the role of individual super-shedders and factors related to susceptibility and environmental exposure in the transmission of VTEC O157 among dairy calves are explored. Methods: The association between sex, age, pen hygiene, pen type and stocking density and colonisation of individual calves, established by recto-anal mucosal swabs, on farms where pathogenic VTEC O157 had been confirmed was investigated. In a follow-up sampling, the consistency of previously identified risk factors and the role of shedding pen mates was assessed by studying the risk of new/re-colonisation. Results: The results suggest an important role of stocking density that decreases with age, possibly due to increased resistance to colonisation following exposure. However, previous colonisation did not influence the risk of being colonised in the second sampling. Super-shedders (shedding >103 colony forming units/g faeces) significantly increased the risk of colonisation in peers (OR = 10, CI 4.2-52). In addition, environmental factors associated with survival of the bacteria, affected risk. Conclusion: The results confirm the suggested importance of super-shedders but also emphasises the importance of considering the combined exposure from peers and the environment.

Current research considering social behavior to improve the welfare of commercially raised dairy calves

Social contact in early life has broad benefits for behavioral development and welfare of the developing dairy calf. The most accessible approach to providing social contact for commercially raised dairy calves is rearing calves in same-age groups, a practice that is growing in popularity. This symposium review highlights developing areas of research relevant for widespread implementation of social housing on commercial farms. I discuss the onset of social behavior in young calves, development of social preferences, implications of calf management and housing for expression of social behavior, individual differences in social behavior, and implications of environmental complexity within the context of social housing. Under both naturalistic and commercial settings, calves interact socially within the first days of life and develop preferences for familiar social companions. Early introduction to social housing appears to benefit the development of social behavior, which may affect integration in later social groups, with potential long-term effects. Housing and management factors affecting socially housed calves have potential to disrupt social synchrony compared with behavior under more natural conditions, which can reduce social lying, cause competition for access to feed, and may have implications for social bond formation and social learning within the social group. Although calves exhibit preferences for familiar individuals and motivation for social synchrony, social behavior is also widely variable between individuals and over time. Individual differences in social behavior may be attributed to personality as well as transient states such as disease or pain, and accommodating individual preferences for social interaction or isolation may be important within groups of larger calves. Throughout this paper, I contrast behavior of commercially raised calves in social housing with behavior of calves under more naturalistic conditions and address both short-term effects for calf development and potential longer-term implications for behavior and welfare. Welfare of commercially raised calves may be improved by refining social housing to better accommodate natural social behavior.

Prevalence and characterization of the seven major serotypes of Shiga toxin-producing Escherichia coli (STEC) in veal calves slaughtered in France

Shiga toxin (Stx)-producing Escherichia coli (STEC) belonging to the "top 7″ serotypes (i.e. O157:H7, O26:H11, O45:H2, O103:H2, O111:H8, O121:H19 and O145:H28) are considered as the main pathogenic enterohemorrhagic E. coli (EHEC). As ruminants, including calves, are a reservoir of pathogenic STEC, we investigated the prevalence, major virulence genes and genetic relatedness of top7 STEC in veal calves slaughtered in France, through the analysis of 500 fecal samples collected over one year. Thirty top7 STEC isolates were recovered from 28 calves. The two serotypes O103:H2 and O26:H11 accounted for 73% of STEC strains, followed by O145:H28 and O157:H7. STEC super-shedding levels were identified for two calves carrying STEC O103:H2 and O157:H7, respectively. Thirty-nine atypical enteropathogenic E. coli (aEPEC) were also recovered from calves. Overall, a prevalence of 5.6% top7 STEC-positive calves was found, thus higher than that previously determined for the French slaughtered adult cattle (1.8%), confirming the impact of animals age on STEC carriage. Most top7 STEC strains carried the stx1a subtype suggesting a low pathogenicity for humans. Seasonal variation in STEC carriage was also observed, with two peaks of higher prevalence during spring and fall. Genetic similarity of top7 STEC isolates was found for calves originating from the same fattening facilities, reflecting STEC circulation between animals kept in groups. This study indicates that veal calves grown for meat production are at higher risk of shedding top7 STEC compared to adult cattle. They thus represent ideal targets for the implementation of farm interventions aimed at reducing STEC burden in cattle and the food chain.

Escherichia coli 0157:H7 virulence factors and the ruminant reservoir

PURPOSE OF REVIEW

This review updates recent findings about Escherichia coli O157:H7 virulence factors and its bovine reservoir. This Shiga toxin (Stx)-producing E. coli belongs to the Enterohemorrhagic E. coli (EHEC) pathotype causing hemorrhagic colitis. Its low infectious dose makes it an efficient, severe, foodborne pathogen. Although EHEC remains in the intestine, Stx can translocate systemically and is cytotoxic to microvascular endothelial cells, especially in the kidney and brain. Disease can progress to life-threatening hemolytic uremic syndrome (HUS) with hemolytic anemia, acute kidney failure, and thrombocytopenia. Young children, the immunocompromised, and the elderly are at the highest risk for HUS. Healthy ruminants are the major reservoir of EHEC and cattle are the primary source of human exposure.

RECENT FINDINGS

Advances in understanding E. coli O157:H7 pathogenesis include molecular mechanisms of virulence, bacterial adherence, type three secretion effectors, intestinal microbiome, inflammation, and reservoir maintenance.

SUMMARY

Many aspects of E. coli O157:H7 disease remain unclear and include the role of the human and bovine intestinal microbiomes in infection. Therapeutic strategies involve controlling inflammatory responses and/or intestinal barrier function. Finally, elimination/reduction of E. coli O157:H7 in cattle using CRISPR-engineered conjugative bacterial plasmids and/or on-farm management likely hold solutions to reduce infections and increase food safety/security.

Unraveling the Complexity to Observe Associations Between Welfare Indicators and Hair Cortisol Concentration in Dairy Calves

Using levels of the stress hormone cortisol as an indicator for welfare is a common, but debated practice. In this observational study, hair cortisol concentration (HCC) of samples from 196 dairy calves from 7 to 302 days of age collected from 12 Swedish farms was determined using a commercially available ELISA. An assessment of animal welfare, assessed using animal-based indicators, was performed on the day of sampling. First, methodological factors with the potential to impact HCC and the effect of age were analyzed using generalized additive models. This revealed a significant peak in hair cortisol in young calves (around 50 days of age) and an association between fecal contamination of hair samples and the level of cortisol extracted. Second, associations between welfare indicators and HCC were explored using cluster analysis and regularized regression. The results show a complex pattern, possibly related to different coping styles of the calves, and indicators of poor welfare were associated with both increased and decreased hair cortisol levels. High cortisol levels were associated with potential indicators of competition, while low cortisol levels were associated with the signs of poor health or a poor environment. When running the regularized regression analysis without the contaminated hair samples and with the contaminated samples (including a contamination score), the results did not change, indicating that it may be possible to use a contamination score to correct for contamination.

Occurrence of Campylobacter spp. in Swedish calves, common sequence types and antibiotic resistance patterns

Aims

Cattle are the second most important cause of human campylobacteriosis, after poultry, but there are knowledge gaps regarding Campylobacter in cattle. This study examined the occurrence of Campylobacter, the species present, sequence types and antibiotic resistance in Swedish cattle.

Methods and Results

Faeces samples collected from 154 calves on seven Swedish farms, and 69 follow‐up samples from a second collection occasion, were analysed. Campylobacter were isolated from 77% of calves at the first sampling, with Campylobacter jejuni as the most frequently isolated species. Animals kept on deep straw bedding were less likely to be colonized with Campylobacter. Whole‐genome sequencing of 90 C. jejuni samples resulted in 11 sequence types, among which ST‐19 and ST‐21 were most frequent. Antimicrobial resistance analyses showed that 46% of 142 isolates analysed were resistant to quinolones, while all isolates belonging to ST‐19, ST‐22 and ST‐441 were resistant to ciprofloxacin and nalidixic acid.

Conclusions

Campylobacter jejuni was the species most frequently isolated in calves and a strong association was found between sequence type and antimicrobial resistance pattern.

Significance and Impact of the Study

The high proportion of calves with quinolone‐resistant Campylobacter jejuni should be considered in a One Health perspective.