Salmonella in the slaughter sheep population in England and Wales.

Aims: A survey of Salmonella in sheep caecal content samples was undertaken in England and Wales in 2023.

Methods: Over nine months, repeated sampling was conducted in 12 abattoirs that represented 28% of national annual sheep throughput with good geographical coverage. Samples of caecal content were obtained from 1228 sheep at abattoirs and cultured for Salmonella spp.

Results: Salmonella was isolated from 104 (8.5%) samples, with 21 isolations (1.7%) of S. Typhimurium. The most commonly isolated serovar (80 samples, 6.5%) was the sheep-adapted Salmonella enterica subspecies diarizonae serovar 61: k:1,5,(7), which has low zoonotic potential. Modelling estimated the mean annual Salmonella prevalence to be 10.5% (95% CI 8.5-13.0%). Multivariate logistic regression indicated that the likelihood of Salmonella isolation was significantly associated with animal age, with the odds of a sheep over 12 months old yielding Salmonella being significantly greater than for those under 12 months (OR 7.2, p < 0.001). For serovars of public health importance, particularly S. Typhimurium, analysis was limited by the small number of isolations, but univariate analysis indicated a significant association between over-12-month animals and the likelihood of isolating S. Typhimurium, similar to overall Salmonella isolation risk.

Conclusions: Our study has assessed Salmonella carriage among sheep presented for slaughter and intended for the food chain and found 8.5% of samples positive. It provides an improved understanding of the prevalence, distribution and subtypes of Salmonella in slaughter sheep of different ages indicating that older sheep were more often associated with isolation of Salmonella.