4 reduces risk and is “protective” in relation to bovine TB breakdowns. A case-control study of risk factors for bovine TB in Northern Ireland was undertaken, based on tuberculin test reactors identiﬁed between 1990 to 1992 [29]. The study involved 427 dairy farms (excluding farms with fewer than 30 cattle and herds with reactors in purchased cattle). Variables investigated included the number and nature of farm boundaries, the number of neighbours and their bovine TB history, the number of hedgerows, the presence of badger setts, whether badger carcases had been found on the land, and the possible presence of deer. Two factors were signiﬁcantly associated with bovine TB breakdowns; the presence of badger setts or carcasses on the farm (OR 2.06, 95% CI 1.27–3.33) and contiguous neighbours with conﬁrmed bovine TB (OR 2.44, 95% CI 1.55–3.86). A matched case-control study was undertaken in the Republic of Ireland to provide information on the role of farm management practices, environmental factors, and farmer characteristics in the epidemiology of bovine TB. Eighty dairy herds with chronic bovine TB were compared with the same number of herds which had been free of the disease for many years. A standardized questionnaire was used. The study was conducted from August to October 1990, in Counties Cork and Kilkenny. Factors which were identiﬁed as possibly contributing to recurrent outbreaks of TB included nutritional factors, cattle purchases (especially bulls), the presence of badgers, and the spreading of slurry. Overall, the ﬁndings suggested that intensively managed dairy herds were at greater risk of bovine TB outbreaks than were other herds [26]. Subsequently, a case-control study of 200 herds from East Oﬀaly (Ireland), with cases deﬁned as outbreaks of bovine TB detected at herd test, was undertaken [30]. Herd- level risk factors signiﬁcantly associated with an increased risk of infection were herd size and the presence of TB in a contiguous herd. Diﬀerences between animal types (increased risk in cows, heifers, and bullocks compared to calves) and a reduced risk (protective) in animals purchased since the preceding herd test were found at the animal level. No signiﬁcant diﬀerences were found between cases and controls in the distance to the nearest badger sett or the nearest main sett. Herd-level risk factors for bovine TB breakdowns based on cattle farms enrolled within the GB Randomised Badger Culling Trial (RBCT), prior to the Foot-and-Mouth Disease (FMD) epidemic in 2001, were investigated [27]. The study (the TB99 study) comprised 268 farms from SW England, with questionnaires on farm management practices completed by staﬀ from the local Animal Health Oﬃce. The strongest factors associated with an increased TB risk were movement of cattle onto the farm from markets or farm sales, operating a farm over multiple premises and the use of either covered yard or “other” housing types. Spreading artiﬁcial fertilizers or farmyard manure on grazing land was associated with a decreased risk. The presence of an active badger sett mapped to either the farm land or to within 1 km of the farm boundaries was not statistically signiﬁcant. Veterinary Medicine International Risk factors have been investigated in case-control studies in Europe and the USA. Historical incidence was a robust predictor of the rate of future breakdowns in UK and Irish herds, suggesting that the disease source was not adequately removed, or that some other factor(s) made them particularly susceptible. Herd size was repeatedly identiﬁed as a major risk in many studies. Large herds tend to graze larger areas and may purchase and move more cattle, increasing the probability of having contiguous herds that facilitates cattle-cattle spread. The higher production stress of intensive management has been associated with increased risk [26]. Herd breakdowns tend to recur, especially in larger herds, possibly as a result of failing to clear the source and contact with contiguous herds and infectious wildlife. Larger herds are more likely to have at least one cow with disease. As herd size increases, the probability of at least one case increases and herds of diﬀerent sizes are therefore at diﬀerent risks. The observed size distribution of bovine TB-aﬀected herds suggests that animals pose identical risks. Cattle living in diﬀerent parts of the UK and Ireland probably experience diﬀerent risks, and there was no consistent indication in the GB TB99 and CCS2005 data to suggest that the presence of any wildlife species, or indeed domesticated species, was associated with the risk of multireactor breakdowns [1]. There is evidence that increasing herd size for ﬁnancial gain may actually contribute to increased bovine TB incidence [33]. Mathews et al. [4] examined the association between farm habitat features and other factors and the risk of bovine TB in two areas in West and SW England and involved 120 dairy herds in total (excluding herds with bovine TB breakdowns due to imported cattle). Badger road-kill records within 1 km and 5 km proximity of the farm were used as a proxy measure of badger density. The predictors found to be signiﬁcant included farmland habitat, topography, and indices of badger density and herd size. A comparative case-control study in England in which risk factors in herds with transient or persistent TB break- downs were compared to a common set of control herds (229 herds in total) was reported [28]. Interviews with herd- keepers were conducted (March 2000–February 2003). Data on farm management practices were obtained from on-farm questionnaires, whereas the presence of badger setts and the type of habitat cover was determined by ﬁeld survey of the relevant farms. The purchase of cows was a risk factor for both transient and persistent breakdown. The purchase of >50 cattle and the storage of manure for ≥6 months were risk factors for transient breakdowns, whereas the use of silage clamps increased the risk of persistent breakdown. Rather counter intuitively, decreased odds of both transient and persistent breakdown were associated with higher stocking densities (>3 cattle/ha). Running mixed herd enterprises compared to beef only or dairy only was an additional protective factor against persistent breakdown. Herd size and tuberculin testing interval were also signiﬁcant risk factors for both transient and persistent breakdowns, whereas active badger sett density and regional location only aﬀected the risk of persistent breakdowns.