Chlorate and disinfectant modify Salmonella enterica shedding in weaned pigs

Abstract

The effects of chlorate administration, age at weaning (10 and 21 days), and topically applied disinfectant on Salmonella enterica shedding were evaluated in 80 weaned pigs naturally exposed to Salmonella positive dams. Salmonella spp. were qualitatively detected in samples collected on post-weaning days (PWD) -2, 10 and 14 and the concentration estimated for samples collected PWD 0, 5 and for PWD 14 cecal content. Lower Salmonella prevalence was found in chlorate treated pigs for all post-treatment qualitative samples. An interaction was detected between chlorate and disinfectant for PWD 10 fecal samples and between age at weaning and chlorate for PWD 14 fecal samples. Chlorate reduced number of Salmonella spp. in PWD 5 fecal samples and in PWD 14 cecal samples. Early weaned pigs had a less Salmonella in cecal content and lower prevalence in ileocecal lymph nodes than did late weaned pigs. Introduction Salmonella spp. have been commonly detected in U.S. swine herds. In a study of 160 randomly selected herds, Salmonella spp. were detected fecal samples from 61 herds (38.2%) (Anonymous, 1995). In Midwest U.S. herds, 80 of 134 (60%) had one or more culture positive ileocecal lymph node sample (Bahnson et al., 2003). Salmonella spp. have been detected in 4.3% of carcasses tested by regulatory authorities in the U.S during the period 1998-2003 (Anonymous, 2004). If recontamination of live pigs and carcasses can be prevented, on-farm elimination or reduction of Salmonella in the pig gut would enhance pork food safety. Elimination of Salmonella spp. by segregated early weaning has been previously documented. Salmonella were eliminated from groups of pigs maintained in narrow age ranges in segregated nurseries. However, the technique was not effective in all groups (Fedorka-Cray et al., 1997). Salmonella choleraesuis, a host-adapted serovar, was successfully eliminated by offsite weaning from a single herd of pigs. (Nietfeld et al., 1998) Administration of a single dose of sodium chlorate reduced the concentration of Salmonella Typhimurium by 1.4-2.7 logs in cecal content of challenged pigs. (Anderson, et al., 2001). Consequently, chlorate may be useful to reduce or eliminate Salmonella spp. in conjunction with segregated early weaning. The objectives of this study were to determine whether age at weaning, application of topical disinfectant, and/or administration of sodium chlorate modify the shedding of Salmonella spp. among pigs exposed to naturally infected dams during lactation. Materials and Methods A farm was selected as the source of weaned pigs based on a history of Salmonella spp. detected in weaned pigs. Fecal samples (10g) were tested for Salmonella from sows 0-2 days after giving birth. Litters from sows with Salmonella-positive fecal samples and with at least eight viable pigs were eligible for selection. Non-viable pigs were defined as being at least 30% lower weight than their littermates. Among viable pigs, eight were randomly chosen per litter. One pig from each litter was randomly assigned to one of eight treatment combinations in a 2x2x2 randomized block study design. The treatments were: 1) early(10 days of age, EW) or late(21 days of age, LW) weaning 2) administration of chlorate in water or plain water (CLOR), and 3) application of a topical disinfectant (DIS). Upon arrival to an isolation facility, pigs in the chlorate treatment group were given 10ml water with sodium chlorate (100mMol), sodium nitrate (2.5mMol), and sodium lactate (20mMol). These pigs were also provided the chlorate/nitrate/lactate mixture in the drinking water for five days. The concentration was formulated such that total chlorate consumption was expected to be 80 mg/kg/day, as previously described (Anderson et al., 2004). Povidone iodine was applied topically to pigs in disinfectant+ groups by drenching pigs as they arrived at the isolation facility. Pigs were transported to a sanitized isolation facility at either 10 or 21 days of age. Five pigs were housed together in each of eight rooms. The study was replicated once, for a total of 80 pigs. To minimize the potential transfer of Salmonella between rooms, separate coveralls and