Salmonella Prevalence in Lymph Nodes of U.S. and Mexican Cattle Presented for Slaughter during 2 Seasons in Texas

Abstract

ObjectivesDue to the generalized nature of the lymphatic system, lymph nodes (LNs) have been identified as a potential source of Salmonella contamination in ground beef products. The objectives of this study were to determine if Salmonella prevalence differs (1) between cattle of Mexican and U.S. origins when exposed to the same feedlot environment and (2) between warm and cool seasons.Materials and MethodsPaired subiliac LNs (n = 800 LNs) were collected from 100 carcasses per origin (Mexico and U.S.), per season (warm and cool). Per animal, left and right LNs were pooled yielding n = 400 total LN samples. The LNs were aseptically trimmed of fat and pulverized before microbiological analysis. Salmonella presence/absence was determined by following the USDA-FSIS Microbiological Laboratory Guidebook (MLG) 4.08.ResultsOverall, Salmonella prevalence in LN samples was 52.0% (208/400; data not presented in tabular form). No difference (P = 0.4836; Table 1) was seen in Salmonella prevalence as a function of country of origin, with 54.0% (108/200) and 50.0% (100/200) Salmonella-positive samples from cattle of Mexican and U.S. origin, respectively. Salmonella prevalence differed (P = 0.0354) between seasons, with 46.5% (93/200) and 57.5% (115/200) Salmonella-positive samples from cool and warm seasons, respectively (data not presented in tabular form). Interestingly, Salmonella prevalence in samples of U.S. origin differed by season (P = 0.0160), unlike those of Mexican origin. No difference (P = 0.6705) was seen between seasons in samples of Mexican origin, with 52.0% (52/100), and 56.0% (56/100) Salmonella prevalence for cool and warm seasons, respectively. For samples from beef carcasses of U.S. origin, Salmonella prevalence rates of 41.0% (41/100) and 59.0% (59/100) were seen for cool and warm seasons, respectively (Table 1). Serotyping of PCR-confirmed positive samples resulted in 14 different serovars with Cerro (21.6%), Anatum (19.7%), Muenchen (17.8%), Montevideo (14.4%), and Kentucky (12.0%) comprising the majority.ConclusionThese findings dispel previous concerns that Mexican cattle have a higher prevalence rate of Salmonella than U.S. cattle. These results also suggest that environmental factors may play a large role in the Salmonella prevalence rate in bovine LNs, and that additional research is needed to fully understand factors that influence Salmonella prevalence in bovine LNs.