4Wilesmith J W and Wells G A. Bovine spongiform encephalopathy [J]. Curr Top Microbiol Immunol, 1991, 172: 21-38.
5Veldman A, Vahl H A, Borggreve G J, et al. A survey of the incidence of Salmonella species and Enterobacteriaeeae in poultry feeds and feed components[J]. Vet Rec, 1995, 136: 169-172.
6Jones F T and Richardson K E. Salmonella in commercially mannfactured feeds[J]. Poult Sei, 2004, 83: 384-391.
7Sauli I, Danuser J, Geeraerd A H, et al. Estimating the probability and level of contamination with SalmonelLa of feed for finishing pigs produced in Switzerland-the impact of the production pathway[J]. International Journal of Food Microbiology, 2005, 100: 289-310.