Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2006
Publication Date: 9/1/2006
Citation: Berry, E.D., Wells, J.E., Archibeque, S.L., Ferrell, C.L., Freetly, H.C., Miller, D.N. 2006. Influence of genotype and diet on steer performance, manure odor, and carriage of pathogenic and other fecal bacteria. II. Pathogenic and other fecal bacteria. Journal of Animal Science. 84:2523-2532.
Interpretive Summary: The objective of this study was determine if cattle breed or diet can affect the carriage and shedding of bacterial pathogens and other fecal bacteria by cattle during the growing and finishing phases of beef production. The fifty-one steers were of different proportions of Brahman (representing Bos indicus breeds) and MARC III (representing Bos taurus breeds), including proportions of 0, 1/4, 1/2, and 3/4 Brahman. The steers were divided among eight pens such that each of the four breed types were represented in each pen, and four pens each were assigned to one of two diets: (1) BG, 100% chopped bromegrass or (2) CS, composed primarily of corn silage. These two diets were fed for a 119 day growing period, then all steers were switched to the same high corn finishing diet, which was fed until the cattle reached slaughter weight. Feces and ruminal fluid were collected and analyzed throughout feeding, and examined for the levels of generic E. coli and the presence of E. coli O157 and Campylobacter. Neither cattle breed nor growing period diet affected the levels of generic E. coli in feces or ruminal fluid, in either the growing or finishing phases. However, levels of generic E. coli in both feces and ruminal fluid increased in all cattle when switched from either growing diet to the high corn finishing diet. There was no clear-cut effect of either cattle diet or breed type on E. coli O157 or Campylobacter shedding in feces or ruminal fluid. Forty-one percent of the steers were positive for Campylobacter at least once during the study, and repeated isolations of Campylobacter from the same steers were common, indicating that when colonized, cattle may shed this pathogen for long time periods. The genes for Shiga toxin (stx) were detected frequently in both feces (22.5% of samples) and ruminal fluid (19.6% of samples). There was no correlation between measures of feed efficiency and the numbers of positive samples of E. coli O157, Campylobacter, or stx genes, which agrees with our current understanding that these bacteria occur commonly in healthy cattle.
Technical Abstract: The influence of cattle genotype and diet on the carriage and shedding of zoonotic bacterial pathogens, and the levels of generic Escherichia coli in rumen contents and feces of beef cattle during the growing and finishing periods was assessed. Fifty-one steers of varying proportions of Brahman and MARC III (0 , 1/4 , 1/2 , and 3/4 Brahman ) were divided among eight pens such that each breed type was represented in each pen. Four pens each were assigned to one of two diets (BG: 100% chopped bromegrass hay, or CS: primarily corn silage [87%]) which were individually fed for a 119 d growing period (period 1), at which time the steers were switched to the same high concentrate corn-based finishing diet (HC) and fed to a target weight of 560 kg (period 2). Feces or ruminal fluid were collected and analyzed at alternating intervals of 14 d or less, throughout periods 1 and 2. Generic E. coli concentrations in feces or ruminal fluid did not differ (P < 0.05) by genotype or by growing diet in period 1 or 2. However, concentrations in both feces and ruminal fluid increased in all cattle when switched to the same high corn diet in period 2. There was no effect of diet or genotype (P > 0.25) on E. coli O157 shedding in feces. Forty-one percent of the steers were positive for Campylobacter spp. at least once during the study, and repeated isolations of Campylobacter spp. from the same steer were common. These repeated isolations from the same animals may have been responsible for the apparent diet (P = 0.05) and genotype effects (P = 0.02) on Campylobacter in feces in period 2. Salmonella spp. was isolated only once during the study. As determined by PCR, cells bearing stx genes were detected frequently in both feces (22.5%) and ruminal fluid (19.6%). The number of stx-positive fecal samples were higher (P < 0.05) for 1/2 Brahman steers (42.9%) than for 1/4 Brahman (25.0%) or 3/4 Brahman steers (22.2%), but were not different than for MARC III steers (38.3%). The higher feed consumption of 1/2 Brahman and MARC III steers may have resulted in greater starch passage into the colon, accompanied by an increase in fecal bacteria populations, which may have further improved the ability to detect stx genes in these cattle. There was no correlation between either ADG or daily DMI and the number of positive samples of E. coli O157, Campylobacter spp., or stx genes, which agrees with our current understanding that these microorganisms occur commonly and with no measurable detriment in healthy cattle.