Effect of dietary fiber on E. coli O157:H7 shedding in lambs

Ruminants are reservoirs of enterohemorrhagic Escherichia coli O157:H7, a food-borne pathogen implicated in several human disease outbreaks in the US. Our objective was to compare the influence of dietary acid-detergent fiber (ADF) concentration on fecal shedding of the pathogen and meat production efficiency of lambs. Following oral inoculation with 1010 colony forming units (CFU) of E. coli O157:H7, 14 growing-finishing Suffolk ram lambs averaging 28 ± 1.3 kg in body weight were arranged in two 7 × 7 (seven lambs × seven diets) Latin squares with 1-week adaptation and 2-weeks of fecal sample collection. Lambs were fed diets with 5, 10, 15, 20, 25, 30 or 35% ADF corresponding to 0:100, 10:90, 33:67, 40:60, 67:33, 70:30 and 98:2% forage to concentrate ratio, respectively. Diets were fed at the rate of 1.4 kg/head per day. Fecal samples were collected weekly and analyzed for E. coli O157:H7 using modified tryptic soy broth with novobiocin as a pre-enrichment broth and cefixim tellurite-sorbitol MacConkey agar (CT-SMAC) as a selective media. E. coli O157:H7 was confirmed by its reaction with O157 and H7 antisera. The 5% ADF (100% concentrate) diet resulted in significantly higher (P < 0.05) shedding of the pathogen than the other treatments (6.89 versus 5.12, 4.82, 5.21, 5.05 and 5.04 log 10 CFU/g of feces for the 10, 15, 20, 25, 30 and 35% ADF diets, respectively). Diets with 10, 15, 20, 25, 30 and 35% ADF were comparable (P > 0.05) in E. coli O157:H7 shedding. Lamb growth rate and gain:feed ratio were significantly reduced (P < 0.05) as ADF content increased beyond 20% or 40:60 forage to concentrate ratio (172.0 g and 0.14 for the 25%; 170.0 g and 0.14 for the 30%; and 150.0 g and 0.12 for the 35% ADF diets) as compared to 268.0 g and 0.24 for the 5%; 275.0 g and 0.25 for the 10%; 267.0 g and 0.22 for the 15%; and 250.0 g and 0.2 for the 20% ADF diets). The results suggest that regular all-concentrate diets typically containing around 5% ADF, when fed as the sole nutrient source, increase fecal shedding of E. coli O157:H7. Increasing the ADF content of the concentrate diet between 10 and 20% using alternative feed ingredients decreases fecal shedding of the pathogen and subsequent contamination of meat without adversely affecting meat production efficiency. © 2002 Elsevier Science B.V. All rights reserved.