Dietary supplementation with Lactobacillus- and Propionibacterium-based direct-fed microbials and prevalence of Escherichia coli O157 in beef feedlot cattle and on hides at harvest.

The objective of this study was to describe the prevalence of Escherichia coli O157 in the feces and on the hides of finishing beef cattle fed a standard diet and those fed diets supplemented with direct-fed microbials. Two hundred forty steers received one of four treatments throughout the feeding period: (i) control: no added microbials; (ii) HNP51: high dose of Lactohacillius acidophilus strain NP 51 (10(9) CFU per steer daily) and Propionibacterium freudenreichii (10(9) CFU per steer daily); (iii) HNP51+45: high dose of NP 51 (10(9) CFU per steer daily), P. freudenreichii (10(9) CFU per steer daily), and L. acidophilus NP 45 (10(6) CFU per steer daily); or (iv) LNP51+45: low dose of NP 51 (10(6) CFU per steer daily), P. freudenreichii (10(9) CFU per steer daily), and NP 45 (10(6) CFU per steer daily). Samples were collected from each animal and analyzed for the presence of E. coli O157 using immunomagnetic separation methods on day 0 (feces), 7 days before harvest (feces), and at harvest (feces and hide). At the end of the feeding period, cattle receiving HNP51 were 57% less likely to shed detectable E. coli O157 in their feces than were the controls (P < 0.01). For animals receiving HNP51+45 and LNP51+45, fecal prevalence did not differ from that of the controls. The prevalence of positive hide samples was least among cattle receiving HNP51+45 (3.3%); these animals were 79% less likely (P < 0.06) to have a positive hide sample than were the controls (prevalence = 13.8%). There was poor agreement of the culture results between fecal and hide samples collected from the same animal (kappa = 0.08; confidence interval = -0.05 to 0.2). Cattle supplemented with a high dose of NP 51 had reduced E. coli O157 prevalence in both fecal and hide samples, indicating that this treatment may be an efficacious preharvest intervention strategy.

A diagnostic strategy to determine the Shiga toxin-producing Escherichia coli O157 status of pens of feedlot cattle.

Although cattle are reservoirs, no validated method exists to monitor Shiga toxin-producing Escherichia coli O157 (STEC O157) on farms. In 29 Midwestern United States feedlot pens we compared culturing faeces from the individual cattle to: (1) culturing rope devices that cattle rub or chew; and (2) culturing a composite of faecal pats. Eighty-six per cent (68-96%) of pens were classified correctly using rope devices to detect pens with at least 16% of the cattle shedding STEC O157 [sensitivity=82% (57-96%); specificity=92% (62-100%)]. Ninety per cent of pens (73-98%) were classified correctly using composite faeces to detect pens with at least 37% of the cattle shedding STEC O157 [sensitivity=86% (42-100%); specificity=91% (71-99%)]. Ranking pens into three risk levels based on parallel interpretation of the pen-test results correlated (Spearman's r=0.76, P<0.0001) with the pen's prevalence. This strategy could identify pens of cattle posing a higher risk to food safety.

Effects of live cultures of Lactobacillus acidophilus (strains NP45 and NP51) and Propionibacterium freudenreichii on performance, carcass, and intestinal characteristics, and Escherichia coli strain O157 shedding of finishing beef steers.

In Exp. 1, 240 beef steers (initial BW = 332.8 kg) were used to determine the effects of Lactobacillus acidophilus (LA) plus Propionibacterium freudenreichii (PF) on performance, carcass, and intestinal characteristics; serum IgA concentrations; and the prevalence of Escherichia coli O157 (EC). Cattle were fed a steam-flaked corn-based, 92% concentrate diet, and the four direct-fed microbial (DFM) treatments (12 pens/treatment) included in a randomized complete block design were as follows: 1) control, lactose carrier only (CON); 2) 1 x 10(9) cfu of LA NP51 plus 1 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51H); 3) 1 x 10(9) cfu of LA NP51 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA51); and 4) 1 x 10(6) cfu of LA NP51 plus 1 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51L). No differences (P > 0.10) were detected for pen-based performance data. The average lamina propria thickness for LA51 and LA45-51H steers was less (P = 0.02) than the average for CON and LA45-51L steers. Moreover, LA51 and LA45-51H steers had a lower (P = 0.06) prevalence of EC shedding than CON and LA45-51L steers. In Exp. 2, 660 steers fed 91% concentrate, steam-flaked corn-based diets were used to determine the effects of the following DFM treatments (10 pens/treatment) on performance, carcass, and intestinal characteristics: 1) control, lactose carrier only (CON); 2) 5 x 10(6) cfu of LA NP51 plus 5 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51L); and 3) 1 x 10(9) cfu of LA NP51 plus 5 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51H). Steers were from two weight groups (WG). One group (SDOF; BW at arrival = 351.5 kg) had grazed before arrival, and the other group (LDOF; BW at arrival = 314 kg) had been in a grower yard. A split plot was used with WG as the whole-plot factor and DFM in the split plot. There was an interaction of WG and DFM for ADG (P = 0.05) and for carcass-adjusted ADG (P = 0.08). The simple-effect ADG and carcass-adjusted ADG means for DFM treatments differed (P < or = 0.01) between WG classifications. Within SDOF, ADG for CON and LA45-51L did not differ (P = 0.70), but both were less (P < or = 0.08) than for LA45-51H. Overall, these data indicate that live cultures of LA plus PF did not greatly affect feedlot performance and carcass characteristics. Some of the DFM used decreased fecal EC shedding, which might be related to the results for ileal lamina propria thickness.