Summary

The diet of feedlot cattle may affect the bacterial population in the hindgut, including E. coli O157:H7. Some research studies have shown a relationship between feeding of distillers grains and E. coli O157:H7 shedding. However, other studies do not show the same relationship. Our evaluation of research indicates feeding distillers grains is not related to 2007 ground beef recalls. Furthermore, interventions such as vaccination are more important than identifying various feedstuffs that may influence shedding.

Introduction

There were only eight recalls due to E. coli O157:H7 in ground beef in 2006, and all of them were initiated because of company sampling. However, in 2007, there were 20 recalls, nine of which resulted from illness investigation. Health officials looked for reasons why E. coli O157:H7 seemed to be a greater problem in 2007 compared to the previous four years. Because the ethanol industry grew in 2007 and feeding ethanol byproducts increased, some theorized feeding ethanol byproducts was the cause of the E. coli O157:H7 recalls. Late in 2007, research (Jacob et al., 2008, Applied and Environmental Microbiology 74:38) showing a relationship between distillers grains (DG) feeding and E. coli O157:H7 shedding was reported.

Discussion

Subsequent studies of the relationship between feeding distillers grains and E. coli O157:H7 shedding indicate that some researchers have found a correlation between the two, while others have not.

Jacob et al. (2008, Journal of Animal Science, 86:1182) reported a study using 370 feedlot cattle sampled at 122 and 136 days on feed. Overall prevalence of E. coli O157:H7 was fairly low (under 10%). On day 122, cattle were statistically more likely to shed E. coli O157:H7 when fed 25% DG in the diet. On day 136, feeding DG had no effect on shedding. Jacob et al. (2008, Applied and Environmental Microbiology 74:38-43) sampled cattle for 12 weeks during the feeding period. Fecal samples were collected from the pen floor. Feeding DG significantly increased E. coli O157:H7 shedding, although no difference was reported in five of the 12 sampling periods.

Jacob et al. (Zoonoses and Public Health 55:125) conducted a challenge experiment in which calves were inoculated with nalidixic acid-resistant E. coli O157:H7, allowing researchers to estimate the number of E. coli O157:H7 shed. Fecal samples were collected for 42 days. E. coli O157:H7 shedding was not different for calves fed DG during the first five weeks, but was statistically greater during the last week of sampling. Based on these three studies, researchers concluded that DG feeding increased E. coli O157:H7 shedding. In each of the three experiments there were sampling times when DG statistically increased shedding; however, as with most results in E. coli O157:H7 research, the results were somewhat inconsistent, making interpretation of the results difficult.

Recently, Jacob et al. (Journal of Animal Science 86, E Suppl:26) reported results of an experiment using 700 cattle fed for 150 days — half were fed DG. Pen floor samples were collected weekly or every two weeks; a total of 3,560 samples were collected and analyzed. Overall prevalence of E. coli O157:H7 was fairly low (5.1%). Although prevalence of E. coli O157:H7 in pen floor fecal samples was numerically higher in cattle fed DG in some sampling weeks, there was no significant effect of DG (P = 0.2).

All the previous studies were conducted with steam-flaked corn (SFC) diets with or without 25% (DM basis) DG. This may be important as we compare other research projects and results. Corrigan et al. (2007 Nebraska Beef Report, pp. 33-35) reported DG does not respond the same in SFC diets compared to dry-rolled corn (DRC) or high moisture corn diets (HMC). If cattle gains and efficiencies respond differently to DG levels in SFC and DRC or HMC diets, then it is possible any effects on E. coli O157:H7 vary as well. Our E. coli O157:H7 research is with DRC or HMC only.

It is logical that the diet fed to cattle could influence the growth of E. coli O157:H7 in the hindgut, since research has shown the primary reservoir of E. coli O157:H7 is the hindgut and E. coli O157:H7 attach to the intestinal wall of the hindgut. Interestingly, E. coli O157:H7 have no effect on cattle performance. There are two opposing theories on how the diet affects E. coli O157:H7 in the hindgut. The first theory is that starch escaping digestion in the rumen and small intestine is fermented in the hindgut, producing volatile fatty acids and lowering pH, thus inhibiting growth of E. coli O157:H7. Fox et al. (2007, Journal of Animal Science 85:1207-1212) showed support for this theory; steam flaking corn reduced starch in the hindgut and increased E. coli O157:H7 shedding. However, Depenbusch et al. (2008, Journal of Animal Science 86:632-639) said “E. coli O157:H7 was not related to fecal pH or starch.” We reanalyzed the data of Peterson et al. (2007, Journal of Food Protection 70:287-291) showing that diets with decreasing amounts of corn decreased the amount of starch in the diet. Amount of starch in the diet was not related to E. coli O157:H7 shedding (P = .22).

The opposing theory is starch in the hindgut is the substrate for E. coli O157:H7, so by reducing the amount of starch getting to the hindgut, E. coli O157:H7 would be reduced. Reports of Peterson et al. (2007, Journal of Food Protection 70:287-291) and Folmer et al. (2003, Nebraska Beef Report, pp. 22-23) did not support this theory. While it is logical that diet affects E. coli O157:H7 growth in the hindgut, clearly neither of the two opposing “starch theories” has been “proven.”

Peterson et al. (2007, Journal of Food Protection 70:2568-2577) focused on vaccination as an E. coli O157:H7 intervention. Because the study was superimposed on a nutrition study, we reanalyzed the data (Figure 1).

Wet DG were fed as 0%, 10%, 20%, 30%, 40% and 50% of diet dry matter replacing DRC and HMC. In this experiment, samples of the hindgut mucosa, as well as fecal samples, were analyzed. Results were similar but more consistent for the mucosal samples (Figure 1). There was a significant effect of level of DG on E. coli O157:H7 shedding; however, it was not a linear relationship. None of the levels of DG feeding were statistically different from the control (ODG). The 10%, 20% and 30% DG levels numerically decreased the shedding of E. coli O157:H7. Interestingly, this is within the range of feeding (25%) discussed previously with SFC. Our research is with DRC and HMC while the previous research was with SFC, which may make a difference.

At the 40% and 50% DG feeding level, E. coli O157:H7 shedding numerically increased compared to the control. Note that the statistical difference is between the 10%, 20% and 30% DG levels and the 40% and 50% levels. So does DG decrease or increase E. coli O157:H7 shedding?

Peterson et al. (2007, Journal of Food Protection 70:2568-2577) were studying vaccination. The pattern of E. coli O157:H7 in hindgut mucosa for unvaccinated cattle was similar to that discussed previously (Figure 2). However, only one steer among the vaccinated cattle tested positive, and that was at the 50% DG feeding level. In four studies involving 1,784 cattle, vaccination has reduced E. coli O157:H7 shedding by 65%. This is equivalent to the effect of winter versus summer on shedding. Feeding a direct-fed microbial (Peterson et al., 2007, Journal of Food Protection 70:287-291) reduced shedding over two years by 35%. These two interventions plus others being researched have considerable merit.

Conclusions

It is reasonable to think that what we feed cattle might affect the bacterial population of the hindgut.

Research suggests that under some feeding levels and some other yet-to-be-determined conditions, DG may increase E. coli O157:H7 shedding.

Results of E. coli O157:H7 research in general and specifically with DG feeding are inconsistent. To date, no consistent effect of DG feeding on E. coli O157:H7 shedding has been

Response in E. coli shedding to DG feeding may be affected by DG level and other dietary ingredients such as the corn type.

Interventions and research on interventions are important.

At this point, there is contradictory evidence that feeding DG, at least at levels being used commercially, increases E. coli O157:H7 shedding. Additionally, there is no scientific evidence to suggest that the feeding of DG is the cause of the 2007 recalls.

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¹Terry J. Klopfenstein, professor, and Galen E. Erickson, associate professor, Animal Science, Lincoln, Neb. David R. Smith and Rodney A. Moxley, professors, Veterinary and Biomedical Sciences, Lincoln, Neb.