E. coli in feral swine near spinach fields and cattle

Recent experimental and epidemiologic studies suggest that domestic pigs are biologically competent hosts and a potential reservoir of Escherichia coli O157:H7. Cattle are considered the primary reservoir of E. coli O157, but fecal shedding by other domestic livestock and wildlife has been described. E. coli O157 was isolated from a wild boar in Sweden, but there is limited information on its occurrence in feral swine in the United States.

study reports findings from an environmental and laboratory investigation after a nationwide spinach-associated outbreak of E. coli O157 in which the outbreak strain was isolated from feral swine and other environmental samples.

In September 2006, an outbreak of E. coli O157 was linked to consumption of fresh, bagged, baby spinach, with 26 states and Canada reporting 205 cases of illness and 3 deaths. Contaminated product was traced to one production date (August 15, 2006) at one processing plant and fields located on 4 ranches on the central California coast. The outbreak strain was isolated initially from cattle feces collected on Sept. 27, 2006, ~1 mile from an implicated spinach field on a ranch (ranch A) where numerous free-roaming feral swine were observed. Potential involvement of feral swine in E. coli O157 contamination of spinach fields and surface waterways was investigated.

Ranch A is located in the central coast foothills of San Benito County, where the dominant habitat is coastal oak woodland interspersed with dense riparian vegetation near seasonal waterways. Approximately 2,000 range cattle were grazed on the ranch. Spinach and other leafy green vegetables were grown on a leased portion of the property that was separated from cattle pastures by wire mesh fence. Well water was used for irrigation. No evidence of cattle manure-based fertilizer application, runoff from cattle pastures, or flooding from surface waterways onto the implicated spinach field was found during the investigation.

Feral swine were the most abundant wildlife observed on ranch A, and evidence of intrusion, including tracks, rooting, or feces in crop fields and adjacent vineyards, was documented. Birds, black-tailed deer, cottontail rabbits, coyotes, and ground squirrels also were observed, but the population density of these species appeared lower, and their activity was confined mostly to rangeland areas according to visual observations. Swine visited the traps almost continuously from dusk until dawn with peak activity between 5:00 p.m. and midnight. An average of 3.6 swine/trap/night were live-captured. The actual number of feral swine on ranch A was estimated to be 149 animals. Feral swine used livestock rangelands and gained access to adjacent crop fields through gaps formed at the base of the fence by erosion and rooting. Cattle and feral swine had access to and congregated at surface waterways on the ranch.

Mechanisms of in-field contamination of leafy greens for this and previous outbreaks remain unclear, but hypotheses have emerged. A relatively high-density of feral swine near cattle and spinach fields could represent a risk factor for E. coli O157 contamination. Wildlife may be sentinels for E. coli O157 in the produce production environment, or they may be vectors involved in the contamination of plants directly by fecal deposition or indirectly by fecal contamination of surface waterways or soil.

Notably, baby spinach is harvested with a lawn mower-like machine that could pick up fecal deposits in the field and thereby contaminate large volumes of product during processing. Fecal loading of surface waterways by livestock and wildlife with subsequent contamination of wells used for irrigation represents another possible route of transmission to plants in the field. Although E. coli O157 was not detected in irrigation water, older agriculture wells at ranch A appeared vulnerable to contamination by surface water. Unrecognized environmental and management practices during preharvest and postharvest processing also could have contributed to amplification and dissemination of E. coli O157 in raw spinach.

E. coli O157 contamination of spinach and other leafy greens is likely a multifactorial process. Additional research is needed to develop and implement effective risk assessment and management practices. For example, studies are needed to determine colonization potential of and levels of fecal shedding by feral swine, and the importance of interspecies transmission to other vertebrate or invertebrate (e.g., flies) populations near agricultural fields. 

This information was excerpted from: Jay MT, Cooley M, Carychao D, Wiscomb GW, Sweitzer RA, Crawford-Miksza L, et al. Escherichia coliO157:H7 in feral swine near spinach fields and cattle, central California coast. Emerg Infect Dis. 2007 Dec. Available from www.cdc.gov/EID/content/13/12/1908.htm.

Market dairy cow feeding

If $68.82 per head of market dairy cows is lost due to quality defects, on a national level a 30% cull rate among the nine million dairy cows in the U.S. results in a collective loss of approximately $185 million from 2.7 million market dairy cows harvested annually, says Jason Ahola, PhD, University of Idaho.

Several researchers have improved the quality and value of market cows by feeding them for a short period (typically 70 to 90 days) prior to harvest (Jones, 1983; Apple et al., 1999). Economically-relevant improvements can be generated through body weight gain, body condition score gain, dressing percent improvement, muscle tissue replenishment including rib eye area (REA), and changing fat color from yellow to white. “In addition, feeding market dairy cows for a short period prior to harvest enables better market timing to access higher prices, overcoming lameness by removal from concrete, reducing antibiotic residues, and utilizing low-cost feeds such as refusal feeds from lactating cows,” Ahola explains.

Researchers at Cornell University and Penn State University collaborated to determine the effects of market-cow feeding, ractopamine hydrochloride feeding and implant usage on end-product quality of market dairy cows. “In our study, implants and ractopamine did not increase performance,” explains Mike Baker, PhD, PAS, Cornell University. “However the combination of the two increased ribeye area 8% and the round 17%.”

The study

For the study, market dairy cows (non-diseased, young cows) were purchased from local auction barns by a commercial market cow packer. At the time of purchase, one-third of all cows were randomly sent to harvest in order to characterize typical dairy cow carcasses prior to feeding. The remaining cows (n = 65) received a hay diet for 8 to 10 days prior to being sorted by age (determined by dentition), body condition score (BCS), and condition of feet and legs. Once sorted, cows were randomly assigned to one of two pens in a non-replicated design.

One pen received a finishing diet with ractopamine hydrochloride, a recently-approved beta-agonist feed additive that stimulates muscle synthesis when fed for 28 to 42 days prior to harvest. The other pen received only the finishing diet. In addition, within each pen 50% of the cows received an implant.

The cows were fed until they reached a final BCS of 3.5 (dairy scale, 1 = emaciated, 5 = obese). Of the original 65 cows delivered to Cornell, 24 were sent to harvest before their target BCS due mainly to poor performance. Following a 24 to 48 hour chill, carcass data were collected.

Performance in the first month was quite low given the ration being fed. Intakes were fairly constant over the entire feeding period resulting in poor conversion for the first 25 days. With the exception of REA, there were no differences in any of the performance factors as affected by treatment. Average daily gain tended (P = 0.09) to be higher in the implanted cattle fed ractopamine vs. other treatments. In addition, the cattle receiving ractopamine and an implant had a larger (P < 0.05) REA than cattle that were not implanted and did not receive ractopamine. While treatment had a minimal effect on the performance of the dairy cows, treatment had an effect on the weight and percent of hot carcass weight (HCW) of several primal cuts.

General feeding of market dairy cows increased carcass quality (see following table). The carcasses from the fed cows were heavier, contained more external and intramuscular fat, the fat color was whiter, and a higher percentage were of the desired quality grade of Boning Utility and White Cow. In addition, all of the primal cuts measured were heavier and represented a higher proportion of the HCW in fed vs. non-fed cows.

In this pilot study, the economics of feeding market dairy cows did not show a sizable profit. The net return per head was $10. It should be noted that the increase of 34.1% White Cows in the fed cows was not reflected in the average carcass value ($89.51/cwt), due to an unpredicted short-term change in the value of White Cows, Ahola notes.

Market beef cow study

In contrast to limited market dairy-cow research, several trials have evaluated the economic implications of feeding market beef cows prior to harvest. A 2002 Iowa State University demonstration trial included 48 market beef cows fed for either 69 or 90 days.

After cows gained 294 lbs (3.87 lbs/day) at a cost of $0.85/lb of gain, their average profit per head was $66.03. Cattle-Fax has reported similar results, Ahola says. In 2007, they reported that feeding market cows from November through February has been profitable in 27 of the last 27 years. On average, an average profit of $60/head would have been returned based on feed costs and market prices at the time. Profit for each year ranged from $10-126/head, and was based on feeding cows for 95 days and an average gain of 1.5 lbs/day.