Mark Blackford

Ecological relationships between the prevalence of cattle shedding Escherichia coli O157:H7 and characteristics of the cattle or conditions of the feedlot pen.

This study was designed to describe the percentage of cattle shedding Escherichia coli O157:H7 in Midwestern U.S. feedlots and to discover relationships between the point prevalence of cattle shedding the organism and the characteristics of those cattle or the conditions of their pens. Cattle from 29 pens of five Midwestern feedlots were each sampled once between June and September 1999. Feces were collected from the rectum of each animal in each pen. Concurrently, samples of water were collected from the water tank, and partially consumed feed was collected from the feedbunk of each pen. Characteristics of the cattle and conditions of each pen that might have affected the prevalence of cattle shedding E. coli O157:H7 were recorded. These factors included the number of cattle; the number of days on feed; and the average body weight, class, and sex of the cattle. In addition, the temperature and pH of the tank water were determined, and the cleanliness of the tank water and the condition of the pen floor were subjectively assessed. The samples of feces, feed, and water were tested for the presence of E. coli O157:H7. E. coli O157:H7 was isolated from the feces of 719 of 3,162 cattle tested (23%), including at least one animal from each of the 29 pens. The percentage of cattle in a pen shedding E. coli O157:H7 did not differ between feedyards, but it did vary widely within feedyards. A higher prevalence of cattle shed E. coli O157:H7 from muddy pen conditions than cattle from pens in normal condition. The results of this study suggest that E. coli O157:H7 should be considered common to groups of feedlot cattle housed together in pens and that the condition of the pen floor may influence the prevalence of cattle shedding the organism.

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 (Spearmans r=0.76, P<0.0001) with the pens prevalence. This strategy could identify pens of cattle posing a higher risk to food safety.

Sorting Strategies for Long Yearling Cattle Grown in an Extensive Forage Utilization Beef Production System1

One hundred sixty English-cross steers (244 kg, SD=23 kg) were used in each yr of a 2-yr study to determine effects of sorting on performance, carcass characteristics, variability, and profitability in a long yearling system utilizing ranch-source calves. Steers were backgrounded during winter then grazed smooth bromegrass pastures followed by warm season native range prior to entering the feedlot in the fall. Steers were stratified by BW and allotted to 1 of 4 treatments: 1) 40 head sorted by pre-grazing BW where heavy steers entered the feedlot in July

Effect of Intensive Winter Management, Partial Season Grazing, and Sorting on Performance and Economics of a Long Yearling Steer Production System1

A 2-yr study (200 steers/yr) was conducted to evaluate effects of grazing management and sorting by BW at feedlot entry on performance and economics of yearling steers. At receiving, steers (247 ± 21 kg) were randomly allotted to 1 of 2 treatments: low (0.75 kg/d, NORM) or high (0.90 kg/d, INT) gains during backgrounding. After wintering, NORM and INT grazed native range for 128 and 78 d, respectively. At feedlot entry, steers were randomly allotted to 1 of 2 treatments: sorted by BW (25% heavy, 50% medium, or 25% light; SORT) or unsorted (UNSORT). Heavy, medium, light, and UNSORT steers were fed for 78, 100, 115, and 92 d, respectively. At feedlot entry, NORM was 10 kg heavier than INT (P < 0.01); however, final BW was not different (P = 0.52). Compared with INT, NORM had increased (P < 0.01) marbling scores; however, NORM had smaller LM area (P < 0.01). At the end of the winter period (P < 0.01) and at harvest (P < 0.01), NORM was more profitable. However, INT was more profitable at the end of summer grazing (P < 0.01). Sorting increased final BW (P = 0.02) due to increased days fed (P < 0.01). Sorting reduced overweight carcasses by 8.1 percentage units (P < 0.01). Sorting produced no significant difference in profitability (P = 0.13). In this study, management of steers before feedlot entry affected subsequent performance and profitability. Additionally, SORT increased final BW and reduced overweight carcasses but did not change profitability.