C. T. Milton

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.

Effects of Final Implant Type and Supplementation of Melengestrol Acetate® on Finishing Feedlot Heifer Performance, Carcass Characteristics, and Feeding Economics1

Three finishing experiments were conducted in commercial feedlots to determine effects of implant programs on finishing heifer performance, carcass characteristics, and economics. A total of 3,307 heifers were used in the three experiments. Overall, four treatment comparisons were tested within the three separate experiments. Treatment groups included the following: 1) heifers implanted with Synovex® Plus (Fort Dodge Animal Health; Fort Dodge, IA) but not fed melengestrol acetate (MGA®; Pharmacia and Upjohn Company; Kalamazoo, MI), 2) heifers implanted with Synovex® Plus and fed MGA®, 3) heifer implanted with Revalor®-H (Intervet Inc.; Millsboro, DE) and fed MGA®, and 4) heifers implanted with Finaplix®-H (Intervet Inc.) and fed MGA®. Common treatments of Synovex® Plus and dietary MGA® as well as Finaplix®-H and dietary MGA® were used in each of the three experiments. Finishing heifers fed MGA® and implanted with Synovex® Plus had 3.9 and 4.1% greater (P<0.10) ADG than did heifers implanted with Revalor®-H or Finaplix®-H and fed MGA®, respectively. Daily gain did not differ for heifers implanted with Revalor®-H or Finaplix®-H. Feeding MGA® to heifers implanted with Synovex® Plus increased ADG and decreased deleterious effects on quality grade; however; carcasses had greater fat thickness. Fewer carcasses of heifers fed MGA® and implanted with Synovex® Plus or Revalor®-H were graded Choice in comparison with the carcasses of those implanted with Finaplix®-H. When selling heifers on a carcass-merit basis, net returns did not differ among heifers implanted with Synovex® Plus, Revalor®-H, or Finaplix®-H when fed MGA®. When selling heifers on a dressed basis, net return was maximized (P<0.10) with the use of Synovex® Plus and supplementation with MGA® compared with Synovex® Plus and no MGA® supplementation, Revalor®-H and MGA® supplementation, and Finaplix®-H and MGA® supplementation.