Full methodological detail of their isolation has been described previously [12], Maraviroc molecular weight and is described briefly below. Animals, housing and diets The study was conducted at the Lethbridge Research Centre feedlot (Lethbridge, Alberta, Canada) using crossbred steer calves penned in groups of 10. Cattle were housed in rows of parallel pens with the same antibiotic treatment administered to 5 adjacent pens. Pens were separated by porosity fencing and

a pen-specific feed bunk lined the front of each pen. The bunk was of a sufficient length so that all individuals within a pen could feed at the same time. Cattle were retained in the pen throughout the feeding period and there was no need for equipment to enter any of the pens during the feeding period. Adjacent pens within each treatment shared a common water bowl, but the assignment of treatments to pens ensured that water

bowls were shared only by steers in the same treatment group. Cattle were processed through a common handling area, but handled in the order of the control group first followed by the virginiamycin group, chlortetracycline group and finally the chlorotetracycline-sulfamethazine Staurosporine mw group (see below). The area was thoroughly cleaned after each group passed through the handling area. The calves used in the study received no antibiotics prior to or during shipment to the Lethbridge Research Centre feedlot. Furthermore, no subtherapeutic or therapeutic antibiotics were administered prior to this start of this study. Throughout the study, care of the steers was in accordance with guidelines set by the Canadian Council on Animal Care [13]. Diet composition and feeding duration were typical of the feedlot industry in western Canada. A silage-based growing diet containing 70% barley silage, 25% barley grain and 5% vitamin/mineral supplement was fed

for 115 days, followed by a step-wise 21-d transition to a grain-based finishing diet (85% barley grain, 10% barley silage and before 5% supplement) that was fed to slaughter. For two discrete periods indicated in Figure 1, the antibiotics described below were mixed daily into 5 kg of supplement and spread manually (top-dressed) over the feed for each pen immediately after its delivery into the feed bunk. Figure 1 Feeding and antibiotic administration timeline. Numbers indicate day of the feeding period and B, C, D, and E represent points where fecal samples were collected from cattle. Silage-based diets were fed for 115 d, followed by 21 d of transition to the grain-based diet, which was then fed until shipment of cattle to market. Shaded areas indicate the periods that antimicrobials were included in the diet.