Reference | Feye_2016_PoulScie (10287)

An experiment was conducted at Iowa State University (Ames) using one-day-old Cobb broiler chicks that were obtained from Welp Hatchery (Bancroft, Iowa). Three separate and independent replications of this experiment were conducted using a total of 50 chicks per experiment (25 per treatment group), resulting in a total of 75 chicks per treatment. On day zero (D0), birds were housed in a BL-2 facility in pens (0.09 m^2; 10 birds/pen) within rooms that were both humidity (∼40%) and temperature controlled (35◦C for 3 d, then 28 to 31◦C for the remainder of the study). On D14, birds were moved to elevated Tenderfoot-type decks (13.4 m^2 per treatment group) for the remainder of each experiment. Feed was provided in a metal feed trough and water through a bell drinker. All birds were confirmed to be Salmonella-free by fecal culture upon arrival. On D2, 9, and 16, birds were orally inoculated with Salmonella Typhimurium strain LNWI. The dose increased from 2 × 10^8 CFU/bird on D2 to 4 × 10^8 CFU/bird on D9 to 8 × 10^8 CFU/bird on D16. The inoculum was slowly introduced into the mouth of each bird using a pipette tip. All birds were fed a non-medicated starter diet (24% crude protein; Tractor Supply Company, Brentwood, TN) from D0 to 21. On D21, treatments began for each group of birds (n = 19 to 22 per group after removing non-shedders in each experiment). Birds were randomly assigned on D21 to one of 2 feed treatment groups: 1) finisher control diet only (CON), or 2) finisher diet that contained 1.25 kg/MT XPC. From D21 to 49, the basal diet was a non-medicated finisher diet (18 to 19% crude protein; Solon Feed Mill, Solon, IA) and birds were allowed ad libitum access to feed and water. Each room held one treatment group to avoid inadvertently administering the wrong treatment within a room. Throughout the 3 consecutive studies, treatment groups were alternated in the 2 different rooms to avoid a potential room effect. The investigators at Iowa State University were blinded as to which birds received the CON or XPC diet during the entire study.

On D6, 13, and 20, one to 5 g of freshly voided feces from each bird was diluted in 10 mL of Lennox L broth. On D28, 35, and 42, approximately 0.5 g of freshly voided feces (from each bird) was collected. On D49, all remaining birds were euthanized and a 5 cm section (approximately 3 g) of distal intestine (between the cloaca and ceca) was aseptically removed from each bird and cut longitudinally. Each section was placed in 10 mL Lennox L broth (Invitrogen, Carlsbad, CA) and briefly vortexed to dislodge the Salmonella.

AST Method: Unclear

Reference explicitly reports AST breakpoints: True

Reference reports using a MIC table: False