|Schroeder, S - TX A&M UNIVERSITY|
Submitted to: American Society of Animal Science
Publication Type: Proceedings
Publication Acceptance Date: May 15, 2004
Publication Date: June 20, 2004
Citation: Schultz, C.L., Edrington, T.S., Schroeder, S.B., Genovese, K.J., McReynolds, J.L., Anderson, R.C., Nisbet, D.J. 2004. The effects of melatonin supplementation on fecal shedding of E. coli O157:H7 in wethers. Proceedings of Western Section of American Society of Animal Science. 55:300-303. Interpretive Summary: Sheep and beef and dairy cattle may contain the bacteria E. coli that can make people sick. The incidence of infection among these animals is greater during the summer months when temperatures are higher and the day length is longer. This is also a time when the animal may endure some stress. We examined if a hormone associated with day length altered the incidence of infection. Melatonin did not alter fecal shedding or gut populations of E. coli O157:H7 in sheep.
Technical Abstract: To determine if exogenous melatonin (MEL) influences E. coli O157:H7 shedding patterns and immune function, 16 mature wethers of mixed breeding (avg. wt. 53±7 kg) were randomly assigned to one of two treatment groups: 1) control (CONT) or 2) 25 mg MEL daily for 21 d (MEL). Both groups were exposed to 16 h light and 8 hr dark (16L/8D) to simulate a summer photoperiod. Treated wethers were dosed with a gel capsule containing 25 mg MEL and 500 mg of ground alfalfa meal. Control animals received a vehicle capsule containing 500 mg ground alfalfa. All animals received ad libitum access to water, alfalfa pellets and hay. Seven days (d 7) post initial dosing of MEL, all animals were experimentally infected with E. coli O157:H7 via oral gavage followed by daily (14 d total) fecal sampling to examine shedding patterns. Blood was collected on d 6, 14, and 21 to determine total WBC counts and differentials. On day 21 all animals were sacrificed to determine rumenal, ileal, cecal and rectal populations of the experimental strain. Daily fecal shedding patterns were analyzed as repeated measures using the MIXED procedure of SAS. Total WBC counts, differentials and gut E. coli O157:H7 were analyzed using GLM procedure of SAS, with all data reported as least square means. Daily shedding patterns of E. coli O157:H7 were similar between treatments with fecal populations of E. coli O157:H7 decreasing daily (P < 0.001). No differences were observed in the populations of E. coli O157:H7 in the luminal contents of the rumen, ileum, cecum or rectum of CONT or MEL treated animals. Total white blood cells did not differ between treatment groups (10.6x10**3/mm**3 vs. 9.6x10**3/mm**3 for CONT and MEL, respectively). Differential leucocyte counts were also similar between treatments with lymphocytes accounting for 59.1 and 56.3% of the white blood cells in CONT and MEL, respectively. Monocytes and polymorphonuclear leukocytes accounted for 3.9 and 5.4% and 36.3 and 39.8% of white blood cells in CONT and MEL treated animals, respectively. Administration of exogenous MEL did not alter bacterial shedding patterns of experimentally infected wethers exposed to a long photoperiod.