title: Response to reimplanting beef steers with estradiol benzoate and progesterone: performance, implant absorption pattern, and thyroxine status.
abstract: This study determined the influence of the estrogenic ear implant Synovex-S on feedlot performance, tissue deposition, and thyroid status of growing-finishing beef steers implanted either once or reimplanted. The pattern of implant absorption was also determined. Two 112-d feeding trials were used with 48 Hereford steers per trial. Each trial was a randomized block design with eight groups (lots) of six steers each assigned to four treatments (two lots/treatment). Treatments were 1) no implant or control, 2) implanted on d 0 and reimplanted at 60 d on trial, 3) implanted at 30 d on trial, and 4) implanted on d 0 only. These implant treatments resulted in withdrawal periods before slaughter of approximately 60, 90 and 120 d for Treatments 2, 3, and 4, respectively. All steers were given ad libitum access to water and a 60% concentrate diet. Group intakes were determined daily, BW weekly, estimated body composition every 28 d, plasma thyroid hormone concentrations at 112 d and at slaughter, and carcass measurements and liver tissue deiodinase at slaughter. Approximately 25% of the original implant dose remained in the ear 60 d after implanting and this residual amount was absorbed linearly at the rate of approximately .15% of the original dose per day. Implant treatments increased (P less than .05) DMI, BW gain, feed conversion, and empty body gains for water and protein. Carcass measurements suggested a nonsignificant trend (P greater than .10) for leaner carcasses for implanted steers. An immediate shift toward greater protein and less fat deposition occurred within 28 d after initial implanting (Treatment 3).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Livestock and Poultry Sciences Institute, ARS, U.S. Department of Agriculture, Beltsville, MD 20705.
authors.forename: T S
authors.initials: TS
authors.lastname: Rumsey
authors.forename: A C
authors.initials: AC
authors.lastname: Hammond
authors.forename: J P
authors.initials: JP
authors.lastname: McMurtry
mesh_terms: D000042:Absorption; D000273:Adipose Tissue / Q000187:drug effects / Q000254:growth & development; D000818:Animals; D001823:Body Composition / Q000187:drug effects; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism; D004343:Drug Implants; D004435:Eating / Q000187:drug effects; D004958:Estradiol / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D007453:Iodide Peroxidase / Q000032:analysis; D008099:Liver / Q000201:enzymology; D008297:Male; D008460:Meat / Q000592:standards; D011374:Progesterone / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D011897:Random Allocation; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood; D015430:Weight Gain / Q000187:drug effects
chemical_list: D004343:Drug Implants; D014284:Triiodothyronine; D011374:Progesterone; D004958:Estradiol; D007453:Iodide Peroxidase; D013974:Thyroxine