Effects of growth-promoting agents and season on yearling feedlot heifer performance.
Angus x crossbred heifers (270 per trial) were used in an experiment conducted over one 105-d summer and one 104-d winter feeding period. Treatments were identical for each trial and included: 1) control, 2) estrogenic implant (E), 3) trenbolone acetate implant (TBA), 4) E + TBA (ET), 5) melengestrol acetate (MGA) in the feed, and 6) ET + MGA (ETM). Each treatment was replicated in five pens, with nine heifers per pen in each season. Initial weights (mean = 384 kg, SE = 57) were the same for each season. There were no treatment x season interactions for final BW, ADG, G:F, water intake, or carcass characteristics. Heifers receiving a growth-promoting agent were 11.6 kg (SE = 4.08) heavier and gained 0.108 kg/d (SE = 0.04) more (P < 0.05) than control heifers. Heifers receiving ET gained 0.09 kg/d (SE = 0.032) more (P = 0.05) than heifers not receiving ET. Heifers receiving ET (with and without MGA) had greater G:F (P < 0.05) than control, E, and TBA heifers. Carcass weights of ET-treated heifers were greater (P < 0.05) than carcass weights for unimplanted heifers, those fed MGA only, and heifers receiving either E or TBA implants. Marbling scores were increased (P < 0.05) by feeding MGA to ET-treated heifers. Water intake was greater (P < 0.01) in the summer (31 L/d) than in the winter (18 L/ d), with no difference among implant treatments. Heifers fed in the winter had heavier carcasses, less 12th-rib fat, greater marbling scores, larger LM area, and a greater incidence of liver abscesses than heifers finished in the summer (P < 0.01). A treatment x season interaction (P = 0.07) was evident for DMI during the 35-d coldest and hottest portions of the year. Heifers fed MGA and implanted with ET tended (P = 0.07) to have greater DMI in the summer but lesser DMI in the winter. In general, differences among growth-promotant programs were relatively similar over the entire summer and in winter.
Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.
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Kreikemeier
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Mader
D045930:Anabolic Agents / Q000494:pharmacology*; D000821:Animal Feed; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000254:growth & development*; D004338:Drug Combinations; D004343:Drug Implants; D004435:Eating / Q000187:drug effects; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology; D008552:Melengestrol Acetate / Q000494:pharmacology*; D011897:Random Allocation; D012621:Seasons; D014204:Trenbolone Acetate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D015430:Weight Gain / Q000187:drug effects
D045930:Anabolic Agents; D004338:Drug Combinations; D004343:Drug Implants; D004967:Estrogens; D005938:Glucocorticoids; D008552:Melengestrol Acetate; D014204:Trenbolone Acetate