Growth-promoting systems for heifer calves and yearlings finished in the feedlot.
In a 172-d finishing trial (Exp. 1), 210 recently weaned crossbred heifers were allotted to six growth promotant treatment groups, involving implanting initially with Synovex-C (C) or H (H) followed by reimplanting with Finaplix-H (F) or H and F. Melengestrol acetate (MGA) was provided in the diet to four of the treatment groups. Heifers fed MGA and administered only F as the terminal implant had the greatest (P = .01) number of mature ovaries with follicles but also had lower (P = .01) gain/DMI. In a 182-d finishing study (Exp. 2), 270 recently weaned crossbred heifers were allotted to the following six implant (d 0)/ reimplant (d 70) groups using no implant (N), Ralgro (R) or H: N/R, R/H, R/R, N/R, H/H and R/R for Treatments 1 through 6, respectively. On d 70, all heifers were implanted with F. Heifers were fed MGA from d 70 to 182 (Treatments 1, 2, and 3) or for the entire trial (Treatments 4, 5, and 6). Implanting on d 0 increased (P < .05) overall ADG. Differences (P > .05) in performance were not found between MGA treatment groups. Using an H implant/reimplant regimen decreased (P = .01) ovarian and(or) follicular development when compared with an R implant/reimplant regimen. In a 126-d finishing trial (Exp. 3), 360 crossbred yearling heifers were used to evaluate F and estrogen (Implus-H) implants when used in combination with an MGA feeding program. Heifers receiving only F in combination with MGA had greater (P < .05) ADG, whereas all heifers fed MGA had greater (P < .05) gain/DMI than heifers not fed MGA. These data suggest that feeding MGA was not beneficial for young heifers, particularly if they are provided an initial estrogenic implant followed by a second implant. In older (yearling) heifers, increased gains and gain/DMI were obtained by feeding MGA and implanting initially or 56 d later with F.
Mader
T L
TL
Department of Animal Science, University of Nebraska, Concord 68728, USA. tmader@unlnotes.unl.edu
Lechtenberg
K F
KF
D000821:Animal Feed; D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D002417:Cattle / Q000254:growth & development*; D003692:Delayed-Action Preparations; D004338:Drug Combinations; D002149:Energy Intake; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology*; D005260:Female; D008552:Melengestrol Acetate / Q000008:administration & dosage / Q000494:pharmacology*; D010053:Ovary / Q000187:drug effects; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology*; D045167:Progesterone Congeners / Q000008:administration & dosage / Q000494:pharmacology*; D013739:Testosterone / Q000008:administration & dosage / Q000494:pharmacology*; D014611:Vaccination / Q000662:veterinary; D015430:Weight Gain / Q000187:drug effects
D003692:Delayed-Action Preparations; D004338:Drug Combinations; D045167:Progesterone Congeners; C046521:estradiol benzoate, testosterone propionate drug combination; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate; C025370:estradiol benzoate, progesterone drug combination