Effects of prenatal androgenization, melengestrol acetate, and Synovex-H on feedlot performance, carcass, and sensory traits of once-calved heifers.
Three studies were designed using a 2 x 2 factorial arrangement of treatments within each experiment to evaluate the effects of various management techniques on growth and carcass traits of once-calved heifers. In Exp. 1, 33 yearling (16 control [C] and 17 prenatally androgenized [PA]) and 39 once-calved (20 C and 19 PA) nonpregnant heifers were used to evaluate the effects of age and PA. Once-calved heifers were approximately 31 kg heavier (P < .03) on-test, initially consumed 11% more (P < .01) DM, and gained 11% faster (P < .08), but had similar (P = .44) gain to feed ratios (.138 vs. .131) as yearlings. Growth performance was not affected by PA. The yearling and once-calved heifers were then slaughtered at approximately 707 and 1,080 d of age, respectively. Despite maturity differences (P < .01), marbling scores (P = .26) and percentage of choice carcasses (P = .27) were similar. However, on the basis of newly accepted grading changes, percentage of once-calved heifer carcasses grading choice decreased from 57.3 to 34.4%. Organoleptic properties did not differ. Experiments 2 and 3 were then conducted to evaluate effects of commercially available products (melengestrol acetate [MGA] and Synovex-H) on feedlot characteristics of heifers following weaning of their first calf. In Exp. 2, 48 once-calved Simmental-based heifers were fed during the summer to a constant compositional fat thickness of .8 cm. Experiment 3 was conducted in the late fall and early winter, during which 52 moderately sized heifers were fed for 116 d postweaning and slaughtered. Performance of heifers in Exp. 2 was not affected by MGA. However, heifers fed MGA in Exp. 3 gained 9% faster (P < .05) than controls. In Exp. 2, Synovex-H tended to improve ADG (P < .09) and feed efficiency (P < .07), but did not affect performance in Exp. 3. Most carcass traits were not affected by either treatment. Nonpregnant, once-calved heifers seem to have a large capacity for efficient weight gain as compared with yearling heifers. However, hormonal compounds, such as testosterone propionate provided pre- or postnatally (Synovex-H), and MGA do not appear to provide the consistent, positive responses often seen with younger, more typical feedlot heifers.
Reiling
B A
BA
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
Berger
L L
LL
Faulkner
D B
DB
McKeith
F K
FK
Nash
T G
TG
Ireland
F A
FA
D000375:Aging / Q000502:physiology; D000818:Animals; D001823:Body Composition / Q000187:drug effects* / Q000502:physiology; D002417:Cattle / Q000254:growth & development* / Q000502:physiology; D004338:Drug Combinations; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D005524:Food Technology / Q000592:standards; D008460:Meat / Q000592:standards*; D008552:Melengestrol Acetate / Q000494:pharmacology*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D045167:Progesterone Congeners / Q000494:pharmacology*; D011897:Random Allocation; D013739:Testosterone / Q000494:pharmacology*; D015430:Weight Gain / Q000502:physiology
D004338:Drug Combinations; D045167:Progesterone Congeners; C046521:estradiol benzoate, testosterone propionate drug combination; D013739:Testosterone; D004958:Estradiol; D008552:Melengestrol Acetate