Response of feed lot heifers to certain exogenous hormones Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/fj236483s

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  • Some effects of hormone treatment on feedlot heifers were studied. The treatments were 15 mg diethylstilbestrol (DES) implant, Synovex H implant, .25 mg oral melengestrol acetate (MGA) per head per day, and .40 mg oral MGA per head per day. One hundred heifers, 20 to each treatment, were used. All heifers received a standard fattening ration consisting of 10% beet pulp, 10% alfalfa pellets, 5% molasses, and 75% steam rolled barley. In addition, a 40% protein supplement was fed at a rate of one pound per head per day. MGA was incorporated into the supplement of two groups to provide .40 and .25 mg per head per day. The heifers were marketed in two groups after 99 and 120 days on feed. At slaughter, the urogenital tracts were removed. The uteri were weighed and discarded. The ovaries were frozen on dry ice and held for further study. Sixty four of the heifers were pregnant during the trial. The urigenital tracts of these animals were not studied. Carcass data were collected in the cooler three days after slaughter. Carcass grade, conformation score, marbling score, rib eye area, and backfat were recorded for statistical analysis. The Synovex treated heifers gained 3.50 pounds per day which was higher (P <.05) than all others. The .40 MGA heifers gained 3.11 pounds per day which was higher (P <.06) than the .25 mg MGA group which gained 2.72 pounds per day. The control and DES groups gained 2.79 and 2.89 pounds per day, respectively. There were no statistically significant differences among groups in rate of gain for the pregnant heifers. The DES treated heifers had the least amount of marbling but this difference was not statistically significant. The hormonal treatments produced no significant differences in any of the carcass characteristics studied. The ovaries of the heifers from the two MGA treated groups had significantly (P<.01) larger follicles than all others. There was no significant variation among groups in either largest number of follicles on one ovary or total ovarian weight. A bioassay of the ovaries was performed to determine estrogenic activity. The two MGA treatments resulted in an increase and the DES treatment resulted in a decrease in ovarian estrogenic activity. None of these differences were significant due to the wide variation among individuals on the same treatment. Simple linear correlation coefficients were determined for the characteristics studied. The size of largest follicle was positively correlated with ovarian estrogenic activity. There was a significant negative correlation between total number of follicles and conformation score. There was also a negative but not significant correlation between conformation score and size of largest follicle. The correlation between total number of follicles and ovarian estrogenic activity was positive but not significant. Heifer uterine weight was negatively, but not significantly, correlated with estrogenic activity of the ovaries. The correlation between rate of gain and ovarian estrogenic activity was slightly negative and not significant. This would tend to indicate that estrogen production of the ovaries, in itself, is not responsible for increases in gain in heifers on the treatments tested. Further testing with larger numbers is necessary to determine the role, if any, of the ovaries in the response of heifers to DES, MGA, or Synovex H.
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  • File scanned at 300 ppi using Capture Perfect 3.0 on a Canon DR-9050C in PDF format. CVista PdfCompressor 5.0 was used for pdf compression and textual OCR.
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