Norgestomet implants prevent pregnancy in beef heifers on pasture

T. W. Geary, J. J. Reeves, D. W. Schafer, R. R. Evans, R. D. Randel, L. M. Rutter, R. G. Sasser, R. Guardia, B. Alexander, D. Holcombe, D. R. Hanks, D. B. Faulkner

    Research output: Contribution to journalArticlepeer-review

    4 Scopus citations

    Abstract

    The efficacy of erodible norgestomet implants for preventing pregnancy in postpubertal heifers was evaluated in two experiments at five locations each. Heifers (n = 896) within each study location were stratified by weight and allotted randomly to receive an ear implant containing either 0, 24, 36, or 48 mg of norgestomet (d 0). Heifers were exposed to fertile bulls immediately after implantation for 75 d (d 0 to 74) in Exp. 1 (n = 476) or for 80 d (d 75 to 154) in Exp. 2 (n = 420). Weights were recorded on d O and 74 (Exp. 1 and 2) and d 154 (Exp. 2). Each heifer was palpated rectally for pregnancy at the end of each experiment. Pregnancy rates were higher (P < .01) for control heifers (0 mg implant) than for heifers that received 24, 36, or 48 mg of norgestomet. In Exp. 1, pregnancy rates were 96, 29, 6, and 4% for heifers that received 0, 24, 36, and 48 mg implants of norgestomet, respectively. In Exp. 2, pregnancy rates were 85, 36, 19, and 9% for heifers that received 0, 24, 36, and 48 mg implants of norgestomet, respectively. Estrous activity during the first 3 wk of bull exposure was reduced (P < .05) among heifers that received norgestomet implants compared to control heifers but was not completely abolished at any dosage in Exp. 1. During the first 75 d of Exp. 1 and 2, heifers treated with 36 or 48 mg norgestomet implants gained weight faster (P < .05) than control heifers. Combined across both experiments, ADG during the first 74 d were .53, .56, .59, and .60 kg/d for heifers treated with 0, 24, 36, and 48 mg implants of norgestomet, respectively. These data indicate that norgestomet implants increased rate of weight gain, reduced estrous activity, and reduced the occurrence of pregnancy in heifers on pasture.

    Original languageEnglish (US)
    Pages (from-to)3089-3093
    Number of pages5
    JournalJournal of animal science
    Volume75
    Issue number12
    DOIs
    StatePublished - Dec 1997

    Keywords

    • Beef Cattle
    • Females
    • Fertility
    • Heifers
    • Pastures
    • Progestogens

    ASJC Scopus subject areas

    • Food Science
    • Animal Science and Zoology
    • Genetics

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