OESTROUS RESPONSE OF OVARIECTOMIZED BEEF HEIFERS TO OESTRADIOL BENZOATE AND HUMAN CHORIONIC GONADOTROPHIN

Abstract

A total of 60 ovariectomi-zedbeef heifers were involved in 2 trials to study the effects of estradiol benzoate (ODB) and human chorionic gonadotropin (HCG) on induced estrous behaviour. Both hormones were administered in single injections, ODB subcutaneously in sesame oil and HCG intramuscularly in physiological saline. Dosages evaluated were: ODB[long dash]0.2, 0.3, 0.4, 0.5 or 0.6 mg; HCG[long dash]0, 2000 or 5000 i.u. Animals were observed twice daily and scored for estrous behavior on a scale from 0 to 5. The minimal dose of ODB sufficient to induce ''standing'' estrus was 0.3 mg. The proportion of animals in heat, length of estrus and total score tended to increase with increasing levels of ODB. HCG administration (concurrent with ODB) significantly delayed the onset of estrus following injection in one trial, with the same tendency (non-significant) observed in the other trial. Inexplicable estrous behavior was observed in several heifers after ovariectomy and hormone treatment.