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Effects of altrenogest on behavior and reproductivee function of stallions
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The objective of this study was to determine if short-term (30 days) altrenogest administration at two different dosages (0.044 mg/kg or 0.088 mg/kg) could be used in stallions to alter objectionable behavior without having detrimental effects on reproductive performance. In Experiment 1, five mature stallions received the label dosage (0.044 mg/kg) of altrenogest for 30 consecutive days. In Experiment 2, five mature stallions received the double dosage (0.088 mg/kg) of altrenogest daily for 30 days. In both experiments, three mature stallions served as controls and received Neobee' M5 oil daily for 30 days. Stallions were evaluated before treatment, at the end of treatment, and at 30 and 60 days following cessation of treatment. Numerous behavioral measures were used to assess inter-male aggressiveness and breeding behavior. Semen measures included numerous motility variables (as measured by computerized analysis), spermatozoal morphology, and daily spermatozoa output (DSO). Plasma concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone, estrogen conjugates, and inhibin were determined. Within each experiment, an analysis of variance procedure was used to compare the change from pretreatment values to values at the end of treatment, 30 days post treatment, and 60 days post-treatment between the treated and control stallions. Both dosages of altrenogest decreased the total number of strikes toward another stallion (p<0.05). Neither dosage affected measures of breeding behavior, spermatozoal motility, or spermatozoal morphology (P>0.05). Testicular volume and DSO were also unaffected by both dosages (p>0.05). The label dosage decreased concentrations of testosterone, estrogen conjugates, and inhibin (p<0.05) at the end of treatment. The double dosage decreased concentrations of LH and inhibin (p<0.05) at the end of treatment. The concentration of LH returned to pretreatment values by 30 days post-treatment. These data suggest that altrenogest may act at the level of the hypothalamus and/or pituitary gland. Suppression of LH response to gonadotropin releasing hormone (GNRH) administration for up to 60 days after the double dosage of altrenogest treatment suggests altrenogest has a prolonged effect on pituitary responsiveness to GNRH. The effectiveness of altrenogest therapy, as a means to alter objectionable behavior in stallions, remains questionable.
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Includes bibliographical references: p.36-40.
Issued also on microfiche from Lange Micrographics.
Miller, Corey D. (1998). Effects of altrenogest on behavior and reproductivee function of stallions. Master's thesis, Texas A&M University. Available electronically from
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