Estrous cycle characteristics and response to estrus synchronization in mammoth asses ( equus asinus americanus)

Abstract

Breeding records from a herd of mammoth asses ( Equus asinus americanus) maintained on pasture in southeast Texas from 1990 to 1998 were reviewed. Jennies were pasture or hand mated, and estrus was either observed while the jennies were on pasture or when exposed to a jack after being penned. Eighty-one estrus periods and 43 diestrus intervals were recorded in 33 jennies over 4 seasons of the year (January–March, April–June, July–September, and October–December). Estrous cycle length and the duration of estrus were similar among seasons. Over all seasons, estrous cycle length was 23.3 ± 2.6 d, duration of estrus was 5.9 ± 2.1 d, and diestrus length was 17.4 ± 2.6 d (mean ± SD). During these same 9 yr, 58 injections of PGF 2α (5 mg, im) were administered to 38 jennies without regard to stage of estrous cycle. Seventy-six percent (44/58) of the jennies showed signs of estrus after PGF 2α treatment, with an interval to estrus of 4.4 ± 1.6 d and a duration of estrus of 5.6 ± 1.7 d. Two estrus synchronization schemes were also assessed. Trial 1 was performed in October to November 1996, and Trial 2 was performed in February to March 1998. In Trial 1 (Group PE+PGF, n = 10), each jenny was injected intramuscularly once daily for 10 d with 150 mg progesterone and 10 mg estradiol-17β in sesame oil, and PGF 2α (10 mg) was injected intramuscularly on the last day of treatment. In Trial 2 (Group PGF-2X, n = 11), each jenny was injected intramuscularly twice, 16 d apart, with 10 mg PGF 2α. All Group PE+PGF jennies responded to treatment. One jenny in Group PGF-2X did not respond to either injection of PGF 2α, while 2 jennies responded to the first but not the second PGF 2α injection (8 of 11 jennies returned to estrus and ovulated after the second PGF 2α injection). Duration of estrus was 6.8 ±1.9 d for Group PE + PGF and 7.1 ± 1.8 d for Group PGF-2X jennies. Interval to estrus and interval to ovulation following the last treatment were 9.0 ± 0.9 d and 14.5 ± 1.7 d, respectively, in Group PE+PGF jennies, and 4.5 ± 0.9 d and 10.4 ± 1.8 d, respectively, for Group PGF-2X jennies. In summary, estrous cycle characteristics of mammoth asses are similar to those reported for standard jennies, and estrus synchronization schemes used in horses are effective in mammoth asses.