Endocrine and behavioral events of estrous cyclicity and synchronization in wood bison ( Bison bison athabascae )

Abstract This study was designed to noninvasively characterize estrous cycles and evaluate the effectiveness of estrous cycle synchronization protocols in wood bison. Daily urine and fecal samples and behavioral observations were collected over 2 breeding seasons from a captive herd of 18 adult, female wood bison. All samples were analyzed by enzymeimmunoassay for pregnanediol-glucuronide (PdG: urine) or progesterone (P 4 : feces). In Year 1, animals were divided into 3 treatment groups: 1) natural estrous controls, n = 6; 2) PG, 2 injections of cloprostenol, 11 d apart, n = 6; 3) SMB, Syncro-Mate-B implants left in place for 9 d with an estradiol valerate injection at the time of implantation, n = 6. In Year 2, control animals remained the same and synchronization regimens were repeated, but with each animal receiving alternate treatments. In both years, 11 d after treatment cessation, females were subjected to ultrasound examination to evaluate ovarian activity. Combined endocrine and behavioral data from natural estrous cycles demonstrated seasonal effects, with mean cycle lengths of 20.8 ± 0.3, 21.5 ± 0.5 and 21.1 ± 0.4 d, based on behaviors, PdG and P 4 respectively. Females which demonstrated behavioral estrus did so within 4 (SMB, 11 12 ) or 5 (PG, 10 12 ) days after treatment. The SMB-treated animals exhibited estrous behavior within a 3-d span, with 55% exhibiting estrus 3 d after treatment ended, while the onset of estrus in PG-treated animals occurred over 4 d, with only 40% occurring on a single day. At the second estrus, 77% of SMB-treated animals and 74% of PG-animals demonstrated estrous behavior within 4 d, while at the third estrus, 88 and 90% of treated animals showed estrous behavior within 3 or 4 d, respectively. Ultrasound assessment revealed that only 50% ( 12 24 ) of treated animals possessed corpora lutea (CL), 67% in PG-treated females and 33% in SMB-animals. The total number of CL tended to be greater in PG- (10) than in SMB-(5) treated animals. Females with no CL demonstrated attenuated progestin profiles compared to those with ovulations. Additionally, a total of 28 follicles was detected, with a greater proportion (P