No abstract

In a previous study involving the use of the aromatase inhibitor letrozole to synchronise ovulation, incomplete luteolysis appeared to confound the synchronising effect in letrozole-treated heifers. Experiments were done to determine whether letrozole treatment interferes with luteolysis and affects the timing of oestrus (Experiment 1) and whether pregnancy rate is affected by the stage of the oestrous cycle during which letrozole treatment is initiated (Experiment 2). In Experiment 1, Hereford heifers were fitted with a HeatWatch sensor and given prostaglandin F2α (PGF2α). Ovulation (Day 0) was determined by daily ultrasonography, and on Day 3 heifers were given an intravaginal letrozole-releasing device or a sham device for 4 days (n=16 per group). Half of the heifers in each group were given PGF2α on Day 7 (PGF 1×) or on Day 7 and 7.5 (PGF 2×). Ultrasonography and blood sampling were done daily from device insertion to removal, every 12h for 72h following PGF2α and daily for 14 days following ovulation. In Experiment 2, heifers were randomly assigned to three groups (n=10-11 per group) in which a 4-day letrozole-releasing device treatment was initiated during metoestrus (Days 0-2), diestrus (Days 7-9), or pro-oestrus (Days 15-17). Prostaglandin F2α was given at device removal and again 12h later. Heifers were inseminated with frozen-thawed semen and given gonadotrophin-releasing hormone 66h after device removal. Ultrasonography and blood sampling were done twice daily from device removal until ovulation. End points examined included dominant follicle and corpus luteum (CL) diameters, onset of oestrus, and plasma concentrations of oestradiol determined by radioimmunoassay. Nominal data were compared using GENMOD, analysis of variance, or mixed model for repeated-measures and were expressed as means±s.e.m. Proportional data were analysed using chi-square. In Experiment 1, no main effects or interactions were detected between device or PGF treatment for onset of oestrus following PGF2α (overall 60.0±2.5h) or CL diameter profiles during luteolysis. Residual variation was reduced in the timing of the first PGF to ovulation in the PGF 2× group versus the PGF 1× group (5.6±2.2h vs. 15.2±3.2 h; P<0.01). The CL diameter following ovulation was greater in the PGF 2× group compared with the PGF 1× group (P=0.03). Circulating plasma oestradiol during treatment was greater (P=0.04) in both the PGF 1× and sham groups. In Experiment 2, a greater proportion of heifers in the pro-oestrus group ovulated ≤24h after device withdrawal compared with the metoestrus and diestrus groups combined (6/11 vs. 0/22, respectively; P<0.05). Pregnancy rate tended to be greater in the metoestrus group than in the diestrus group (10/11 vs. 6/10; P=0.08), and pregnancy rate in both groups was greater than that in the pro-oestrus group (0/11; P<0.05). In conclusion, letrozole treatment did not interfere with luteolysis, and PGF2α given 2× at a 12-h interval on Day 7 after ovulation decreased variance in the timing to ovulation. Treatment initiated during metoestrus and diestrus yielded greater pregnancy rates than that started during pro-oestrus and warrants efficacy testing in a large fixed-time AI field trial. This research was supported by Alberta Agriculture and Forestry and by Dechra.

Wood bison (Bison bison athabascae) are a threatened species native to Canada. In a conservation setting such as zoos, females are preferred over males and sex-sorted sperm may help skew the proportion of females born. The objective of this study was to determine the efficacy of sex-sorted sperm in fixed-time artificial insemination (FTAI, Experiment 1) and in vitro fertilization (IVF, Experiment 2). In Experiment 1, females in bison herds at the University of Saskatchewan and Toronto Zoo were synchronized with 3.3 mg estradiol-17ß + 50 mg progesterone and given a progesterone-releasing intravaginal device for 8 days. At device removal, bison were given 500 µg of cloprostenol, and 72 h later were given 2500 IU human chorionic gonadotropin (hCG) and inseminated with either sex-sorted or conventional sperm. A second insemination occurred 24 h after hCG. Pregnancy diagnosis and fetal sexing was done by transrectal ultrasonography at 30- and 70-days post-AI, respectively. In Experiment 2, cumulus oocyte complexes collected transvaginally from live bison were fertilized in vitro with either sex-sorted or conventional sperm. Cleavage and embryo rates were determined at 3- and 7-days post fertilization, respectively. Proportional data were compared by chi-square. In Experiment 1, there was no effect of herd (P=0.17) or sperm (P=0.68) on pregnancy per AI (P/AI) at 30 days (total=25/51 [49%]). The proportion of female calves was greater in the sex-sorted than conventional group (9/10 [90%] vs 3/11 [27%]; P< 0.01). In Experiment 2, the cleavage (122/222 [55%] vs 62/94 [66%];P=0.07) and embryo rate (18/222 [8%] vs 14/94 [15%]; P=0.07) tended to be lower in the sex-sorted than the conventional group. In summary, sex-sorted sperm increased the proportion of female bison calves born following FTAI. Future efforts will include improving embryo production rates following IVF with sex-sorted sperm. Funding provided by Toronto Zoo, Mitacs, and STGenetics.

No abstract

Wood bison (Bison bison athabascae) and plains bison (Bison bison bison) are threatened subspecies native to North America. The creation of a germplasm biobank will connect valuable and inaccessible genetics from geographically distant herds in a biosecure manner. Protocols that are feasible in field conditions are required for cumulus-oocyte complex (COC) collection for the purpose of invitro embryo production (IVP). The efficacy of a single dose of equine chorionic gonadotrophin (ECG) was tested in an effort to develop a minimum-handling ovarian superstimulation protocol for bison. The experimental design enabled comparison between ECG-treated and non-superstimulated bison. Transvaginal ultrasound-guided follicle ablation was performed in mature wood bison (n=24) during May (anovulatory season) to induce follicular wave emergence the following day. Immediately after ablation, the bison were assigned to one of three groups (n=8 per group) and treated intramuscularly with 5000IU of ECG (Folligon, Merck), 2500IU of ECG, or saline (control). Transvaginal COC collection was performed 5 days later. Follicular and COC data were recorded, and only grade 1 and 2 COC were used for IVP. The COC were matured invitro for 25-28h at 38.8°C, fertilised (2×106 spermmL−1), and co-incubated at 38.8°C in 5% O2, 5% CO2, and 90% N2 for 18h. Presumptive zygotes were denuded and cultured at 38.8°C in 5% O2, 5% CO2, and 90% N2. Nominal data were compared among groups using analysis of variance, and proportional data were compared using GLIMMIX. The total number of follicles ≥3mm on the day of COC collection was greater in the 5000-IU ECG group than in the 2500-IU ECG and control groups (37.5±6.9, 17.5±2.0, and 16.9±2.0, respectively; P<0.005). The number of follicles 5-8mm was also greater in the 5000-IU ECG group than in the 2500-IU ECG and control groups (12.5±2.1, 7.6±1.0, and 5.8±0.9, respectively; P<0.01), as was the number of follicles >8mm (21.1±5.4, 3.3±1.2, and 0.9±0.2, respectively; P<0.0005). The proportion of grade 1 and 2 COC/total COC recovered was greater in the 5000-IU ECG group than in the 2500-IU ECG and control groups (84/124 (68%), 39/76 (51%), and 37/75 (49%), respectively; P<0.05). The proportion of cleaved zygotes/number of COC matured, assessed at 56h after fertilisation, was similar among the 5000-IU ECG, 2500-IU ECG, and control groups (42/84 (50%), 27/39 (69%), and 21/37 (57%), respectively; P=0.20). The proportion of embryos of IETS grades 1-3/number of COC matured was also similar among the 5000-IU ECG, 2500-IU ECG, and control groups (15/84 (17.9%), 8/39 (20.5%), and 7/37 (18.9%), respectively; P=0.94), but the bison in the 5000-IU ECG group produced twice as many embryos than those in the other groups. In summary, a single dose of 5000IU of ECG increased the number and size of follicles available for COC collection, more than doubled the number of COC collected for IVP, and resulted in the production of more embryos than the other groups. A single dose of 5000IU of ECG is effective in a minimum-handling protocol for ovarian superstimulation and IVP in bison. This research was supported by NSERC.