207 EFFECT OF REPEAT HORMONE STIMULATION ON THE YIELD AND IN VITRO DEVELOPMENT OF JUVENILE CALF OOCYTES

Juvenile in vitro embryo transfer can markedly reduce animal generation intervals. The purpose of this study was to investigate the ovarian response of juvenile calves and in vitro oocyte developmental capacity after superstimulation. Experiments on calves were performed in accordance with the Animal Welfare Regulations. A total of 36 donor juvenile calves on standard nutrition and in a disease-free environment, were selected from the breeding farm of the Beijing Dairy Cattle Center. At 60 days of age, calves were randomly assigned into three groups of four calves each, replicated three times. On day 1, Group 1 received a progesterone vaginal insert (CIDR, 300 mg per device); Group 2 received a CIDR and 0.5 mg oestrogen benzoate (China); Group 3 received a CIDR, 0.5 mg oestrogen benzoate, and 50 mg progesterone (China). Then, calves were injected with FSH (Folltropin-V, Bioniche Animal Health, Belleville, ON, Canada) twice daily on days 5 (40 mg/40 mg) and 6 (30 mg/30 mg) at 12 h intervals. Cumulus–oocyte complexes (COCs) were recovered from the superstimulated calves 12 to 14 h after the final FSH treatment. COCs were considered usable unless they were damaged or had expanded cumulus layers. Usable COCs were matured in vitro for 24 h in maturation medium consisting of TCM199, 10% FBS, 10 μg mL–1 FSH, 1 μg mL–1 LH, 1 μg mL–1 E2–17β, 100 IU mL–1 penicillin, 100 μg mL–1 streptomycin, with (+Cys) or without (–Cys) 100 μM Cysteamine. Each calf oocyte was cultured in one well. The final concentration added to each fertilization drop was 5 × 106 sperm mL–1. Sperm and oocytes were co-cultured in IVF-100 medium (BO liquid+10 μg mL–1 heparin, Japan) at 38.5°C, 5% CO2 and a saturated humidity for 6 to 8 h. Blastocyst production rates were determined after 7 and 8 d of in vitro culture in CR1aa medium without the addition of cysteamine. Differences among treatments in each experiment were determined by one-way ANOVA and a multiple range test. Superstimulatory results indicated that more follicles were aspirated (63.2 per calf) and more usable oocytes were recovered (48.0 per calf) in Group 1 than in the other two groups (Group 2–45.2 and 31.8, respectively; Group 3–35.4 and 28.3, respectively; P < 0.05). No difference was observed between Groups 2 and 3. Superstimulation of calves twice at 30 day intervals in Group 2 (n = 12) did not affect the number of follicles or usable oocytes (overall, 44.2 and 28.0 per calf). Maturation rates (86.5% v. 85.0%, respectively) and cleavage rates (84.4% v. 80.0%, respectively) did not differ whether cysteamine was not (–Cys; n = 318) or was (+Cys; n = 330) added to the maturation medium. However, the blastocyst rate differed significantly (12.9% v. 35.2%, respectively; P < 0.01). This study established a protocol for the superstimulation of juvenile calves with an average of 48 oocytes obtained per calf. Superstimulation and surgical oocyte recovery twice at an interval of 30 days had no adverse effect on follicle development or oocyte recovery. The novelty of this research is that the blastocyst production rate of calf oocytes (35.2%) in maturation medium supplemented with cysteamine was similar to that reported in the cow.