IN-VITRO DEVELOPMENT OF EMBRYOS FROM SUPEROVULATED GILTS TREATED WITHTHE PROGESTERONE AGONIST, ALTRENOGEST (REGU-MATE) OR THE PROSTAGLANDIN ANALOG, CLOPROSTENOL (PLANATE)

This study was conducted to compare the in vitro development of embryo s from superovulated postpubertal gilts synchronized with progesterone agonist altrenogest (REG, Regu-Mate) and those from superovulated pre pubertal gilts synchronized with prostaglandin analogue cloprostenol ( PLA, Planate). Ten postpubertal gilts that had exhibited estrus at lea st once were fed 20 mg/d of REG from Day 0 (the first day of treatment , may have been any day of the estrous cycle) to Day 17. The gilts rec eived intramuscularly (im) 1500 IU of equine chorionic gonadotropin (e CG) on the afternoon of Day 17, followed by 1000 IU of human chorionic gonadotropin (hCG) 84 h later. Eight prepubertal gilts received intra muscularly one dose of a combination of 400 IU of eCG and 200 IU of hC G (PG 600) on Day 0 (the first day of treatment), followed by 750 IU o f hCG on Day 3. From Day 16 to Day 19, the prepubertal gilts received 350 mg/d of PLA, followed by 1500 IU of eCG on the afternoon of Day 19 , then 1000 IU of hCG 84 h later. Gilts were checked for estrus with a n intact boar. At estrus, all gilts were artificially inseminated and/ or mated twice at 12-h intervals. Then 50 to 54 h after the hCG inject ion, a mid-ventral laparotomy was performed on each gilt. Corpora albi cans (CA) and corpora hemorrhagica (CH) were counted, and oviducts wer e flushed in situ. The embryos recovered (1- to 2-cell) were cultured in modified Whitten's medium at 38.5 degrees C under an atmosphere of 5% CO2 in air for 144 h. The number of CA per gilt did not differ betw een the postpubertal and prepubertal gilts (11.9 vs 7.9, respectively; P>0.05). However, the number of CH per gilt (27.5 vs 18.1, P=0.05) an d the number of embryos per gilt (26.2 vs 15.3, P<0.05) were higher in postpubertal gilts than in prepubertal gilts. Furthermore, after 144 h of in vitro culture, the percentage of embryos cleaving to the great er than or equal to 16-cell (morula+blastocysts) or greater than or eq ual to 32-cell (blastocysts) was greater (P<0.05) in prepubertal gilts than in postpubertal gilts (85.2 vs 68.5, 55.7 vs 44.2, respectively) . The total numbers of embryos examined were 122 and 260 in prepuberta l and postpubertal gilts, respectively. These results show that postpu bertal gilts treated with REG produced a higher number of embryos. How ever, better embryo development was noted with zygotes from prepuberta l gilts primed with exogenous gonadotrophin, followed by synchronizati on with prostaglandin before induction of superovulation and inseminat ion.