EFFECT OF EXOGENOUS PROGESTERONE ON SUPEROVULATORY RESPONSE IN HEIFERS INSEMINATED WITH FRESH OR FROZEN-SEMEN

Superovulation in cattle normally involves the administration of gonad otrophins at specific times of the oestrous cycle, followed by the ind uction of luteolysis and insemination with high quality semen. The fir st aim of this experiment was to examine the effect of supplementary p rogesterone when used in conjunction with porcine FSH (pFSH) to induce superovulation in heifers. The methods compared were PGF(2 alpha) giv en at mid-cycle or a progesterone-releasing intravaginal device (PRID) inserted at different phases of the cycle. The second aim was to dete rmine whether site of insemination or use of fresh or frozen semen aff ected embryo production. A factorial design was used involving 185 bee f heifers. The main factors were (i) synchronization methods (PGF(2 al pha) or PRID); (ii) semen type (fresh or frozen); (iii) insemination r egimens (involving two inseminations and variations in the sites) and number of straws used (one or two) at the second insemination. Eight i njections of pFSH were given twice a day for 4 days starting either on days 9, 10 or 11 of the oestrous cycle or on the fourth day after ins ertion of a PRID. Heifers were checked for oestrus, inseminated twice and embryos were recovered on day 7 of the superovulated cycle. There was no difference between heifers given either PRID or PGF,, in the oe strous response (93% versus 96%), number of ovulations (15.9 +/- 1.11 versus 13.4 +/- 1.06), large follicles (2.5 +/- 0.24 versus 2.3 +/- 0. 23) or embryos recovered (9.1 +/- 0.77 versus 9.1 +/- 0.74). The numbe r of embryos that could be frozen was lower (P = 0.05) in heifers give n PRID. The stage of the cycle at which the PRID was inserted affected the number of ovulations, large follicles and embryos recovered (P < 0.04). The use of fresh or frozen semen had no effect on the number of embryos recovered, but the use of frozen semen resulted in fewer grad e 1 and 2 embryos and more grade 4 and 5 embryos in PRID-treated heife rs. The number of straws did not affect the number or quality of embry os recovered. In conclusion, the use of a PRID, inserted at different stages of the cycle, in conjunction with PGF(2 alpha) and pFSH resulte d in fewer freezable embryos recovered compared with the use of PGF(2 alpha) and pFSH given at mid-cycle. The use of frozen semen did not af fect the number or quality of embryos recovered following the use of P GF(2 alpha) and pFSH at mid-cycle, but it did decrease the number of g rade 1 and 2 embryos recovered following the use of PRID and pFSH; the number (two versus three) of straws used did not affect the yield or quality of embryos recovered.