INVITRO FERTILIZATION OF PIG OOCYTES AFTER DIFFERENT COINCUBATION INTERVALS

The effects of gamete coincubation time on porcine in vitro fertilizat ion for 4, 6 or 8 hours in Trial 1 or for 1, 2, 3 or 4 hours in Trial 2 were studied. The 876 oocytes were recovered from oviducts of prepub ertal gilts. Ovulation was induced. Excessive spermatozoa attached to zona pellucida were removed by pippeting after coincubation (1 to 8 ho urs). Optimum results were obtained after 3 to 4 hours of coincubation , when 23 to 29% of the oocytes were fertilized by a single spermatozo a. Shorter intervals of coincubation were characterized by reduced per centages of fertilized oocytes and longer intervals of coincubation by increased rates of polyspermic fertilization. The employed sperm conc entration was deliberately high (2 x 10(6) sperm/ml). The results show that a coincubation time of 4 hours may be optimal for pig in vitro f ertilization. Under these assay conditions, modification of other fact ors such as sperm concentration, medium volume and physiological envir onment may increase the percentage of monospermic fertilization.