EFFECT OF TIME OF MATING RELATIVE TO OVULATION ON MORPHOLOGICAL DIVERSITY OF SWINE BLASTOCYSTS

The effect of time of mating relative to ovulation on the amount of em bryonic diversity was investigated in 37 mature crossbred gilts. Ovula tion was induced by injecting proestrous gilts with 1000 IU of hCG. Gi lts were naturally mated once at 24-32 (control), 41, or 43 h after hC G injection (n = 10, 9, and 18. respectively). Blastocysts were collec ted surgically 288 h post-hCG from gilts mated at 24-32 h post-hCG, fr om those mated at 41 h post-hCG, and from 8 of those mated at 43 h pos t-hCG. Collection of blastocysts was performed at 295 h in 10 gilts ma ted at 43 h post-hCG. Blastocysts within the ranges 1.0-4.0, 4.5-7.0, 7.5-10.0, 10.5-15.0, and 15.5-40.0 mm and those > 40.0 mm were classif ied morphologically as small, medium, and large spheres and as ovoidal , tubular, and filamentous, respectively. Blastocysts were incubated f or 6 h to quantify secretion of estradiol-17beta (estradiol). Morpholo gical diversity (standard deviation of size) did not differ among blas tocysts of treatment groups. Delaying the time of mating reduced (p < 0.07) the subsequent size and estradiol secretion of blastocysts. Wait ing until 295 h after hCG to evaluate blastocysts of gilts mated at 43 h resulted in blastocyst size and estradiol secretion similar to that of concepti of controls. Estradiol secretion by medium and large sphe rical blastocysts of gilts mated at 43 h post-hCG and evaluated at 288 h was lower (p < 0.05) than that by blastocysts of the same classific ations from controls. Delaying mating, relative to ovulation, decrease d size and estradiol secretion of blastocysts but did not affect the e xtent of their morphological diversity.