OVARIAN MORPHOLOGICAL CONDITIONS AND THE EFFECT OF INJECTION OF HUMAN CHORIONIC-GONADOTROPIN ON OVULATION RATES IN PREPUBERAL GILTS WITH 2 MORPHOLOGICALLY DIFFERENT OVARIAN TYPES

The purpose of this experiment was to determine the ovulation rate after treatment with human chorionic gonadotropin (hCG) in two groups of gilts characterized by different ovarian morphology: grape-type (GT; n = 11) and honecomb-type (HT; n = 7). At 170 d of age (d 0), gilts were examined by laparoscopy and ovarian type was determined by the distribution of macroscopic follicles present on the ovarian surface. Five to ten minutes after surgery, each gilt received a single injection (i.m.) of 750 IU of hCG. At d 0, GT ovaries had a greater number of large follicles (greater-than-or-equal-to 6 mm) than HT ovaries (10.0 +/- .5 vs 2.6 +/- .3; P < .05), whereas HT ovaries had more small follicles (1 to 3 mm; HT: 42.3 +/- .8 vs GT: 26.7 +/- .9; P < .05) and total follicles (HT: 59.4 +/- 2.3 vs GT: 52.2 +/- 1.5; P < .05), although numbers of medium follicles (4 to 5 mm) were similar (GT: 15.6 +/- .8 vs HT: 14.6 +/- 1.7; P > .10). Number of induced corpora lutea (CL) per ovary was greater (P < .05) in gilts with GT ovaries (10.59 +/- 2.9 CL) than in gilts with HT ovaries (5.21 +/- .66 CL). Total weight of luteal tissue (LT) per ovary and serum progesterone concentrations 8 d after induction of ovulation were greater in GT gilts than in HT gilts (GT: 6.37 +/- 1.09 g vs HT: 3.31 +/- .49 g for LT, P < .05; GT: 21.08 +/- 4.76 ng/ml vs HT: 13.40 +/- 2.05 ng/ml for progesterone, P < .07). However, the average weight of each CL was similar (P > .10) in GT (.68 +/- .08 g) and HT gilts (.63 +/- .04 g). Additionally, 8 d after injection of hCG, the population of follicles (large and small follicles) was similar between GT and HT gilts. Results of the present experiment demonstrate that the ovarian morphology has a significant influence on the ovulatory response to hCG injection in prepuberal gilts.