Measures of the ovaries and uterus during development of gilts selected for differences in uterine capacity

Direct selection for uterine capacity (UC) increased the number of live pigs born. A method to indirectly estimate UC in developing gilts is needed for this trait to be incorporated into commercial selection strategies. We tested the hypothesis that selection for UC alters phenotypic characteristics of the reproductive tract of prepubertal gilts and that these changes could be estimated in live animals using transrectal ultrasound (TRU). Gilts from lines selected for UC and a randomly selected control (CO) line were submitted for TRU at 130, 150, or 170 d of age and harvested 24 h later (n = 10 gilts/line per age). Diameter of the uterine horn was measured (2 to 4 measurements per animal) at TRU. At harvest, measurements of the ovary (height, width, length, weight, and number of visible follicles >1 mm) and uterine horn (weight, length, diameter, and endometrial diameter) were taken. There was no line × age interaction for any of the traits. All ovarian traits increased (P < 0.03) with age. Weight and length of the uterine horn was not different at 130 or 150 d but were increased (P < 0.01) at 170 d of age. Diameter of the uterine horn tended (P = 0.06) to be increased at 170 d compared with 130 or 150 d, but age did not affect (P = 0.38) endometrial diameter. Ovarian weight and width were increased (P < 0.01) and ovarian length and height tended (P = 0.07) to be greater for UC than CO gilts, but the number of visible follicles did not differ. The UC gilts had increased (P < 0.02) weight of uterine horns, which tended (P = 0.09) to be longer than in the CO gilts. Diameter of the uterine horn and the endometrium were greater (P < 0.01) for UC gilts than for CO gilts. Uterine horn diameter measured with TRU was not affected by age or line and was not highly correlated with any of the measured traits. Selection for increased UC results in larger ovaries and uterine horns, but TRU was not useful for estimating these traits in gilts of the age studied.