Increased plasma follicle-stimulating hormone concentrations in prepubertal gilts from lines selected for increased number of corpora lutea

Plasma follicle-stimulating hormone (FSH) was evaluated in gilts from two s tudies in which ovulation rate was increased through direct selection for n umber of corpora lutea (CL) to determine whether selection for ovulation ra te affected FSH secretion during prepubertal development. In the first stud y, 76 control and 110 selected gilts of University of Nebraska gene pool li nes were bled twice during prepubertal development. Plasma FSH concentratio ns were greater (P < 0.05) at 53 (13.5%) and 75 (21.3%) d of age in selecte d than in control gilts. In the second study, 254 control gilts, 261 gilts from a line selected for ovulation rate, and 256 gilts from a line selected for uterine capacity were bled at three prepubertal ages. Plasma FSH was g reater (P < 0.05), relative to controls, on d 34 (> 24%), 55 (> 13%), and 8 5 (> 10%) in White Composite gilts selected for either increased ovulation rate or for greater uterine capacity. Unilateral ovariectomy and hysterecto my were performed at 160 d of age on random gilts in these three lines (n = 377); weights of these organs were evaluated to determine whether selectio n affected their development. Ovarian and uterine weights were less (P < 0. 01) in the control than in the ovulation rate line. Subsequently, ovulation rate was determined during pregnancy (n <greater than or equal to> 130 gil ts/line). Controls had fewer (P < 0.01) CL (14.6) than gilts of the ovulati on rate line (17.7) but numbers similar (P <greater than> 0.10) to those of gilts of the uterine capacity line (14.7). Within each line, plasma FSH on ly on d 85 correlated positively with subsequent ovulation rate (P < 0.03, 0.001, and 0.08; r = 0.17, 0.30, and 0.15 for control, ovulation rate, and uterine capacity lines, respectively). Ovarian weight at 160 d of age also correlated with subsequent ovulation rate (P < 0.03 and 0.001; r = 0.23 and 0.38) in control and ovulation rate gilts but not in uterine capacity gilt s (P > 0.10; r = 0.11). Gilts selected for increased number of CL, in two i ndependent studies, had greater concentrations of FSH during prepubertal de velopment than respective controls. The modest but significant, positive as sociation of FSH at 85 d of age with subsequent ovulation rate provides add itional support for using plasma FSH in prepubertal gilts to indirectly sel ect for ovulation rate.