Mature gilts classified by low (12 to 16 corpora lutea [CL], n = 6) or high (17 to 26 CL, n = 5) ovulation rate (OR) were compared for plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, estradiol-17beta, and inhibin during an estrous cycle. Gilts were checked for estrus at 8-h intervals beginning on d 18. Blood samples were collected at 8-h intervals beginning on d 18 of the third estrous cycle and continued for one complete estrous cycle. Analysis for FSH and LH was performed on samples collected at 8-h intervals and for ovarian hormones on samples collected at 24-h intervals. The data were standardized to the peak of LH at fourth (d 0) and fifth estrus for the follicular phase and analyzed in discrete periods during the periovulatory (-1, 0, +1 d relative to LH peak), early-luteal (d 1 to 5), mid-luteal (d 6 to 10), late-luteal (11 to 15), periluteolytic (-1, 0, +1 d relative to progesterone decline), and follicular (5 d prior to fifth estrus) phases of the estrous cycle. The number of CL during the sampling estrous cycle was greater (P < 0.005) for the high vs low OR gilts (18.8 vs 14.3) and again (P < 0.001) in the cycle subsequent to hormone measurement (20.9 vs 14.7). For high-OR gilts, FSH was greater during the ovulatory period (P = 0.002), the mid- (P < 0.05) and late-luteal phases (P = 0.01), and tended to be elevated during the early-luteal (P = 0.06), but not the luteolytic or follicular periods. LH was greater in high-OR gilts during the ovulatory period (P< 0.005), but not at other periods during the cycle. In high-OR gilts, progesterone was greater in the mid, late, and ovulatory phases (P < 0.005), but not in the follicular, ovulatory, and early-luteal phases. Concentrations of estradiol-17beta were not different between OR groups during the cycle. Inhibin was greater for the high OR group (P < 0.005) during the early, mid, late, luteolytic, and follicular phases (P < 0.001). The duration of the follicular phase (from last baseline estrogen value to the LH peak) was 6.5 +/- 0.5 d and was not affected by OR group. These results indicate that elevated concentrations of both FSH and LH are associated with increased ovulation rate during the ovulatory phase, but that only elevated FSH during much of the luteal phase is associated with increased ovulation rate. Of the ovarian hormones, both inhibin and progesterone are highly related to greater ovulation rates. These findings could aid in understanding how ovulation rate is controlled in pigs.

SummaryAge at puberty was determined for 205 Gene Pool gilts; 68 fed a 10% protein diet (HLC) consisting of high-lysine corn, minerals and vitamins and 137 fed a 14% protein corn soybeam meal diet (CS). Gilts fed the CS diet reached puberty 18.7 days earlier than gilts fed the HLC diet. Use of postweaning daily gain as a covariable reduced the difference between diets to 9 days. The pooled within diet regression of age at puberty on post-weaning gain was -22.75 days per kilogram. The correlation between pubertal age and daily gain was significantly higher on the HLC diet (-.30 vs. -.57; P < .025) but the regressions for the two diets did not differ significantly (-26.0 vs. -18.4 days per kilogram).Daughter-dam regressions were calculated for each diet separately. The coefficient for the 14% protein diet (0.32) was significantly higher than for the 10%protein diet (-.14)indicating the existence of a genotype-environment interaction.

The effect of volume and frequency of administration of porcine follicular fluid (pFF) on FSH concentration was determined in mature gilts during the period of the secondary FSH surge (d 0 to 5; d 0 = onset of estrus) and following withdrawal of pFF (d 5.5 to 9). Crossbred gilts (n = 14) were randomized in a 3 x 2 factorial treatment design involving three doses of pFF (0, 5, or 10 ml) and once- vs twice-daily pFF administration. Porcine FF was aspirated from medium and large follicles and treated with 5 mg of activated charcoal per milliliter of pFF to remove steroids. Once-daily administration of pFF, regardless of dose, failed to suppress mean concentrations of FSH during the secondary FSH surge. Treatment of gilts twice daily with 10 ml of pFF suppressed (P less than .05) area under the FSH curve during the secondary FSH surge compared with gilts given saline. Gilts treated twice daily with 5 ml pFF showed comparable suppression of plasma FSH from d 0 to 3 but began to overcome FSH inhibition after d 3. As a result, FSH release only tended to be lower than controls for the entire treatment period (P less than .1). Mean FSH concentrations were increased (P less than .05) during the post-treatment period (d 5.5 to 9) by treatment with intermediate (5 ml pFF, two times daily and 10 ml pFF, one time daily) and high (10 ml pFF, two times daily) doses of pFF. Neither ovulation rate nor interestrous interval was affected by pFF administration.(ABSTRACT TRUNCATED AT 250 WORDS)