Duroc sows farrowed second litters in March and lactated 35 ± 2 days. At 36 hr before weaning, electrocautery of follicles ≥3 mm in diameter (n=8) or sham surgery (n=5) was performed to test the hypothesis that ablation of medium-sized follicles would prolong the duration of postweaning anestrus. Number of follicles and diameters at surgery were: 1.3 ± .6 (> 5 mm diameter), 26 ± 1 (3 to 5 mm) and > 20 (< 3 mm). Blood samples were collected at 15 min intervals for 3 hr beginning at −12, 0, 12, 60 and 96 hr from weaning. Interval to estrus was 3.4 ± .2 days in seven of eight cauterized sows and 3.6 ± .6 days for sham-surgery sows. The remaining cauterized sow was anestrus at slaughter, 40 days after weaning. Number of corpora lutea and pregnancy rate were 15.8 ± .6 and 92%, respectively, and were similar between sham-surgery and cauterized sows. Concentration of follicle stimulating hormone (FSH) at 12 hr before weaning was greater in sows subjected to electrocautery than for sham-surgery sows, but FSH values were similar at other sampling times. Concentrations of estradiol were similar at all times for both treatment groups. Luteinizing hormone (LH) was higher (P



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