Influence of season on estrous and luteinizing hormone responses to estradiol benzoate in ovariectomized sows

N. M. Cox, J. L. Ramirez, I. A. Matamoros, W. A. Bennett, J. H. Britt

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40 Scopus citations


The objective of this experiment was to determine whether seasonal differences existed in estrous and LH responses to estradiol benzoate (EB) in ovariectomized sows. Sows were ovariectomized after weaning their first litter, and treatment was begun 120 d after ovariectomy. Sows were given 400 μg EB intramuscularly (i.m.) on July 24, 1982 (summer), October 24, 1984 (fall), January 29, 1985 (winter), and March 27, 1985 (spring). Beginning 24 h after EB, sows were checked for estrus four times daily. Proportion in estrus was affected by season, with all sows exhibiting estrus within 5 d after EB in summer, winter, and spring. Only three of five sows exhibited estrus within 5 d after EB in fall. Interval (h) to estrus was delayed in fall (80 h) compared to other seasons (62.6 h; SEM = 4.5). Concentrations of LH were suppressed within 6 h after EB in all seasons but rebounded to pre-injection levels more slowly in fall and spring than in winter and summer. Frequency of LH peaks (3.2 ± .4 4 h) was not affected by season, but amplitude (1.9 vs 0.9 ng/ml) and baseline (2.7 vs 1.6 ng/ml) were greater (P < 0.05) for summer than for the other seasons combined. At 6 h after injection, concentrations of estradiol-17β (pg/ml) were greater in summer (58.3) than in fall (19.0), winter (32.4), or spring (16.6; SEM = 10.4). We conclude that environmental factors associated with season alter responsiveness of the brain to estradiol, thereby controlling sexual behavior and LH secretion.

Original languageEnglish
Pages (from-to)395-405
Number of pages11
Issue number2
StatePublished - Feb 1987

Bibliographical note

Funding Information:
aPublication No. 6438, Mississippi Agriculture and Forestry Experiment Station. Purified porcine LH (LER 786-3) was kindly supplied by Dr. L.E. Reichert, Jr., porcine LH antiserum by Dr. G.D. Niswender, and antiestradiol serum by Dr. N.R. Mason. Partial funding for this project was provided by USDA Special Grant No. 82-CRSR-2-1069.


  • LH
  • estradiol benzoate
  • estrus
  • season
  • sow

ASJC Scopus subject areas

  • Small Animals
  • Food Animals
  • Animal Science and Zoology
  • Equine


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