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Biology of Reproduction, Vol 24, 341-353, Copyright © 1981 by Society for the Study of Reproduction
1 Department of Animal Science,
North Carolina State University,
Raleigh, North Carolina 27650 Concentrations of LH, FSH, prolactin, estrogen, and progesterone were measured in blood
samples collected at various intervals during and immediately following lactation to determine the
role of the ovary in controlling gonadotropin and prolactin secretion and initiation of estrous
cycles in the pig. Ten primiparous sows were ovariectomized (ovex, n = 5) or left intact (n = 5) 2 to
4 days after farrowing. Serum progesterone and estrogens in samples collected daily during lactation were not different between intact and ovex sows. Serum FSH increased immediately after
ovariectomy and remained elevated during lactation, but LH concentrations were similar between
ovex and intact sows. Both LH and FSH were higher during the last 2 weeks of lactation than
during the first 3 weeks. On Days 10 and 20 of lactation, all sows received (i.v.) two challenges of gonadotropin releasing
hormone (GnRH; 400 µg each) at 135 min intervals. Peak change (maximum value minus baseline)
in FSH after GnRH was higher in ovex than in intact sows on both Days 10 and 20. Peak change in
FSH in ovex sows was higher on Day 20 than on Day 10, but peak change in FSH in intact rows
was similar between Days 10 and 20. Peak change in LH after GnRH was similar between ovex and
intact sows. Peak change in LH after the second GnRH challenge on Day 10 was higher than that
after each of the other three challenges. Although serum prolactin concentrations in selected samples collected on Days 10 and 20 were
not significantly different between treatment groups, intact sows had consistently higher concentrations compared with ovex sows. Separation of four sows from their litters for 4 h during the last
week of lactation resulted in a decline in serum prolactin, but prolactin increased fivefold within
15 min and tenfold during the second hour after piglets were replaced. In contrast, LH did not
change prior to or after piglets were allowed to nurse. After weaning, concentrations of estrogens peaked during 24 h around onset of estrus prior to
the preovulatory surge of LH and FSH. In ovex sows treated with estradiol-17 Results from these experiments indicate that 1) LH is low during lactation in both intact and
ovex sows; 2) FSH increases following ovariectomy, presumably because of removing some ovarian
inhibitor of FSH secretion; 3) prolactin, but not LH, changes acutely with suckling or weaning; and
4) surges in LH, FSH, and prolactin at estrus are induced by estrogen whether of endogenous
(intact sows) or exogenous (ovex sows) origin.
on Days 8, 9, and
10 after weaning, estrous behavior and LH and FSH responses were indistinguishable from those
observed in intact sows at the postweaning estrus. Serum LH, FSH, and prolactin increased in
response to estrogen, and duration of estrus was similar to that observed in intact sows.
Note:
ACKNOWLEDGMENTS
We wish to thank Dr. G. D. Niswender, Colorado
State University, Ft. Collins, for providing the porcine
LH antiserum; Dr. V. L. Estergreen, Washington State
University, Pullman, for donating the estrogen anti-serum; Drs. R. J. Ryan and R. J. Whitley, Mayo Clinic,
Rochester, MN, for supplying the porcine FSH anti-serum and purified porcine FSH (IA3-c2); Dr. L. E.
Reichert, Jr., for providing the purified porcine LH
(LER 786-3); the Hormone Distribution Office,
NIAMDD, Bethesda, MD, for donating the LH (NIH-S20), and Dr. R. H. Rippel, Abbott Laboratories,
for providing the GnRH. Technical assistance of J. K.
Huff and T. E. Steffel is gratefully appreciated.
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