Abstract
Thirty-six sows and gilts (hereafter called sows) received one of three prostaglandin F 2α(PGF 2α) treatments on day 6, 10, or 14 of the estrous cycle to determine the effect of prostaglandin treatment on subsequent concentrations of luteinizing hormone (LH) and progesterone. Also, the effect of treatment on estrous cycle lengths was evaluated. Blood was sampled every 15 min for 6 h. Starting from time 0, sows received 25 mg of PGF 2α at 4 h (treatment 1), 50 mg at 4 h (treatment 2), or 25 mg at both 1 h and 4 h (treatment 3). Treatment and day of cycle that sows were treated modified estrous cycle lengths ( P<0.05). Release of LH was episodic prior to PGF 2α treatment. After PGF 2α injection, progesterone in blood sera increased ( P< 0.0001) with higher progesterone continuing for about 1 h. Concentrations of LH in blood sera decreased following PGF 2α, suggesting negative feedback of progesterone. Initial response of LH and progesterone to PGF 2α was not distinguishable ( P>0.05) among the three cycle stages nor altered by quantity of PGF 2α although the response to a second injection (treatment 3) was diminished ( P<0.01). Correlations between LH and progesterone were not significant ( P>0.05) at any time. Therefore, it appears that resistance of naturally occurring corpora lutea (of the estrous cycle) in swine to the luteolytic action of PGF 2α is not due to gonadotropic support from the pituitary.
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