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The effects of intracranial implants of estradiol in the ventromedial hypothalamus (VMH), the anterior hypothalamus (AH), or the medial amygdala (AMG) on aggression, sexual behavior, and serum estradiol were examined in female Syrian hamsters. Estradiol implants in the VMH, followed by systemic progesterone, stimulated sexual behavior and inhibited aggression. Estradiol implants in other intracranial sites activated sexual behavior but did not reliably inhibit aggression. Intracranially implanted and systemically treated animals had equivalent peripheral estradiol concentrations at sacrifice. These results suggest that: (a) the VMH is an important neural site for estradiol actions on sexual and aggressive behavior, (b) the caudal AH and AMG also may be sites of estradiol action on sexual behavior, and (c) these intracranial implants may only be effective given systemic estradiol exposure or the concurrent stimulation of multiple brain areas.

One-hundred-twenty crossbred gilts from two experiments were assigned randomly to a 2 × 5 factorial experiment. Gilts were reared in two environments (confinement or outside) and assigned to be slaughtered at 4, 5, 6, 7 or 8 mo of age. Beginning at 6 mo of age, blood samples were taken at weekly intervals from each gilt via venipuncture. Serum concentrations of progesterone were analyzed to determine when gilts attained puberty. On the day prior to slaughter, six pigs within a treatment group were cannulated and blood samples were taken at 20-min intervals for 4 h. At slaughter, follicular fluid (FF) was aspirated and the volume determined from those follicles having a diameter of at least 4 mm. No effect of environment was found on the proportion of gilts that attained puberty by 8 mo of age. For the 12 gilts that reached puberty during the study, the age at puberty for gilts reared in outdoor lots (202 ± 5 d) was less (P<.05) than those reared in confinement (224 ± 8 d). Mean concentrations of serum luteinizing hormone (LH; P=.98) and number of secretory spikes of LH (P=.76) were similar between gilts reared in confinement and those reared in outdoor lots. No differences in average serum concentrations of follicle stimulating hormone (FSH) or number of secretory spikes of FSH were found between gilts subjected to these environments (P=.95). Concentrations of estradiol-17βin FF were not affected by environment or age (P>.25). Progesterone concentrations in FF from small and medium follicles of pigs reared outdoors decreased steadily with advancing age (4.8 mo), while progesterone concentrations in FF from small and medium follicles of pigs reared in confinement were not related to age.

Two experiments were conducted to determine if the secretory patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) and serum concentrations of progesterone change immediately preceding induced puberty in gilts. To help predict when prepubertal gilts would attain puberty, gilts were induced into puberty by relocation from confinement housing to an outdoor lot and exposure to mature boars. In Exp. 1, 17 prepubertal gilts were bled on two successive days from 0800 to 1200 h before relocation and boar exposure and until the second day of estrus or for 8 d in gilts that failed to exhibit estrus. Blood samples were collected from indwelling cannulas at 20-min intervals for 4 h. In Exp. 2, blood samples were collected from 20 prepubertal gilts at 20-min intervals from 0800 to 1200 h and from 2000 to Z400 h until the second day of estrus or for 6 d if the gilt failed to exhibit estrus. In each experiment, 11 gilts exhibited pubertal estrus 3 to 6 d after relocation and boar exposure. When the frequency of LH spikes in each gilt was normalized to the day of her preovulatory surge of LH (d 0), a decline in the frequency of LH secretory spikes was observed as gilts approached puberty. However, neither the average magnitude of LH spikes nor mean LH concentrations were different among these days. Mean serum concentrations, frequency of spikes or average magnitude of secretory spikes of FSH or PRL did not change on the days preceding the preovulatory peak of LH. In Exp. 1, 8 of 11 gilts that exhibited estrus had higher (P<.05) serum concentrations of progesterone on d −1 and 0 than on d −3 and −2. In Exp. 2, 7 of 11 gilts that achieved estrus had greater (P<.05) serum concentrations of progesterone on d −.5 than on d −1.5, −1.0 and 0. No increases in serum progesterone were observed in the gilts that failed to exhibit estrus in either experiment. In both experiments, serum concentrations of estradiol-17β were elevated as gilts approached puberty. Serum concentrations of Cortisol remained unchanged on the days immediately preceding the preovulatory surge of LH. These results indicate that the frequency of LH secretory spikes decreased in gilts immediately preceding puberty induced by relocation and boar exposure. Of the 22 gilts that attained puberty, only 15 had a prepubertal rise of serum progesterone. Thus, it appears that a preovulatory rise in serum progesterone is not a necessary event for estrus or ovulation to occur in gilts.

Purified zearalenone (Z) was added to the diet of gilts from d 2 to 15 postmating. Gilts received either 0, 5, 15, 30, 60 or 90 ppm Z (three to five gilts per dose) in 1.8 kg of feed daily. Serum concentrations of progesterone and estradiol-17β were determined weekly. On d 13 to 15 and 40 to 43 postmating, blood samples were drawn from a cannula at 20 min intervals for 4 h and analyzed for luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin (PRL). Gilts were killed 40 to 43 d postmating and embryonic development was assessed. Treatment with 5, 15 or 30 ppm Z had no effect on embryonic development when compared with 0 ppm. No fetuses were present in gilts fed 60 to 90 ppm Z, but two gilts given 60 ppm Z had remnants of fetal membranes in the uterus. The histologic appearance of reproductive tract tissues from the gilts given 60 ppm Z was similar to that from pregnant gilts. Tissues from gilts given 90 ppm Z appeared to be stimulated by both estrogen and progesterone. Serum concentrations of progesterone were decreased at 2, 3 and 6 wk postbreeding in gilts fed 60 and 90 ppm Z. Serum concentrations of estradiol-estradiol-17ß were decreased at 4 wk postbreeding in gilts fed 60 and 90 ppm Z. No differences (P> .05) were noted in the number of secretory spikes of LH, FSH, or PRL among treatment groups either during the feeding of Z (d 13 to 15 postmating) or at the termination of the experiment (d 40 to 43 postmating). These data indicate that ingestion of high concentrations of purified zearalenone by pregnant gilts on d 2 to 15 postmating interferes with embryonic development. This effect occurred in the absence of obvious changes in the secretory pattern of LH, FSL, or PRL, but was associated with retention of corpora lutea and changes in serum concentrations of progesterone and estradiol-17β.

Sixty-four crossbred gilts were assigned randomly to one of four treatments at 9 to 11 wk of age: (1) supplemental lighting and boar exposure, (2) supplemental lighting without boar exposure, (3) no supplemental lighting with boar exposure and (4) no supplemental lighting and no boar exposure. Gilts in all treatment groups received natural daylight through windows of a growing and finishing house from February to July (Exp. 1) or from August to January (Exp. 2). Gilts in treatment groups 1 and 2 received supplemental lighting from a 250 w incandescent bulb (300 1x) from 0520 and 0830 h and from 1630 to 2020 h, for a total daily photoperiod of 15 h. No differences in weight gain or feed efficiency were found among any of the treatments. In Exp. 1, the proportion of gilts displaying estrus by 8 mo of age were 77, 13, 79 and 31% for treatments 1, 2, 3 and 4, respectively. As expected, the proportion of gilts that reached puberty was greater (P<.01) in gilts that had received boar exposure than gilts that did not receive boar exposure. However, supplemental lighting given during periods of increasing natural daylength did not increase (P>.05) the proportion of pubertal gilts or reduce the age of puberty. In Exp. 2, the proportion of gilts displaying estrus by 8 mo of age were 75, 7, 80 and 12% for treatments 1, 2, 3 and 4, respectively. Boar exposure increased the proportion of gilts reaching puberty by 8 mo of age. In addition, gilts exposed to boars and supplemental lighting (Exp. 2) attained puberty an average of 20 d earlier (P<.01) than gilts that received boar exposure alone. Incidence of secretory spikes of luteinizing hormone (LH) or serum concentrations of follicle-stimulating hormone (FSH), prolactin (PRL), or LH in thrice weekly bleedings were similar in all treatments for both experiments. These data indicate that the effectiveness of supplemental lighting on the age of puberty in gilts was dependent upon season. However, supplemental lighting did not affect serum concentrations of LH, FSH or PRL. Furthermore, the lack of an effect of supplemental lighting on serum concentrations of PRL in gilts contrasts with published results from studies on cattle and sheep.