Follicle Dynamics and Aromatase Activity: DISCUSSION(7)

DISCUSSION(7)

Since total estradiol production in vitro by both the theca and granulosa layers combined was higher by the population of follicles > 2 mm from Meishan than from Large-White hybrid sows, and the Meishan preovulatory population alone synthesized more estradiol, secretion of estradiol from the ovary per animal into the circulation would presumably be higher during the follicular phase in Meishan animals. Recent reports have indeed shown that plasma estradiol concentrations were higher in Meishan sows and, furthermore, that there was an earlier rise in plasma estradiol relative to the preovulatory LH surge, which may be responsible for the controversial earlier onset of behavioral estrus relative to the preovulatory LH surge and ovulation in Meishans compared with Large-White hybrid animals. Tilton et al. showed that acutely ovariec-tomized Meishan gilts were less sensitive to the negative feedback of estradiol on gonadotropin release, and this explains how FSH levels were maintained in the face of increased estradiol secretion by the follicular population. This sheds light, therefore, on the mechanism whereby the Meishan can maintain FSH secretion and a large number of estrogenic follicles during the follicular phase. buy antibiotics online

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Follicle Dynamics and Aromatase Activity: DISCUSSION(6)

This observation means that the larger follicles recovered from Meishan sows contained higher follicular fluid estradiol concentrations on Day 16 than did follicles recovered from Large-White hybrid sows. Since the first endocrine signal for recruitment is thought to be declining plasma progesterone and an earlier decline in plasma progesterone has been reported in Meishan pigs, this could result in relatively earlier recruitment of follicles from the proliferating pool and hence induce an earlier commencement of the follicular phase and follicle maturation. It is possible, therefore, that some of the follicles recovered on Day 16 from Meishan but not from Large-White hybrid sows had already undergone recruitment. Buy Asthma Inhalers Online

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Follicle Dynamics and Aromatase Activity: DISCUSSION(5)

DISCUSSION(5)

Both granulosa cell number and theca weight per follicle increased with follicle size and were not different either between breeds or between days when follicles of similar sizes were compared. However, follicles defined as preovulatory in the analysis were of a smaller diameter and contained fewer granulosa cells and less theca tissue in Meishan than in Large-White hybrid sows. This is consistent with similar observations in Meishan gilts and highly prolific breeds of sheep.

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Follicle Dynamics and Aromatase Activity: DISCUSSION(4)

In Meishan sows, there were more follicles present in the smaller size categories than in Large-White hybrid sows on both days. The maximal diameter of follicles recovered on Day 19 of the cycle from Meishan sows was smaller than that of those recovered from Large-White hybrid sows. Similar observations have previously been reported in gilts. In Large-White hybrid sows there was a reduction in the number of follicles recovered from Days 16 to 19 despite an increase in the number of follicles in the larger size classes, and this can be attributed to a reduction in the numbers of mid-size follicles (3-6 mm diameter) and a block to their replacement in the proliferating pool. ventolin inhaler

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Follicle Dynamics and Aromatase Activity: DISCUSSION(3)

DISCUSSION(3)

Recruitment of follicles from the proliferating pool occurs between Days 14 and 16 of the estrous cycle, while selection occurs between Days 16 and 20. Day 16 of the estrous cycle, five days before predicted es-trus onset, was therefore chosen as the first time point to study in the current experiment, corresponding to around the time of recruitment but preceding selection. Day 19 of the estrous cycle, two days before predicted estrus onset, was chosen as the second time point for study during the follicular phase, after a substantial number of the ovulatory follicles had been selected, but before the time when only those follicles destined to ovulate, the preovulatory population, were present.

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Follicle Dynamics and Aromatase Activity: DISCUSSION(2)

The number of follicles l mm diameter recovered from Meishan sows was higher than that from Large-White hybrid sows when data from Days 16 and 19 were combined. Studies of pigs with increased ovulation rates and of highly prolific breeds of sheep have reported that animals with higher ovulation rates possess a larger number of follicles in the proliferating pool than do nonprolific breeds. The present results suggest that although the number present on Day 16 was not significantly different between the breeds, a higher number of follicles were maintained in the Meishan up to Day 19. The number of follicles Э: 1 mm present in the Meishan proliferating pool on Day 16 may in fact be an underestimate, due to the smaller overall diameter of follicles recovered from Meishan sows. birth control pills

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Follicle Dynamics and Aromatase Activity: DISCUSSION(1)

DISCUSSION(1)

Meishan sows had a higher ovulation rate than did their Large-White hybrid contemporaries in the present experiment. Early studies of the mechanism by which the Meishan pig gained its enhanced prolificacy failed to observe any difference between the ovulation rate of Meishan gilts and Western breeds. More recently, however, it has been reported that ovulation rate increases with reproductive age in Meishan gilts and that this increase is more pronounced after parity. The high ovulation rate observed in the present study therefore confirms the previous reports that ovulation rate is increased in Meishan sows compared with their Western contemporaries. ventolin inhalers

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