Category: Gonadotropin

To our knowledge, this is the first study to clearly demonstrate that circulating FSH concentrations vary significantly over the course of a day. Furthermore, our data suggest that FSH is secreted in an episodic fashion, resulting in distinct pulses of FSH in the adult male fowl. As discussed below, it appears that FSH and LH pulses are asynchronous and are not derived from a common hypothalamic pulse generator.

The management program for the birds used in the present experiments was developed for elite male broiler breeders. Birds raised under this program were feed-restricted to prevent obesity and exposed to a long-day photostimulation after 20 wk of age to maintain reproductive performance throughout adult life. One consequence of this management system is the variability in testis size of sexually mature males.

Despite a slight decrease of the LH baseline on Day 0, concentrations were not significantly different from those on Day 1 and Day 2. Moreover, we did not observe any depressive effect on LH secretion over time, suggesting that frequent withdrawal of blood samples using the present cannulation procedure did not interfere with the normal secretion of LH in blood. Conversely, LH concentrations tended to decrease over time as a result of the handling associated with repeated blood sampling of cockerels in previous reports.

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RESULTS

Testis Size

Birds used in these experiments had similar body conformation as well as normal comb and male secondary sexual characteristics, and they weighed 4063 ± 160 g. In experiment 1, testis weights (n = 8) varied by as much as 4.4-fold, from an individual mean of 6.3 to 27.6 g (Table 1). In contrast, testis weight (n = 20) varied from 25.5 to 52.1 g in experiment 2.

Gonadotropin Secretion

Experiment 1. Average concentrations of LH and FSH in plasma varied among individual broilers (Table 1). However, concentrations of LH (8.3 ± 1.8 ng/ml) and FSH (8.1 ± 1.1 ng/ml) did not differ between Day 0 and Day 1 or between Day 0 and Day 2 (Table 2).

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Animals

All animal rearing, handling, cannulation, and euthanasia procedures were approved by the University of Arkansas Institutional Animal Care and Use Committee. One-day-old broiler breeder chicks were used in two experiments. Birds were banded, vaccinated, and reared on a 23L:1D photoperiod with ad libitum food and water intake in floor pens. At 8 wk of age, males were placed on a restricted diet to maintain a weight gain of approximately 0.75% of their initial body weight per week. At the same time, photoperiod was reduced to 8L:16D as recommended by the breeder. At 20 wk of age, males were placed in a 14L:10D photoperiod that was gradually raised to 16L:8D by 28 wk of age. After 28 wk of age, 14 birds were transported to a surgery and animal isolation suite and confined in individual cages (0.6 X 0.5 X 0.5 m). Birds were provided with the same photoperiod and feed as described before and were checked at least twice each day for signs of stress or discomfort. At caging, birds were fitted with a canvas saddle ‘‘jacket’’ (~22 X 15 cm) similar to those previously described.

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INTRODUCTION

Proper gonadal function in birds depends on gonadotropins secreted from the pituitary gland in an appropriate manner. That LH secretion is distinctly pulsatile is generally well known, but the overall pattern and control of FSH secretion is not well understood in birds. The hypothalamus, in turn, controls the secretion of LH and, most likely, FSH by the pulsatile secretion of GnRH into the portal circulation of the pituitary.

The pattern of LH secretion in intact male chickens appears to be episodic, with a frequency of 0.3 to 0.7 pulses/ h. However, LH concentrations in plasma have been shown to be depressed over time as a result of the handling associated with repeated blood sampling. Moreover, it has been demonstrated that no pulses of LH were recorded when LH concentrations were minimal because of handling.

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