אסיף מאגר המחקר החקלאי

Pituitary response to GnRH and ovariectomy in Booroola-Awassi and Awassi ewe lambs

Year:

1989

Source of publication :

Authors :

Volume :

87

Co-Authors:

Braw-Tal, R., Institute of Animal Science, A.R.O., Volcani Center, Bet Dagan 50250, Israel
Gootwine, E., Institute of Animal Science, A.R.O., Volcani Center, Bet Dagan 50250, Israel

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Abstract:

Booroola-Awassi ewe lambs were heterozygous (F+) for a major gene F, influencing their ovulation rate, while Awassi lambs were non-carriers (++). Basal plasma FSH concentration (mean ± s.e.m.) in Booroola-Awassi ewe lambs at 4 weeks of age was significantly higher than in Awassi lambs of the same age (5.06 ± 0.60 and 2.04 ± 0.32 ng/ml respectively; P < 0.001). After GnRH administration, FSH increased from 3.89 ± 1.10 to 10.58 ± 1.30 ng/ml in Booroola-Awassi (N = 6) and from 1.87 ± 0.29 to 4.64 ± 0.33 ng/ml in Awassi (N = 6) ewe lambs (P < 0.05). Ovariectomy caused an increase in plasma FSH in Booroola-Awassi (N = 4) and Awassi (N = 4) ewe lambs. At 1 week after ovariectomy plasma FSH increased from 5.96 ± 1.02 to 7.06 ± 1.05 ng/ml in F+ and from 1.67 ± 1.06 to 5.21 ± 0.66 ng/ml in ++ ewe lambs, suggesting a stronger negative feed-back effect exerted by the ovaries of Awassi lambs. At 15 weeks after ovariectomy FSH values were similar in Booroola-Awassi (18.28 ± 1.96 ng/ml) and Awassi (16.07 ± 0.70 ng/ml) lambs. Although the overall pattern of pituitary response to ovariectomy was similar in the F+ and ++ ewe lambs, Booroola-Awassi lambs had small ovaries (132.5 ± 24.9 mg) and follicular development did not proceed beyond the preantral stage in 3/4 animals, and Awassi lambs had large ovaries (600.0 ± 233.9 mg)(P < 0.05) with many preantral and antral follicles. The present results suggest that (1) the elevated plasma FSH concentration between 3 and 6 weeks of age in Booroola-Awassi compared to Awassi ewe lambs might be due to (a) greater responsiveness of the F+ pituitary to GnRH and (b) reduced ovarian suppression of FSH release and (2) the ovaries of Booroola-Awassi lambs, although lacking antral follicles, secrete a factor that controls FSH values. We suggest that differences between the two genotypes can be attributed to the F gene or to other minor genes that came from the Booroola-Merino sires used to create the Booroola-Awassi progeny.

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