Co-Authors:
Gootwine, E., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel
Bor, A., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel
Braw-Tal, R., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, P.O. Box 6, Bet Dagan 50-250, Israel
Abstract:
Tonic plasma FSH levels at 4, 6 and 8 weeks of age were determined in 32 Finn × Awassi, 36 Assaf (East-Friesian × Awassi) and 23 Awassi ewe lambs. The prolificacy (No. of lambs born/ ewe lambed) of these genotypes is 1.85, 1.55 and 1.20, respectively. FSH plasma levels (ng/ml, mean ± s.e.m.) at 4 weeks were 4.1 ± 0.4, 2.8 ± 0.3 and 1.7 ± 0.4; at 6 weeks, 4.5 ± 0.5, 2.3 ± 0.5 and 1.9 ± 0.6; and at 8 weeks, 3.1 ± 0.3, 2.1 ± 0.3 and 3.3 ± 0.4, for the Finn × Awassi, Assaf, and Awassi genotypes, respectively. FSH levels differed (P < 0.01) among the three genotypes at 4 and at 6 weeks. While FSH levels in the Finn × Awassi and in the Assaf declined during the studied period, in the Awassi ewe lambs a significant increase (P < 0.05) in FSH plasma levels was detected. Following administration of 400 IU PMSG at 20 weeks of age 18/22 (82%) of the Finn × Awassi, 27/34 (79%) of the Assaf and 17/28 (61%) of the Awassi ewe lambs ovulated. Ovulation rates (number of corpora lutea/ewe lamb ovulating) were 1.78 ± 0.22, 1.41 ± 0.12 and 1.23 ± 0.10 for the three genotypes, respectively. Our results were interpreted to indicate that the higher prolificacy in the Awassi crosses compared with the pure Awassi breed is followed by higher plasma FSH levels at 4-6 weeks of age and by greater ovarian sensitivity to gonadotropins at 5 months of age. © 1989.
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