אסיף מאגר המחקר החקלאי

Reproductive performance of Assaf and Booroola-Assaf crossbred ewes and its association with plasma FSH levels and induced ovulation rate measured at prepuberty

Year:

1993

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Volume :

31

Co-Authors:

Gootwine, E., Institute of Animal Science, Agricultural Research Organization (A.R.O.), The Volcani Center, Bet Dagan, 50250, Israel
Braw-Tal, R., Institute of Animal Science, Agricultural Research Organization (A.R.O.), The Volcani Center, Bet Dagan, 50250, Israel
Shalhevet, D., Institute of Animal Science, Agricultural Research Organization (A.R.O.), The Volcani Center, Bet Dagan, 50250, Israel
Bor, A., Institute of Animal Science, Agricultural Research Organization (A.R.O.), The Volcani Center, Bet Dagan, 50250, Israel
Zenou, A., Institute of Animal Science, Agricultural Research Organization (A.R.O.), The Volcani Center, Bet Dagan, 50250, Israel

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Abstract:

Reproductive performances of Assaf and Booroola-Assaf crossbred ewes were compared. Assaf were non-carriers while Booroola-Assaf (F1) and about half of 75% Assaf-25% Booroola (BClAs) were heterozygous for a major gene influencing the ovulation rate (FecB). Mean ovulation rate (corpora lutea per ewe ovulating) increased by 1.2 and prolificacy (lambs per ewe per lambing) by 0.8 in F1 ewes as compared with Assaf, while values in BC1As were intermediate. Three or more ovulations were observed in 90% of F1 but only in 11% cyclic Assaf ewes. Plasma follicle-stimulating hormone (FSH) levels between 3 and 9 weeks of age were significantly higher in F1 ewe lambs than in Assaf. At 4 weeks of age FSH concentrations were (geometric means) 4.58 ng ml-1 and 2.68 ng ml-1 in F1 and Assaf, respectively. High levels of FSH (more than 6 ng ml-1) were found in 35% F1 and 42% BC1B, but only in 6% Assaf ewe lambs. Following administration of 400 IU pregnant mare serum gonadotrophin (PMSG) at 20 weeks of age, most ewe lambs ovulated, but the ovulation rate differed between the genotypes, being high in F1 (2.9) and low in Assaf (1.4), with BC1As having an intermediate value (2.1). Higher prolificacy was found in BC1As ewes which had three or more induced ovulations at 20 weeks of age, when compared with BC1As ewes which had two or less. Our results show that the prolificacy of the Assaf ewes can be improved significantly by the introduction of the FecB allele of the Booroola-Merino. An incidence of at least 3 corpora lutea per ewe can be used to identify individual FecB carriers. At prepuberty, an ovulation rate of three or more following PMSG treatment may be useful for identification of FecB carriers among Booroola-Assaf crosses, while the prepubertal plasma FSH concentration may be of only limited use for differentiating between the individuals. The possibility that the FecB allele is operating in a multiplicative rather than an additive fashion is discussed. © 1993.

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