Abstract
The objective of this study was to verify the effects of GnRH on ovulation and pregnancy of ewes subjected to a short-term synchronization of estrus. Santa Ines and crossbred Santa Ines/Dorper ewes received 60 mg MAP sponges during 6 days plus 300 IU eCG and 30 μg d-cloprostenol 24 h prior to sponge withdrawal (SW). Ewes were assigned to receive 0.9% NaCl solution (T control ; n = 32) or 25 μg GnRH (licerelin, T GnRH ; n = 34) 24 hours after SW. Each group was assigned to intrauterine insemination by laparoscopy (n = 25) or to natural mating (n = 41). Artificial insemination was performed with a single dose of fresh semen. For controlled mating, females were exposed to males 12, 24, 36 and 48 hours after SW. Ten females per treatment were subjected to transrectal ultrasound examination at 12-hour intervals (SW to 60 hours after). Estrous response (100.0% vs 95.2%), interval from SW to estrus (32.9±7.4 vs 29.8±6.9 hours), estrous length (37.4±9.0 vs 31.5±10.4 hours), pregnancy rates (57.0% vs 41.0%), ovulation rate (100.0% vs 90.0%), number of ovulations/ewe (1.1±0.3 vs 1.2±0.4), maximum follicular diameter (6.4±0.7 vs 6.1±0.6 mm), interval from SW to ovulation (59.1±3.5 vs 58.4±3.5 hours) did not differ between T control and T GnRH , respectively. Administration of GnRH 24 hours after SW does not improve ovulation or pregnancy rate in estrous synchronization in ewes.
Highlights
The use of reproductive biotechnologies associated to induction of a synchronized estrus is a valuable tool that favors productivity, offers homogeneous groups of animals and allows the constancy of products offered irrespective to season
Many authors have successfully used Gonadotropin-releasing hormone (GnRH) treatment in combination with progestagens, gonadotropins and prostaglandin (Husein & Kridli, 2003; Reyna et al, 2007; Rubianes et al, 2007; Beilby et al, 2009) or prostaglandin only (Murdoch & Van Kirk, 1998; Deligiannis et al, 2005); and it is well known that all preovulatory events and ovulation can be induced in seasonally anovular ewes if they are treated with multiple injections of GnRH
Reyna et al (2007) confirmed ovulation in 100% of Merino ewes during the breeding season using sponges impregnated with 30 mg Flugestone Acetate for 12 days plus an intramuscular injection of 400 IU pregnant mare serumgonadotrophin (PMSG) at sponge withdrawal (SW) and 40 μg of a synthetic GnRH given at 36 h after SW
Summary
The use of reproductive biotechnologies associated to induction of a synchronized estrus is a valuable tool that favors productivity, offers homogeneous groups of animals and allows the constancy of products offered irrespective to season. The Gonadotropin-releasing hormone (GnRH) is the key neuro-peptide controlling reproductive function in all vertebrate species. In females of spontaneously ovulating species, including sheep, ovarian steroids secreted by maturing ovarian follicles control a pulsatile pattern of GnRH release from the hypothalamus that, in turn, stimulates a preovulat ory secretion of luteinizing hormone (LH) by the anterior pituitary gland (Bakker & Baum, 2000). Many authors have successfully used GnRH treatment in combination with progestagens, gonadotropins and prostaglandin (Husein & Kridli, 2003; Reyna et al, 2007; Rubianes et al, 2007; Beilby et al, 2009) or prostaglandin only (Murdoch & Van Kirk, 1998; Deligiannis et al, 2005); and it is well known that all preovulatory events and ovulation can be induced in seasonally anovular ewes if they are treated with multiple injections of GnRH. It has been demonstrated that exogenous GnRH treatment immediately after artificial insemination increases the multiple birth rate in synchronized ewes (Türk et al, 2008)
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