Increased production of sheep embryos following superovulation of Merino ewes with a combination of pregnant mare serum gonadotrophin and follicle stimulating hormone

Abstract

In a factorially designed experiment (N = 321), 0, 800 or 1600 I.U. pregnant mare serum gonadotrophin (PMSG) were administered in combination with 0, 12 or 18 mg follicle stimulating hormone (FSH-P) to superovulate Merino ewes in autumn and spring. A moderate dose of PMSG (800 I.U.) in conjunction with 12 or 18 mg FSH-P increased the ovulation rate above that observed when FSH-P was used alone. This was accomplished by (i) increasing the proportion of ewes that exhibited a superovulatory response (greater than 3 corpora lutea (CL) or persistent large follicles (LF): 69/70 (99%) v. 55/74 (74%), P less than 0.001), and (ii) in those ewes that exhibited a superovulatory response, by an additive effect of exogenous gonadotrophin (14.8 +/- 0.9 CL (69) v. 11.3 +/- 0.9 CL (55), P less than 0.01) without increasing the incidence of LF. The use of 1600 I.U. PMSG in conjunction with 12 or 18 mg FSH-P was characterized by an increase in the number of LF and, in comparison with 800 I.U. PMSG, a reduction in ovulation rate. Season had no effect on the numbers of CL, but total ovarian response (CL + LF) was higher in autumn than in spring (P less than 0.01), because of a greater incidence of LF (P less than 0.001). The proportion of ewes with regressed CL was higher in autumn than in spring (53/143 (37%) v. 32/156 (21%), P less than 0.01), and increased with increased dose of gonadotrophin. Furthermore, a nutritional component to the incidence of ewes with regressed CL was suggested by the observation that the mean concentration of plasma glucose was higher for ewes with normal CL than for ewes with regressed CL (P less than 0.05). Rates of ova or embryo recovery, fertilization and embryo development generally declined with an increase in the incidence of LF as a result of increases in the dose of gonadotrophin and season of administration.

Incidence of Premature Luteal Regression in Ewes Superovulated with a Single Injection of Follicle-Stimulating Hormone Combined with Equine Chorionic Gonadotropin.

“…Similar results have been reported in ewes [10] and goats [11]. However, prematurely regressed CL has been observed in suprovulated ewes [12][13][14], cows [15] and goats [16][17][18]. Ryan et al [13] reported that the proportion of ewes that ovulated and subsequently had M chorionic gonadotropin (eCG) has been conventionally used for superovulation in ewes [1][2][3][4].…”

“…Premature luteal regression has been reported in superovulated ewes [12][13][14]22], and has impaired the yield of normal fertilized embryos. Jabbour et al [12] and Ryan et al [13] reported that more ewes had regressed CL in autumn (24% and 37%, respectively) than in spring (6% and 21%, respectively).…”

“…However, prematurely regressed CL has been observed in suprovulated ewes [12][13][14], cows [15] and goats [16][17][18]. Ryan et al [13] reported that the proportion of ewes that ovulated and subsequently had M chorionic gonadotropin (eCG) has been conventionally used for superovulation in ewes [1][2][3][4]. FSH has been administered by decreasing or constant doses in 6-8 injections with approximately 12 h interval due to the short half-life [1,5].…”

Effect of exogenous melatonin on the ovary, the embryo and the establishment of pregnancy in sheep

“…Inadequate luteal function has also been reported in superovulated ewes following oestrous synchronization using a dual prostaglandin injection treatment (Trounson et al, 1976;Schiewe et al, 1991). In embryo donor ewes, the incidence of premature luteal regression after a progestagen protocol and superovulation seems to be higher in the seasonal anoestrus than in the breeding season, even at temperate latitudes (Jabbour et al, 1991;Ryan et al, 1991). Corpora lutea from ewes undergoing premature luteolysis have a reduced population of small luteal cells compared to normal corpora lutea (Schiewe et al, 1991).…”

Short communication. In vitro embryo production can be modified by the previous ovarian response to a superovulatory treatment in sheep

“…In fact, early luteal regression is assumed as a failed response to superovulation and has also been reported by our group in both Rasa Aragonesa and Ojalada breeds (Forcada et al, 2000(Forcada et al, , 2006(Forcada et al, , 2011a, although always associated with multiple FSH injection protocols, not including eCG (Simonetti et al, 2008;Forcada et al, 2011b). This regression after superovulatory treatments seems to be related with a lack of progesterone priming before treatment, so that its incidence should be higher during anestrus (Ryan et al 1991). Some authors have indicated that a simplified superovulatory FSH protocol produced the higher percentage of premature CL regression (Riesenberg et al, 2001) with no eCG in the treatment.…”