Use of melengestrol acetate and gonadotropins to induce fertile estrus in seasonally anestrous ewes

Abstract

Ewes of three genotypes (Hampshire, n = 59; Rambouillet, n = 36; crossbred, n = 57) were used to determine the efficiency of melengestrol acetate (MGA) and(or) PG-600 (a combination of pregnant mare's serum gonadotropin and human chorionic gonadotropin) in inducing fertile estrus in seasonally anestrus ewes. Ewes were assigned randomly, within genotype, to treatments in a 2 x 2 factorial arrangement. Treatments were control, .125 mg of MGA given twice per day for 9 d (MGA), a single 5-mL injection of PG-600 (PG-600), and the combination of treatments MGA and PG-600 (MGA/PG-600). Feeding of MGA began on May 14, 1990, and ended on May 23. Injections of PG-600 were given immediately after the last feeding of MGA or vehicle on May 23. All ewes were exposed to fertile, brisket-painted rams on May 24 (d 0) for 40 d. Ewes were checked for estrus twice daily for 9 d. Laparoscopy was performed, to assess ovulation rate (OR), on d 6 for ewes that were not detected in estrus and on d 12 for ewes that exhibited estrus. Percentage of ewes mated was increased by MGA (P less than .001). Ovulation rate of ewes exposed to rams was increased by PG-600 (P less than .01) and this effect was enhanced by MGA (P less than .05), whereas MGA alone tended to decrease OR (P less than .10). Melengestrol acetate decreased the interval to lambing by 6.5 d (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of short- and long-term administration of Melengestrol acetate on estrus activity and reproductive performance of nulliparous Barki ewes

“…In this study, prolificacy rate (number of lambs born/number of ewes lambing) did not different among groups which were 1.0 in the three groups and therefore the use of PMSG had no effects on increasing lambs born. This opinion is consistent with what Safranski et al (1992) reported, the number of lambs born per ewe lambing (prolificacy rate) was not different among treatments or genotypes. Consequently, the advantage that was obtained in ovulation rate through the use of PG-600 was not realized at lambing, although the number of luteal structures increased when PG-600 was injected on the last day of feeding MGA, the number of lambs born per ewe was not significantly affected.…”

“…Our results of lambing rate were higher than those obtained in control, MGA and MGA+PG 600 groups (14.8, 40.5 and 41.2%, respectively) according to Safranski et al (1992). But close to those obtained by (Windorski et al, 2008) who found that lambing rate in Rambouillet ewes was 80.4, 77.8 and 80.4% in control, MGA and MGA+PG-600, respectively.…”

“…Among the various methods or biotechnologies, which can be employed to control the reproductive cycle of the ewes is the use of synthetic progestins, like melengestrol acetate (MGA), which represents an ideal choice for this type of production in rural areas, where the farmers do not have the economic resource and sufficient technology (Álvarez and Ducoing, 2005). MGA is a low cost product, easy to administer (can be mixed with feed) and does not cause abortion (Salas et al, 2011).The percentage of ewes lambing after treatment with MGA has been reported to range from 25 to 85%, and appeared to depend on ewe breed (Safranski et al, 1992), length of treatment or length of breeding period (Powell et al, 1996), or use in combination with gonadotropins (Morrical et al, 1995).…”

Efficacy of various five-day estrous synchronization protocols in sheep

“…600 only, had significantly reduced mating rates (6.6%) when compared to ewes receiving both MGA and P.G. 600 (69.8%, Safranski et al, 1992). Ovulation rate can be increased through the administration of P.G.…”

“…600. Safranski et al (1992) documented that P.G. 600 when coupled with an MGA treatment lasting 10 d had no beneficial effects on conception rate and number of lambs born per ewe.…”