Reproductive performance of hormonally-treated anestrous Awassi ewes
Anim Reprod, vol.3, n3, p.347-352, 2006
An experiment was conducted to evaluate the effect of administering melatonin alone or in combination with a progestagen and equine chorionic gonadotropin (eCG) on reproductive performance and inducing estrus in Awassi ewes. Fifty-nine, multiparous, winter-lambing Awassi ewes, ranging from 3 to 6 years of age, were randomly assigned during the late anestrous period (Spring) to one of six treatment groups as follows: no treatment (CON; n = 9), melatonin implant only (M; n = 10), flourogestone acetate (FGA) sponge only (P; n = 10), melatonin implant plus FGA sponge (MP; n = 10), FGA sponge plus eCG (PE; n = 10), or melatonin implant plus FGA sponge and eCG (MPE; n = 10). Ewes in P, MP, PE, and MPE groups were fitted with intravaginal progestagen sponges for 14 days. On the day of sponge removal, each ewe in the PE and MPE groups received a 600-IU dose of eCG. Ewes in the M, MP, and MPE groups received subcutaneous melatonin implants (18 mg melatonin) 36 days before sponge insertion. Estrus expression was lower (P < 0.001) in the CON and M groups than in the remaining groups. The interval to onset of estrus was shorter (P < 0.001) in the PE and MPE ewes compared to ewes in the remaining treatments. Ewes in the P, PE, and MPE groups lambed earlier (P < 0.01) than those in the remaining groups. Fecundity during the induced estrus was greater (P < 0.05) in the PE and MPE groups than the CON, M, and MP groups. The overall lambing rate during the two estrous cycles following sponge removal was similar among all groups. The overall prolificacy and litter birth weight were greater (P < 0.05) in the groups that received eCG. Results of the present study indicate that melatonin alone failed to induce estrus in a manner similar to FGA-primed ewes. Melatonin administration in combination with FGA and eCG can be successfully applied to improve induced estrus reproductive parameters in sheep.
Awassi sheep, eCG, estrus, FGA sponges, melatonin