The Effect of Injection of GnRH Dissolved in Aluminum Hydroxide Gel Nanoparticles or Propyleneglycol on Estrus Synchronization, Ovulation Induction and Fertility Outcome after Artificial Insemination in Mehraban Ewes

The banning of equine chorionic gonadotropin (eCG) application for estrus synchronization by ethics committee for protection of animal rights, has caused the development of alternative protocols. One of the alternative protocols based on a short-term progesterone treatment and single dose injection of GnRH after termination of progesterone treatment. Half-life of GnRH is very short and it is rapidly degraded by peptidases and cleared by glomerular filtration. One of the suggested approaches is to prolong the action of GnRH and protect it against peptidases. Propyleneglycol and aluminum-hydroxide-gel nanoparticles absorb protein compounds and reduce their release rate. Therefore, the aim of this study was to compare the effect of GnRH dissolved in aluminum-hydroxide-gel nanoparticles or propyleneglycol on estrus synchronization, ovulation induction and fertility outcome after artificial insemination in Mehraban ewes.

In the breeding season total of 67 non-pregnant ewes (with weight average of 57.72±5.33 Kg, aged 2-4 years and BCS 3-3.5) were selected and treated by progesterone impregnated sponge for a 7 days period. All of ewes were received 5 mg PGF2α (Dynoprost) with sponge removal and were divided into four treatments, randomly. Each ewe in T1 was received 400 IU eCG (i.m) immediately after removing the sponge. Ewes in T2 and T3 were received 50 µg of GnRH (s.c) dissolved in aluminum-hydroxide-gel and propyleneglycol 36 h after removing the sponge, respectively. Each ewe in T4 was received 50 µg of GnRH (i.m) dissolved in distilled water 56 h after removing the sponge. All of the ewes were inseminated laparoscopically at 56 h after removing the sponge. During insemination, ewes with estrus signs were determined and uterine status were scored by uterine tone. Blood plasma estradiol (E2) concentration was evaluated at 36 and 56 after removing the sponge. Ovulation rate and plasma progesterone (P4) concentration was measured 11 days after insemination. Conception rate, fecundity and prolificacy were calculated after parturition.

Percentage of estrus, estrus quality, occurrence of ovulation, ovulation rate, and plasma P4 concentration were similar among groups. Plasma E2 concentration in T1 was significantly higher 36 after removing the sponge (P<0.05) but, it was similar among groups at 56 after removing the sponge. Conception rate with regards to ovulated ewes was higher in T3 compared to T2 (P<0.05). Conception rate with regards to inseminated ewes, lambing rate and fecundity were higher in T3 compared to other groups although these differences were not statistically significant.

Slowing and extending the release of GnRH by dissolving in propyleneglycol or aluminum-hydroxide-gel nanoparticles induces estrus and ovulation similar to eCG. However, propyleneglycol has better efficiency in synchronizing the animals for artificial insemination.