The effect of GnRH is similar in small ruminant. For ovulation the effect will be same. For recruitment of follicular wave I have not seen any article. Synchronization effect is same.Only you have to give the injection according to size of the animals as within and between species there is large variation in adult weight.

Thank you Dr Mohantry,

actually, I compared between 3 regimes for estrus synchronization in sheep, namely (i) controlled internal drug releasing (CIDR)-eCG group, treated with

CIDR for 12 days and eCG at insert withdrawal, n = 13;

(ii) PGF2a-PGF2a group, treated with two PGF2a injections at

11 days interval, n = 14; and (iii) GnRH-PGF2a-GnRH

group, treated with GnRH, followed 5 days later with PGF2a

and 24 h later with a second GnRH, n = 16. Oestrus-mating

detection was carried out at 4 h intervals starting on day 0 [the

day of CIDR withdrawal (CIDR-eCG group), the day of

second PGF2a treatment (PGF2a-PGF2a group) and the day

of PGF2a treatment (GnRH-PGF2a-GnRH group)]. Ovarian

dynamics was monitored by ultrasound every 12 h beginning

on day 0 and continued for 4 days.

Results demonstrated that oestrus and

ovulation synchronization could be efficiently achieved in

Farafra ewes using either CIDR-eCG or PGF2a-PGF2a

regimes; however, the GnRH-PGF2a-GnRH treatment

induced a more spread oestrus and ovulation that may make

the protocol inadequate for timed artificial insemination. So, my question was about  the efficiency of GnRH in sheep

see: attached 

I think dose of GnRH and stages of estrus cycle or anestrus make all the difference in response to GnRH agonist. You have to standardize the dose first.

GnRH will cause and LH surge.  This will ovulate dominant follicles, if and only if they are present.  If present then it will be followed by a new wave emergence.  If absent then the GnRH / LH surge will have no effect.  If you cause ovulation then the follow up PGF to cause regression needs to be about 7 days later.  But if there are no healthy dominant follicles present at the GnRH injection then a GnRH-PGF-GnRH programme will have no effect.  In sheep progestagen pessaries work so well I am unclear why you would want to look at developing other strategies for oestrous synchronisation.

Hi Mark,

thank you very much for your explanation. This program (Ovsynch) is well function in cattle. I have had a trial to compare it with the well established  protocols (FGA sponge and CIDR). Estrus expression and fertility were lower for the ovsynch program. I think, the external GnRH is not working well for induction of ovulation as the case in cattle. 

Yes and that is likely due to stage of follicle growth at the time of GnRH.