Smaller doses of gonadorelin (25mcg and 100mcg) were shown to be only partially effective (100mcg) or incapable (25mcg) of ovulating a luteal phase DF (Mihm et al. 1998).
The synchronised incidence of ovulation was only 68% in cycling cows as reported by Cartmill et al., (2001) when a 100mcg gonadorelin dose was used in Ovsynch protocol. Simultaneously however Vasconcelos et al., (1999) and Fricke et al. (1998) showed comparable results in terms of ovulation induction rates when low and standard dose of gonadorelin were used. However, some recent studies indicated that many of the ovulations induced with the lower gonadorelin dose may not result in normal LC formation. This in turn would have a clear detrimental effect on subsequent pregnancy maintenance and pregnancy rates in treated cows.
Cordoba and Fricke (2002) and Shephard (2002) reported an increased incidence of short lcycles occurring in cows treated with Ovsynch protocol using a dose of 50mg or 100mcg of gonadorelin, indicative for a shortened luteal phase and failure of conception. These short cycles occurred in cycling and anoestrus cows. This would indicate that the abnormal CL formation was most likely associated with both the injection of the lower dose of GnRH having limited effectiveness on follicle atresia, ovulation and CL development.