Modifications of the Ov-Synch Protocol
One of the simplest modifications of the classical Ovsynch system used is so called Co-Synch protocol. The second injection of GnRH and AI are performed at the same time e.i. 48h after the treatment with prostaglandins (Small et al., 2000).
Although most research using the Cosynch protocol has focused on a 48h interval between prostaglandin injection and GnRH+AI, intervals to oestrus following the treatment indicates a 60-64h interval post PGF as used in Ovsynch, would more closely match appropriate insemination timing for beef (Geary et al., 2000; Stevenson et al., 2000; DeJarnette et al., 2001a) and dairy (DeJarnette et al., 2001b)
Reported results have been comparable or only slightly lower than obtained with the Ovsynch while the handling of animals is reduced (DeJarnette et al., 2003).
A presynchronisation protocol prior to implementation of Ovsynch protocol was developed by giving one or two injections of PGF 14 days apart, with the second injection given 12 days prior to the first GnRH of the Ovsynch protocol.
The Presynch-Ovsynch protocol increased pregnancy rates by 18% (25% to 43%) in lactating cyclic cows as reported by Moreira et al. (2001).
Post partum presynchronisation with GnRH can also be performed at 7 days before the actual Ovsynch protocol. This approach also has the advantage of being potentially effective in both cyclic and anoestrus cows (Thompson et al., 1999; Stevenson et al., 2000).
Combination of prostaglandin and GnRH as a presynchronisation treatement proceeding the classical Ovsynch or Cosynch protocol were also tried with various success rates usually resulting however in some improvement of pregnancy rates to the final Ovsynch AI (DeJarnette et al., 2003).
Heat Synch protocol, more widely used in the US involves replacement of the second GnRH injection with oestradiol esters (Geary et al., 2000; Stevenson et al., 2004).
Enthusiasts of this system indicate that oestradiol synchronises the ovulation of dominant follicle more precisely and increases behavioural demonstration of oestrus in treated cows. With growing considerations about the use of estrogens in food producing animals and practically no possibility of use in Europe, the geographical spread of this system is.