i agree with most comments here. it all has to do with the time you have on hand. my vet has routinely told me the Lut is essentially ineffective for less than 10 days, so to wait atleast 10-12 days so that time and drugs are not wasted. the thing is if you give her a shot of lut at 10 days to kick out an unwanted pregnancy, then my paranoia/gut instict would tell me to wait one full cycle to rebreed her (i.e. wait 10 days -> lut -> she aborts-> she cleans-> she recycles -> wait a full cycle -> then rebreed her. may cost you on the order of 40 or more days.