I had a set of yearling crossbred heifers that I began to ai back in Dec. They are all clubby bred and are mostly simmy x maine. Of the ten, two of them cycled normally and bred on the first service. I continued to observe them for heat with none detected. In Jan. I gave the remaining eight a shot of Lut. and still no heat. In Feb. I set them up with GnRH and Lut. and timed bred them and turned them out with a clean up bull. I preg checked them last week and none of them are bred. They will all be coming two years old in Sept. All were developed the same and fed the same as a group. What could be going on here and what can I do to get them bred?