What gives better results GnRH at 12d post AI or hCG at 4-6d post AI?
It is very difficult to give a direct answer. Both treatments were shown to give a substantial improvement in pregnancy rates at certain conditions and in certain herds. In general it is thought that in case of cows that can be classifies as early repeats (new oestrus <21d post AI) better results are obtained with hCG. Cows that can be called the late repeats (new oestrus 35-40d post AI) generally seem to benefit more from GnRH treatment at mid-cycle.
