** Surge frequency varies between species, dependent on the length of their [[Female_Reproductive_Tract_-Oestrous_Cycle_-_Anatomy_%26_Physiology|oestrous cycles]]. | ** Surge frequency varies between species, dependent on the length of their [[Female_Reproductive_Tract_-Oestrous_Cycle_-_Anatomy_%26_Physiology|oestrous cycles]]. |