Bison reach sexual maturity at about 2 years of age. Furthermore, females must weigh a minimum of 700 pounds (275 kg) before the oestrous cycle begins. The heat period (or oestrous cycle) generally starts in July and ends in October. Ovulation will last two to three days. To pinpoint this critical period, the bull uses the Jacobson's organ, specifically designed for this function. During summer, you can observe the strange behaviour of the male activating this olfactory organ by curling its upper lip. This allows the male to determine if the female is in oestrus from the smell of its urine.

Before and after the rut period, the males will establish a hierarchical order that will determine the mating dominance. The age, the animal's weight, its conformation and personality will be leading factors in the conservation of this order when the oestrus cycle occurs, because the male will follow the ovulating female continually during these 2-3 critical days. To maintain its role with the bison cow, the male will literally have to drive away its fellow bulls. Considering the incessant male-female activity, added to the dominance contests, the dominant males will loose 70-90 kilos (150-200 pounds) during rutting season. In order to allow all the females to be sired, the male-female ratio should be one bull for 10-15 cows.

The gestation period lasts 270 to 290 days and births occur between April and July. Newborn calves are cinnamon or ochre in colour and they will retain this protective colour for the whole summer. The newborn blends into the forage rendering it completely imperceptible. Their weight at birth is approximately 18 to 32 kilos. One year later, the bison calf will weigh between 135 and 180 kilos.