This graph shows an increase in the referral of these cases during the winter months, which is consistent with cases of rank-related aggression between dogs in the family. The low points in April and August are consistent with the lower numbers of cases referred in these months. The data presented in this graph shows very little monthly or seasonal change. This graph follows a similar pattern to the graph published in the 1994 Annual Report. It is commonly believed that dogs experience oestrus cycles twice yearly, in the spring and again in the autumn.
Several studies indicate that dogs as a group cycle throughout the year.
160 cycles began in February whilst August had the fewest cycles with approximately 110. The level of activity seen in the early portion of the year was not equalled later in the year, but the time between October and January had more oestrus cycle activity than the relatively quiescent period between June and September. This finding agrees with the previously noted reports, in which proestrus was seen most commonly in February. Breeding seasons must depend on both genetic and management factors. Vt Med Assoc 1978.