The winnings of a horse consist of its gross winnings. Winnings during the year shall include all prizes from the first of January preceding the time appointed for the start and include races in any country, and include walkover purses. Winning of a fixed sum means winning it in any one race unless otherwise specified in the conditions of the race. Foreign winnings shall be estimated on the basis of the normal rate of exchange on the day of winning. Winnings in Canada when such winnings are expressed in dollars shall not be considered as foreign winnings.