Quadratic fitting was used to regress semen characteristics of 1441 samples consisting of 12-month collection from 58 Duroc boars against animal age varied from 10 to 80 months. Data was divided into two groups of cool (14.0-22.7 degrees C, RH 81.5%) and hot season (22.9-29.9 degrees C, RH 86.6%), to test effects of age, season and their interactions. Results revealed that young boars of around 1 year old could endure the hot season. The endurance gradually diminished as animals grew. In the hot season animals exhibited peak performance at age around 33 month and it remained for 1 month, while cool-season kept boars could last for 48 months from 16 months old onward. The reproductive longevity should be 51 month in a subtropical environment and it may extend to 70 month if heat stress can be avoided. The estimated total sperm contribution of a Duroc boar would be 1.8 times more when kept below 22 degrees C than in a natural subtropical environment. It is concluded that to maintain Duroc boars as semen donor to at least 4 years of age is feasible in a subtropical environment and boar longevity could reach 6 years old if well kept in a temperate region.
