Why should gilts be mated on their second or third estrous instead of their first?

Mating gilts on their second or third estrous cycle instead of the first is primarily done to increase litter size. When gilts are bred during their first estrous cycle, they may not be psychologically or physically mature enough to support a successful pregnancy. This lack of maturity can lead to issues such as lower conception rates and smaller litter sizes. By waiting until the second or third cycle, the gilt's reproductive system has had more time to develop, increasing the chances of a more successful breeding outcome, which can result in larger litters.

Additionally, maturing through these cycles allows gilts to build up their body condition and overall health, effectively preparing them for the demands of pregnancy and lactation.