As the boar matures, semen volume and sperm numbers increase. Larger testes produce more sperm, and if boars are fed insufficient energy, testes size will be reduced. If protein intake is low, boar libido, semen volume, and sperm output will also be reduced.
Sow gestation diets are generally satisfactory for meeting the needs of the mature boar. An additional amount of feed (i.e., energy) must, however, be provided to maintain the boar, particularly during the winter months in cold housing environments. Inadequate feed consumption will result in a low energy intake and can affect semen production.
Mature skeletal size in the boar is reached at approximately one to two years of age. Maintaining structural soundness in mature boars is critical, particularly in pen mating conditions. If the boar is fed a diet inadequate in calcium and phosphorous, the bone structure will continue to grow, but the bones will not mineralize properly, and weakened bones and joints may occur. It is therefore essential that an adequate concentration of dietary vitamins and minerals be provided when the boar is fed a restricted quantity of feed. Boars used in pen-mating situations need to be heavier than boars used for hand mating or for artificial insemination. Boars used for pen mating also need to be heavier than the females they are to breed. The behavioral interactions of animals within the pen increases the rigors of mating and the potential number of leg and foot problems that can occur.