The boar's retention in the herd is largely dependent on the size and the subsequent maintenance of its skeleton. This is largely influenced by genetics, but it is also dependent upon a sound nutritional program during the boar's developmental period. Structural soundness at sexual maturation is essential for optimum breeding performance and subsequent semen production. Grouping young boars during the pre-pubertal developmental period results in fewer feet and leg problems and has also been shown to improve sexual behavior. Although bone structure is an inherited trait, adequate dietary macro- and micromineral concentrations must be provided for proper bone development.
Boars have bones of a greater length and diameter than either gilts or barrows.
An increased dietary calcium and phosphorous concentration is therefore necessary for the higher bone mass and bone-mineral content, both of which are essential in withstanding breeding stresses on the legs. An adequate dietary vitamin D concentration will ensure optimum absorption and utilization of calcium and phosphorus. However, an excessive amount of vitamin D may cause calcification of connective tissue and decalcification of bone tissue. Sexual maturation in the boar is a gradual process, with sexual activity and sperm production starting at approximately four months of age. Semen collected as early as five months of age is at a low volume and contains a high proportion of immature and abnormal sperm.