The studies in this thesis examine two important areas of reproductive performance. Firstly, the topic of improving boar reproductive performance by means of nutritional supplementation is explored. Supplementation of a boar's diet with high levels of selenium, or high levels of a vitamin-mineral combination did not result in improvements in semen quantity or quality. Secondly, the method of insemination was studied. A breeding trial was conducted on a commercial farm, where a modified insemination technique (MIT) was compared to the traditional breeding method. The MIT group was bred using 3.5 billion sperm in a 42 ml volume, following by a flush of 24 ml of extender. There was a not statistically significant difference in the two groups but the MIT group tended to have numerically better reproductive performance compared to the traditional insemination method. More research is required to verify whether a modified technique might be of value on certain farms where reproductive performance is low. 'Keywords.' boar nutrition, selenium, semen evaluation, artificial insemination