Fertility management of bulls to improve beef cattle productivity.

Global demand for animal proteins is increasing, necessitating increased efficiency of global food production. Improving reproductive efficiency of beef cattle, especially bull fertility, is particularly critical, as one bull can breed thousands of females (by artificial insemination). Identifying the genetic basis of male reproductive traits that influence male and female fertility, and using this information for selection, would improve herd fertility. Early-life selection of elite bulls by genomic approaches and feeding them to optimize postpubertal reproductive potential are essential for maximizing profitability. Traditional bull breeding soundness evaluation, or systematic analysis of frozen semen, eliminates bulls or semen samples that are grossly abnormal. However, semen samples classified as satisfactory on the basis of traditional approaches differ in fertility. Advanced sperm function assays developed for assessing compensatory and noncompensatory (submicroscopic) sperm traits can predict such variations in bull fertility. New knowledge on epigenetic modulations of sperm DNA, messenger RNA, and proteins is fundamental to refine and expand sperm function assays. Sexed semen, plus advanced reproductive technologies (e.g., ovum pickup and in vitro production of embryos) can maximize the efficiency of beef cattle production. This review is focused on genetic considerations for bull selection, physiology of reproductive development, breeding soundness evaluation, recent advances in assessing frozen semen, and existing and emerging uses of sexed semen in beef cattle production.