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Invited Review: Focusing on bull management and puberty attainment in the genomic era1

      ABSTRACT

      An increased emphasis on decreasing generation intervals due to genomic selection has greatly influenced the management of bulls at AI organizations. Before genomics, the genetic value of an AI sire was determined by examining the phenotype and production traits of his daughters (i.e., proofs), and the minimum age at which sires were debuted to the industry (proven) was approximately 4 to 4.5 yr of age. Currently, one decade after the introduction of genomics to the industry, unproven, genomically tested sires between 1.5 and 4 yr of age account for half or more of AI unit sales for most major AI organizations. Accordingly, bulls destined for AI use receive optimum care and nutrition from birth, and there is a renewed interest in examining endocrine modulation’s role in puberty attainment and testicular development in bulls. In practice, hastening puberty in bulls can be used concurrently with modern techniques of oocyte collection in prepubertal heifers to minimize generation intervals in cattle, thus increasing the rate of genetic advancement. The use of young genomic bulls will likely increase or remain stable in the future, and accordingly, AI organizations will continue to focus on optimizing bull management to ensure top tier genetics are available to the industry.

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