| dc.description.abstract | Reproductive efficiency of beef females directly impacts the overall efficiency and profitability of cow-calf operations. By making use of reproductive management technologies, such as estrus synchronization, presynchronization, and sex-sorted semen, reproductive efficiency, and thus profitability of beef cattle production systems may be improved. Three experiments were performed to evaluate the effects of estrus intensity, and presynchronization and delayed fixed-time artificial insemination (TAI) on fertility in beef females. In experiment one, the impacts of estrus expression and intensity, assessed via physical activity, were evaluated on parameters associated with fertility in beef cows. Lactating, multiparous cows were classified as not expressing estrus, or expressing estrus with net physical activity greater or below the median. Expression of estrus during the 7-d CO-Synch + controlled internal drug release (CIDR) protocol increased (P < 0.01) pregnancy rates to TAI (PR/AI), whereas estrus intensity increased (P < 0.01) dominant follicle and corpus luteum dimensions but not PR/AI (P = 0.46). Experiment two was performed to determine the effects of presynchronization with prostaglandin F2α (PGF) and a CIDR insert in conjunction with delayed TAI on PR/AI in beef heifers. Heifers presynchronized with PGF and a CIDR insert had greater (P = 0.03) PR/AI than control heifers. Moreover, there was a tendency (P = 0.10) for greater PR/AI when heifers were presynchronized with PGF and had delayed TAI when compared to control heifers. Finally, experiment three was performed to determine whether delayed timing of TAI after presynchronization with PGF enhances PR/AI with sex-sorted semen. Pregnancy rates to TAI were greater (P < 0.04) when conventional semen was utilized as opposed to sex-sorted semen; however, the combination of PGF administration 7 d prior to the initiation of the 7- d CO-Synch + CIDR protocol and TAI at 72 h after CIDR removal succeeded in enhancing (P = 0.02) PR/AI with sex-sorted semen. Outcomes of these experiments will be utilized to develop strategies to improve reproductive efficiency in beef females. Furthermore, these results will be utilized to develop a decision aid tool that will assist beef cattle producers in their decision on whether or not to incorporate sex-sorted semen in their operations. | en |
