Estrous synchronization (ES) protocols enhances profitability of beef cow-calf operations by improving percentage of cows pregnant early in the breeding season and increasing kg of calf weaned per cow exposed. Many factors, however, influence the fertility of cattle enrolled to ES protocols. The overall goal of this work was to determine the influences of estrus expression and timing of artificial insemination (AI), as well as temperament on fertility of Bos taurus beef females exposed to ES protocols. Multiparous cows (n = 1,676) were enrolled to the 7-d CO-Synch+ Controlled internal drug releasing device (CIDR) protocol and cows expressing estrus were inseminated. Cows not expressing estrus received a gonadotropin-releasing hormone injection and were either inseminated immediately or delayed by 8 hours. Pregnancy rates were greater for cows expressing estrus to the protocol. Delaying AI for 8 hours in cows that failed to express estrus did not improve pregnancy rates. The effects of temperament on fertility of beef heifers enrolled to the 7-d CO-Synch+CIDR protocol were investigated. Heifers (n = 297) had temperament assessed by chute score and exit velocity, and classified as adequate or excitable. Hair and blood were collected for cortisol evaluation. Pregnancy rates were greater for adequate temperament heifers. Circulating cortisol concentrations were greater for excitable heifers, and overall plasma and hair cortisol concentrations were reduced from the start of the protocol to the end. Heifers with adequate temperament have improved fertility and ES protocols acclimated heifers and reduced plasma and hair cortisol concentrations due to handling. / Master of Science / Infertility is a major issue that affects profitability of beef cow-calf producers. Estrous synchronization (ES) protocols are a tool that allow artificial insemination (AI) without estrus detection and increases the proportion of females pregnant at the start of the breeding season, providing a strategy to improve profitability. However, females enrolled in the ES protocol and that fail to express estrus have reduced pregnancy rates when compared to females expressing estrus. Furthermore, beef females with excitable temperament have reduced fertility when compared to females with adequate temperament. The effects of delaying insemination to 8 hours post injection of gonadotropin-releasing hormone for animals failing to express estrus during ES were determined in beef multiparous cows. Cows expressing estrus had greater pregnancy rates compared to cows not expressing estrus, and delayed insemination did not improve pregnancy rates. To determine the effects of temperament on fertility heifers were enrolled in an ES protocol and had temperament determined as adequate or excitable based on chute score and exit velocity. Hair and blood samples were collected for cortisol evaluation. Excitable heifers had reduced pregnancy rates and greater circulating cortisol concentrations, but hair cortisol did not differ between temperaments. Overall cortisol profiles indicate that heifers became acclimated to handling during ES protocol. Development of ES that maximizes estrus expression prior to AI and selection of cattle with adequated temperament can enhance profitability of cow-calf operations.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/86484 |
| Date | 20 December 2018 |
| Creators | Wege Dias, Nicholas |
| Contributors | Animal and Poultry Sciences, Mercadante, Vitor R. G., Ealy, Alan D., Rhoads, Michelle |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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