Feed represents a large portion of input costs for dairy operations. Decreasing the feed consumed, measured here as dry matter intake (DMI), would therefore be advantageous to producers. However, this decrease could result in cows that do not supply the necessary energy to maintain high production, growth, and reproduction. Measures of feed efficiency try to capture important energy expenditures to ensure that cows consume less while maintaining production. Feed efficiency in this study is measured in residual feed intake (RFI), which is calculated as the difference between DMI and expected DMI based on production and growth measures. However, the RFI model does not capture the energy stores required for reproduction; therefore, selection for RFI may lead to reduced reproductive performance. In this thesis, I explored the phenotypic and genetic relationships between RFI, DMI, and reproductive performance as measured by number of services (NS), days open (DO), and days to first calving (DFC). First, ANOVA tests and phenotypic correlations determined the phenotypic relationship between the traits. Then, heritability and genetic correlations were used to estimate the genetic parameters. Phenotypically, results indicated mixed relationships between traits. Heritability estimates were low for reproductive traits and moderate for DMI and RFI. There was no unfavorable genetic relationship between DMI or RFI with any of the reproductive traits. Therefore, neither selection for DMI nor RFI will unfavorably impact reproduction. / Master of Science / Dairy cows consume significant resources in the form of feed. Decreasing the feed consumed, measured here as dry matter intake (DMI), would therefore be advantageous to producers and consumers. However, this decrease could result in cows that do not supply the necessary energy to maintain high production, growth, and reproduction. Measures of feed efficiency try to capture important energy expenditures to ensure that cows consume less while maintaining production. Feed efficiency in this study is measured in residual feed intake (RFI), which is calculated as the difference between DMI and expected DMI based on production and growth measures. However, the RFI model does not capture the energy stores required for reproduction; therefore, selection for RFI may lead to reduced reproductive performance. In this thesis, I explored the phenotypic and genetic relationships between RFI, DMI, and reproductive performance as measured by number of services, days open, and days to first calving. First, ANOVA tests and phenotypic correlations determined the phenotypic relationship between the traits. Then, heritability and genetic correlations were used to estimate the genetic relationship between traits. Heritability estimates were low for reproductive traits and moderate for DMI and RFI. There was no unfavorable genetic relationship between DMI or RFI with any of the reproductive traits. Therefore, neither selection for DMI nor RFI will unfavorably impact reproduction.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/77700 |
| Date | 22 May 2017 |
| Creators | Cayford, Eleonor Marilyn |
| Contributors | Dairy Science, Cockrum, Rebecca R., Hanigan, Mark 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/ |
Page generated in 0.0018 seconds