Swine feed efficiency: Implications for swine behavior, physiology and welfare

The overall goal of this dissertation was to address how improving feed efficiency impacts swine welfare through two objectives: 1) assess how altering feeding behavior impacts pig feed efficiency of lean tissue gains and 2) evaluate how selection for altered feed efficiency impacts pig ability to respond to and cope with stressful events. The results of this dissertation identify a relationship between pig behavior and feed efficiency of lean tissue gains, and suggest that improving feed efficiency did not negatively impact pig welfare in regards to the ability to respond to stress.;Swine feed efficiency and welfare are interrelated and represent both producer goals and consumer concerns. Feed efficiency can be defined as the efficiency at which an animal utilizes dietary nutrients for maintenance and tissue accretion. Increasing swine feed efficiency of lean tissue gains is an important goal that is critical for improving sustainable pork production and profitability. In order to improve feed efficiency, a deeper understanding of the environmental and biological factors underlying feed efficiency is essential. It is also necessary to ensure that feed efficiency modifications do not negatively impact animal welfare, as concerns have specifically been raised in which genetic selection for and improvement in feed efficiency impacts how livestock cope with various forms of stress. Therefore, the overall goal of this dissertation was to address these concerns by evaluating how altering feed efficiency impacts swine welfare in regards to feeding behavior and the stress response. To address this goal, four research chapters (2-5) focused on the following objectives: 1) To assess how altering feeding behavior impacts grow-finish pig feed efficiency of lean tissue gains. 2) To evaluate how selection for altered feed efficiency impacts pig ability to respond to and cope with stressful events.;In the first research chapter (Chapter 2), we utilized commercial pigs to evaluate behavior and efficiency of lean tissue gains in pigs fed utilizing two divergent feeding patterns: twice daily feeding and ad libitum feed. Altering feeding regimen did not impact feed efficiency or behavioral expression of hunger. However, gilts fed twice daily had a lower fat to protein ratio than gilts fed ad libitum. Research chapters 3-5 utilized two genetic lines of pigs divergently selected for residual feed intake (RFI) as a model to evaluate how genetic selection for feed efficiency may alter the stress response in pigs. Chapters 3 and 5 evaluated pigs from the 8th generation and Chapter 4 utilized pigs from the 9 th generation of the Iowa State University RFI selection lines. Chapters 3 and 4 utilized two novel stimuli tests, the human approach and novel object tests, to evaluate behavioral stress response. In Chapter 3, low-RFI (more feed efficient) barrows expressed fewer stress behaviors than high-RFI (less feed efficient) barrows. Interestingly, in Chapter 4, few RFI selection line differences were observed and sex (barrows vs. gilts) had a larger impact on behavioral stress responses during the human approach test than genetic line. Additionally, phenotypic expression of RFI was related to behavior during the novel object test. To further understand the physiological mechanisms underlying feed efficiency, pigs divergent in RFI were subjected to an intravenous glucose tolerance test and an adrenocorticotropin hormone (ACTH) challenge (Chapter 5). More feed efficient (low-RFI) pigs had a greater insulin response to the glucose tolerance test and a lower cortisol and NEFA response to the ACTH challenge than less feed efficient (high-RFI) pigs.