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 9th 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

Comparison of Gilt Behavior when Fed Ad Libitum or Twice Daily

The objective of this study was to compare two divergent feeding patterns and evaluate their impact on gilt behavior. Eleven gilts were provided ad libitum access to feed (ad lib) and 12 gilts were allowed to eat twice daily (2x). Video of gilt behavior was analyzed 51 days after the start of feed treatments. Gilts fed 2x tended to stand more, spent longer interacting with environmental enrichment, and spend less time eating than ad lib gilts. These results suggest that feeding regimen slightly altered the behavior of individually housed gilts

How has selection for residual feed intake (RFI) affected the grow-finish pig’s ability to cope with stress?

Feed is the largest cost in pork production; therefore, improving feed efficiency can increase producer profitability. Furthermore improved feed efficiency can support industry competitiveness, decrease the demand on global feed resources, and complement environmental sustainability. Genetically, selective breeding for residual feed intake (RFI) shows promise in meeting these increased demands. However, it is important to balance the benefits of feed efficiency selection with the pig’s ability to cope with stress and its welfare. Therefore, this factsheet will discuss physiological and behavioral stress research on swine selected on the basis of RFI

Association of Vocalizations and Swine Behavior during a Human Approach Test

The objective of this study was to determine if the duration and total number of pig vocalizations when divided into low and high call categories was related to pig behaviors during a fear test. Twenty barrows and 20 gilts were tested over two consecutive weeks between 1300 and 1900 hours using a human approach test (HAT). Throughout the test, vocalizations and behavior were recorded. These results suggest that while high calls are typically the primary measure of stress vocalizations, low calls are also meaningful measures during the stressor of HAT

Barrow and Gilt Vocalizations during a Human Approach Test

The objective of this study was to investigate differences between barrow and gilt vocalizations during a fear test. Twenty barrows and 20 gilts were tested over two consecutive weeks between 1300 and 1900 hours using a human approach test (HAT). Throughout the test, vocalizations were recorded. Gilts expressed a greater number of low calls compared to barrows; however, barrows expressed a greater number of high calls compared to gilts. Further research should be done to better understand vocalization differences between barrows and gilts during a HAT

Effect on Gilt Behavior and Postures when Selected for Residual Feed Intake Selection in Response to a Lipopolysaccharide Challenge

The objective of this study was to determine low and high-RFI gilt sickness behavior when challenged with lipopolysaccharide (LPS). This work was conducted with seven low residual feed intake gilts (RFI) and eight high RFI gilts (63±4 kg BW) from the 8th generation of the ISU Yorkshire RFI selection lines. Gilts were challenged intramuscularly with 30 µg/kg BW Escherichia coli O5:B55 LPS at 1000±1 hour. Gilts were video recorded one day before the LPS challenge (baseline) and on the treatment day (LPS challenge). Video was analyzed for lying, sitting, standing, eating and drinking using a 1-minute scan sample at two time points on the baseline and treatment days; 1) 1000 to 1200 hour and 2) 1700 to 1800 hour. There were no line by treatment interactions for behaviors and postures in response to the LPS challenge (P ≥ 0.32). There were no RFI selection line differences in behavioral and postural responses to the LPS challenge (P ≥ 0.45). Regardless of the RFI selection line, after the LPS challenge gilts laid more (P \u3c 0.0001) and stood less (P \u3c 0.0001). However, there were no differences observed in the percent of time engaged in sitting, eating and drinking (P ≥ 0.16). Regardless of the RFI selection line, gilts laid more (P = 0.0004) and stood and ate less (P \u3c 0.0001) during the first (AM) compared to the second time point (PM). In conclusion, gilts from both RFI selection lines similarly expressed classical sickness behaviors and postures when challenged with LPS

Approachability to a Human in Gilts Divergently Selected for Feed Efficiency

The objective of this study was to evaluate approachability of gilts divergently selected for residual feed intake (RFI) to a novel human. Twenty low-RFI and 19 high-RFI gilts were tested using a human approach test. Testing occurred over two consecutive weeks between 1300 and 1900 hours. Gilts were tested individually within a 4.9 x 2.4 m test arena. Throughout the test, latency to first enter, duration of time spent, and frequency of entrances within 1 m and 0.5 m of the human were recorded. These results suggest that divergent selection for RFI did not alter gilt approach behavior to a novel human