Early life stressors and their influence on behavioral, immunological, physiological, and hormonal responses of young pigs

In the first month of life, a pig’s homeostasis can be disrupted by environmental, nutritional, psychological, and physiological stressors deriving from sow management, piglet processing, and weaning. Sow-related challenges, including inadequate milk let-down, poor pig-to-teat ratios, dysgalactia, and insufficient colostrum or milk intake, can weaken passive immunity, cause hypothermia and undernutrition, and increase mortality. To mitigate these early-life stressors, strategies such as cross-fostering and artificial rearing are employed. Cross-fostering, a common practice in the swine industry, involves transferring piglets from the birth sow to a “foster” sow that has more teats than piglets. Artificial rearing, in contrast, removes piglets from the sow entirely, placing them in a controlled environment where they receive all necessary nutrients. While this method can enhance growth rates, it can also increase stress due to environmental changes, influencing hormonal responses and agonistic behaviors. This dissertation examines how early-life stress influences piglet stress resiliency and responses. Specifically, we explore how feeding style (ad libitum vs. prescribed based on body weight), rearing environment (artificially- vs. sow-reared), and handling frequency (daily vs. weekly) impact physiological, immunological, behavioral, and endocrinological outcomes. Our findings indicate that when piglets have uninterrupted access to milk replacer (ad libitum), they regulate their own intake, improving growth by eliminating the sow’s milk provision limitations. The timing and quantity of milk intake are crucial for growth, triggering endocrine responses such as insulin, which promotes early lean protein deposition. In contrast, when milk provision mimics sow milk let-down by utilizing small, scheduled quantities approximately once an hour, piglet behavior and spatial preference shift. Pigs fed in a prescribed manner remained closer to the food source and visited the bowl more frequently, mimicking natural behaviors that could stimulate sow milk let-down. While the interaction between rearing environment and handling frequency had minimal impact on stress responses, each factor independently influenced stress resilience. Increased handling frequency was associated with elevated cytokine and tight-junction protein expression, possibly due to greater pathogenic exposure or psychological stress. Behavioral assessments, including tonic immobility and human approach tests, revealed that frequently handled pigs developed a proactive coping style, while minimally handled pigs exhibited a passive coping style. This insight could inform pig allocation in nursery pens, potentially reducing agonistic behaviors by housing pigs with differing coping strategies in the same pen. Rearing environment significantly influenced growth performance, with artificially reared pigs gaining more weight by study’s end, likely due to their ability to self-regulate milk intake rather than relying on sow milk let-down. Additionally, artificial rearing limited pathogen exposure, potentially shaping immune responses pre- and post-weaning. Notably, artificially reared pigs exhibited elevated cortisol levels in the first week of life, which correlated with improved stress resilience, as indicated by lower cortisol concentrations post-weaning when exposed to the same stressors. These findings underscore how early-life stressors including feeding style, environment, and human interaction shape piglets' physiological, psychological, endocrinological, and immunological responses. Overall, this research highlights the profound impact of early-life feeding paradigms, rearing conditions, and handling frequency on piglet development, offering insights into mechanisms such as insulin signaling, gut-brain axis communication, coping strategies, and stress resilience.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Animal Sciences

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Sommer, Kaitlyn Marie

Contributors dc:contributor

• Dilger, Ryan N
• Swanson, Kelly S
• Dilger, Anna C
• Johnson, Jay S

• Pig
• artificial rearing
• immunological
• physiological
• behavioral
• hormonal
• stress.

Statement dc:rights

• Copyright 2025 Kaitlyn Sommer

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129201

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129201