Sow Stress During Lactation: Impact on Piglet Behavior & Cortisol Levels

Sows in modern pig production systems face numerous challenges, many stemming from suboptimal housing conditions. These conditions can increase the risk of maternal stress during lactation, potentially altering maternal care and impacting piglets’ early experiences. Recent research is exploring the complex interplay between maternal stress, hormonal changes, and subsequent piglet behavior and development.

Investigating the Link Between Maternal Stress and Piglet Development

A new study, published in Applied Animal Behaviour Science, investigated how maternal stress during lactation influences maternal care by analyzing changes in sow behavior – including aggression, nursing bouts, and social contact with offspring – and physiology, focusing on key hormones regulating stress (cortisol) and social bonding (oxytocin). Researchers also evaluated how different rearing environments might influence early behavioral and physiological responses of piglets during maternal separation. The study further examined the effects of separating piglets with or without littermates, analyzing the impact of “social isolation” on their responses.

Study Design: Simulating Stress in Sows

From days 2 to 15 of lactation, sows were treated with an injection of adrenocorticotropic hormone (ACTH) – designed to simulate a high-stress condition – or a saline solution (the control group). Milk and saliva samples were collected during the treatment period to assess the effect of maternal stress on cortisol and oxytocin concentrations in the sows. Behavioral data were also recorded, along with saliva samples for cortisol analysis, during a four-hour maternal separation followed by reunion, and during a corresponding control day. During maternal separation, plasma samples were collected from piglets to analyze cortisol and oxytocin levels. Behavioral data from a subset of piglets were also recorded at regular intervals.

Key Findings: Physiological Changes in Sows, Behavioral Responses in Piglets

The study found significant increases in cortisol concentrations in both the saliva and milk of sows treated with ACTH during lactation. However, no significant behavioral differences were observed between the ACTH-treated and control sows during separations or reunions. There was a trend toward ACTH-treated sows lying on their side less frequently on control days. Importantly, the rearing environment did not have significant effects on piglet activity or hormone levels.

However, during reunions, piglets from the control group – those born to sows not treated with ACTH – showed a greater preference for contact with the sow compared to contact with other piglets, a difference not seen in piglets born to ACTH-treated mothers. Piglets housed in groups during separations exhibited lower cortisol concentrations than those housed individually, suggesting a buffering effect of social support during stressful events.

Implications of the Findings

While the ACTH-treated sows showed few overt behavioral signs of increased stress response, the physiological changes observed in their milk suggest potential long-term implications for piglets. The altered cortisol and oxytocin levels in the sow’s milk could influence the development of the piglets’ own stress response systems and their ability to cope with future challenges.

The finding that piglets prefer contact with their mothers after separation, particularly when their mothers haven’t been artificially stressed, highlights the importance of the maternal bond. This preference was diminished in piglets born to stressed mothers, suggesting that early maternal stress can alter social preferences.

The Role of Social Support

The study also reinforces the importance of social support for piglets experiencing stress. Piglets separated from their mothers and housed with littermates exhibited lower cortisol levels than those housed individually, demonstrating the protective effect of social interaction during a stressful event. This finding aligns with research in other species, including humans, which consistently shows that social support can mitigate the negative effects of stress.

Context and Further Research

Previous research, as highlighted in a 2018 study published in the Journal of Animal Science, suggests that removing confinement on the fourth day postpartum may have small, short-term positive effects on sow behavior and stress levels, without impairing piglet performance. This study builds on that work by examining the physiological mechanisms underlying these behavioral changes and exploring the impact on piglets.

Another study, from 2025, found that musical stimulation in lactating sows can affect pre-weaning piglet mortality and maternal behavior. These findings, combined with the current research, underscore the multifaceted nature of maternal stress and its impact on both sow and piglet well-being.

Research also indicates that reducing sow stress during lactation can improve both sow and piglet performance and welfare. Lower cortisol concentrations in sows have been linked to better piglet growth rates. The current study adds to this body of knowledge by demonstrating the potential for maternal stress to alter piglets’ physiological responses to stress and their social preferences.

While this study provides valuable insights, further research is needed to fully understand the long-term consequences of maternal stress on piglet development and to identify effective strategies for mitigating these effects. Understanding these complex interactions is crucial for optimizing pig production practices and ensuring the welfare of both sows and their offspring.