Systematic review of animal-based indicators to measure thermal, social, and immune-related stress in pigs

Abstract

The intense nature of pig production has increased the animals’ exposure to stressful conditions, which may be detrimental to their welfare and productivity. Some of the most common sources of stress in pigs are extreme thermal conditions (thermal stress), density and mixing during housing (social stress), or exposure to pathogens and other microorganisms that may challenge their immune system (immune-related stress). The stress response can be monitored based on the animals’ coping mechanisms, as a result of specific environmental, social, and health conditions. These animal-based indicators may support decision making to maintain animal welfare and productivity. The present study aimed to systematically review animal-based indicators of social, thermal, and immune-related stresses in farmed pigs, and the methods used to monitor them. Peer-reviewed scientific literature related to pig production was collected using three online search engines: ScienceDirect, Scopus, and PubMed. The manuscripts selected were grouped based on the indicators measured during the study. According to our results, body temperature measured with a rectal thermometer was the most commonly utilized method for the evaluation of thermal stress in pigs (87.62%), as described in 144 studies. Of the 197 studies that evaluated social stress, aggressive behavior was the most frequently-used indicator (81.81%). Of the 535 publications examined regarding immune-related stress, cytokine concentration in blood samples was the most widely used indicator (80.1%). Information about the methods used to measure animal-based indicators is discussed in terms of validity, reliability, and feasibility. Additionally, the introduction and wide spreading of alternative, less invasive methods with which to measure animal-based indicators, such as cortisol in saliva, skin temperature and respiratory rate via infrared thermography, and various animal welfare threats via vocalization analysis are highlighted. The information reviewed was used to discuss the feasible and most reliable methods with which to monitor the impact of relevant stressors commonly presented by intense production systems on the welfare of farmed pigs.

A critical review on experimental Streptococcus suis infection in pigs with a focus on clinical monitoring and refinement strategies

“…As recently shown blood cortisol levels are significantly elevated in piglets suffering from severe S. suis disease [ 58 ]. However, there are limitations due to the influence of the circadian rhythm and the handling of the animals on the cortisol level [ 100 ]. Different S. suis research teams have been using score sheets to define different levels of severity of the various clinical signs of S. suis disease (Table 1 ).…”

“…Contactless infrared thermometry is less invasive, but it reflects body surface temperature which can be affected by environmental factors. Nevertheless, good correlations between infrared thermometry and rectal temperature have been described, especially for ear and eye [ 78 , 100 , 115 ]. Comparative evaluation of different methods of body temperature measurements has however not been conducted for piglets experimentally infected with S. suis , in contrast to PRRSV infected pigs [ 116 ].…”

Animal Welfare Assessment and Meat Quality through Assessment of Stress Biomarkers in Fattening Pigs with and without Visible Damage during Slaughter

“…Physiological markers are valuable indicators to assess the stress severity in animals, allowing for the interpretation of discomfort levels, including the nature of stressors, such as hydration status, fear, muscle fatigue, and nutritional and energy status [ 3 ]. The main types of indicators are as follows: (A) causative indicators, measuring factors the cause stress; (B) biological response indicators, measuring the physiological response of organisms to cope with stress; and (C) consequence indicators, quantifying the productive consequences of physiological responses to stress [ 16 ].…”

Novel saliva biomarkers for stress and infection in pigs: Changes in oxytocin and procalcitonin in pigs with tail-biting lesions

“…There is a need to develop feasible, reliable, and valid measures of animal health and welfare to improve on-farm diagnostics and to assess the welfare of domestic animals (Guevara et al, 2022). Saliva biomarkers are promising alternatives to more intensive methods, such as blood sampling, as they can be collected with minimal stress to the animal (Cerón et al, 2022).…”