Assessing and Managing Pain in Postpartum Mares: Development of a Targeted Clinical Pain Scale

Pain is a fundamental biological defense mechanism that affects both physiological systems and emotional state, most commonly arising in response to tissue injury. In animals, pain activates reflexive changes in respiratory and cardiovascular function and alters neuroendocrine pathways, including increased secretion of cortisol, catecholamines, and β-endorphins, alongside inflammatory mediators such as prostaglandin E2, bradykinin, and substance P. Behavioral responses to pain vary considerably between species. While some animals freeze or hide, horses often attempt to flee from perceived danger or discomfort, even when severely injured¹. These species-specific responses make pain recognition in equids particularly challenging and underline the importance of structured assessment tools. 

Postpartum pain in mares: a clinical reality 

Mares commonly experience nociceptive pain during the postpartum period, even following an apparently normal foaling. This discomfort primarily arises from edema and irritation of the birth canal, uterine involution, and generalized muscle soreness associated with the physical demands of labor. Pain intensity can be markedly amplified by dystocia or postpartum complications such as genital tract trauma, retained fetal membranes, laminitis, mastitis, or post-foaling colic¹. Failure to recognize and adequately manage pain in these cases has significant welfare and clinical consequences. Unrelieved pain triggers excessive sympathetic nervous system activation, metabolic derangements, and immunosuppression, thereby increasing morbidity and delaying recovery². 

The challenge of pain assessment in animals 

Because animals cannot verbally communicate pain, veterinarians must rely on indirect indicators, including changes in behavior, posture, facial expression, and physiological parameters. Behavioral pain scales are therefore central to modern veterinary pain assessment. An effective scale defines species-specific behavioral and physical criteria, allowing clinicians to detect even subtle deviations from normal appearance or vital signs that may indicate pain^1,2. For such tools to be clinically meaningful, they must undergo validation, demonstrating acceptable reliability and validity. A key component of validation is comparison of scale scores with independent biological indicators of pain or stress. 

Cortisol as a physiological anchor 

Cortisol is a well-established biomarker of stress and pain in equids³. Pain activates the hypothalamic–pituitary–adrenal (HPA) axis (CRH → ACTH → adrenal cortex), resulting in increased cortisol secretion¹. Importantly, cortisol passively diffuses from blood into saliva, and salivary cortisol concentrations closely reflect the free, biologically active fraction of plasma cortisol with only a short delay. Saliva collection is non-invasive, requiring only a cotton swab or Salivette® placed briefly in the horse’s mouth, and therefore does not exacerbate existing pain ⁴. This makes salivary cortisol particularly suitable for validating equine pain scales. 

Why existing equine pain scales fall short 

Despite the availability of several validated equine pain scales, none are specifically designed for postpartum mares. Existing tools include multidimensional composite scales developed mainly for orthopedic pain or colic in horses^1,5,6,7 and donkeys^8,9,10, as well as facial expression-based scales for adult equids^1,9 and foals^11,12. While valuable, these instruments do not adequately capture pain originating from the genital tract or mammary system, which are central to the postpartum period. As a result, there has been a clear unmet need for a pain scale tailored to postpartum mares. 

Development of a postpartum mare pain scale 

The present work addresses this gap by describing the creation of a concise, pragmatic pain scale specifically designed for postpartum mares. Unlike purely experimental instruments, this scale was developed with day-to-day clinical applicability in mind, offering rapid decision support for veterinarians, technicians, owners, and breeders¹. 

In the initial evaluation, higher pain scores were consistently associated with higher salivary cortisol concentrations across multiple statistical models, supporting biological plausibility and indicating that the scale captures at least part of the physiological stress response related to pain. Within the observed range of scores, this relationship was approximately linear, with residuals showing a symmetric, bell-shaped distribution. Future studies including mares with a wider spectrum of pain severity—particularly at the upper end—should explore whether this relationship remains linear or becomes nonlinear, for example plateauing or rising more steeply at higher scores. Over broader ranges, salivary cortisol may also show right-skewed distributions, in which case logarithmic transformations or log-normal models would be more appropriate for analysis¹. 

Key features distinguishing the scale 

In contrast to existing composite or facial expression-based scales, this postpartum mare pain scale deliberately emphasizes criteria relevant to the peripartum context. These include udder and perineal changes, abdominal edema, hoof monitoring, and posture, alongside behavioral indicators. This focus is clinically important, as retained fetal membranes and subsequent endotoxemia frequently precipitate laminitis, a potentially life-threatening condition where early pain recognition is critical^1,13. By integrating genital tract and mammary findings, the scale captures pain sources that generic equine pain tools may overlook. 

Survey feedback indicated that observers felt confident assessing signs such as sweating, swelling, fecal output, and certain behaviors, but had low to moderate confidence in detecting digital pulses and temperature-related changes in hooves or udders. To address this, the scale incorporates illustrative images and clear instructions to improve consistency and usability¹. 

Scoring, monitoring, and clinical use 

The postpartum mare pain scale is designed to be both comprehensive and flexible, with a maximum attainable score of 47 points when all parameters are assessed. Recognizing that some mares may be uncooperative or unsafe to handle, the system allows exclusion of certain items (e.g., limb palpation), with pain expressed as a percentage of the adjusted maximum score. This ensures flexibility without sacrificing comparability across individuals or time points¹. 

Consistent with broader equine pain literature, serial assessments are more informative than single observations. Scoring once or ideally twice daily enables clinicians to monitor trends rather than isolated values. In postpartum mares, transient discomfort is expected, but persistently high or rising scores should prompt investigation for complications such as metritis, laminitis, or systemic inflammation and guide timely adjustments in analgesic therapy¹. 

Role of behavior and salivary cortisol 

Behavioral indicators, changes in facial expression, posture, activity, and response to palpation, remain central to pain assessment, as horses often display subtle pain-related behaviors^1,13,14. Incorporating elements aligned with the Horse Grimace Scale enhances objectivity and inter-observer consistency. Salivary cortisol, while influenced by non-pain stressors such as handling or transport¹, remains one of the best non-invasive physiological anchors for validation when interpreted alongside clinical findings. Its utility as a biomarker of pain-related stress has been demonstrated in acute equine abdominal disease¹⁵. 

Conclusion 

Postpartum pain in mares is common and clinically significant, yet difficult to assess using existing equine pain scales. The postpartum mare pain scale presented here addresses this gap by focusing on behavioral and physical indicators specific to the peripartum period, including genital, mammary, abdominal, and hoof-related parameters. Its association with salivary cortisol concentrations supports its biological relevance and clinical utility. 

Designed as a practical tool, the scale allows flexible application and benefits from serial use to detect abnormal pain trajectories that may indicate postpartum complications. While further validation is required, this targeted approach represents an important step toward improving pain recognition, clinical decision-making, and welfare in postpartum mares. 

References: 

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