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ProKalm - Affect on Stereotypical Behaviors

QUESTION: Does an oral supplement containing Melissa Officinalis extract and L-Theanine reduce stereotypical behavior in horses?


  • Stereotypical behaviors (a repetitive behavior that has no discernible function, often destructive or harmful in some way) are commonly seen in domesticated horses with a reported prevalence of 2.1-10.5% for cribbing/windsucking1-3.
  • Stereotypical behaviors have been associated with an increased prevalence of gastric ulceration4, poor body condition and weight loss5, and colic6,7. Cribbing/windsucking behavior has also been reported as a specific risk factor for simple colonic obstruction and distention colic8 and epiploic foramen entrapment9-11.
  • Lemon balm12 (Melissa Officinalis) and L-theanine13-15 have been shown to have anti-anxiety and behavior modifying properties in multiple species.

Aim of Study

To investigate if a calming supplement containing lemon balm and L-theanine (ProKalm, Science Supplements) reduced stereotypical behaviors of horses.

Study Design

  • Prospective clinical case series = a group of horses selected for a particular reason (stereotypical behavior in this study) was followed over several days.

Study Outline

Eighteen horses exhibiting chronic (over 6 months) stereotypical behavior were recruited. Owners completed a questionnaire categorizing the stereotypical behavior and rating the severity on a scale with 0 being no stereotypical behavior and 10 being most severe stereotypical behavior seen by that horse. Horses were fed 64 g ProKalm split equally in morning and evening feeds for 3 days. Owners repeated scoring of stereotypical behavior once daily.

Study Results

  • Fourteen horses displayed one stereotypical behavior, three horses displayed two behaviors and one horse showed three (Table 1). Wind-sucking was the most frequently reported stereotypical behavior (Table 1).
    Stereotypical behavior counts

Table 1: Stereotypical behaviors demonstrated by 18 horses. Note that four horses exhibited more than one behavior.

  • All horses ate supplement in feed without palatability issues. Two owners anecdotally reported improvement but did not return scoring sheets and therefore two horses were excluded from further analyses.
  • Behavior scores decreased from day 1 to day 3 in 12/16 (75%) of horses with 7/16 (44%) showing a decrease of 50% or greater. Two horses completely stopped exhibiting stereotypical behavior by day 3, one of which had exhibited 3 stereotypical behaviors on day 1.
  • Mean severity score decreased significantly across the study (Fig. 1). Scores were significantly decreased from day 1 at day 2 and day 3.
    Change in behavior scores with ProKalm

Figure 1: Mean (±SD) severity score of stereotypical behavior in 16 horses during 3 days of ProKalm supplementation. Median score decreased significantly from Day 1 to Day 2 (0.004) and from Day 1 to Day 3 (0.001).

Take Home Message

  • Feeding 64 g ProKalm for 3 days significantly decreased severity of stereotypical behavior in 75% of horses. Approximately half of responding horses showed a 50% or greater reduction in severity score and two ceased exhibiting stereotypical behavior completely.
  • The dose of Melissa Officinalis extract and L-Theanine used in this study is considered low-medium. Feeding a higher dose or for a longer period may be of additional benefit to non-responsive or poorly responsive horses.


  1. McBride SD and Long L: Management of horses showing stereotypic behaviour, owner perception and the implications for welfare. Vet Record 2001, 148(26):799-802.
  2. Albright JD, et al. Crib-biting in US horses: Breed predispositions and owner perceptions of aetiology. Equine Vet J 2009, 41(5):455-458.
  3. Waters AJ, et al. Factors influencing the development of stereotypic and redirected behaviours in young horses: findings of a four year prospective epidemiological study. Equine Vet J 2002, 34(6):572-579.
  4. Nicol CJ, et al. Study of crib-biting and gastric inflammation and ulceration in young horses. Veterinary Rec. 2002;151(22):658
  5. McGreevy P, Nicol C. Physiological and behavioral consequences associated with short-term prevention of crib-biting in horses. Physiology & Behavior. 1998;65(1):15-23.
  6. Malamed R, et al. Retrospective evaluation of crib-biting and windsucking behaviours and owner-perceived behavioural traits as risk factors for colic in horses. Equine Vet J. 2010;42(8):686-692.
  7. Scantlebury C et al. Recurrent colic in the horse: Incidence and risk factors for recurrence in the general practice population. Equine Vet J. 2011;39:81-88.
  8. Hillyer MH, et al. Case control study to identify risk factors for simple colonic obstruction and distension colic in horses. Equine Vet J. 2002;34(5):455–463.
  9. Archer DC, et al. Association between cribbing and entrapment of the small intestine in the epiploic foramen in horses: 68 cases (1991-2002) JAVMA 2004;224(4):562-564.
  10. Archer DC, et al. Risk factors for epiploic foramen entrapment colic in a UK horse population: A prospective case-control study. Equine Vet J. 2008;40(4):405–410.
  11. Archer DC, et al. Risk factors for epiploic foramen entrapment colic: An international study. Equine Vet J. 2008;40(3):224–230.
  12. Watson K, et al. A randomised controlled trial of Lavender (Lavandula Angustifolia) and Lemon Balm (Melissa Officinalis) essential oils for the treatment of agitated behaviour in older people with and without dementia. Complement Ther Med. 2019 42:366-373.
  13. Kimura K, et al. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007 74(1):39-45.
  14. Dramard V, et al. Effect of L-theanine tablets in reducing stress-related emotional signs in cats: an open-label field study. Irish Vet J. 2018 9;71:21.
  15. Ogawa S, et al. Effects of L-theanine on anxiety-like behavior, cerebrospinal fluid amino acid profile, and hippocampal activity in Wistar Kyoto rats. Psychopharmacol (Berl). 2018 235(1):37-45.
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