Geldings “dropping”

I've seen too many posts with incorrect information and have had enough clients ask about this topic that it's time for me to clear things up.

There are a lot of discussions circulating about geldings (or stallions) dropping during positive reinforcement (R+) training sessions. And, as always, this has sparked the debate: Is it stress or happiness?

Many professionals have been weighing in on this lately, with most leaning toward the explanation of stress. However, there's a crucial piece of information I rarely see discussed. Thank you, reproductive physiology classes, for locking this into my brain years ago! Funny how certain facts just stick with you.

First, let me be clear: You cannot take a snapshot of a behavior and definitively declare the motivation or emotion behind it. Behavior is far more nuanced than that. Every behavior must be interpreted within its full context, considering other observable behaviors.

For example, consider pawing. It could indicate:

Distance-creating or defensive behavior
Anxiety
Anticipation due to excitement
A trained behavior offered calmly
A trained behavior offered excitedly
A foraging behavior
A precursor to rolling
Pain

The function, motivation, and emotion behind pawing can vary widely, which is why context and accompanying behaviors are essential for interpretation. The same applies to dropping. Now, let's circle back and take a look at what is going on inside the body, when dropping is observed.

Biochemical Lesson: The Physiology Behind Dropping

While emotions can't be reduced to pure biochemistry, biochemistry can offer significant insights. Let's break down the biological processes involved.

Biochemical Process of Penile Erection:

Sexual Arousal Triggers Neural Activation:

The parasympathetic nervous system releases nitric oxide (NO) from non-adrenergic, non-cholinergic (NANC) nerve terminals and endothelial cells.

Nitric Oxide (NO) Production:

NO is synthesized from L-arginine by nitric oxide synthase (NOS) enzymes (eNOS and nNOS).
Calcium influx activates these enzymes, leading to NO release.

Guanylate Cyclase Activation and cGMP Production:

NO activates soluble guanylate cyclase (sGC), converting guanosine triphosphate (GTP) into cyclic guanosine monophosphate (cGMP).
cGMP reduces intracellular calcium, inhibiting calcium channels and promoting calcium storage.

Smooth Muscle Relaxation:

Reduced calcium allows smooth muscle relaxation in the corpora cavernosa, causing penile arteries to dilate and fill with blood.
Increased intracavernosal pressure compresses venous outflow, maintaining the erection.

Biochemical Process of Detumescence (Penile Retraction):

Sympathetic Nervous System Activation:

Norepinephrine (NE) and endothelin-1 (ET-1) activate G-protein coupled receptors in smooth muscle cells.
This triggers the RhoA/Rho-kinase pathway, increasing intracellular calcium.

Calcium-Dependent Contraction:

Increased calcium activates myosin light-chain kinase (MLCK), which phosphorylates myosin, causing smooth muscle contraction and reducing blood flow.

PDE5 and cGMP Breakdown:

The enzyme phosphodiesterase type 5 (PDE5) breaks down cGMP, reversing smooth muscle relaxation.

Stress (Cortisol) vs. Oxytocin (Relaxation)

Cortisol (Stress Response):

Released during stress, cortisol inhibits NO release and reduces cGMP production.
This results in increased smooth muscle contraction and penile retraction.

Oxytocin (Relaxation and Bonding Hormone):

Released during positive emotional states, oxytocin stimulates NO production and vasodilation.
This promotes smooth muscle relaxation and penile engorgement.

In Simple Terms:

Simply put, norepinephrine (also called noradrenaline) is part of the sympathetic nervous system (the fight-or-flight response). It triggers the body's process that causes the penis to retract. There is also evidence that cortisol, a stress hormone, can reduce or even block nitric oxide activity, which is essential for blood vessel relaxation (vasodilation). Additionally, when the sympathetic nervous system is active, the retractor penis muscle contracts, pulling the penis back into the sheath.
On the other hand, oxytocin and other neurotransmitters released by the parasympathetic nervous system (the rest-and-digest or feed-and-breed response) help the body relax. During positive reinforcement training, these chemicals promote smooth muscle relaxation, sometimes leading to penile engorgement.
In summary, when a horse "drops" during a positive reinforcement session, the biochemistry behind the behavior would indicate relaxation, not stress. According to the biochemistry, this physiological response cannot happen when the horse is in a stressed or fearful state.

What This Means for R+ Training

When a gelding drops during a positive reinforcement session, the biochemical processes occurring in the body suggests the horse is in the parasympathetic nervous system, not the sympathetic nervous system. The physiological response you’re seeing (smooth muscle relaxation and penile engorgement) cannot occur when the sympathetic nervous system (stress response) is active.

HOWEVER - I want to reiterate, that we cannot interpret a behavior looking at biochemistry alone. There are MANY things at play for each and every behavior.

Both animals and humans can become overly excited or aroused, even when the excitement is positive. This state of being over threshold (even in a positive way) can lead to distraction and loss of focus, or even frustration, anxiety, and conflict behaviors, even if the emotions are positive. This is not a place we want to hang out in either! That is also something we want to address and change.

Important Considerations

Superstitious Behaviors: Dropping can become conditioned during training, just like other behaviors such as ears forward or back. If a horse is consistently reinforced while dropping, the behavior might become linked with the training itself. (The old “click-a-dick” phenomenon.)
Individual Differences: Not all horses respond to pressure or learning challenges the same way. Some horses thrive when working through minor challenges, while others may struggle or shut down. Training should always be adapted to the individual horse in front of you.

Conclusion

Let’s not rush to judge a behavior based on a single observation. Behaviors have many possible functions, motivations, and emotional underpinnings. It’s crucial to consider the context and accompanying behaviors before making assumptions. Understanding the biochemistry behind behavior can also offer valuable insights into what hormones and neurotransmitters are active at the time.

When in doubt, remember Dr. Susan Friedman’s words: “Behavior is the study of ONE.” Trust your observations, stay curious, and keep learning.

I encourage you to explore this topic further—I've linked some excellent articles and studies below for more in-depth information.

Happy Training!

**** EDIT ****

To clarify and reiterate - dropping can go one way or the other. It depends on the horse and the situation. But if we JUST look at the biochemistry - THAT would suggest that it can not occur under stress. However, like I said, behavior cannot be interpreted solely on the biochemistry.

Pain and physical issues are a whole other thing.

Dropping (or SEAM) can be observed in MANY contexts and have MANY reasons

More info:

Horse Sport. (2023, October 6). Observing pain in elite event horses at Badminton and Burghley. Horse Sport. Retrieved from https://horsesport.com/magazine/behaviour/observing-pain-elite-event-horses-badminton-burghley/

Pedrosa, K., & Clinton, R. (2012). Mechanisms in Erectile Function and Dysfunction: An Overview. InTech. doi: 10.5772/39088 https://www.intechopen.com/chapters/30215

Salvio, G., Martino, M., Giancola, G., Arnaldi, G., & Balercia, G. (2021). Hypothalamic–Pituitary Diseases and Erectile Dysfunction. Journal of Clinical Medicine, 10(12), 2551. https://doi.org/10.3390/jcm10122551 https://www.mdpi.com/2077-0383/10/12/2551

Stress in horses: what impact on health and performance? Mar 15, 2022 | Physiology, Welfare https://vet.arioneo.com/en/blog/stress-in-horses-what-impact-on-health-and-performance