animal health consulting

The problematic behaviour

I have yet to see it for myself, having moved to this farm only last summer, but the gelding I see from my desk goes through the same thing in the spring, year after year, some years worse than others.

He becomes hyperactive, running and even charging around in the pasture for no good reason. He paces the fences when he is normally quite calm. He vigorously, even aggressively, paws at the ground and splashes at the water trough. In short, he seems unable to be still.

In research circles, this sort of hyperactivity is known as hyperlocomotion. It's a restlessness that is characterised by excessive and even compulsive walking or running, for no particular purpose.

He also becomes behaviourally hyper-reactive or hypersensitive to everything. He even becomes belligerent, barging at gates, refusing to be caught, and otherwise forgetting his ground manners, such as threatening to bite when being rugged or unrugged. It is really quite something to behold in a horse who is usually such a gentleman.

His pasturemate is a mare. Her erratic behaviour is generally more muted than his. In fact, I initially thought she was simply showing the inconsistent or ambiguous oestrous behaviour we see in mares during the spring and autumn transitions into and out of the equine breeding season (spring–summer in horses). However, while she has fewer and generally milder episodes of the abnormal behaviour I'm attempting to describe and understand, she can go crackers, too.

She is what I would term a highly sensitive horse, along the lines of the highly sensitive person and the highly sensitive dog. She is easily overstimulated and thus easily overwhelmed, so it doesn't take much to set her off. But despite her constitutional sensory-processing sensitivity (the research term for this normal personality trait), the gelding is far more affected by changing pasture conditions than she, which I find very interesting and noteworthy. Not every horse on lush pasture develops laminitis or becomes obese; not all experience digestive upsets (colic and/or diarrhoea); and not all exhibit behavioural problems, nor all to the same degree.

This tremendous individual variation among horses plagues equine studies of all sorts, yet it is seldom addressed. It is generally considered just the cost of doing business, as it were; it's the statistical price one pays for studying such expensive research subjects that most equine studies include only a handful of horses. But to me, the individual variation is the most interesting thing about most equine studies. Why do some horses do this, while others do that, under the very same conditions? I'll come back to this question, in relation to individual responses to the same pasture conditions.

The most bizarre behaviour I've witnessed is what I call “seeing monsters.” On several occasions I've seen both horses, but especially the gelding, alert to something in the distance that I just could not see. Sometimes one or both have reacted with great alarm, very fearful of whatever it was they were seeing that I did not.

Or perhaps they're alerting to something they're smelling rather than seeing, and they look in the direction the wind is coming from; that is, they turn into the wind for more information. The nasal passages are rich in trace amine receptors, which are sensitive to very low levels of trace amines, the social roles of which include predator detection. But I'm getting ahead of myself.

The only other times I've witnessed this psychotic behaviour, when the horse appears to be hallucinating some imagined terror, was in horses who had accidently received an intravascular dose of procaine penicillin — when some of the dose was inadvertently injected directly into a blood vessel rather than being deposited into the muscle.

There are two other telltale signs the gelding intermittently shows in connection with these episodes of abnormal behaviour: mild colic and poor appetite. Both are transient, but they may recur multiple times over the problematic pasture season. They are telltale for a reason: they point us to the digestive system as the epicentre of these physical and behavioural disorders.

. . .