Thursday, 20 February 2020

Horses as individuals (not statistics)


Asking a good equine behaviourist questions about your horse may initially be frustrating. They are often going to say something like ‘it depends’.

Why is my horse bucking after jumps?
Why won’t my horse go in the trailer?
Why does my horse pin his ears when people pass her stable?
Why does my horse yawn after I put his bridle on?
What should I do if my horse is pulling away from me for grass when I lead her?
  
And so on.

The answer to all of these questions is – it depends…

Part of the reason ‘it depends’ is that every horse is an individual, and whilst research and experience may both reveal patterns in horses’ body language and behaviour, the individual may well not conform to the norm. So a behaviourist will want to ask an awful lot of questions and actually see your horse if at all possible before giving any sort of opinion.

In a recent journal club with IAABC colleagues, we discussed an interesting paper, ‘Horses associate individual human voices with the valence of past interactions: a behavioural and electrophysiological study’ Serenella d’Ingeo, Angelo Quaranta, Marcello Siniscalchi, Mathilde Stomp, Caroline Coste, Charlotte Bagnard, Martine Hausberger & Hugo Cousillas. Scientific Reports | (2019) 9:11568 | https://doi.org/10.1038/s41598-019-47960-5.

The authors of this paper were interested in how horses responded to a voice they associated with a negative experience (V-) as opposed to their response to a voice they associated with a positive experience (V+). The figure below is reproduced from the paper (Many thanks to Springer Nature for their generous copyright policy!), with my simple additions of the letters A, B, C and D and a vertical blue line. Each dot in the figure represents a horse, so 16 horses in total are represented.


Figure from above cited paper: Theta wave relative frequency in % of the power profile (right hemisphere): correlation between data obtained for each horse during the playback of V+ and V− respectively.


Without reviewing the findings in this paper, we can simply use this as an example. Please don’t worry if, like me, you are not well versed in the significance of brain waves!

Here, a notable observation might be that 12 of the 16 horses are to the left of the blue line drawn from 0 on the x axis; the majority of horses have a negative measurement in response to the voice associated with a positive experience. This would be a typical and very valid point for discussion – we have found a pattern. 

However, this figure is also an excellent reminder to consider the individual.

For example, horse A measures 30 for the voice associated with the negative experience (V-), and around -15 for the voice associated with the positive experience (V+), whilst horse B is -20 and 20 for V- and V+ respectively. So they are showing opposite responses in this test. Horse C has negative readings for both experiences, whilst horse D has positive readings for both experiences. Horse D also has a strongly positive measure for V+, whilst most other horses are negative or close to 0.

Furthermore, if we were to look at, say, the mean average of V+ measurements, we would get a figure around -5. We need to be very aware that several individuals showed very different measurements.

Statistics gathered for groups give us useful information, but should not be assumed to relate to the individual. 

That this figure beautifully illustrates the point that each horse is an individual was observed by Dr Robin Foster at the journal club, so all credit is due to her for highlighting this. The explanation given here, and any mistakes therein are down to me.


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