The amine hypothesis - the problematic weather

animal health consulting

The amine hypothesis

high-protein diets and behavioural problems in horses

Christine King BVSc, MANZCVS (equine), MVetClinStud

The problematic weather

In Figure 3 (below), I've charted the daily temperature and rainfall data for our location in the 3 weeks before the August (winter) sample collection, and then for the following two weeks or so.

Table of Contents

Introduction

1. The problematic behaviour

2. The problematic pasture

3. The problematic weather

4. The amine hypothesis

5. The (failed) amine–laminitis hypothesis

6. The amine–behaviour hypothesis

First published on 31 August, 2026. Last updated 08 September, 2026.

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Figure 3. Daily temperature and rainfall data for this area in the 3 weeks before the grass was sampled (dark-blue line) and for the next 2 weeks. Other notable events are marked with different coloured lines: pink, an episode of abnormal behaviour; light-blue, oral bicarbonate started; light-salmon, a mild episode of abnormal behaviour.[ Source: EldersWeather.com.au/month-history/vic/gembrook.]

Note that the bout of abnormal behaviour (pink line) I logged 4 or 5 days after sample collection (dark-blue line) followed a run of 3 days in which there was a big difference between the high and low temperatures on those days. And not only were they dry days (no rain), they were bright, sunny days, followed by crisp, clear nights with low temperatures only a little above freezing.

A few days later (light-blue line), we started both horses on an enterically coated bicarbonate product (EquiShure®, Kentucky Equine Research) in their feed to help buffer acidity in the caecum and colon (the 'hindgut').

I assumed that the short run of bright, sunny, relatively warm days, followed by overnight lows cold enough to inhibit plant metabolism — the period between the dark-blue and pink lines — could be resulting in sudden increases in NSC that were high enough to cause an increase in acidity in the hindgut. More on that later, but that's the rationale for trying the encapsulated bicarb.

The horses were on the low end of the dose range for their size (30 grams twice a day) when we had another mini-run of 2 days in which there was a big gap between the highs and lows, which dropped to near-freezing overnight. A relatively warm, wet front ended that short run. Even so, the gelding was a little grumpy the following day (light-salmon line).

When his bicarb dose was increased 50% (from 30 to 45 grams, so by only 15 grams), his mood and behaviour once again returned to normal. In fact, both horses are now feeling good and working well, he on 45 g/meal and she on 30 g/meal, even though they are a similar height and weight.

Oh, and as an important aside, we learned the hard way not to use hot water to moisten the dry feed when using this encapsulated bicarb product. Apparently, the vegetable oil coating is temperature sensitive, so the bicarb fizzed up in the bucket when hot water was added to the dry feed. Lukewarm water is fine.

Note that to the right of the light-salmon line (the last episode of problematic behaviour), we've had more potentially problematic weather:

* big gap between highs and lows for at least 2 days in a row

* overnight lows in the low-single digits

* clear skies (a component of both the relatively high highs and the low lows)

... and yet both horses are calm and content on their hindgut buffer.

. . .

So, was it the sugars? Was it the protein? Or was it both?

I think it's both. Here's where we get to the amine hypothesis — the subject of this article.

So, let's dive in...