animal health consulting

Key points

* lush grass may be high in 'sugars' (nonstructural carbohydrates) and protein

* spillover of 'sugars' into the hindgut (caecum and colon) → ↑ acidity as the microbes in the hindgut ferment the sugars that escaped digestion in the small intestine

* spillover of protein into the hindgut → ↑ trace amines by the microbes in the hindgut when acidity is ↑

* ↑ amines in the hindgut → ↑ amines in the bloodstream, with distribution throughout the body, including the brain

* these amines are central nervous system stimulants, with effects similar to adrenaline and amphetamines; one even has hallucinogenic potential

* this is how lush grass may cause intermittent behavioural problems in some horses, in certain circumstances (e.g., conducive weather patterns)

Can high-protein diets cause behavioural problems in horses?

I had never given any thought to that question until the two horses I see from my office window started behaving erratically as summer turned to autumn. These two mature horses have lived together for years on the same pastures here in southern Victoria, where autumn is practically indistinguishable from spring, pasturewise.

The pastures are green and lush (vigorous growth, abundant and tasty forage) for most of the year; for only a few months in the summer is it dry. It is often said about this region that “it rains for nine months of the year and drips off the trees for the rest!” It's not quite that wet; it's just that our annual rainfall is spread out over a longer period of time than in warmer climates.

For example, Melbourne VIC averages 65 cm (26 in) of rain per year, whereas Brisbane QLD gets an average of 103 cm (41 in).

Melbourne only feels like it gets more rain because it averages 100 days/year with at least 1 mm of rain, whereas for Brisbane it's 85 days/year.

And Melbourne gets more cloudy days than Brisbane: 179 days vs 99 days.

Put another way, Melbourne has fewer sunny days than Brisbane: 49 days vs 133 days.

As a consequence of our temperate climate, our pastures in southern Victoria remain green and variably lush — and potentially problematic — for most of the year.

. . .

In this multi-part, multi-page article, I examine the question of whether high-protein diets can cause behavioural problems in horses — and if so, why, and what can we do about it?

Because this article is long and I may continue to add to it as more data comes to hand, I've provided a handy Table of Contents on each page so that you can go directly to the parts that interest you, and you can mark your place if you need to leave and return later.

The 'Read on...' link in green at the bottom of each page takes you to the next page so that you can continue reading without interruption if you want.

Enjoy! No matter where you are in the world, if you keep horses, this article is for you, because it's not just about pasture.