Grass Tetany in Horses

Grass Tetany DOES Happen in Horses

I have lost count of the number of times I have been told that “Horses don’t get Grass Tetany”!

Yet when you look at the ‘symptoms’, mild to moderate forms are extremely prevalent amongst our domestic horses when grazing short or lush green grass.

They become vulnerable to their symptoms worsening when there is a sudden change in the season/weather which causes a rapid change to the nutrient composition of the grass.

Horses that have been showing milder signs, either ‘off and on’ or low-grade for a long time, can become ‘acute’ over-night.

Hence while acute Grass Tetany isn’t common when it does crop it is serious and multiple animals in an area will be affected around the same time. This seems to be happening particularly in NSW at present.

HOW DOES IT HAPPEN?

Because Potassium helps grass uptake water, when it rains grass becomes very high in both potassium and water, and LOW in sodium and magnesium.

This means the horses grazing it are consuming grass that is EXTREMELY UNBALANCED, severely impacting the horse’s ability to maintain internal equilibrium.

The lusher the grass the lower in Dry Matter (fibre) and the higher in Potassium it becomes, disturbing critical calcium and magnesium balances (See post Grass & Calcium” on Jan 29th).

Grass Tetany is primarily caused by the high potassium which pushes magnesium out of the way, exacerbates low sodium intake and causes LOW calcium levels in the bloodstream.

Trouble soon follows!

- even mild Grass Tetany can cause colic from ‘intestinal paresis’ (a slowdown of gut motility)

- symptoms of Grass Tetany can resemble colic. Consequently it is often misdiagnosed.

Either way it is a Medical Emergency and URGENT Veterinary Intervention is necessary.

Ideally the vet would give an intravenous infusion of both calcium & magnesium…………….

Here is what happened to the 2 year old Fresian filly in the photograph who was found one late winter morning down, head arched back, with her legs absolutely rigid apart from spasmodic ‘paddling’ - all signs of acute Grass Tetany - which is excruciatingly painful! (The rigidity with the head arched back are clear signs it is Grass Tetany)

She had been turned out on the hill all winter with no supplementation. Remember growing horses have an increased requirement for all minerals including salt, calcium, magnesium, & phosphorous so this little horse was already struggling (as you can see by her condition) when the seasonal change in the grass tipped her over into this metabolic emergency.

She was in a very bad way when we were contacted, down flat and unable to get up because her legs were too stiff and couldn’t bend.

At the time, the vet in attendance had treated her for colic. But it wasn’t colic and she didn’t respond.

When we were contacted we concluded it was Grass Tetany and there was nothing to lose by syringing in AlleviateC (Ca, Mg, & Boron – an oral version of what a vet would give intravenously for grass tetany in cattle) along with salt (all done by the neighbour who fortunately had some on hand.

Within 15 minutes her legs had loosened up to the point a team of guys could help her to stand up. This is when the picture was taken.

We left instructions to repeat the syringing multiple times over the following days but unfortunately on return the vet announced that “Horses don’t get Grass Tetany” so it was not continued and the filly went down again and tragically died.

WHAT ARE THE SIGNS?

As with all ‘syndromes’ there is a broad range of ‘symptoms’ from mild or moderate to acute.

Mild Signs include: Nervousness, restlessness, easily startled, muscle twitching, wild eyes, stumbling, ‘knuckling over’, staggering, ‘shuffling’ gait,

Moderate signs include – nose-rubbing due to peri-oral numbness and tingling, grinding their teeth or the bit, walking stiffly (note this is also an early sign of laminitis) , tight back muscles, travelling hollow, scooting off, choppy movement, ‘sacro-iliac’ issues, bunny-hopping, disuniting, locking stifles, stringhalt, frequent urination and defecation, hard/dry manure

Acute Signs include – Muscle tremors, excessive salivation, inability to drop their head or bend their neck laterally

Difficulty eating/swallowing and breathing, lockjaw, wheezing

Down flat on their side, can’t get up

Violent muscle contractions, convulsions, seizures, death

PREVENTATIVE MEASURES

- Ideally avoid your horse eating very lush grass but where control over grass intake isn’t possible, supplement with as much plain grass hay as possible.

- Add SALT to feeds at a rate of 10g per 100kgs

- Increase resilience by giving a daily feed that includes GrazeEzy & AlleviateC/SOS plus a high spec multi vitamin & mineral (Premium/Supreme MVA)