Spring Grass: Friend or Foe?

October 11, 2026

The Truth About Your Spring Paddock

Spring means green paddocks, warm days, and horses feeling very good about themselves. But as much as we love watching our horses enjoy the flush of new growth, this is also one of the riskiest times of year for pasture-related health issues and it's not just about the good grass growing. The not-so-good grasses (and weeds) are thriving right alongside it.

Here's what to watch for as the season turns. (Sources for the claims below are listed in the References section at the end of this article.)

Spring Fever: More Than Just High Spirits

If your usually sensible horse has suddenly turned into a bucking, spooking, can't-stand-still version of themselves, you're not imagining it. Rich, fast-growing spring grass is high in sugars (non-structural carbohydrates) and can genuinely affect behaviour - giving horses a rush of extra energy that shows up as excitability, spookiness, or general "silliness" under saddle.

What helps:

Introduce lush pasture gradually rather than turning out for full days straight away
Consider limiting grazing time during peak sugar periods (grass sugar content is typically highest in the afternoon on sunny days, lowest in early morning)
A grazing muzzle can help if your horse needs pasture access but not unlimited intake

Laminitis Risk: The Season's Biggest Threat

Spring grass is the single biggest laminitis trigger for many horses and ponies, particularly those who are overweight, insulin resistant, or have a history of laminitis (including horses with PPID/Cushing's). Environmental conditions in spring can trigger sharp increases in the sugar, starch and fructan content of pasture, and it's this rapid sugar load that can overwhelm a sensitive horse's system, triggering inflammation in the laminae of the hoof - a genuinely painful and potentially serious condition [1].

Signs to watch for:

Reluctance to move, or a short, shuffling gait
Heat in the hooves
A stronger-than-usual digital pulse
Reluctance to turn or stand on hard ground

If you notice any of these, restrict pasture access immediately and call your vet. Laminitis is a genuine emergency, not a "wait and see."

Toxic Plants and Weeds: A Nationwide Risk

While your horse is enjoying the flush of spring growth, it's worth knowing that a number of common Australian pasture grasses and weeds carry real risks of their own - some found Australia-wide, others more prevalent in particular regions [2][3]:

Perennial Ryegrass (Lolium perenne): widespread nationally. Can host a native fungus producing toxins that peak over summer and autumn, causing "ryegrass staggers": tremors, incoordination, and stiffness [4].

Annual Ryegrass (Lolium rigidum): most commonly reported in WA and southern Australia. A more serious risk again, linked to bacterial toxins in the seedhead causing severe, sometimes fatal, staggers during warmer months [5].

Phalaris (Phalaris aquatica): common nationally, with Australia noted as having higher prevalence of toxicity than most other regions worldwide. Most dangerous when young and rapidly growing; can cause staggers or sudden death [6][7].

High-Oxalate ("Big Head") Grasses): Buffel, Kikuyu, Setaria, Pangola, Green Panic, Para, and Signal Grass, widespread across the northern half of Australia, with Kikuyu extending down the east coast into north-eastern Tasmania and coastal WA. This group of subtropical/tropical grasses is high in oxalates, which bind calcium during digestion and make it unavailable to the horse. Prolonged grazing (generally two months or more) without adequate calcium supplementation can lead to Nutritional Secondary Hyperparathyroidism, commonly called "Big Head" disease, a progressive, insidious condition where the horse's body draws calcium from its own bones to maintain blood calcium levels, weakening bone structure over time [8]. It's a slow-developing risk rather than an acute one, but a well-documented and continuing problem in horses grazing these pastures, particularly in South East Queensland and along the eastern seaboard.

Paterson's Curse (Echium plantagineum): widespread across southern Australia. Horses are highly susceptible to its toxic alkaloids, causing irreversible liver damage [9].

Fireweed (Senecio madagascariensis): particularly prevalent on the NSW Central Coast and other parts of eastern Australia. Associated with irreversible liver and brain damage [10].

St John's Wort (Hypericum perforatum): found across southern and eastern Australia. Causes photosensitisation (sunburn-like skin reactions) and gastrointestinal irritation [11].

Ragwort (Jacobaea/Senecio spp.): common in southern and eastern states, flowering roughly July–October. Causes cumulative, irreversible liver damage [12].

Bracken Fern (Pteridium esculentum): found nationally, particularly around wooded pasture edges in higher-rainfall regions. Causes thiamine (vitamin B1) deficiency with neurological effects [12].

Flatweed / Catsear (Hypochaeris radicata): common nationally in lawns and pastures. Linked to Australian Stringhalt, a distinctive hind-leg gait abnormality [13].

This list is not exhaustive, but it isn't a reason to panic. Many horses graze around these plants without issue, but it's worth walking your paddocks (and boundary fence lines) this spring, getting familiar with what's actually growing, and checking in with your state agriculture department or local vet if anything looks unfamiliar.

Grass Seeds and Prickly Pasture: The Physical Risks

Beyond toxicity, there's a more mechanical risk that shows up every spring as grasses mature and go to seed: barbed grass seeds (awns) that can lodge in a horse's eyes, ears, mouth, nostrils, and skin.

Barley grass (Hordeum spp.) is one of the most common offenders in Australian paddocks. Its seeds have a sharp point and fan-shaped awns that allow the seed to travel forward through tissue but not back out - similar to the barb on a fishhook.

Spear grass and corkscrew grass (Austrostipa spp.) cause similar problems, with long, twisting awns that can work their way into skin, mouths and eyes.

Prickly grasses caught early can usually be removed quickly and easily. But left, can cause ulceration, abscess and a great deal of discomfort. Whilst not specific to horses, the effects of grass seeds in animals is described in many articles, one of which has been provided in the references below [14]. There's also horse-specific veterinary literature describing painful mouth ulceration (stomatitis) in horses caused by barley grass awns embedded in gums and cheek tissue [15].

What to watch for:

Excessive blinking, squinting, or weeping from one eye
Head shaking or ear sensitivity
Reluctance to eat, or dropping food while chewing
Small lumps or discharge under the skin, particularly around the lower legs, girth area, or anywhere tack sits

A few simple precautions:

Keep an eye on paddocks as grasses mature and go to seed. Slashing or mowing before seed heads fully dry out can reduce the problem significantly
Check your horse's eyes, ears, and mouth area regularly during grass seed season, especially after time in long or dry pasture
If you notice persistent eye irritation, head shaking, or reluctance to eat, don't wait it out. A vet check is the safest option, as seeds can migrate and cause deeper damage the longer they're left

New Season Hay: Choose Your Supplier Carefully

Spring is also when a lot of new season hay starts coming onto the market and it's worth applying the same "know what's in it" thinking to your hay as you do to your paddocks. Hay can carry its own risks if it hasn't been grown, cut, or stored properly [16]:

Noxious weeds baled in with the hay - weeds that a horse might normally avoid in the paddock can become more palatable once dried, meaning horses are more likely to eat them mixed into hay than they would growing in a pasture.
Grass seeds and prickly awns - this is a particular risk with hay, since barley grass and similar seeding grasses are often baled once mature and dried, right when their barbed awns are at their sharpest. Horses can pick these up in their mouths and gums while eating, and awns can also work their way into the coat and skin from hay in bedding or feed bins.
Botulism risk - this is a rare but extremely serious one. Contaminated hay is one of the more common sources of botulism exposure in horses, particularly if the hay was baled with damp patches or if a small animal was inadvertently caught up during cutting and baling. Horses are especially sensitive to botulinum toxin, and contaminated hay won't necessarily look or smell spoiled.
Mould and dust - poorly cured or improperly stored hay can promote mould growth, which affects palatability, nutritional value, and can worsen respiratory conditions like heaves.

The best protection is simple: buy from a reputable, known supplier. A supplier who inspects their paddocks for noxious weeds before cutting, cures and bales hay correctly, and stores it well is your best safeguard against all of the above. If you're trying a new supplier or a new batch, it's worth giving the hay a visual and smell check before feeding. Look for weeds, seed heads, discolouration, mould, or a musty smell, and trust your instincts if something seems off. And like any dietary change, introduce the new season’s hay gradually.

A Few Simple Seasonal Habits

Walk your paddocks regularly and learn to identify what's growing, not just how much
Introduce spring pasture gradually, especially for good-doers or horses with any metabolic history
Keep an eye on body condition - spring grass can pack on weight quickly
If in doubt about a plant or grass in your paddock, a quick photo to your local agricultural department or vet can settle it fast

Spring is a wonderful time to watch our horses enjoying life in the paddock. A little extra awareness now goes a long way toward keeping that enjoyment safe.

🐴Together, making our horses' lives better

Disclaimer: These are my thoughts and opinions and should not be considered expert or medical advice. I recommend that you seek professional advice in relation to your horse/s.

References: