HAY might look “grand” from the top of the bale, but a new Swiss study suggests your nose and your eye can still catch a fair bit of trouble, and quickly, before it ends up in a horse’s lungs.

Researchers recently set out to test something every horse person already does: the basic, common-sense “sensory check” of hay (smell, look, feel). The question was whether that old-fashioned yard habit actually flags the two big respiratory risks in forage: dust (especially the fine particles that reach deep into the airways) and microbiological contamination (moulds, bacteria and yeasts).

Dry hay samples

The team collected 50 dry hay samples supplied by horse owners and put them through three layers of scrutiny. First came a structured sensory exam (odour, texture, colour, visible impurities) carried out by two trained assessors. Then they measured dust released under controlled conditions, capturing different particle sizes including those most relevant to equine asthma risk. Finally, they ran microbiology, grading hay from normal (grade 1) through to “significantly altered” (grade 4; not acceptable).

The headline result is wonderfully practical: an abnormal, musty smell was the strongest and most consistent predictor of higher dust levels and total particulate matter. In other words, if it smells wrong, it’s far more likely to be putting more inhalable dust into the horse’s breathing zone. That matters because fine dust and the organic “hitchhikers” it carries (mould spores, endotoxins) are closely linked with airway inflammation and equine asthma.

Meanwhile, visible impurities (dirt, debris, obvious contamination) were the clue most associated with microbiological problems. Nearly half the hay met “normal” microbiological standards (46%), but a worrying 18% fell into the “significantly altered” bracket.

Sensory assessment

The authors are careful: sensory assessment won’t replace laboratory testing, and not every “minor deficiency” equals danger. But their message lands: a standardised sniff-and-look protocol is a low-cost screening tool that could help yards avoid feeding the worst hay, especially to horses with asthma or chronic cough. In a world where respiratory management often starts with forage, that’s advice worth taking seriously.