Dust exposure and airway inflammation in horses fed round bale hay
Honours research projects are available investigating dust exposure and pulmonary inflammation in horses fed round bale hay using a metal, round bale feeder.
Equine asthma (EA) describes non-infectious lower airway inflammatory disorders that closely resemble various asthma phenotypes in humans (Bond et al., 2018).
Equine asthma has been identified as an important cause of poor performance and racing interruptions in athletic horses (Richard et al., 2010; Wilsher et al., 2006) and is of economic concern to horse racing industries, worldwide (Hinchcliff et al., 2005; Rossdale et al., 1985).
The reported prevalence of EA in racehorse populations range from 56.5% to 81% (Depecker et al., 2014; Ivester et al., 2018). Recently a survey conducted by our group identified a prevalence of 58.7% in the general Australian horse population (Tan et al., 2020).
The term ‘equine asthma’ is used to describe horses with both mild to moderate (previously called inflammatory airway disease – IAD) and severe (previously called recurrent airway obstruction – RAO and summer pasture associated RAO) non-infectious lower airway inflammation (Couëtil et al., 2016).
The pathogenesis of mild/moderate EA (mEA) is not as well defined as for severe EA, and is likely multifactorial. However, the inhalation of airborne particles and antigenic triggers such as dust, endotoxin and fungal, mould and mite debris appear to be central to the development of mEA (Couëtil et al., 2016; Ivester et al., 2018).
Feed appears to have a greater relative impact on airborne particle and antigenic trigger exposure than housing and bedding (Clements and Pirie, 2007a; Ivester et al., 2012).
Changing a horse’s diet from dry hay to haylage, immersed hay or a complete pelleted diet has been demonstrated to reduce respirable particle exposure by 60-70%, 60% and 99% respectively (Clements and Pirie, 2007a, b; Hunt, 2000).
Additionally, feeding dry hay at ground level was associated with an 80% reduction in respirable particle exposure compared with the same hay being fed in hay nets (Ivester et al., 2014).
Round bale hay is commonly used in the Australian horse industry to provide forage to horses housed in dry lots and poor pastures. It is widely accepted and commonly stated in publications (Davis and Sheats, 2019; Wasko et al., 2011) that use of round bale hay is associated with the development of lower airway inflammation due to increased dust exposure. However there appears to be little of evidence to support this.
As such, the effect of round bale hay feeding on airborne particle and antigenic trigger exposure and its effect on lower airway health warrants further investigation.