Evaluation of nebulised hay dust suspensions (HDS) for the diagnosis and investigation of heaves. 3: Effect of fractionation of HDS.

The research focuses on the role of inhaled particulates and soluble components in causing responses in horses with a condition known as heaves (analogous to chronic obstructive pulmonary disease in humans). The study distinguishes between the responses to different components of hay dust suspension (HDS) and indicates that a combination of particles and soluble elements may provoke a stronger reaction, suggesting that HDS is more suitable for studying and diagnosing heaves.

Methodology

• The study involved seven horses with heaves and six control horses. Both groups were subjected to inhalation challenges using whole and fractionated HDS.
• The HDS was divided into different components through centrifugation, yielding a supernatant (SUP) and particulate debris.
• The particulate debris was then further processed using saline solution to separate into a washed particulate (WP) fraction, composed mostly of fungal spores, and a wash fraction (WF) that contained soluble components extracted from the particulates’ surface.

Findings

• Both the HDS and SUP led to significant airway neutrophilia—a condition characterized by an excess of neutrophils, a type of white blood cell—in both control and heaves horses. However, the response was stronger in heaves horses.
• It was found that SUP induced less airway neutrophilia compared to HDS, although the levels of endotoxins and protease in HDS and SUP were similar. This suggests that the presence of particulates may have an impact on the strength of the response.
• Inhaling WP and WF triggered a mild airway neutrophilia in horses with heaves, yet a combined SUP and WP challenge triggered a neutrophilic response almost as strong as that caused by HDS, further indicating the relevance of dust particulates in the process.

Implications

• This study suggests that for a greater diagnostic precision and a better understanding of heaves, it may prove useful to use HDS, which encompasses both particulates and soluble dust components, rather than aqueous dust extracts that only contain soluble components.