Dust exposure and lung inflammation in horses fed dry hay or haylage

Haylage is available commercially and a suitable forage for horses. This paper found there is a significant reduction in lower airway inflammation likely due to the decreased dust in haylage compared to hay. There is a very small risk of botulism poisoning however. If you decide to feed haylage it is recommended you vaccinate with the botulism toxoid first.
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Dust exposure and pulmonary inflammation in Standardbred racehorses fed dry hay or haylage: A pilot study
Vet J. 2021 May;271:105654.
Authors
C J Olave 1 , K M Ivester 1 , L L Couetil 2 , J E Kritchevsky 1 , S H Tinkler 1 , A Mukhopadhyay 1
Affiliations

1 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, 625 Harrison St., West Lafayette, IN 47907, USA.
2 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, 625 Harrison St., West Lafayette, IN 47907, USA. Electronic address: couetill@purdue.edu.

PMID: 33840486
DOI: 10.1016/j.tvjl.2021.105654

Abstract

Respirable dust exposure is linked to airway inflammation in racehorses. Feeding haylage may reduce dust exposure by 60-70%. The objective of this study was to compare dust exposure, airway cytology, and inflammatory cytokine concentrations between horses fed haylage or hay over 6 weeks while in training. Seven healthy Standardbred horses were randomly assigned to be fed alfalfa hay (n = 3) or grass-alfalfa mix haylage (n = 4) for six weeks while training on a treadmill. Dust exposure was measured gravimetrically at the breathing zone. Endotoxin and β-glucan concentrations in respirable dust were measured. Bronchoalveolar lavage fluid (BALF) cytology was determined at baseline and after 2, 4, and 6 weeks. Cytokine concentrations (interferon-γ, tumor necrosis factor-α, and interleukin-4) were measured in BALF at baseline and week 6. The effect of forage on exposure, airway cytology and cytokines were evaluated using generalized linear mixed models. Respirable dust and β-glucan exposures were lower in horses fed haylage than hay (0.02 ± 0.001 mg/m3 vs. 0.06 ± 0.01 mg/m3; P = 0.03, and 69 ± 18 pg/m3 vs. 160 ± 21 pg/m3; P = 0.02, respectively). In horses eating haylage, BALF neutrophil proportion decreased between baseline (2.2 ± 0.5%), week 2 (0.8 ± 0.3%; P = 0.01) and week 6 (0.7 ± 0.2%; P = 0.03). By week 6, horses fed haylage had lower BALF neutrophilia than horses fed hay (4.0 ± 0.7 %; P = 0.0004). Interleukin-4 concentration in BALF was higher at week 6 (14.4 ± 4.6 pg/mL) in horses fed hay compared to baseline (2.9 ± 4.6 pg/mL; P = 0.007). In conclusion, feeding haylage instead of hay to horses in training can reduce exposure to respirable irritants and mitigate airway neutrophilia.

Keywords: Asthma; Beta-glucan exposure; Horse; Neutrophils; Respiratory tract.