<p>Mild-moderate equine
asthma (EA) is a commonly encountered disease of racehorses that affects
performance. Decreasing dust exposure is crucial in the treatment of equine
asthma. Dry hay, because of its high dust content, is known to increase the
risk of airway inflammation. Feeding haylage, steamed hay, or hay pellets
instead can help to decrease dust exposure. Haylage may also contribute to the
resolution of airway inflammation by providing higher levels of omega-3 polyunsaturated
fatty acids (Ω-3). Higher levels of Ω-3 are associated with an increase in
pro-resolving lipid mediators (PRLM), essential molecules in the resolution of
airway inflammation. </p>
<p> The studies presented in this dissertation
were designed to test the hypothesis that feeding low-dust forages would
decrease airway inflammation in racehorses, and that haylage would provide
superior resolution of airway inflammation compared to other low dust forages
due to changes in systemic Ω-3 and PRLM concentrations associated with
increased dietary Ω-3 intake.</p>
<p>Three clinical trials
were conducted to determine the effect of low-dust forages on airway
inflammation. Environmental exposures were measured at the breathing zone, and bronchoalveolar
lavage (BAL), and differential cytology counts were performed as measure of
airway inflammation. </p>
<p>The first clinical
trial was a pilot study performed with 7 Standardbred racehorses. Horses were
randomly assigned to eat hay (n=3) or haylage (n=4) for 6 weeks while in
training. Measurements were performed at baseline and after 2, 4, and 6 weeks.
Results showed a decrease in respirable dust, and β-glucan exposure in the
horses fed haylage when compared to those fed hay. BAL neutrophil proportion
was significantly lower at weeks 2, 4, and 6 when compared to baseline and at
week 6 when compared to horses fed hay. </p>
<p> The second clinical trial was performed on 19
mild asthmatic horses from the teaching herd. The diet of these horses was
changed from dry hay to haylage (n=9) or hay pellets (n=10) for 6 weeks.
Measurements were performed at baseline, week 3, and week 6. Results indicated
that horses eating haylage and hay pellets were exposed to similar dust levels
that were significantly lower than when they were eating dry hay. BAL
neutrophil proportion was significantly lower in horses eating haylage when
compared to baseline and to horses eating hay pellets at week 6. Horses eating
haylage exhibited a significant decrease in stearic acid concentration at week
6. Pro-resolving lipid mediators (Resolvin D1, Resolvin E1, and Lipoxin A<sub>4</sub>)
did not affect neutrophil apoptosis or efferocytosis <i>in vitro</i>.</p>
<p>The third clinical trial was performed
on 73 thoroughbred racehorses actively racing and training. Horses were
randomly assigned to eat dry hay or to change the forage to steamed hay or
haylage. No other change in the management of the horses was allowed. Measurements
were performed at baseline (n=73), week 3 (n=69), and week 6 (n=53). Results
indicated that respirable dust exposure was significantly reduced when
racehorses were fed steamed hay or haylage in place of dry hay. Respirable dust
exposure was positively associated with BAL neutrophil proportions. Feeding
haylage also significantly decreased exposure to respirable endotoxins. Horses
eating haylage for 3 weeks had significantly lower BALF neutrophil proportion
when compared with baseline. Also, at week 3, horses eating haylage showed a
significant decrease in mast cell proportion, and horses eating steamed hay had
a significant decrease in eosinophil proportion. At week 6, horses eating
haylage maintained significantly lower BALF neutrophil proportions compared to
baseline, and horses eating hay for 6 weeks. Concentration of Ω-3 and PRLM were
not increased in horses eating haylage when compared to horses fed hay.
Eicosapentaenoic acid was significantly higher on the horses eating haylage
when compared to horses eating steamed hay. </p>
<p>In conclusion, feeding low-dust forages
is sufficient to decrease breathing zone exposure of horses to respirable dust.
Despite similar dust exposure, haylage was the only low-dust forage that resulted
in resolution of neutrophilic airway inflammation; however, the mechanism
remains unclear.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12563690 |
| Date | 25 June 2020 |
| Creators | Carla Olave (9027407) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/The_effect_of_low-dust_forages_and_the_role_of_pro-resolving_lipid_mediators_in_mild-moderate_equine_asthma/12563690 |
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