Higher mold content in oats has been linked to coughing in horses in a German study exploring aspects of feed hygiene.
For many horses, forage-based rations are complemented by concentrates. Individual feedstuffs such as cereals or compound feeds in pelleted or non-pelleted (“muesli”) forms are generally used for this purpose.
Cereals are used to meet energy requirements, whereas compound concentrates may also contain protein-rich ingredients such as soya, peas or beans, as well as mineral supplements.
Compound feedstuffs are mostly produced and marketed industrially, whereas cereals such as oats are mostly obtained directly from agricultural production.
In Germany, the Association of German Agricultural Investigation and Research Institutions (VDLUFA) set out values in 2017 to indicate normal microbial loads.
Sandra Intemann and her fellow researchers set out to learn about the potential effects of feedstuffs with microbial contents exceeding the values set by the VDLUFA on horse health.
In their study, reported in the journal Veterinary Sciences, the differences in microbial counts of different concentrate types were investigated in order to gain further insights into their hygienic quality. Another focal point of the study was to clarify whether microbiological differences can be predicted by means of sensory analysis – using sight, smell, and touch.
Further, they sought to clarify whether the occurrence of microbiological deviations in feedstuffs might have a role in gastrointestinal disorders in horses after consuming the feed.
The study team re-examined reports on the hygienic quality of concentrates submitted to the Institute for Animal Nutrition at the University of Veterinary Medicine Hannover, Foundation, between 1993 and 1999, and 2010 to 2016.
In 9% of cases, the feeds were submitted for routine checking; in all other cases, the feedstuffs were suspected of inducing disturbances or disease symptoms in horses because of insufficient hygienic quality. Reported issues included gastrointestinal problems, elevated liver enzymes, poor performance, and a cough.
The study involved 517 concentrate samples, for which oats accounted for the largest share, at 45.8%.
To investigate the hygienic quality of the samples, several methods were used at the institute. The dry matter content was determined and feedstuffs were examined sensorily in a standardized way.
Microbiological examination was then performed at the university’s Institute for Microbiology to determine counts of aerobic bacteria, molds and yeasts, and thus, quantify the microbial load.
It was found that the microbial counts of compound feed exceeded VDLUFA orientation values significantly more frequently than cereals (38.4% versus 22.6%). However, average counts of bacteria, molds and yeasts were higher in cereals than in compound feeds.
Deviations occurred most frequently in aerobic bacteria (in 26.1% of samples).
Mold counts in grains were found to be significantly higher if the dry matter content was below 86%.
The study team could find no relation between the reported gastrointestinal disorders or elevated liver enzyme activities and the microbiological deviations seen in the results.
However, mold counts of concentrates that were suspected of causing coughing in horses were found to be significantly higher than the mold counts of control samples.
“It was shown that a connection can be made between mold content of oats and coughing in horses,” they said.
They continued: “On the one hand, inhaling mold spores is known to induce coughing in sensitive horses. On the other hand, the exceedance of mold counts occurred less frequently in concentrate samples than in forage samples of a previous study.”
They noted the findings of a previous study that concentrates (except for rolled oats) play a minor role as a source of airborne allergens in dust, since the emission of dust is low. Dust emission was shown to be lower in pelleted feedstuffs than in grains and lower in pelleted than in non-pelleted compound feedstuffs.
“This suggests that the contribution of concentrates to dust contamination in horse stables may depend on the type of concentrate used. The results of the present study give further indications that concentrates may play a role in the emission of airborne allergens, since average mold counts were significantly higher in concentrates that were suspected of inducing coughing.”
The comparison of the two investigation periods showed that the hygienic quality of compound feeds was constant, which was not the case with cereals.
“It has to be taken into account that cereals are mostly obtained directly from agricultural production, and thus, no hygienization comparable with pelletizing takes place after harvest.
“Due to this, cereals may be more susceptible to variations in hygienic quality. For example, changing weather conditions during the growing season can influence the extent of colonization with fungi such as Fusarium.”
All in all, the hygienic quality was better in the intact than in the processed oats, they found.
No significant predictor of poor feed hygiene by sensory analysis could be established, they said.
The results indicate that the hygienic status of concentrates is relevant for horse health in the respiratory tract, they concluded.
The study team comprised Intemann, Bernd Reckels, Dana Carina Schubert, Josef Kamphues and Christian Visscher, all with the Institute for Animal Nutrition, part of the University of Veterinary Medicine Hannover, Foundation; and Petra Wolf, with the Institute for Nutrition Physiology and Animal Nutrition at the University of Rostock, also in Germany.
Intemann, S.; Reckels, B.; Schubert, D.C.; Wolf, P.; Kamphues, J.; Visscher, C. The Microbiological Quality of Concentrates for Horses—A Retrospective Study on Influencing Factors and Associations with Clinical Symptoms Reported by Owners or Referring Vets. Vet. Sci. 2022, 9, 413. https://doi.org/10.3390/vetsci9080413
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