Masters Theses

Date of Award

8-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Comparative and Experimental Medicine

Major Professor

Frank Andrews

Committee Members

Alan Mathew, James T. Blackford, Robert A. Argenzio, Arnold Saxton

Abstract

Six 7 year old, mixed breed mares with chronic gastric cannulae were used to determine the effect of two different diets on pH, acidity (hydrogen ion concentration), volatile fatty acid (VFA) production, and number and severity of lesions in the stomach of horses. VFAs are produced from the fermentation of carbohydrates. High concentrations of VFAs have been found in the gastric contents of pigs and rabbits and have been associated with acid injury and ulceration. High carbohydrate diets are often fed to performance horses. Excess VFAs produced from these carbohydrates may cause acid injury and gastric ulceration due to the lack of normal protective factors (mucus and bicarbonate) found in the squamous mucosa of the horse. In part I of the study, the mares were fed a bromegrass hay meal ad libitum for 12 hours. Part I of this study was used to determine methodology for part II of the study. In part II of the study, the six 7 year old cannulated mares were fed a bromegrass hay and an alfalfa hay/grain diet in a randomized two period crossover design. Gastric juice was collected immediately postfeeding and 1, 2, 3, 4, 5, 6, 7, 8, 10, 12 and 24 hours in part I of the study and after the morning meal on day 14 of each period of part II of the study while the horses fasted. Gastroscopy was performed on the horses before and after each diet, by a researcher blinded to the test diets, to determine ulcer number and severity using an ulcer scoring system. In each gastric juice sample collected, pH was measured using a pH electrode, hydrogen ion concentration (mmol/l) was measured by electrometric titration to end point 7.0 using 0.1 N NaOH, and VFA concentrations (acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, and isovaleric acid) were measured using a Hewlett-Packard Model 5890 Gas Chromatograph (Hewlett-Packard, Avondale, PA). D- and L+ lactic acid concentrations were also measured in the gastric juice samples using a prepared kit. The pH and acidity of the gastric contents were variable throughout the 24 hour collection period in parts I and II of the study. The alfalfa hay/grain diet generally produced a higher pH in the gastric juice samples collected for the first seven hours. Acetic acid concentration was highest in gastric contents immediately postfeeding to five hours, followed by a decrease from 5 to 12 hours. All other VFAs remained at low concentration throughout the sampling period. Acetic acid, propionic acid and isovaleric acid were significantly higher when horses were fed the alfalfa hay/grain diet. D- and L+ lactic acid concentration remained low throughout the study. Mean dry matter remained less than 10% throughout the study. Gastric lesion number was higher in horses fed the bromegrass hay diet when compared to horses fed the alfalfa hay/grain diet, but this difference was not significant. However, gastric lesion severity was significantly higher in horses fed the bromegrass hay when compared to horses fed alfalfa hay/grain. A stepwise model for each diet was used to determine which parameters (pH, acidity, VFA, D- lactate, L+ lactate, dry matter) would be the best predictors of lesion severity. It was found that isobutyric acid (69.6%) was able to predict lesion severity in the bromegrass hay diet fed in part I. It was found that valeric acid (78.2%), pH (14.3%), butyric acid (7.3%), and propionic acid (0.2%) were able to predict lesion severity in the alfalfa hay/grain diet fed in part II. It was found that valeric acid (64.1%) and butryic acid (2.1%) were able to predict lesion severity in the bromegrass hay diet fed in part II. VFA from the fermentation of carbohydrates, are present in the stomach of horses, can be measured by gas chromatography, and are higher in horses fed the alfalfa hay/grain diet. An increase in VFA concentrations in the stomach may, if absorbed, lead to acid injury of the non-glandular squamous mucosa causing a predisposition to ulceration.

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