140 Measuring gastric emptying in horses with the 13C-acetate breath test when changing feeding order

Abstract

Feeding order of oats and forage may influence the rate of gastric emptying (GE), but knowledge of GE is limited as it can be challenging to measure. The 13 C-acetate breath test (ABT) has been suggested as a minimally invasive way to measure GE using spot samples of breath air. The objective of this study was to determine the effect of feeding order of oats and forage on GE in horses. It was hypothesized that feeding oats before forage increases the rate of GE of oats as compared with feeding oats after forage. Four adult horses (15–24 yr) were used in this 2 × 2 crossover study, with 2 periods of 12 d. Each period consisted of a 10 d diet adaptation and 2 d sampling. Horses were fed the same amount of oats (470g dry matter (DM)) and forage (6900g DM) per day. Forage was fed 3 times per day (06, 14 and 20h), while oats were only fed in the morning either before or after forage. On d 2 of sampling, oats were mixed with 1g of 13 C-acetate. Before feeding oats, 3 baseline samples of exhaled breath air were taken. After feeding oats, a total of 12 samples were taken every half hour for 4 h, and then every hour until 8 h after administration of 13 C-acetate. Exhaled breath was collected in 1L breath bags using a mask connected to a 2-way non-rebreathing valve system. The mask covered one of the nostrils and a breath sample was taken within 30s. The breath bags were analyzed for 13 C-enrichment of CO 2 by means of an infrared isotope analyzer. The 13 C excretion curve (% dose recovered/h), was plotted using the formula y = a tb e −ct where y is the exhaled 13 C per hour in % of the dose (PDR, %/h), t is time (h) and a, b and c are regression constants. Half dose recovery time (T 1/2 ) was calculated from the area under the fitted cumulative 13 C excretion curve using the Excel function Gammainv (0.5;b+1;1/c), and time of peak excretion (T max ) was calculated as b/c. The effect of feeding order was compared using PROC mixed in SAS and considered significant if P < 0.05. The results indicate a faster rate of GE of oats when feeding oats before hay and there was approximately 1 h difference in T max . Oats will spend less time in the stomach when feeding oats before hay, but how this affects the digestion of starch in the stomach, small intestine and hindgut needs further investigations. In conclusion, the 13 C-ABT is a promising minimal invasive technique for measuring GE in horses.