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Effects of Intragastric Loads of Xylose, Sodium Chloride and Corn Oil on Feeding Behavior of Ponies¹

University of Pennsylvania, Kennett Square 19348

Abstract

This series of experiments was designed to investigate gastrointestinal (GI) stimuli that contribute to the normal control of feed intake in ponies. Osmotic stimuli were tested using intragastric (IG) infusion of .83 osmolar solutions of xylose (250 g) and NaCl (48 g) vs 2-liter water controls. Treatments were given 15 min before ponies were allowed ad libitum access to pelleted feed after a 4-h fast. Both hyperosmotic solutions delayed onset of the first meal (xylose: 72 ± 32 min, P<.05; NaCl: 71 ± 40 min, P<.1), resulting in an immediate reduction (P<.01) in feed intake. No effects were observed 3 to 18 h post-treatment and 24-h intake was not affected. The behavioral responses to the hyperosmotic solutions, however, were different. The xylose-treated ponies displayed normal sequences of satiety behaviors before eating their first meal, whereas the salt infusion caused moderate to severe colic in five of seven of the same animals. Nutrient stimuli were tested using infusions of corn oil (133 g) or mineral oil (133 g) administered 15 min before the ponies were fed after a 4-h fast. Corn oil did not alter the onset of feeding or the size or duration of the first meal relative to control values. The first intermeal interval, however, was prolonged (91 ± 27 vs 29 ± 4 min; P<.05) and feed intake 3 to 18 h post-treatment was reduced (1.00 ± .42 vs 2.01 ± .30 kg; P<.05) by corn oil relative to mineral oil. These results are comparable to those obtained in earlier experiments testing nutrient vs bulk solutions. It appears that nutrients in the gastrointestinal tract of ponies provide stimuli that affect subsequent feeding responses primarily by delaying onset of meals. Osmotic stimuli do not appear to play a major role in the satiety responses.

¹ This research was supported in part by grants in aid from the fund for the study of Feeding behavior, Dept. of Clinical Studies, School of Vet. Med., Univ. of Pennsylvania; USDA Grant PENN-5-26121 and NIH Training Grant GM-02051-10

² The authors would like to thank Ms. Terri Jordan and Ms. Lisa Delano for their technical assistance and Mr. Richard Barker for performing the xylose assays.