Lipolysis of Milk Fat by Pregastric Esterase in the Abomasum of the Calf

The role of pregastric esterase in the abomasal digestion of milk fat was studied in calves having fistulae both in the rumen and the duodenum. Two systems of feeding were employed. Whole milk either was nipple-fed (oral feeding) or was infused directly into the abomasum via the rumen fistula (abomasal feeding). The latter method bypasses the site of pregastric esterase secretion. After feeding, serial collections of the digesta passing from the abomasum into the duodenum were taken for 10 hr. Each hourly sample was analyzed for butyric acid, both total and free, and for higher fatty acids, both total and free. When the milk was fed orally, a high proportion of the total butyric was present as the free acid. When pregastric esterase was excluded by abomasal feeding, however, only a small percentage of the total butyric was present as the free acid. A similar contrast between the two feeding systems was noted also for the higher fatty acids, though the difference was not so great as that observed for butyric acid. These observations suggest that pregastric esterase may be of greater importance than gastric lipase in the abomasal digestion of milk fat.