Abstract
This study was investigated the effects of dietary supplementation of leucine and phenylalanine on the development of the gastrointestinal tract and the intestinal digestive enzyme activity in male Holstein dairy calves. Twenty calves with a body weight of 38 ± 3 kg at 1 day of age were randomly divided into four groups: a control group, a leucine group (1.435 g·l−1), a phenylalanine group (0.725 g·l−1), and a mixed amino acid group (1.435 g·l−1 leucine plus 0.725 g·l−1 phenylalanine). The supplementation of leucine decreased the short-circuit current (Isc) of the rumen and duodenum (P<0.01); phenylalanine did not show any influence on the Isc of rumen and duodenum (P>0.05), and also counteracted the Isc reduction caused by leucine. Leucine increased the trypsin activity at the 20% relative site of the small intestine (P<0.05). There was no difference in the activity of α-amylase and of lactase in the small intestinal chyme among four treatments (P>0.05). The trypsin activity in the anterior segment of the small intestine was higher than other segments, whereas the α-amylase activity in the posterior segment of the small intestine was higher than other segments. Leucine can reduce Isc of the rumen and duodenum, improve the development of the gastrointestinal tract, and enhance trypsin activity; phenylalanine could inhibit the effect of leucine in promoting intestinal development.
Highlights
The gastrointestinal tract is the main place for all animals and humans to digest diets and absorb nutrients
Milk can directly reach the abomasum without going through the rumen and reticulum to undergo preliminary digestion, and milk can reach the small intestine to be digested and absorbed [18], thereby avoiding changes of nutrient components in the diet caused by microorganisms in the rumen and reticulum. Taking advantage of this physiological characteristic and with slaughter testing, this study examined the effects of leucine and phenylalanine supplementation up to 8 weeks after birth on gastrointestinal tract development indices, changes in gastrointestinal tract electrophysiology, and changes in digestive enzyme activity in the intestines of calves
This study explored the role of leucine and phenylalanine in the development of the gastrointestinal tract and in the regulation of intestinal digestive enzymes, thereby providing a theoretical basis for the potential supplementation of leucine and phenylalanine for the efficient production of dairy cows
Summary
The gastrointestinal tract is the main place for all animals and humans to digest diets and absorb nutrients. Different dietary nutrient levels can affect the gastrointestinal development in calves [1,2,3], with diets with suitably high protein levels shown to promote gastrointestinal development in calves [4,5]. As a functional amino acid [6], can activate the mammalian target of rapamycin pathway to regulate protein synthesis and catabolism in the animal body [7,8,9,10] and promote the development of the gastrointestinal tract in animals [11]; phenylalanine is an aromatic amino acid and can promote the secretion of cholecystokinin (CCK) through calcium-sensing receptors [12,13].
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