The Effect of Oat Hay, Alfalfa Hay, and Their Combined Diets on the Morphology and Function of the Pancreas in Preweaning Yak Calves

SIMPLE SUMMARY: The purpose of this study was to investigate the effects of different source forages fed to preweaning yak calves on growth performance, pancreatic morphology, and functional development. In the experiment, we performed three different sets of experimental treatments by feeding tests, collected pancreatic tissues and recorded their organ indices at the end of the experiment, collected pancreatic tissue samples to observe morphological structures by tissue sectioning, determined the activity of main digestive enzymes and hormone levels in the pancreas by enzyme-linked immunosorbent assay, and obtained metabolic pathways and their small-molecule differential metabolites by nontargeted metabolomics techniques. The endocrine and exocrine divisions of the pancreas, which functions as a metabolic organ, are involved in the control of glucose and the organism’s digestive metabolism. We discovered that feeding preweaning yak calves a combination of oat hay and alfalfa hay was better for the morphological and functional development of the pancreas than feeding either hay alone. This is essential for the early development of the pancreas in yak calves and serves as a critical resource for their healthy growth and scientific feeding. ABSTRACT: In this study, we used a combination of animal nutrition and nontargeted metabolomics to investigate the effects of feeding different sources forages rations on the morphology and function of the pancreas in preweaning yak calves, providing theoretical guidance and important references for the healthy and high-quality rearing of yak calves. At 45 days old, 21 yak calf males were divided into OP, AP, and AOP groups, with seven animals in each group, which were fed with oat hay, alfalfa hay, and mixed oat and alfalfa hay, respectively. Five calves from each group were selected randomly to slaughter after a pretest period of 21 days and the official period of 120 days, when the average daily feed intake reached 1 kg. During the test, the growth and pancreas weight of yak calves were recorded, and the morphology and function of the pancreas tissues were determined using tissue sectioning methods, enzyme-linked immunosorbent assay (ELISA) tests, and nontargeted metabolomics strategies. The results showed that the body weight and pancreatic organ index of yak calves in the AOP group were significantly higher than those of the AP and OP groups. Compared to the AP and OP groups, the AOP group had considerably lower ratios of the area of the pancreatic endocrine component and overall percentage of that section of the organ, and the AOP group increased pancreatic amylase activity and a higher concentration of growth inhibitor. The AP group had significantly higher levels of the differential metabolites L-ascorbic acid, spermidine, spermine, and dopaquinone in the glutathione, β-alanine, and tyrosine metabolic pathways than the OP group. The AOP group had significantly lower levels of the differential metabolites spermine and phenylacetylglycine in the glutathione and phenylalanine metabolic pathways than the AP group. In summary, compared to feeding oat or alfalfa hay alone, combined feeding oat hay and alfalfa hay is more beneficial to promote the morphological and functional development of the pancreas in preweaning yak calves, so as to enhance the digestion and absorption of nutrients in the diet and maintain the positive regulation of blood glucose levels. This provides an important basis for the optimized forage supply of healthy and high-quality rearing in preweaning yak calves.