## 1 Introduction  
In the 21 st century, microencapsulation technology has been extensively applied to nutrients delivery. Microencapsulation is a process that involves the entrapment of a substance within a continuous film of a polymeric material [1]. Microencapsulation provides a physical barrier to protect substances that are vulnerable to external environments, e.g., acidity, alkalinity, heat, oxidation, or moisture, before nutrient release to improve the stability of the nutrients [2]. Vitamins are a large class of drugs in this group and have received much attention [3; 4; 5]. Microencapsulated vitamins are now available as vitamin sources for feed plants, and microencapsulated vitamins have greater stability during storage and processing [3; 4; 5]. Moreover, microencapsulated vitamins target their release in the small intestine to improve absorption efficiency [6] and regulate vitamin concentrations in the blood through a slow and controlled release in the gastrointestinal tract [6; 7]. However, there is a lack of information on the absorption and bioavailability of microencapsulated vitamins in pigs. There are numerous publications related to microencapsulation, but these studies are limited for real industrial applications. This is mostly due to the cost and the feasibility of the process on a large scale. The variety of suitable encapsulants has been even further restricted by their composition and regulations. For these reasons, evaluating the bioavailability of commercially available microencapsulated vitamins for pigs is extremely urgent.  
Vitamins play many essential roles in the normal metabolism and maintenance of body tissue. Vitamin A is essential for the protection and regeneration of mucous membranes; protection of the epithelium, ovulation, and implantation; embryonic and fetal development; and resistance against infection [3; 8; 9]. The main function of vitamin D is the regulation of calcium and phosphorus absorption; thus, vitamin D is important for bone mineralization [8]. Vitamin E is a biological fat-soluble antioxidant at the cellular membrane level, and vitamin K contributes to blood clotting and coagulation [6; 8]. T Water-soluble vitamins are generally required as co-enzymes and are involved in the metabolism of energy (e.g., vitamin B\({}_{2}\) and niacin), amino acid (e.g., vitamin B\({}_{6}\) and folic acid), carbohydrates (e.g., vitamin B\({}_{1}\)), and fat (e.g., biotin and pantotheanate) [8], whereas vitamin B\({}_{12}\), as a coenzyme, is involved in the de novo synthesis of labile methyl groups and their transfer to homocysteine to form methionine. This vitamin is also important in the methylation of uracil to form thymine, which is converted into thymidine and used for the synthesis of DNA [8]. The National Research Council (NRC) has established the recommended requirements of vitamins for pigs, but over time, the NRC requirements of vitamins for pig have not changed much [10]. However, pigs have the potential to grow rapidly and may need more vitamins. Therefore, the concentration of vitamins in pig diets has generally been fortified far beyond NRC recommendations. Adding some vitamins beyond NRC levels in the diet has increased the average daily gain and feed intake of nursery pigs [10; 11].  
We hypothesized that microencapsulation technology can improve the bioavailability of vitamins and that increasing dietary vitamin levels would improve the performance and plasma vitamin concentrations in piglets. Therefore, the objectives of this study were to quantify the relative bioavailability of microencapsulated vitamin A and E in nursery pigs and determine the effects of vitamin form and level on the growth performance and plasma vitamin concentration of weaned piglets.