## 2 Materials and Methods
### Animals, Housing, and Sample Collection  
The swine in the present study were selected from the herd at the Swine Research Unit of China Agricultural University. The pigs were housed indoors throughout the study. In experiment 1 (Exp. 1) a total of twelve healthy castrated male piglets (from 3 litters, Duroc \(\times\) Landrace \(\times\) Yorkshire) were selected one week after weaning (weaned at 28 d of age). These pigs subsequently adapted to a specific diet (Table 1), which did not contain vitamin A (retinyl acetate) and vitamin E (D, L-\(\alpha\)-tocopherol acetate). Seven days before the start of the experiment (48 d of age for the pig), the piglets were individually housed in stainless steel metabolism crates (cage size: \(1.4\times 0.7\times 0.6\) m) and adapted to twice daily meal feeding based on 4% of their body weight (BW). Seven days before the beginning of the experiment, the pigs were catheterized in the jugular vein by inserting a needle into the vein, and then insertingthe catheter through the needle. Once the catheter was in place, the needle was withdrawn, and the catheter was taped to the pig's neck. This procedure was modified from that of [PERSON] et al. [12]. The piglets were anesthetized using Zoletil (6 mg/kg BW; Virbac Laboratories, Nice, France), and Butorphanol (200 ug/kg BW; Intervet International, Boxmeer, The Netherlands). After catheterization, Butorphanol was administered once as a painkiller, and Depocillin (0.05 mL/kg BW; MSD Animal Health, Wellington, New Zealand) was intramuscularly administered for 3 consecutive days to prevent infections. Catheters were flushed daily with heparinized sterile saline (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China). Before the beginning of the experiment, all pigs were fasted for 12 h to assure that the pigs would be hungry, allowing the test meal to be consumed within a shorter period. The average BW of the pigs was \(20\pm 1\) kg at the beginning of the experiment. Twelve pigs with a starting age of 56 d were allocated into 2 groups. Pigs in the non-microencapsulated group received a diet with non-microencapsulated 13,500 IU/kg retinyl acetate and 30 mg/kg D, L-\(\alpha\)-tocopherol acetate. The pigs in the microencapsulated group received a diet with microencapsulated 13,500 IU/kg retinyl acetate and 30 mg/kg D, L-\(\alpha\)-tocopherol acetate. These vitamins were provided by Wellroad Animal Health Co. Ltd., Taiyuan, China. Immediately before feeding of the test meal, the blood sample at 0 h was obtained from all pigs in the experiment. The time when providing vitamins A and E was set as time 0. Subsequently, blood samples were taken via the jugular catheters from all individuals at 1, 3, 6, 9, 12, 16, 18, 21, 24, 27, 30, 36, 48, and 72 h. These blood samples (approximately 8 mL) were collected in 10-mL EDTA-containing tubes (Becton Dickinson Vacutainer Systems, Franklin Lakes, NJ, USA). In experiment 2 (Exp. 2), a total of 216 weaned piglets (Duroc \(\times\) Landrace \(\times\) Yorkshire) with an average BW of \(7.04\pm 0.34\) kg were assigned to 6 treatments with 6 replicate pens (3 barrows and 3 gilts \begin{table}
\begin{tabular}{c c} \hline \hline
**Items** & **Amount, \%** \\ \hline Corn & 68.61 \\ Soybean meal & 24.00 \\ Soybean oil & 3.02 \\ Monocalcium phosphate & 1.60 \\ Limestone & 0.80 \\ Salt & 0.30 \\ L-lysine HCL & 0.53 \\ DL-methionine & 0.13 \\ L-threonine & 0.24 \\ Tyyptophan & 0.04 \\ L-valine & 0.20 \\ Trace mineral premix 1 & 0.50 \\ Vitamin premix without vitamins A and E 2 & 0.03 \\ Total & 100.00 \\ Calculated nutritional values & \\ Metabolized energy (Kcal/kg) & 3452.39 \\ Crude protein & 17.30 \\ SID Lysine & 1.23 \\ SID Methionine & 0.36 \\ SID Threonine & 0.73 \\ SID Typyptophan & 0.20 \\ SID Valine & 0.78 \\ Total Calcium & 0.74 \\ STTD Phosphorus & 0.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the diet in the experimental 1 (as-fed basis). per pen) per treatment according to sex and BW in a randomized complete block design.