The objective of this study was to evaluate different forms of carotene can influence gilt growth, immune function, and mammary development. Finishing hogs (n = 224) were randomly assigned to split-sex pens (n = 4 pigs per pen) and to one of four diets: control (7,640 IU vitamin A/kg), supplemented with vitamin A (4.36 ppm for a total of 12,000 IU vitamin A/kg; Rovimix A 1000; DSM: NJ, US – retinyl acetate), supplemented with beta-carotene (163.28 ppm, assuming 26,700,000 IU vitamin A equivalent per kg of product to obtain 12,000 IU vitamin A/kg; Rovimix β-Carotene 10%; DSM; NJ, US), or supplemented with oxidized beta-carotene (OxBC; 40 ppm fed as instructed; 10% active ingredient, Avivagen, Ottawa, ON, Canada). Pigs had ad libitum access to feed and water during the study. Pigs and feeder weights were obtained four times during the study, at the start of the study (d 0), the end of phase 1 (d 21), the end of phase 2 (d 42), and the end of phase 3 (d 63). Diets were adjusted during each phase to meet the pig’s nutritional requirements. At the start of the study, a sub-group of 48 gilts were selected based on the mean weight. These gilts were subjected to a blood sample (K2EDTA vacutainer blood tube; BD Vacutainer, Franklin Lankes, NJ) via jugular stick on d 0, a blood sample and vaccination of Lawsonia intracellularis (2 mL; Porcilis Ileitis from Merck Animal Health USA) and porcine circovirus type 2 (PCV2; 1 mL; Circumvent PCV-M G2 from Merck Animal Health USA) on d 18, a blood sample and booster vaccination of PCV (1 mL) on d 39, a blood sample on day 60 and a final blood sample on day 63. Gilts were euthanized at the end of the study to obtain a liver (right lobe) and a jejunum sample. Additionally, mammary tissue from the second and fourth anterior mammary glands on the right side of the pig were collected to assess mammary gland development. The second glad was fixed for immunohistochemical staining. The fourth gland was snap-frozen for DNA extraction. All samples were stored at -80°C until further analysis, except the liver and muscle samples were stored at -20°C. Liver and muscle were analyzed for vitamins A and E at the Iowa State University Veterinarian Diagnostic Laboratory (Ames, IA). Plasma samples were analyzed for immunoglobulins (Ig) G and M from blood samples taken on d 0 and d 63 of the study via enzyme-link immunoassay. All data were analyzed in SAS 9.4 via GLIMMIX. Pen was the experimental unit with fixed effects of diet and time and random effect of pen for growth parameters. Means were reported from LSMeans using a Tukey adjustment. P-values < 0.05 were considered significant while 0.05 < P-values≤ 0.10 were considered a tendency.  There were no differences (P > 0.05) in bodyweights, average daily feed intake, or gain:feed across dietary treatments. Average daily gain was significantly (P < 0.05) increased in diets supplemented with OxBC over the vitamin A supplemented diets in phases 1 and 3. Vitamin A in the plasma or liver was not significant (P > 0.05) across diets throughout the study. There were no differences (P > 0.05) in IgG or IgM levels. While there was no dietary differences (P > 0.05) across diets for the percent inhibition caused by the Lawsonia intracellularis vaccination, there were significant differences (P < 0.05) across diets for the circovirus vaccination. Additionally, the vitamin A diet had a higher (P < 0.05) PCV2 titer than the control or OxBC diet on d 60 of the study. Immune cell counts in the mammary glands were not different (P > 0.05) across diets for T cells (CD3), B cells (CD20), or macrophages (Iba). There were no differences (P > 0.05) in extracted DNA from the parenchymal tissue from prepubertal gilts. In conclusion, the addition of vitamin A did not improve growth; however, it did improve immune function by increasing antibody titers.