Vitamin D is essential for sow health and productivity. Standard sow feed is therefore supplemented with vitamin D₃ or 25-hydroxyvitamin D₃ (25(OH)D₃ ). However, it is uncertain whether the levels achieved are adequate for optimal performance. Currently, information on serum levels of vitamin D in pigs reared under both indoor and outdoor conditions is lacking. In August 2020, we obtained blood samples from 97 organic newly weaned sows housed outdoors during pregnancy and farrowing and used these to test for vitamin D in serum. The average concentration was 67 ± 16 ng 25(OH)D₃ /mL with a range of 32 to 134 ng 25(OH)D₃ /mL. The vitamin D₃ content was 21 ± 7 ng/mL, ranging from 9 to 48 ng/mL. The average number of hours of sun from June to August was 7.0 ± 0.5 h/day. Parity, farm and body condition score did not significantly affect serum levels of 25(OH)D₃ .