Indoor rearing of pigs and naturally low levels of vitamin D in sow milk mean supplementation to piglets is recommended to avoid vitamin D deficiency. This project looked at serum levels of vitamin D3 with or without supplementation, and the effect of supplementation of ADG, mortality, and morbidity. In the first trial, piglets were orally given 1ml of vitamin D3 or a placebo at  1-5 days of age, and had there serum tested then as well as 23 days later. Supplementation led to D3 serum levels of 23.29±12.06 ng/ml, rather than 8.01±5.91 for the control group. Trial 2 gave 1ml of vitamin D3 or a placebo to piglets at weaning, piglets were weighed and serum levels tested. Mortality and morbidity were tracked, and 28 days later serum levels were retested and piglets reweighed. Control pigs had serum levels of 18.68±3.99 ng/ml, and supplemented pigs had 22.34±6.01. There was no difference in ADG, mortality or morbidity. Trial 3 was similar to trial 2, but pigs were in pens with 27-56 others, not weighed and serum levels tested for 5 pigs/pen. Supplemented pigs had serum levels of 30.60±2.36 ng/ml 28 days post-administration, and control pigs had 17.65±2.40 ng/ml. There was no difference in mortality and morbidity. Oral supplementation of vitamin D3 did increase serum levels, but had no impact on pig performance.