After a 56-day period of adaptation to a high-concentrate
diet, the animals were confined for 45 days with different
sunlight exposure conditions. Twenty steers were held in
pens without sunshade (the pens on the southwest side),
and the other 21 steers were held in shaded pens (the pens
on the northeast side). On the 25th day of exposure to different
sunlight exposure conditions, all the animals were conditioned
to receive part of their diet in a small trough to
simulate the vitamin D3 supplementation procedure, before
receiving the remaining portion of the diet. On the 37th or
43rd day at the feedlot, the animals began supplementation
with vitamin D3 for 8 or 2 days.