This is a common question when feeding cull cows that have come from pasture situations into a drylot to be conditioned for harvest. White fat is more desirable than yellow fat. Yellow fat is a result of the cows consuming high amounts of carotene, which is high in forages. High-grain diets, which are inherently low in carotene, will help convert yellow fat to white fat. Some research suggests that feeding a high-grain diet for as few as 56 days will result in a significant change from yellow to white. However, other research has not documented a change in the amount of yellow fat in cows on feed for as long as 105 days. A best guess might be somewhere in the 80 to 90 day range. There are no data on this, but it can be supposed that it would be no different for yearlings that graze pasture, then enter the feedlot after a spring/summer grazing period. If you are asking about calves that are weaned at 7 to 9 months of age that have been on pasture with their dams, the information above may not be useful because these calves are usually fed for 180 to 210 days, and the finishing period would be on a high-grain diet.

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