Straw in the diet of growing heifers “strongly influences” sorting behavior, according to Canadian research in the July Journal of Dairy Science. However, diluting the diet with 10 percent or 20 percent straw can still be done without hurting growth potential and feeding behavior.

During the study, researchers at the University of British Columbia and the University of Guelph fed three different diets to seven-month-old heifers. All heifers received each diet over the course of the study. The control diet consisted of 17 percent corn silage, 52 percent grass silage and 31 percent concentrate. The other two diets consisted of the control diet with the addition of either 10 percent or 20 percent straw. Given their nutrient intake, the heifers would still be able to attain a growth rate of 2.2 pounds per day on the control and 10-percent straw diets and 1.98 pounds of gain on the 20-percent straw diet, says Trevor DeVries, dairy scientist at the University of Guelph in Ontario. Here are some additional results:

  • Sorting behavior. Sorting for medium, short and fine particles increased linearly as straw in the diet increased.
  • Dry matter intake. Intakes decreased linearly as the amount of straw in the diet increased.
  • Feeding behavior. Feeding time and meal duration increased linearly with the addition of straw in the diet. However, feeding rate, meal size and meal frequency decreased with the addition of straw.