Developing breeding heifers were fed two levels of modified distillers’ grains with solubles (MDGS), 17.7 and 32.7% of ration dry matter, in combination with haylages over a 122 day period. Heifers that received 32.7% MDGS in their diet started on feed significantly slower and gained significantly less during the first 46 day period. However, during the remainder of the test the 32.7% MDGS heifers gained significantly faster while consuming less feed than either the controls or the 17.7% MDGS treatment group. After 122 days on trial there were no significant difference in ADG or dry matter conversion between the control or treatment groups, but the 32.7% MDGS group consumed significantly less dry matter per day. There were no significant differences between treatment groups for either synchronized AI pregnancy rate or overall pregnancy rate.