A study was conducted to test the hypothesis that cows fed a diet that does not meet nutrient requirements for production will alter their behavior to maximize nutrient consumption, particularly when fed a more easily sorted diet. Holstein cows (n = 30) were followed for a 2-wk baseline period where they were fed (on a DM basis) a lactating diet (NE_L = 1.66 Mcal/kg; 68% forage), and then exposed for 3 wk to 1 of 2 treatment diets: a TMR, formulated for a 12% reduction in energy available for milk (NE_L = 1.56 Mcal/kg; 73% forage), containing 17% straw chopped to: 1) 2.54 cm (Short; n = 15) or 2) 10.16 cm (Long; n = 15). TMR samples (fresh and orts) were collected every 3 d and separated into 4 fractions: long (>19mm), medium (<19mm, > 8mm), short (<8mm, > 4mm), and fine (<4mm) particles. Feed sorting was calculated as: actual intake of each particle fraction expressed as a % of its predicted intake. Data were analyzed in repeated measures, mixed-effect linear regression models. Cows consumed 25.3 ± 1.1 kg/d during the baseline. DMI decreased (P < 0.01) on the experimental diets; DMI was greater for the Short diet as compared with the Long diet (23.2 vs 22.4 kg/d; SE = 0.5; P = 0.04). During the baseline period, cows sorted against long particles (95.4 ± 2.0%), did not sort medium particles (99.8 ± 0.23%), and sorted for short (101.1 ± 0.4%) and fine (101.9 ± 0.6%) particles. Cows did not change (P = 0.99) sorting of long particles on the Short diet (95.1 ± 1.0%), but increased (P < 0.01) sorting against these on the Long diet (89.4 ± 1.0%). Medium particle sorting did not change (P > 0.8) on the Short (100.1 ± 0.2%) and Long (99.9 ± 0.2%) diets. On the Short diet cows did not change (P > 0.2) their sorting of short (100.9 ± 0.9%) and fine (100.6 ± 0.9%) particles. On the Long diet, cows increased (P < 0.01) sorting for short (103.3 ± 0.9%) and fine (104.5 ± 0.9%) particles. During baseline, cows produced 44.6 ± 1.2 kg/d of milk; this decreased (P < 0.01) on the experimental diets. Despite differences in DMI, milk yield remained similar between treatments (Short = 38.7, Long = 39.5 kg/d; SE = 1.9; P = 0.5), possibly due to sorting. This suggests that cows exposed to a diet that does not meet their nutrient requirements will sort that diet, when possible, to maximize nutrient consumption.