Changes in the milk lactose concentrations (%) of lactating cows fed diets with alfalfa hay (AH), corn stover (CS), or rice straw (RS) as the main forage source. The x-axis represents the weeks during the feeding experiment. The first 2 wk (−2 to −1) was considered the dietary adaptation feeding period. *During the indicated week, the lactose concentrations in the cows fed the RS diet were similar to those in the CS-fed cows (P > 0.05). The other weeks without symbols were different in the comparisons for CS vs. RS (P < 0.05). Across the sampling weeks, the lactose concentrations were similar in AH vs. CS (P > 0.05) but were different for AH vs. RS (P < 0.05).