Using a slaughter study design a research team in Germany looked at the relationship between different milk feeding levels and rumen development. While not stated in the abstract it seemed clear that the calves were group housed and fed with a computer-controlled automatic feeder.
The low milk replacer feeding rate was 1 2/3 pounds of powder daily. The high milk feeding rate was unlimited milk replacer. These "unlimited-feed" calves increased their consumption of milk powder to well over 2.5 pounds per day with some calves peaking at over 3 pounds by 35 days of age.
The low-fed group continued at 1 2/3 pounds per day until slaughter at 60 days. The high-fed group was stepped down starting at 35 days to 1 2/3 pounds per day. By the end of the study they found that intensive milk feeding did not impair concentrate intake.
Let me add here that from my experience with intensive feeding my own calves I found these calves came up rapidly on grain intake after I cut back their milk around 35 days. I achieved the most rapid increases in grain consumption by making an abrupt 50 percent drop in milk ration with an extended period between feedings rather than using an extended step down in small increments with a continuation of the regular feeding intervals.
On one hand, by examining the entire rumen tissue from the two groups of calves they found no differences in rumen empty weight and papillae length. On the other hand, looking at the same rumen tissue they were able to find differences in papillae density in two of the rumen surfaces.
I conclude that when the step-down process from peak milk consumption is done correctly intensive milk feeding does not significantly depress rumen development in preweaned dairy calves.
Nevertheless, it is easy to screw up the step-down process. You can calculate from the information above that the intensive-fed calves had their last 25 days on the lower milk replacer feeding rate. I regularly see calf operations that are trying to use a three to five day step-down from full feed rates with predictable poor results when intensively fed calves are weaned.
Source: H.M. Hammon and Others, "Intensive milk feeding in calves affects growth performance, metabolic and endocrine traits, but not rumen development" Journal of Dairy Science Vol 97, E-Suppl, #619, page 310.