We have suspected from field observations that intensive-fed preweaned calves have problems digesting solid feeds in the early post-weaning period.
In an abstract entitled, "Performance of and digestion in calves fed conventional, moderate, and aggressive milk replacer programs," [Hill and Others, J.Dairy Sci Vol 97, E-Suppl 1, #613] results are reported for intensively-fed calves that received 2 pounds of milk replacer daily. These calves were compared to those fed 1 lb. and 1.5 lb. of powder daily. Thus, there were three treatment groups.
The intensive-fed calves were fed the full ration of powder up to 49 days. In contrast the calves receiving the lower amounts of powder until 42 days. The method of weaning is not described - perhaps it was done by abruptly in one day.
Not surprisingly, the calves fed less milk replacer powder ate more calf starter grain than the intensively-fed calves. Though not included in the brief abstract we can almost be certain that the calves fed less milk replacer powder began regularly consuming grain earlier in life than the calves receiving more powder. These facts would lead us to the conclusion that the levels of rumen development would vary with the highest level being among the calves that began to consume grain earliest in life and among the calves that consumed the largest volume of grain.
NDF digestibility was analyzed on fecal samples collected on days 51-55 on trial from calves in all three treatment groups. The values reported were:
- Lowest milk replacer group = 54%
- Middle milk replacer group = 51%
- Highest milk replacer group = 26%
Thus, what we have seen on farms is documented. Intensive-fed calves that are not weaned with enough time to let their rumen maturation reach the "mature enough to feed me" level are at a severe disadvantage.
These data showing a NDF digestibility level of only one-half of the other calves reinforce the need to carefully plan a "step-down" weaning program for intensively-fed calves.