I am looking at heifers in a transition pen. The owner tells me, "When I move heifers into this pen they stop growing. After three or four weeks they seem to take off again."
I checked out the ration for this pen - it is the first pen into which calves are moved as they come from individual pens after weaning. The ration before the move was calf starter grain and water for one full week after the calves were weaned. The ration in this pen was free-choice haylage topped off with a grower pellet.
The heifers in this transition pen found the haylage quite palatable - they were eating lots of it. Remember, however, that before moving into this pen they had no exposure to any kind of forage, especially this haylage.
What was going on here? Heifers consuming the haylage for the first week in the pen did not have the appropriate microbial population to break down this fiber source. The haylage just went into the front, turned brown and came out the back - not much nutrition there. Eventually, after a week or two the rumen microbial population reached a new equilibrium with the digesting microbes matching the dietary content.
So, the heifers were, in fact, put on an involuntary negative-energy ration the first week or two in this pen - they were eating but not benefiting from what was eaten. No wonder they stopped growing. This dairy was fortunate that circumstances did not otherwise stress the calves and they had very few problems with respiratory illness in this pen.
I looked at the older heifers and they appeared to be in good health. However, an opportunity for growth was slipping away from this dairy. They could have introduced the haylage in the individual pens during the last week calves were housed there. They could have introduced the haylage in smaller amounts in this first group pen - maybe the amount the heifers would clean up in half an hour each day for the first ten days or so before going to free-choice feeding.
Just a thought here - remember that just like mature cows, in these 2-4 month-old heifers we are feeding a rumen, not the animal.