The group of animals that have recently been weaned and grouped together are often called the Transition Calf Group. However I also hear this called the 'stunting group' on too many farms. Meaning that what was a very healthy calf growing at a good rate of gain per day and on track to freshen at 22 to 23 months of age now slows down her growth, battles health issues, and may not be fresh until 25 or 26 months. So why is this? Maybe it's poor nutrition, but more than likely it is improper housing, animal care, and management.
This group of animals is far too often the forgotten group. We focus labor and capital on keeping calves healthy and growing and on catching heifers in heat and getting them bred, but if we lose a month of time between these two points we will never get it back.
So what things should we look at for this group? First this is often the first time animals are in a group. I like to compare it to Kindergarten. When it was just you, or maybe you and one other sibling, you didn't have much competition for your parents' attention, getting lunch, or something to drink. However, when you went to school you had to compete with 15 or more other kids for the teacher's attention. Lunch and recess were only at certain times of the day, and you had to go someplace else for it. Are your calves being put in a sink or swim environment?
Secondly, the ventilation for this group needs to be looked at a little differently than older heifers. Transition animals are less than 300 pounds at this age. So while lots of fresh air to remove moisture and provide good ventilation is important, care must be taken to not have cold drafts in this shelter. Linked to this is bedding. Because they lack the body mass to hold in heat, during cold weather bedding like straw or fodder that allows the animal to make a nest is a better option than most other sources. Bedding is also an important part of controlling moisture in the shelter by soaking up manure and urine and keeping high traffic areas like the feeder and waterer areas dry.
To help stop drafts in cold weather the recommendation is to provide a solid divider from floor to ceiling every 20 to 30 feet between pens. This does two things; it gives animal something solid to lie against and also stops air from traveling the entire length of the shelter at animal level.
Next, look at resting space per animal. Common recommendations are 30 to 35 square feet per animal. However, remember that space does not include the 6 to 8 feet around the feeder and waterer area, where we don't really want animals lying anyway. If animals will be housed here until they weigh 500 to 600 pounds, I would move that resting area recommendation up to 40 square feet per animal.
Now think of this shelter in the other extreme. What happens in the summer? Can the shelter be opened enough to provide control of not only moisture but also heat? Perhaps circulation fans need to be added to help provide a cooling breeze on hot summer afternoons. The tough part of ventilation with this group of animals is that what is a draft on a 20-degree winter day is a cool breeze on a hot summer afternoon, and the design and management of the shelter must be able to cover both extremes.