Step 1: Understanding the Concept:
A pen barn (or loose housing system) is a cattle housing layout where animals are kept loose in partitioned enclosures, except during scheduled milking.
Step 3: Detailed Explanation:
In modern dairy farming, specialized pens are designated for distinct functional needs:
1.
Calf rearing (B): Young calves are housed in dedicated individual or group pens for specific feeding and sanitary control.
2.
Calving (C): Pregnant cows are moved to spacious calving (maternity) pens to ensure a safe, clean birthing environment.
3.
Housing sick animals (D): Separation pens (isolation pens) isolate sick animals to prevent disease spread.
4.
Milking (A): Milking is not conducted within these loose pens; animals are guided to a highly sanitized, separate milking parlor.
Thus, pen barns are utilized for (B), (C), and (D).
Step 4: Final Answer:
The correct option is 2, which corresponds to (B), (C) and (D) only.