Final answer:
BRD in feedlot calves is commonly diagnosed within the first few weeks after arrival due to transportation stress and changes in diet compromising their immune systems. Feedlot operators must watch for signs and provide early treatment.
Step-by-step explanation:
The most common time to diagnose BRD (Bovine Respiratory Disease) in feedlot calves is typically within the first few weeks after their arrival at the feedlot. During this period, the stress of transportation, changes in diet, and mixing of herds can suppress the immune system, making the calves more susceptible to respiratory infections. Feedlot operators must monitor the cattle closely during this high-risk period for signs of BRD, which can include coughing, nasal discharge, lethargy, and reduced feed intake. Early diagnosis and treatment are crucial to preventing the spread of the disease and ensuring the health and well-being of the feedlot calves.