Step 1: Understanding the Concept:
During milking, the physical action of milk withdrawal dilates the teat canal and relaxes the teat sphincter muscle. It takes some time for this physiological barrier to close completely.
Step 3: Detailed Explanation:
1. Immediately after milking, the teat sphincter muscle remains relaxed, and the teat canal stays open for approximately 30 to 40 minutes.
2. If the animal lies down on a contaminated floor or pasture during this time, environmental pathogens can easily enter the open teat canal, leading to mastitis.
3. Therefore, animals must be kept standing for at least 30-35 minutes after milking.
4. Farmers usually achieve this by offering fresh, palatable feed or green fodder immediately after milking, enticing the animals to remain standing while eating.
Step 4: Final Answer
The correct option is (D).