Which of the following is a sign of ketosis in livestock?

The correct indication of ketosis in livestock is the protruding tongue. Ketosis is a metabolic disorder commonly seen in dairy cows, particularly during the early lactation period when there is a negative energy balance. As the animal's body begins to utilize fat reserves due to insufficient energy intake, the metabolism produces excess ketone bodies, leading to various physiological signs.

A protruding tongue can occur as the animal becomes lethargic and may show signs of incoordination, indicating potential neurological effects from ketosis. The difficulty in managing energy levels during ketosis can lead to decreased feeding and potential complications, which can manifest physically, including changes in tongue position.

Considering the other options, rapid weight gain would generally not be associated with ketosis, as affected animals typically lose weight due to decreased feed intake and energy utilization. Excessive urination does not directly signify ketosis; while certain metabolic states can alter urinary output, this symptom is not uniquely indicative of ketosis. Lastly, high energy levels are not characteristic of ketosis; rather, affected livestock often exhibit low energy as they struggle with metabolism due to a lack of available glucose. Thus, the protruding tongue stands out as a notable clinical sign associated with ketosis.