Which of the following would be considered a source of energy in livestock feed?

Corn is recognized as a primary source of energy in livestock feed due to its high starch content. Starch is a carbohydrate that livestock can efficiently metabolize into energy, making corn an ideal ingredient for energy-dense rations. The energy derived from corn is essential for supporting the growth, maintenance, reproduction, and overall productivity of livestock.

Other feed options listed play different roles in livestock nutrition. Soybean meal, while providing protein and amino acids, isn't primarily an energy source. Alfalfa serves mainly as a source of fiber and protein, which contributes to digestive health and provides nutrients but does not significantly boost energy levels. Flaxseed oil contains fats, which can provide energy but isn't a carbohydrate source like corn. Therefore, corn is the correct answer as it serves specifically as a concentrated source of energy in livestock nutrition.