Which two trace elements must be added to swine diets?

The correct answer highlights the importance of iron and zinc as essential trace elements that must be added to swine diets. Iron is crucial for various physiological functions, including the formation of hemoglobin in red blood cells, which is vital for oxygen transport. Young piglets, in particular, are often born with low iron reserves and can develop anemia if not supplied with adequate amounts through their diet or supplementation.

Zinc plays a critical role in maintaining immune function, skin integrity, and overall growth and development in pigs. It is also necessary for various enzymatic reactions and contributes to the health of the reproductive system. Ensuring that swine diets are supplemented with these two trace elements is essential for the health and productivity of the animals.

The other options involve elements that either do not need to be added to swine diets or are harmful. Lead and mercury are toxic substances and should never be included in animal diets. Copper and iodine, while important in other contexts, are not the primary trace elements that are typically supplemented in swine diets. Calcium and phosphorus are important but are classified as macroelements rather than trace elements.