Concept:Rickets is a bone disease caused by a deficiency of calcium, phosphorus, or vitamin D.
Explanation:For healthy bone formation, farm animals require adequate calcium and phosphorus in their diet.
Fish meal and oyster shell are natural sources that are rich in calcium and essential minerals.
Adding these supplements to animal feed helps prevent and control rickets effectively.
Quality grasses and legumes supply protein and energy, but they do not provide enough calcium to cure rickets.
Therefore, mineral-rich feed supplements are the correct control measure.
Answer:D. adding fish meal and oyster shell to animal feed