Answer:
Price and quantity of chickens sold will increase.
Explanation:
Due to the prevalence of the mad cow disease, demand for cow meat will go down. Since chicken is a substitute for cow meat and there is a breed that grows twice as much with the same feeds, the demand for chicken will rise.
In economics when other factors apart from price changes it results in demand shift. In this instance demand will shift to the right.
As illustrated in the attached diagram, there will be higher quantity demanded at higher prices than before.