Should a cow and a bull that both carry recessive alleles for a mutation that causes decreased milk production be bred? wjy or why not?

No, because their recessive alleles combining would cause mutations in their offspring that would lead to decreased milk production. 

During exercise, blood pressure, pulse and respiration increase to meet the increased demand for oxygen and nutrients by your musculoskeletal system. The adjustment of vital signs to match your body's level of physical activity is an example of homeostasis in action.