It's just that keeping your heart rate in the target range during regular aerobic exercise has been shown to be safe and effective for increasing your aerobic fitness. Exercising above this range can be very uncomfortable and may increase your risk of injury.
Typical daily weight gains for feedlot animals ranges between 0.5kg to 2.5kg per day, while grass fed animals are somewhat lower than this. The following data was collected from a small beef cattle company in Dallarnil in Queensland (approximately 300km north of Brisbane).
Growth implants will increase the daily gain of steers fed supplements on pasture by 12 to 15 percent and increase total gain by 20 to 30 pounds in a 130-day pasture period. A second implant of Ralgro at mid season increased the total pasture gain of steers by 9.5 pounds in a summary of 11 Missouri farm trials.