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).
A general rule of thumb for feeder space is to provide 18 to 22 inches for calves up to 600 pounds, 22 to 26 inches per head for calves 600 pounds to market weight, 26 to 30 inches per head for mature cows, and 14 to 18 inches per head for calves. If you have feed available at all times, these sizes can be decreased.