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).
Per head daily of protein supplement should be fed along with a small amount of grain Dairy Cattle: Lactating cows:2.lbs of dry roughage daily per 100lbs of live weight. 2 to 3 lbs of concentrates per head Dairy Heifers:2 to 3 lbs of concentrates per head on good roughage.