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).
Graph 3. The regression output found that the average weight gain for the grass-fed animals was linear over the age range examined. The resulting regression equation was found to be very useful in allowing the owners of the cattle property to predict the weight gains of the animals.