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).
As a general guide, a mature cow will consume 10kg dry matter (DM) grass in the first week after calving. This should rise by 1kg per week for eight weeks into lactation, when daily feed intake reaches a plateau (Figure 1). First calving heifers will eat 1.5-2kg less grass DM than mature cows, reducing average daily grass demand by around 0.5kg per cow during spring. DM Intake of Mature Cow For herds that reach peak production of around 2.0kg milk solids per day (27kg milk), the daily deficit in energy before maximum grass intake is achieved equates to 3-4kg high energy concentrate per day where high quality grass is available.