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).
1 Liver fluke infection in growing cattle has been shown to depress liveweight gain by between 0.07 kg/week and 1.2 kg/week, depending on the size of the fluke burden.11.  Suggested values for milk loss due to liver fluke infection are up to 1.0 kg/day over a 305 day lactation.11.