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).
In the wild, birth occurs in the dry months, but in captivity, births can happen year-round. The mother delivers a single calf while standing upright. At birth, calves weigh 104-154 pounds (47-70 Kg), and stand 72-76 inches (183-193 cm) tall. Calves grow about 1.2 inches (3 cm) per day during the first week, and are 10 feet (3 m) tall by age 1. Calves can walk within an hour of birth, and usually can run within 24 hours.