Plasma leptin has become an indicator of body fat accumulation and body fat metabolism. The involvement of body fat or plasma leptin in long-term feed intake regulation has become clearer, showing 25% reduction from 16 – 23 months (fattening period) of adlibitum feeding in fattening steers. Likewise, the insulin – induced short – term reduction in feed intake (24%) suggests the involvement of plasma leptin. The association of breed (Purebred Hereford vs Backcrossed Hereford) and feeding system shows significant elevation of plasma leptin of breed with higher growth potential coupled with the sensitivity of plasma leptin to low and high energy level of feeding. At an early period of compensatory growth, plasma IGF-1 shows downregulation of IGF-1 receptors as manifested by lower plasma BUN, indicative of lean deposition. While at latter period of compensatory growth, plasma leptin seems elevated, indicative of increase in body fat deposition. However varying individual responses exists, leading us to investigate the leptin resistance or leptin gene polymorphism in domestic animals.