Parameterization of different breeds of cattle and the future development of the Davis Growth Model

Abstract

The Davis growth model (DGM), a dynamic steer growth model (Oltjen et al 1986) that includes 4 fat deposition models (McPhee 2006; Sainz and Hastings 2000) is currently being used by the phenotypic prediction program of the Cooperative Research Centre (CRC) for Beef Genetic Technologies. The concepts of cellular hyperplasia and hypertrophy are integral components of the DGM. The net synthesis of total body fat is calculated from the net energy available after accounting for energy needs for maintenance and protein synthesis. Total body fat is then partitioned into 4 fat depots (intramuscular, intermuscular, subcutaneous, and visceral). Three of the fat depots are then converted to carcass characteristics: intramuscular fat (kg) to intramuscular fat as a percentage (%), subcutaneous fat (kg) to 12/13th rib fat (mm) (McPhee et al., 2008) and subsequently 12/13th rib fat to P8 fat (mm) (B. Walmsley, unpublished), and visceral fat (kg) to kidney, pelvic, and heart fat (KPH, %). The 4th fat depot, intermuscular fat, is not converted to any carcass characteristic. The P8 fat site is the Australian industry's standard.