Partitioning of Energy into Muscle and Fat in Relation to Beef Composite Type and Age at Harvest

Beef composite types have combined favourable traits of pure breeds. The energy requirement for Muscle (EM) and Fat (EF) deposition, the ratio of EF:EM and proportions of energy required to produce M and F were different (P < 0.01) for Beef composite types (CT) and harvest ages (HA). EF was dependent on both CT and HA due to interaction (P=0.03). The proportion of energy required to produce Fat (Prop F) increased from 60.2% at 274 d to 76.8% at 456 d (P<0.01) and the proportion of energy required to produce Muscle (Prop M) decreased from 39.8% at 274 d to 23.2% at 456d (P<0.01). Based on EF:EM ratio (3.0 or 75 % as a reference value) and energetic efficiency of producing M and F, M1, M2 and M3 can be harvested at 399d, M4 at 456d and TX can be harvested at or after 456 d to avoid the production of excessively fat carcasses.