Prediction equations for fat-free lean place more emphasis on loin eye area measurements than the empty body protein accretion prediction equations. For these reasons, the protein accretion and fat-free lean curves from different sexes and genotypes are slightly different. Daily protein accretion and lean growth rates increase and reach maximum at 120 to 160 lb. After 160 lb, daily lean gain and protein accretion decline. The protein accretion rates of barrows and gilts are similar.
Barrows achieve their maximum lean growth rate at lighter weights than gilts.
After 205 lb, gilts have increasingly higher lean growth rates than barrows. The fat gain of barrows increases more rapidly and is noticeably higher than for gilts after 160 lb. Barrows have more energy available for fat deposition from their higher feed intakes. At 40 lb, pigs gain 2.2 lb of fat-free lean for each lb of carcass fat. The poorer feed conversion observed in barrows after 200 lb liveweight is caused by a lower ratio of lean gain to fat gain for barrows than for gilts.