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. Another method to quantify pig growth is to evaluate the amount of carcass lean and fat gain which occurs with each additional pound of liveweight gain. Percent lean decreases as lean growth rate declines and fat gain increases. Thus, as pigs grow, they become less efficient at converting feed to lean primarily due to the decreasing ratio of lean gain to fat gain.