Gilts usually gain weight less rapidly than barrows, particularly above 100 lbs. body weight. Gilts generally deposit the same amount of lean tissue per day as barrows but deposit a lower quantity of fat because of the lower amount of feed or energy consumed. Gilts are therefore somewhat older and leaner by the time they reach market weight. Consequently, because of the lower feed intake but a similar amount of body lean tissue, gilts require a higher concentration of amino acids in their diets than barrows. Gilts may, however, exhibit estrus in the finisher pen before they reach slaughter weight, which can affect the other pigs' feed consumption and daily gain. Consequently, it is desirable to feed gilts and barrows in separate pens.
Barrows consume more feed than gilts, particularly during the finisher phase. This in itself accounts for some of the higher carcass fatness in barrows. Consequently, the addition of fat to finisher diets may be beneficial for gilts who have a lower energy intake, but could be detrimental for barrows who have a proportionally higher feed intake. Five percent added fat to the diet increases the backfat thickness of industry average pigs by approximately 0.08 inches.
Because of the sex and feed-intake differences, split-sex feeding allows for the more precise formulation of diets to meet the nutrient needs of barrows and gilts. Splitting pigs by sex to different pens at weaning or at the start of the grower period allows the producer to market leaner gilts and to feed barrows more economically. It also results in pigs of a more uniform weight within each pen.