Gilts typically grow slower, are more efficient in the utilization of feed, and are leaner than barrows. We would predict that gilts require greater concentrations of amino acids than barrows. Split sex feeding (feeding gilts and barrows, separately) offers the potential to take advantage of these differences between barrows and gilts. In addition, the improved targeting of amino acid needs of barrows and gilts separately could help tighten weights when pigs are marketed.
An experiment was conducted to evaluate the response of gilts and barrows to two levels of lysine. The experiment was conducted at the Jim Charles Swine Finisher Research Barn. Nine hundred ninety-six pigs, initially weighing 64 pounds, were allotted to four treatments and fed to a market weight of 281 lb. Gilts and barrows were fed separately and fed either standard diets or the standard diets with a 0.1% increase in lysine (1st limiting amino acid in swine diets).
Overall, barrows grew faster than gilts (2.21 vs. 2.10 lb/day) but were less efficient in the utilization of feed (2.37 vs. 2.25 feed:gain) than gilts. The increase in growth rate of barrows was consistent throughout the experiment. During the grower stage (64 to 91 lb body weight), barrows and gilts had similar feed conversion rates. However, barrows were less efficient in the utilization of feed during the rest of the experiment, and the difference between barrows and gilts increased as pigs approached market weight. At slaughter, barrows produced heavier carcasses, had more backfat, and produced a lower percentage of primal cuts than gilts.
Split sex feeding (feeding gilts and barrows, separately) offers the potential to take advantage of these differences between barrows and gilts.
An increase in dietary lysine improved the growth rate of pigs from 64 to 129 lb body weight and feed conversion from 64 to 91 lb body weight. This response was similar for barrows and gilts. Overall, there was no benefit to the increase in dietary lysine for barrows or gilts.
These results indicate that the standard lysine level used in this experiment was sufficient to support maximum growth rate in barrows and gilts. However, both barrows and gilts did benefit from increased lysine in the grower stage. Because barrows grew faster than gilts, we would estimate that the lysine levels of barrows could have been reduced and still maintained performance; although additional research would be needed to confirm.