Researchers conducted a study in mice to improve weight gain while keeping feed intake stable. They selected mice for 10 generations based on postweaning weight gain from 3 to 6 weeks of age. The heritabilities of the selected traits were found to be around 0.18 to 0.19. The study showed significant changes in weight gain in the desired direction, but feed intake did not change significantly. A method was developed to estimate the genetic correlation between feed intake and weight gain, which was found to be around 0.36. Positive and negative changes were observed in feed efficiency and body weight, but not in feed intake adjusted for body size or litter size.