In 1988, USDA scientists at the Miles City, MT station allotted a composite population of cows to two selection lines; 1) Control line in which bulls were selected purely at random; 2) Index line in which bulls were selected based on the following index, I = 365-day wt. – 3.2 (birth wt.). There were approximately 120 cows per line and the study was carried out for 12 years (3 generations). The objective was to determine if selection using the Index would improve efficiency by increasing postnatal growth while holding birth wt. in check. For the Index line, direct genetic changes per generation were as follows: birth wt., 0.99 lb; 200-day wt., 7.54 lb; 365-day wt., 17.07 lb; mature cow wt., 13.89 lb. For the Control line, direct genetic changes in these traits were small and close to zero. On the maternal side, genetic changes were small for both lines. These results show that selection for the Index had a favorable impact on the shape of the growth curve, restricting response in birth wt. and mature cow wt. The authors concluded that despite a genetic antagonism that compromises selection response for decreased birth wt. and increased postnatal growth, favorable genetic responses can be achieved with the selection index used in this study. They added that even greater selection intensity would be available across a breed using National Cattle Evaluation and AI than was the case in this study (McNeil. 2003. J. Anim. Sci. 81:2425).