Selection in guinea pigs: II. Direct response for litter size and body weight.

Four generations of selection for litter size, 13-wk weight and an index combining litter size and 13-wk body weight were conducted in a guinea pig population formed by intercrossing several local lines from different areas of Peru. A random selection control line was maintained also. Responses in the selected traits per generation were .069 +/- .069, 19.1 g +/- 16.2 and 2.5 +/- 20.3 for the litter size, 13-wk weight and index lines, respectively. Realized heritabilities were estimated by two methods. Estimates obtained from regression of response on cumulative selection differentials were .01 +/- .45 for litter size, .27 +2- .06 for 13-wk weight and -.09 +/- .13 for index values. Estimates from weighted multiple regression procedures were .07 +/- .01, .18 +/- .004 and .04 +/- .01 for litter size, 13-wk weight and index, respectively.