Use of estimated breeding values in a selection index to breed Yorkshire pigs for high and low immune and innate resistance factors

Abstract

A random bred population of Yorkshire pigs (G_o) was characterized using fourteen various indicators of immune and innate resistance. Based on initial heritability estimates and correlations between these traits, two measures of antibody (serum IgG, and antibody response to HEWL), and cellular activity (blastogenic response to Con A and cutaneous DTH to BCG/PPD), and one indicator of innate monocyte function (uptake and killing of S. typhimurium) were chosen as breeding criteria to be used in a composite selection index. Based on these five traits a combined estimated breeding value (EBV) was calculated for each animal and pigs were assigned to High, Low or Control breeding groups. Approximately 120 first generation piglets (G₁) were then similarly evaluated. Based on G_o plus G₁ heritability estimates were 0.25, 0.23, 0.08, 0.08 and zero for secondary antibody response to HEWL, blastogenic response to Con A, cutaneous DTH to BCG/PPD, serum IgG, and monocyte function, respectively. Least squares means reflected these estimates in that there were significant (p ≤ 0.05) differences between High and Low line G₁ pigs in antibody, blastogenic, and DTH responses. However, there were no significant line differences in serum IgG or uptake and killing of S. typhimurium. Response to selection was determined both by differences in least squares means and differences in average EBV between the High and Low lines. After one generation of selection, lines were separated by 1.508 (least squares) and 1.205 (EBV) index points, or slightly more than half a standard (phenotypic) deviation.