Detection of quantitative trait loci affecting haematological traits on swine chromosomes 2, 7 and 8

Haematological traits, which consist of mainly three components: leukocyte traits, erythrocyte traits and platelet traits, play extremely important role in disease resistance. But knowledge of the genetic background controlling variability of these immune traits is very limited, especially in swine. 18 haematological traits including white blood cell count (WBC), neutrophilic granulocyte count (GRAN) and percentage (GR%), lymphocyte count (LYMF) and percentage (LY%), monocytes count (MONO) and percentage (MO%), red blood cell (RBC), hemoglobin (HGB), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concerntration (MCHC), red blood cell volume distribution width (RDW), blood platelet counts (PLT), mean platelet volume (MPV), platelet distribution width (PDW), and plateletocrit (PCT) were measured in a pig resource population consisting of 368 piglets of three breeds (Landrace, Large White and Songliao Black Pig) distributed in 16 boar families, after inoculation with the swine fever vaccine at 21 days of old. A partial genome scan for mapping quantitative trait loci (QTL) for these traits was performed using 35 microsatellite markers on chromosomes 2, 7, and 8. Using variance component analysis based on a linear mixed model and likelihood ratio test based on a chi-square distribution with 2 degrees of freedom, 22 significant QTL (P < 5%) were identified: 9 on chromosome 2 affecting WBC, GRAN, MCV, HGB, MCHC, PLT, MPV, PDW and PCT, respectively; 7 on chromosome 7 affecting WBC, GRAN, MCHC, HGB, PLT, MCV and RDW, respectively; 6 on chromosome 8 affecting GR%, LY%, MCHC, PLT, PCT and MCV, respectively. In order to avoid the increase of false positive rate caused by multiple tests, the FDR (false discovery rate) control approach was adopted to further test these 22 QTL. The results indicated that 14 of them were significant at FDR < 5% level, of which 9 were significant at FDR<1% level.