Exploring the genetic background of parasite resistance in selected lines of black and white cattle

Summary

Regaining importance of keeping dairy cows in grassland systems implies a detailed evaluation of breeding strategies on genetic resistances against endoparasite infections. The present study aimed on i) a comparison of different black and white cattle selection lines for three endoparasite traits, and ii) the estimation of genetic parameters for parasite resistances. A research design was implemented to create three different genetic lines within herds on the basis of a German Holstein cow (GHC) population: line 1 = GHC x New Zealand (NZ) sires, line 2 = GHC x GH sires, line 3 = GHC x GH pasture sires. GH pasture sires represent bulls of German origin with high breeding values for the “grassland traits” being important in NZ. A forth genetic line (line 4) in the cross-classified research experiment included local black and white dual-purpose cows (DSN). 1995 faecal samples were taken during two farm visits from 1139 cows kept in 17 grassland farms located in North-west Germany. Endoparasite traits were the faecal egg counts for gastrointestinal nematodes (FEC_GI) and for trematodes (FEC_FP), and faecal larvae counts for Dictyocaulus viviparus (FLC_DV). Lowest values for nematode infections were identified for the pasture adopted genetic lines 1 and 3. Heritabilities for endoparasites were 0.05±0.04 (FEC_GI), 0.33±0.06 (FEC_FP), and 0.05±0.04 (FLC_DV). The genetic correlation between FEC_GI and FLC_DV was almost one (rg = 0.99), but close to zero between FEC_GI and FEC_FP (rg = -0.06), and between FLC_DV and FEC_FP (rg = 0.05). Antagonistic genetic relationships were identified between endoparasites and milk yield. The genetic correlation between FEC_GI and SCS was 0.36, and also positive between endoparasites and the energy deficiency indicator fat:protein-ratio. Infections with endoparasites contribute physiological imbalances, and other health problems as well.