Genetic line comparisons and genetic parameters for endoparasite infections and test-day milk production traits

Abstract

Keeping dairy cows in grassland systems relies on detailed analyses of genetic resistance against endoparasite infections, including between- and within-breed genetic evaluations. The objectives of this study were (1) to compare different Black and White dairy cattle selection lines for endoparasite infections and (2) the estimation of genetic (co)variance components for endoparasite and test-day milk production traits within the Black and White cattle population. A total of 2,006 fecal samples were taken during 2 farm visits in summer and autumn 2015 from 1,166 cows kept in 17 small- and medium-scale organic and conventional German grassland farms. Fecal egg counts were determined for gastrointestinal nematodes (FEC-GIN) and flukes (FEC-FLU), and fecal larvae counts for the bovine lungworm Dictyocaulus viviparus (FLC-DV). The lowest values for gastrointestinal nematode infections were identified for genetic lines adopted to pasture-based production systems, especially selection lines from New Zealand. Heritabilities were low for FEC-GIN (0.05-0.06 ± 0.04) and FLC-DV (0.05 ± 0.04), but moderate for FEC-FLU (0.33 ± 0.06). Almost identical heritabilities were estimated for different endoparasite trait transformations (log-transformation, square root). The genetic correlation between FEC-GIN and FLC-DV was 1.00 ± 0.60, slightly negative between FEC-GIN and FEC-FLU (-0.10 ± 0.27), and close to zero between FLC-DV and FEC-FLU (0.03 ± 0.30). Random regression test-day models on a continuous time scale [days in milk (DIM)] were applied to estimate genetic relationships between endoparasite and longitudinal test-day production traits. Genetic correlations were negative between FEC-GIN and milk yield (MY) until DIM 85, and between FEC-FLU and MY until DIM 215. Genetic correlations between FLC-DV and MY were negative throughout lactation, indicating improved disease resistance for high-productivity cows. Genetic relationships between FEC-GIN and FEC-FLU with milk protein content were negative for all DIM. Apart from the very early and very late lactation stage, genetic correlations between FEC-GIN and milk fat content were negative, whereas they were positive for FEC-FLU. Genetic correlations between FEC-GIN and somatic cell score were positive, indicating similar genetic mechanisms for susceptibility to udder and endoparasite infections. The moderate heritabilities for FEC-FLU suggest inclusion of FEC-FLU into overall organic dairy cattle breeding goals to achieve long-term selection response for disease resistance.

Genetic correlations between endo-parasite phenotypes and economically important traits in dairy and beef cattle1

“…had close to zero genetic correlations with test day milk yield, fat percentage, protein percentage as well as fat-to-protein ratio for the majority of the lactation. Although May et al (2017) did not specifically measure a F. hepatica phenotype, the present study is in general agreement, in that genetic selection for F. hepatica traits are expected to have little or no impact on the genetic improvement of milk production traits other than through an impact on selection intensity. Yet, May et al (2017) reported that FEC of gastrointestinal worms was negatively genetically correlated with fat percentage, protein percentage, and fat-toprotein ratio, but positively genetically correlated with both milk yield and somatic cell score, for the majority of the lactation.…”

“…In a recent study of 1,166 dairy cows, May et al (2017) reported that FEC for flukes (i.e., sum of F. hepatica, Paramphistomum spp., and Calicophoron spp.) had close to zero genetic correlations with test day milk yield, fat percentage, protein percentage as well as fat-to-protein ratio for the majority of the lactation.…”

Invited review: Phenotyping strategies and quantitative-genetic background of resistance, tolerance and resilience associated traits in dairy cattle

“…Twomey et al (2018b) estimated negative genetic correlations in a low range (−0.04 to −0.14) between IgG antibody titres against F. hepatica and milk production traits. May et al (2017) found negative correlations up to −0.50 between FEC of F. hepatica and protein %. Currently, utilization of FEC or antibody levels to predict resistance or tolerance to endoparasite infections in dairy cows is not feasible, due to the costs and difficulties of measuring phenotypes in a commercial production environment.…”

“…For liver fluke infections, Twomey et al (2018b) used the biomarker 'IgG antibody titres against F. hepatica' in Irish dairy cows, and estimated a heritability of 0.13 (Table 1). A heritability of 0.33 was estimated for the biomarker 'FEC of F. hepatica' in German Holstein dairy cows (May et al, 2017; see Table 1). Twomey et al (2018b) estimated negative genetic correlations in a low range (−0.04 to −0.14) between IgG antibody titres against F. hepatica and milk production traits.…”

Control of helminth ruminant infections by 2030

“…As energetic efforts towards mounting strong immune responses trade off with other desirable host traits, notably weight gain and milk production (Walkden-Brown and Eady, 2003), it is not known whether breeding for this trait is always cost-effective. Nonetheless, a recent study in dairy cattle showed negative genetic correlations of milk yield and protein% with endoparasite infection, indicating that genetic progress in both trait categories simultaneously is possible (May et al 2017). On the other hand, breeding for resilience may, through high infection levels at pasture, lead to clinical disease in less resilient hosts within the population (Gibson and Bishop, 2005).…”