Genetics of colostrum, milk and serum antibodies in dairy cattle: implications for health and production

Abstract: Colostrum with sufficient IgG content is essential for the newborn calf, as it requires this passive immunity to survive during its rearing. Failure of passive transfer (FPT) occurs when a calf does not absorb enough antibodies (<10 g/L of IgG in serum) from the colostrum, which besides timely access to colostrum, can be due to low IgG production of the mother or poor IgG absorption of the calf. The aim of this thesis was to explore the genetics of antibody content in colostrum and newborn calf serum and how they correlate with production and health traits. For papers I, II and III, Swedish Red and Swedish Holstein animals from three experimental farms were studied. Colostrum samples from 1313 cows calving from January 2015 to April 2017 were collected. For two of the farms, serum samples from 868 newborn calves were collected at 1 to 12 days after birth. In paper I, genetic parameters were estimated for antibody traits (total IgG and natural antibodies (NAb)) and indicators (Brix and Serum Total Protein) in colostrum and calf serum. Colostrum traits had heritabilities ranging from 0.16 to 0.31 with repeatabilities from 0.21 to 0.55. Brix had positive genetic correlations with all the other colostrum traits including total IgG (0.68). Genetic correlations with milk yield, protein and fat were non-significant. A negative genetic correlation was observed for Brix and IgG traits with Lactation Average Somatic Cell Score (LASCS), but it was also non-significant. Calf serum traits had heritabilities from 0.25 to 0.59, with a significant maternal effect accounting for 17 to 27% of the variance. Genetic correlations of calf serum traits and calf health for the first three months of life had a negative tendency, but were non-significant. LASCS for the first lactation of the animals studied as calves was negatively genetically correlated with 3 NAb traits. In papers II and III, we performed Genome-wide association studies (GWAS) using an imputed 50K SNP array on colostrum and calf serum. For colostrum (Paper II) genomic regions were found for Brix, total IgG and NAbs, with candidate genes related to immunity. Similarly, calf serum GWAS (Paper III) revealed QTLs for S-IgG, IgM and IgG NAbs with genes linked to molecule transport, gastric acid and salivary secretion, among others. For paper IV, 1,695 milk samples of Holstein Friesian from Dutch herds were analyzed for 16 different NAb traits. GWAS were performed using imputed 777K SNP genotypes. For IgM NAb, significant associations were found with candidate genes related to immunoglobulin structure and early B cell development. We have shown that antibodies in colostrum, milk and serum have an important genetic component and we can pinpoint genomic regions that influence these antibodies. Our results suggest that these traits can potentially provide a tool to reduce FPT using genetic selection.