Identification of single nucleotide polymorphisms associated with serum acute phase proteins during the transition period in dairy cows

The transition period is one of the most challenging phases for dairy cows. High incidences of metabolic and inflammatory disorders occur during this period due to negative energy balance and reduced immune functions. Acute phase proteins (APP), such as haptoglobin (Hp), serum amyloid A (SAA), and C-reactive protein (CRP), are important components of the innate immune response and serve as sensitive biomarkers of systemic inflammation. The current study aims to estimate h² and identify candidate genes associated with serum levels of APP. Serum samples were collected from 700 Holstein cows during the transition period (2 wk prepartum and 2 wk postpartum). Heritability of serum APP ranged from 0.07 ± 0.07 to 0.44 ± 0.08 prepartum and 0.02 ± 0.06 to 0.30 ± 0.09 postpartum. C-reactive protein was the most heritable in both prepartum (0.44 ± 0.08) and postpartum (0.30 ± 0.09) periods. Low h² was observed for haptoglobin at both time periods. Serum amyloid A was moderately heritable in both periods (prepartum 0.26 ± 0.08 and postpartum 0.15 ± 0.07). A GWAS was used to identify genetic variants significantly associated with serum levels of SAA, CRP, and Hp. For SAA, multiple candidate genes (72 pre- and 92 postpartum) and previously identified QTL (128 pre- and 143 postpartum) were mapped on BTA 29 within 100 kb up- and downstream of significant SNPs. For CRP, 6 significant SNPs and 16 candidate genes were identified on BTA 3, 11, and 15 at prepartum. However, no significant SNP was detected at postpartum. For Hp, 2 significant SNPs and 1 candidate gene were associated with prepartum Hp, whereas 1 significant SNP and 2 candidate genes were identified for Hp at postpartum. This study provides insight into the h² of APP and molecular mechanisms of serum APP response, and the results could potentially be used to improve dairy cattle health through genetic selection and breeding.