Genetic correlation analyses of serum biochemical variables with health, fertility, and production traits in Holstein cows

Serum biochemical variables, including concentrations of positive acute phase proteins, metabolic indicators, protein composition, and liver enzymes, reflect metabolic, immune system and production disruptions. Some of these serum biochemical variables exhibit moderate heritability, making them promising indicators for genomic selection. This study aimed to estimate genetic correlations of serum biochemical variables with postpartum health disorders, fertility performance, and production traits. The study included 18 serum biochemical variables, 20 economically important traits, and 80,709 SNPs recoded on 938 Holstein cows from 11 commercial farms in Canada. A bi-variate mixed linear model was applied to estimate genetic correlations between blood biochemical variables and economically important traits. The results demonstrated weak to strong genetic correlations between serum biochemical variables and health, fertility and production traits. Genetic correlations varying from 0.49 ± 0.25 (hypocalcemia) to 0.73 ± 0.29 (metritis) were observed between postpartum serum amyloid A ( SAA-post ) and health disorders. Fertility traits, including pregnancy after first artificial insemination ( PAI1 ), pregnancy by 150 d in milk ( P150 ) and by 250 d in milk ( P250 ) had negative genetic correlations (−0.71 ± 0.36, −0.84 ± 0.40, and −0.88 ± 0.66, respectively) with SAA-post. Negative genetic correlations were observed between prepartum C-reactive protein ( CRP-pre ) levels with total milk yield at 25 d in milk ( MY25 , −0.46 ± 0.23), peak daily milk yield ( Peak , −0.72 ± 0.30), total milk yield at 90 d in milk ( MY90 , −0.63 ± 0.19), average milk production ( AMP , −0.39 ± 0.19), average protein production ( APP , −0.41 ± 0.18), and 305-d total milk yield (−0.45 ± 0.25). Beta-hydroxybutyrate acid ( BHBA ) had significant positive genetic correlations with ketosis (1.00 ± 0.17) and negative correlation with PAI1 (−1.00 ± 0.57) and P250 (−1.00 ± 0.89). Similarly, nonesterified fatty acids ( NEFA ) had positive genetic correlation with ketosis (1.00 ± 0.28) and negative genetic correlations with PAI1 (−1.00 ± 0.71) and P150 (−1.00 ± 0.57). Albumin-to-globulin ratio ( A:G ), had negative genetic correlations with metritis, fatty liver, and hypocalcemia, and positive genetic correlation with MY90 and AFP. Serum glutamate dehydrogenase ( GLDH ) showed negative genetic correlation with metritis (−0.80 ± 0.45) and positive genetic correlations with PAI1 (0.62 ± 0.36) and AMP (0.45 ± 0.27). The study demonstrated favorable genetic correlations between some serum biochemical variables (e.g., SAA-post, CRP-pre, A:G, and GLDH) and economically important traits. This provides the opportunity to include selected serum biochemical variables into selection indices to improve dairy cow health, fertility and production traits.