The objective was to examine the associations of peripartum concentrations of nonesterified fatty acids (NEFA), ß-hydroxybutyrate (BHBA) and calcium with milk production in early lactation and pregnancy at the first artificial insemination (AI) across different management systems.

Fifty-five Holstein freestall dairy herds located across the United States and Canada were visited weekly for blood sample collection from 2,365 cows. For each week of sampling (from week 1 through week 3 relative to calving) and for each metabolite, serum concentrations were dichotomized at various thresholds to identify the thresholds with the best negative associations with milk production and pregnancy at first AI. These thresholds were used to categorize the serum concentrations into higher and lower risk categories. Repeated-measures ANOVA and multivariable logistic regression were conducted for milk production and pregnancy at the first AI data, respectively, considering cow as the experimental unit and herd as a random effect.

In the week before calving, serum NEFA =0.5mEq/L, BHBA =600µmol/L, and calcium =2.1mmol/L were associated with 1.6 to 3.2 kg/d milk loss across the first four Dairy Herd Improvement Association (DHIA) milk tests. High levels of NEFA and BHBA in week 1 and week 2 after calving (=0.7 and =1.0mEq/L for NEFA, and =1,400 and =1,200µmol/L for BHBA), and low levels of calcium (=2.1mmol/L) in week 1, 2 and 3 after calving were associated with milk loss at the first DHIA milk test. Serum concentrations of NEFA and BHBA were not associated with pregnancy at first AI in any sampling week, whereas calcium <2.2 to 2.4mmol/L from week 1 through week 3 postpartum were associated with reduced pregnancy at first AI.

In conclusion, high serum concentrations of NEFA, BHBA, and low concentrations of calcium around parturition, were associated with early lactation milk loss, and low calcium concentration around parturition was associated with impaired early lactation reproduction.

N. Chapinal. M.E. Carson, S.J. LeBlanc, K.E. Leslie, S. Godden, M. Capel, J.E.P. Santos, M.W. Overton, T.F. Duffield/Journal of Dairy Science