PSI-22 - Differential metabolizable energy consumption during late gestation affects serum mineral concentrations before and at calving in beef cattle

Abstract: Mineral homeostasis is tightly regulated but blood mineral concentrations can be adaptive to physiological states, and it is unknown how nutritional adequacy influences mineral homeorhesis in transition beef cattle. The objective of this study was to evaluate how late gestation metabolizable energy (ME) intake affects serum mineral concentrations during late gestation and early lactation in beef cattle. Angus-Simmental cattle (n = 45 primiparous and 107 multiparous) were randomly assigned to receive diets formulated to supply 80 (LME, n = 52; 0.7%DM Ca, 0.3%DM P, 0.2%DM Mg, 1.5%DM K ), 100 (CME, n = 51; 0.7%DM Ca, 0.3%DM P, 0.2% DM Mg, 1.5%DM K), or 120% (HME, n = 49; 0.7%DM Ca, 0.4%DM P, 0.3%DM Mg, 1.6%DM K) of predicted ME requirement for 53 d prepartum and fed a common diet postpartum that exceeded requirements (151%ME requirement, 0.7%DM Ca, 0.3%DM P, 0.3%DM Mg, 1.4%DM K). Serum was collected on d -53 ± 0.4, -39 ± 0.4, -25 ± 0.3, -11 ± 0.2, -3 ± 0.2, 0, 7 ± 0.1, 14 ± 0.2, 28 ± 0.2, and 56 ± 0.2 relative to calving to analyze Ca, P, Mg, Na, K, and Cl concentrations. Data were analyzed by prepartum (d -53 to -3), calving (d 0), and postpartum (d 7 to 56) phases independently using PROC GLIMMIX with the fixed effect of treatment and random effects of parity and cow. The pre- and postpartum models also included the fixed effects of day and its interaction with treatment. At d -39, HME serum Mg was 4.4% greater (interaction: P = 0.01) than LME, but not CME and, at d -25, HME serum Mg was increased respective to LME (5.6% increase) and CME (4.4% increase). Serum Mg was similar between LME and CME cattle at both d -39 and -25 and, otherwise, serum Mg did not differ between treatments on d -53, -11, and -3 respective to calving. Serum K concentration was elevated (interaction: P = 0.04) for LME compared to HME only on d -11, at which point CME serum K did not differ from LME nor HME. Prepartum serum Na was greater (treatment: P = 0.05) for LME relative to CME while neither differed from HME. At calving, HME cattle had elevated (treatment: P = 0.01) serum Mg compared to LME and CME serum Mg was intermediate. Prepartum ME intake did not affect (P ≥ 0.053) prepartum Ca or P concentrations or postpartum serum mineral concentrations. These data demonstrate that serum mineral concentrations are responsive to late gestation ME intake in beef cattle, though changes are subtle and not sustained after calving.