Overfeeding energy during the dry period may affect peripartal insulin sensitivity of dairy cows. The objectives were to describe the effect of different dry period dietary energy strategies on glucose tolerance and on concentrations of insulin, glucagon, glucose, β-hydroxybutyrate (BHBA) and nonesterified fatty acids (NEFA) in the peripartum period. To test our hypothesis that dry period plane of energy leads to changes in glucose tolerance, cows (n = 84) were blocked by expected calving date and randomized into 3 treatment groups 57 d before expected parturition: a TMR formulated to supply 100% of energy requirements (C), or 150% of requirements (H), or 100% for the first 28 d of the dry period followed by a TMR supplying 125% of energy requirements until calving (I). At 28 and 10 d pre-, as well as 4 and 21 d postpartum, intravenous glucose tolerance tests (IVGTT; 0.25 g glucose/kg) were performed and the area under the curve (AUC) of glucose and insulin were estimated. Baseline samples were analyzed for concentration of insulin, glucose, NEFA, glucagon and BHBA. Mixed-effects ANOVA were carried out (SAS, v. 9.3). The AUC for glucose and insulin was not different among groups at any time point (P > 0.10). Differences in baseline values were most notable on d 4 postpartum (Table 1) and indicated increased postpartum lipolysis and ketogenesis in group H whereas we detected a tendency for lower glucose concentration despite higher glucagon concentration in this group. In conclusion, these findings suggest that prepartum plane of energy had an effect on the hormonal regulation of gluconeogenesis and ketogenesis (as reflected by the concentrations of insulin and glucagon), but did not lead to a detectable effect on peripartal glucose tolerance as assessed by IVGTT. Table 1. Mean (95% CI) baseline concentrations on day 4 postpartum

Item	C	I	H	P-value
Glucose (mg/dL)	60 (57–62)a	58 (56–61)ab	56 (53–58)b	0.09
Insulin (μIU/mL)	2.1 (1.2–3.6)a	2.3 (1.3–4.1)a	1.1 (0.5–1.7)b	0.08
Glucagon (pg/mL)	120 (108–132)A	117 (105–129)A	137 (127–150)B	0.01
NEFA (mEq/L)	1.37 (1.26–1.48)A	1.38 (1.27–1.50)A	1.63 (1.52–1.74)B	0.002
BHBA (mmol/L)	0.75 (0.64–0.88)A	0.83 (0.71–0.97)AB	1.0 (0.85–1.2)B	0.06

Row values with different superscript letters differ (^A,BP < 0.05; ^a,bP < 0.10) in Tukey’s HSD.