The objective was to determine the effect of transition cow nutritional management on β-hydroxybutyrate (BHBA) concentration of postpartum dairy cows. Commercial Holstein herds (n = 64) based in New York and Vermont were enrolled in a prospective cohort study in one of 6 herd nutritional strategy groups: 1) low energy dry cow (<16% starch), high energy lactating (>25% starch) (L-H); 2) Step-up dry (far-off < 16% starch, close-up > 16% starch), high energy lactating (S-H); 3) high energy dry (>16% starch), high energy lactating (H-H); 4) low energy dry, step-up fresh (fresh < 25% starch, high > 25% starch) (L-S); 5) step-up dry, step-up fresh (S-S); 6) high energy dry, step-up fresh (H-S). Blood samples were collected from 972 cows, 3–14 DIM and BHBA concentration measured using a Precision Xtra meter. Concentrations of BHBA were log-transformed and a multivariable linear model was used to assess the fixed effects nutritional strategy, season, and parity on BHBA concentration with farm as a random effect. The proportion of cows with hyperketonemia (HYK; BHBA ≥1.2 mmol/L) in each nutritional strategy as well as risk group (low: <15%, moderate: ≥15%, <40%, high: ≥40% of sampled cows HYK) was evaluated. Multiparous cows had higher BHBA concentrations than primiparous (0.61 [0.57–0.67 CI] vs. 0.48 [0.43–0.53 CI] mmol/L, P < 0.0001) and concentrations were higher in summer compared with winter (0.61 [0.56–0.67 CI] vs. 0.48 [0.44–0.53 CI] mmol/L, P < 0.0001; Table 1). Overall, a step-up approach to both dry and fresh diets led to the highest BHBA concentration among all strategies in this study. Table 1.

Item	Strategy
L-H	S-H	H-H	L-S	S-S	H-S
Farms, no.	12	14	12	6	12	8
Cows sampled	178	192	187	90	194	131
% HYK	9.0	15.0	12.0	7.8	33.3	23.7
BHBA mmol/L[95% CI]	0.46a	0.51ac	0.53ac	0.52ac	0.69b	0.58bc
[0.41–0.53]	[0.46–0.57]	[0.48–0.59]	[0.45–0.60]	[0.62–0.77]	[0.52–0.65]
Farms/risk group (%)
Low	8 (66.7)	7 (50.0)	8 (66.7)	5 (83.3)	2 (16.7)	3 (37.5)
Moderate	4 (33.3)	6 (42.9)	4 (33.3)	1 (16.7)	4 (33.3)	3 (37.5)
High	0	1 (7.1)	0	0	6 (50.0)	2 (12.5)

^a,b,cRow means with different superscript letters differ (P < 0.05) Tukey’s HSD.