The objective was to investigate the effects of feed restriction on concentrations of selected milk metabolites in mid-lactation Holstein and Montbéliarde cows, and explore their correlations with energy balance. Nine Holstein and 10 Montbéliarde cows (165 ± 21 DIM) underwent 6 d of feed restriction during which feed allowance was reduced to meet 50% of NE_L requirements calculated before initiation of the challenge. The experiment was divided in 4 periods: Control (CONT; d −3 to −1), restriction (REST; d 1 to 6), WK1 (d 7 to 13) and WK2 (d 18). Milk concentrations of β-hydroxybutyrate (BHB), glucose, glucose-6-phosphate (Glu6P), isocitrate and glutamate were measured and statistical analyses performed using mixed models of SAS with fixed effects of period and breed, and the random effect of cow. Relationships among variables were explored by Spearman correlations. Feed restriction induced a negative EB, increased Glu6P and isocitrate (+38% and +39%, respectively) and decreased BHB, glucose and glutamate concentrations in milk (−20%, −57% and −65%, respectively) compared with pre-challenge values (Table 1). All milk metabolites were significantly correlated with EB (0.46, 0.62, −0.25, −0.41, 0.59 for BHB, glucose, Glu6P, isocitrate and glutamate, respectively). Results suggest that milk metabolites may be used as noninvasive indicators of nutritional status of mid-lactation cows. Table 1 (Abstr. W20). Effects of feed restriction on energy balance and milk metabolite concentrations in mid-lactation cows

		Period1				SEM	P-value
CONT	REST	WK1	WK2	Breed	Period	Breed × Period
EB (MJ/d)	HOLS	46a,y	−40b	41a,y	41a	4.0	0.06	0.001	0.04
MONT	31x	−40	29x	42	3.6
BHB (mM)	HOLS	0.05b	0.04c	0.06a	0.05b	0.01	0.93	0.001	0.55
MONT	0.05	0.04	0.06	0.05	0.01
Glucose (mM)	HOLS	0.54a	0.22c	0.47b	0.51ab	0.03	0.15	0.001	0.17
MONT	0.47	0.21	0.45	0.45	0.02
Glu6P (mM)	HOLS	0.02b	0.03a	0.01c	0.03a	0.01	0.24	0.001	0.12
MONT	0.04	0.05	0.02	0.05	0.01
Isocitrate (mM)	HOLS	0.12c	0.17a	0.13c	0.13b	0.01	0.05	0.001	0.29
MONT	0.14	0.19	0.13	0.16	0.01
Glutamate (mM)	HOLS	0.39a	0.14c	0.39a	0.33b	0.06	0.77	0.001	0.99
MONT	0.38	0.13	0.38	0.31	0.06

^a–dPeriod LSMEANS not sharing a common superscript differ (P ≤ 0.05). ^y,xBreed LSMEANS not sharing a common superscript differ within the period (P ≤ 0.05).