Recent data have shown several benefits of methionine supplementation during the transition period to health parameters of dairy cattle. The objective of this study was to investigate the effects of rumen-protected methionine (RPMet) during the transition on blood metabolites of dairy cows in a commercial herd. One hundred and 66 Holsteins, 58 nulliparous and 108 multiparous cows, were blocked by parity and expected calving date and randomly allocated in 2 treatments groups: Control and RPMet. Cows were individually fed and the RPMet group received a top-dressed methionine supplementation (Smartamine; Adisseo Inc.) during 21 d prepartum (8 g/cow/d) and 16 d postpartum (15 g/cow/d), maintaining a lysine/methionine ratio of 2.81/1. After 16 d postpartum all animals received methionine (15 g/cow/d). Blood samples were collected from the coccygeal vein before morning feeding on −14, −7, +1, +7 and +14 d relative to calving date. Data were analyzed using the MIXED procedure of SAS with a model containing the effects of block, treatment, time, and treatment × time interaction as fixed effects and cow within treatment as a random effect. Metabolites did not differ (P > 0.10) between groups. Nevertheless, there was a trend of RPMet animals to present lower values of AST (P = 0.08) and higher values of total calcium (P = 0.05) on +1 d, and albumin (P = 0.06) on +14 d. In summary, results suggest that RPMet supplementation had small effects on blood metabolites of dairy cows in a commercial herd. Table 1 (Abstr. T170).

Metabolites	Control	RPMet	SEM	P-value
Albumin (g/dL)	3.25	3.29	0.02	0.34
Alanine aminotransferase (U/L)	15.25	14.99	0.47	0.69
Aspartate aminotransferase (U/L)	83.70	74.90	4.17	0.14
BHB(mmol/L)	0.46	0.44	0.01	0.43
Bilirubin (mg/dL)	0.20	0.19	0.01	0.82
Calcium (mg/dL)	8.15	8.19	0.04	0.52
Cholesterol (mg/dL)	73.73	75.76	1.85	0.44
Globulin (g/dL)	3.51	3.54	0.06	0.78
Glucose (mg/dL)	64.70	64.58	1.10	0.94
Nonesterified fatty acids (mmol/L)	0.75	0.73	0.03	0.72
Paraoxonase (U/mL)	102.5	104.1	1.96	0.56
Total protein (g/dL)	6.96	6.99	0.18	0.92
Triglycerides (mg/dL)	11.52	11.59	0.27	0.86
Urea nitrogen (mg/dL)	29.07	30.05	0.66	0.30