Problem statement: The transition period is the most stressful time in the production cycle of a dairy cow because of depressed feed intake, endocrine and metabolic changes at parturition. The aim was to determine the effect of rumen acid load on postpartum performance and metabolic parameters in transition Holstein cows. Approach: The Acidogenicity Values (AV) of the diets were determined using an In-vitro essay. Thirty late pregnant multiparous Holstein cows with the average yielding of 9800 Kg/year were housed. Three weeks before the expected date of calving, cows were randomly assigned to receive either: (a) High AV (AV11.9) diet (n = 16) (b) Low AV (AV10.7) diet (n=14). Blood samples were collected from the coccygeal vein once a week at a consistent time after morning feeding from d 10 till d 42 postpartum and were analysed for Beta Hydroxybutyrate (BHB), Non-Esterified Fatty Acids (NEFAs), glucose and Blood Urea Nitrogen (BUN). Milk samples were collected from each milking once per week and composited for subsequent analysis of milk composition. Results: Overall subsequent milk yield of animals in high AV was higher compared to the other group (41.9 and 37.8 kg). Although milk fat percentage of the low AV group was higher than the other group (3.7 and 3.5%), however there was no significant effect of the diets on milk protein. Plasma NEFA and BHBA was reduced significantly in animals receiving the high AV diet. Although the concentration of glucose was markedly higher in high AV animals, however the BUN concentration was lower compare to the low AV group. Conclusion: The results of the present study demonstrated that high grain prepartum diets have dramatic impact on postpartum performance and blood metabolic parameters.

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