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... Bigham ML: Res Vet Sci, 24, 129-133 (1978) [19] Pinchasov Y, Hasdai A, Gordin, Katznelson D, Volcani R: J Dairy Sci, 65: 28-36 (1982) [21] Ryan R K: Am J Vet Res, 25, 653-659 (1964) [22] Tulleners E P: Bovine Pract, 3, 16-22 (1982) [23] Wilson JR SUMMARY We investigated the relation between diet starch content and lactic-acid levels in bovine rumen fluid and blood. Three Holstein dairy cows were fed orchard grass abundantly for 3 weeks . They were then fed a diet containing 34% starch (dry weight) for another 3 weeks. Specimens were collected two hours after ingestion of the concentrate. Rumen-fluid pH decreased in all three animals. Protozoa (mainly small Ophryoscolex species) increased markedly 7 days after the change in diet. No changes were observed in D-and L-lactic or ammonia concentrations in the rumen fluid. Blood concentrations of D-lactic acid increased rapidly on the eighth day and thereafter. Blood concentrations of L-lactic acid and ammonia, on the other hand, remained unchanged. Positive correlation was observed in relations between pH and L-lactic acid levels in the rumen the rumen fluid and in the blood. Negative correlation was observed between total numbers of protozoa and L-lactic acid levels in the rumen fluid. These results indicate that blood levels of D-lactic acid reflect highstarch feed. -Key words: ammonia, hemodiagnosis, lactic acid, rumen fluid dietary starch.