Four Holstein-Friesian dairy cows (560-600 kg body weight, 67-92 days postpartum) were fed isoenergetic and isonitrogenous diets which differed in the amount of protected starch. Compared to the control ration (diet I), beet pulp was replaced by potato starch, maize meal or wheat meal (diets II, III and IV, respectively). Duodenal, urine and milk samples were collected during the final week of each experimental period for the determination of fatty acids (FA), duodenal diaminopimelic acid (DAPA), purines and urine allantoin. It was shown that differences in the amounts of protected starch induced significant changes in the microbial nitrogen (MN). Duodenal odd and branched chain fatty acids (OBCFA) ranged from 2.89-6.22 mg/g and was positively related to DAPA and purines. Milk OBCFA was not affected by diet and was positively related with DAPA and allantoin MN. These results show the potential of milk OBCFA excretion to predict the duodenal flow of MN in dairy cows
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