effect of feeding frequency of protein sources on fiber digestibility, feeding behaviors and rumen metabolites of holstein cows

four ruminally-cannulated holstein cows were used in a 4 × 4 latin square changeover design within periods of 21 days to evaluate effects of feeding frequency of different sources of rumen degradable nitrogen on total tract digestibility of nutrients, feeding behaviors, rumen and blood metabolites of holstein cows. treatments were: 1) control diet which was as total mixed ration (tmr) offered once daily in the morning (08:00), 2) control diet in which a part of its soybean was offered at 19:00, 3) control diet in which a part of its urea was offered at 19:00 and 4) control diet in which a part of its fish meal was offered at 19:00. rumination time increased in cows fed twice daily with protein sources (p