Effect of forage source and feeding frequency of nitrogen sources on the performance, digestibility and blood metabolites of lactating dairy cows

Twelve multiparous (100±10 d in milk) Holstein dairy cows were used in a 6×6 incomplete Latin square design (five 21-d periods) with a 2×3 factorial arrangement of treatments to evaluate the effect of forage sources and rumen degradable nitrogen fractions and their feeding frequency on performance, total tract digestibility and blood metabolites. Treatments were different proportion of alfalfatocorn-silage (35:15 and 15:35) and different feeding frequency of the rumen degradable nitrogen source: 1- Total mixed ration (TMR) was offered once daily in the morning (09:00); 2- A part of soybean meal was offered at 21:00; 3- A part of urea was offered at 21:00. Dry matter intake and body weight change were not affected by treatments. Milk and 3.5% fat-corrected milk yield increased in corn silage-based diets compared with alfalfa hay-based diets (P