Effect of the decreasing of dietary protein, rumen undegradable and rumen degradable protein on the production performance in high-producing cows in early lactation Holstein

In order to determine optimum level of crude protein and degradable and undegradable protein in high producing dairy cow two separate experiment were conducted. In the first experiment, 12 lactating Holstein cows in the second parities were used in 4×4 Latin square design that included 4 treatments. In the second nine lactating cows were used 3×3 Latin square design that included 3 treatments. Treatments 1 to 4 in the first experiment consisted of diet containing 18, 17.2, 16.4, and 15.6 percent crude protein, respectively. Degradable protein level in all diets was same about 10.9 % of DM, while rumen undegradable protein level was gradually decreased. Treatments 1 to 3 in the second experiment consisted of diet containing 16.4, 15.6, and 14.8 percent crude protein, respectively. Rumen undegradable protein levels were constant across the treatments (5.6 % DM) while rumen degradable protein was gradually decreased. In the first experiment the diets had no significant effect on milk production and composition. Dry matter intake and FCM in third treatment was significantly higher than the other groups (P<0.05). Apparent digestibility of dietary protein in the first treatment was more than other groups (P<0.05). In the second experiment milk urea nitrogen due to decrease rumen degradable protein significantly decreased (P<0.05). The result of first experiment showed that reduction in the level of crude protein and undegradable protein until 15.6 and 4.7 % didn’t had negative effect on producing performance and milk composition, also the result of second experiment showed nonentity of negative effect of reduce in crude protein and degradable protein until 14.8 and 9.3 % on producing performance and milk composition of dairy cows. Moreover results of two the experiments showed that NRC predication of crude protein, rumen degradable and undegradable protein requirement is more than actual requirement of dairy cows.