Produção e composição do leite de vacas leiteiras alimentadas com cana de açúcar suplementada com fontes de nitrogênio não protéico de diferentes degradabilidades ruminal

Abstract

The objective of this study was to evaluate the effects of increasing levels of urea or Optigen II® in the diet on milk yield and composition. Seven multiparous Holstein cows with 45+ 12 days in milk and 25 kg of milk per day were used. The cows were distributed in seven treatments in a balanced incomplete block design. All the cows were in a tie stall barn receiving diets based on fresh chopped sugarcane with increasing levels of urea or OptigenII®: 0.3% of urea, 0.6% of urea, 0.9% of urea, 0.3% of OptigenII®, 0.6% of OptigenII®, 0.9% of OptigenII® and a control group without urea. The level of urea or OptigenII® in the diets was based on the amount of sugarcane in as fed basis. The dry matter intake (DMI) was not affected by the experimental diets (P>0.05) and ranged from 18.05 to 18.70 kg per day. DMI expressed as percentage body weight ranged from 2.95 to 3.45%. The NDF intake kg per day was higher for the control diet compared to the 0.9% of OptigenII® diet (P <0.05), however no difference was detected for NDF intake as percentage of body weight. The milk yield and fat corrected milk 3.5 % yield ranged from 22.23 to 25.58 kg per day and from 19.9 to 21.6 kg per day, respectively, without difference between diets. The milk fat percentage and production ranged from 2.92% to 3.4% and from 0.72 to 0.78 kg per day, respectively. Milk protein percentage and production ranged from 2.7 to 3.11% and from 0.73 to 0.77 kg per day, with coefficient of variation of 1.08% and 16.2%, respectively. The inclusion of 0.9% of urea in the diet resulted in the highest level of milk protein. Different sources of non-protein nitrogen can be used in the diets of dairy cows producing up to 25 kg of milk per day without changing milk yield and composition.