SÍNTESE DE PROTEÍNA MICROBIANA E BALANÇO DE NITROGÊNIO EM NOVILHAS MESTIÇAS HOLANDEZ /ZEBU ALIMENTADAS COM DUAS FONTES DE TANINOS

Tannins have been used to trigger positive effects on ruminal metabolism. So, increasing levels of tannic acid in a sorghum-based diet for five Holstein/Zebu crossbred lactating heifers were subject to a 5 × 5 Latin square experimental design, five heifers x five tannins acid levels x five periods. The excretion of total purine derivatives, through the collection of spot urine samples, and the N concentration values in the milk and urine were used. All heifers received 9.87 kg/DM of corn silage as roughage and 6.38 kg of concentrate (not fed ad libitum). Diet 1 (control) contained low-tannin sorghum (0.027kg total tannin), and the other diets contained high-tannin sorghum. The levels of tannic acid added used were established based on the quantity of condensed tannin in high-tannin sorghum. Thus, diets 2, 3, 4, and 5 were supplemented with 1.5g (13.%DM), 79.5g (2.6%DM), 157.5g (3.9%DM), and 235.5g (5.2%DM) of tannic acid totalling 0.078, 0.156, 0.234, and 0.321 total tannin kg/day respectively. The urinary excretions of urea (2.0055), total allantoin (185.12  mmol/day-1) , and total purine derivatives (222.32 mmol/day-1); absorbed purines 179.3 mmol/day-1); the N microbian synthesis (130.358 (g)N/day-1); and the concentrations of allantoin in milk (36.40 mmol/day-1) were not affected by the diets. Diets using two tannins sources supplementation did not affect the animal’s health, that is, it did not change the blood and metabolic rates above the normality indices for the animal category, neither improved the efficiency of the microbial synthesis nor the balance of N for milk production