Microbial protein synthesis and nitrogen balance in crossbred heifers fed with two tannins sources

Resumo

Low to moderate concentrations of condensed tannins in ruminant diets are considered to increase the post-ruminal flow of non-ammonia nitrogen. The objective of this research was study the microbial protein synthesis and nitrogen balance of lactating cows fed with a diet of two tannin sources, based on sorghum (condensed tannin) with increasing levels of tannic acid (hydrolysable tannin). 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 (0.027 kg 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), 157.5 g (3.9% DM), and 235.5 g (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 (hydrolysable and condensed) sources supplementation didn’t affect the animals’ health, neither improved the microbial synthesis efficiency nor the N balance for milk production.