The effects of replacing ground corn with coffee hulls on N balance and microbial protein synthesis of lactating dairy cows were evaluated in this trial. Twelve crossbred Holstein-Zebu cows yielding on average 23.4 kg/day of milk were used. The microbial protein synthesis was estimated by excretion of purine derivatives in urine and milk. Animas were fed diets containing the following coffee hulls levels (% DM): 0.0, 3.5, 7.0 or 10.5%. Spot urine samples were collected approximately 4 hours post-feeding. Regression analysis showed no effects of dietary coffee hulls levels on total nitrogen intake (441.3 g/day) and excretion of urine N (190.8 g/day) and milk N (114.7 g/day). However, feeding coffee hulls to lactating dairy cows increased fecal N excretion resulting in negative N balance. The increased dietary levels of coffee hulls did not affect excretions of milk allantoin (294.6 mmol/day), urinary allantoin (21.3 mmol/day), uric acid (42.3 mmol/day), and purine derivatives (358.2 mmol/day). Microbial protein synthesis estimated by urinary excretion of purine derivatives averaged 266.3 g/day and did not differ across diets. In addition, efficiency of microbial protein synthesis averaged 136.8 g of microbial N per kg/TDN and also did not differ among diets.
agroindustrial residue; creatinine; microbial nitrogen; purine derivatives; urea N
