Effect of feeding condensed tannins in high protein finishing diets containing corn distillers grains on ruminal fermentation, nutrient digestibility, and route of nitrogen excretion in beef cattle
Koenig, K.M., Beauchemin, K.A. (2018). Effect of feeding condensed tannins in high protein finishing diets containing corn distillers grains on ruminal fermentation, nutrient digestibility, and route of nitrogen excretion in beef cattle. Journal of Animal Science, [online] 96(10), 4398-4413. http://dx.doi.org/10.1093/jas/sky273
Plain language summary
Dried distillers grains can be fed as an energy source in place of up to 40% of the barley and corn grain in the diets of finishing beef cattle with equal or better growth performance. However, when feeding distillers grains as an energy source the animal’s protein requirements can be exceeded by 50 to 80%. particularly in barley-based diets that have a higher protein concentration than corn-based diets. When excess protein is fed, it is digested and absorbed, and the nitrogen is converted to urea for excretion in urine. Urea is then rapidly degraded to ammonia which is readily lost to the atmosphere. Condensed tannins are present in a variety of plants species and are well known for their affinity to bind protein. We fed a condensed tannin extract in a high protein diet containing distillers grains to beef heifers and found that the extract reduced protein digestion and shifted the route of excess nitrogen excretion from labile urea in urine to bound forms in feces. Supplementation of condensed tannins in high protein diets fed to beef cattle can reduce urinary nitrogen and increase the capture of N in manure lessoning the potential for loss of nitrogen as ammonia and providing opportunities for improved nutrient management of beef production.
Eight ruminally cannulated crossbred beef heifers (427 ± 41.2 kg, body weight) were used in a replicated 4 × 4 Latin square to determine the effects of feeding a condensed tannin (CT) extract with high protein diets containing corn dried distillers grains and solubles (DG) on ruminal fermentation, nutrient digestibility, and route of nitrogen (N) excretion. Dietary treatments included [dry matter (DM) basis]: 0 (0DG), 20 (20DG), and 40% DG (40DG), and 40% DG with 2.5% CT extract (1.33% CT) from Acacia mearnsii (40DGCT). The DG and CT extract were substituted for grain in a barley-based diet that contained 91% concentrate and 9% silage (DM basis) and was fed as a total mixed ration once daily. The crude protein concentrations of the diets were 12.9, 16.8, 20.4, and 20.5% for 0DG, 20DG, 40DG, and 40DGCT, respectively. Periods were 5 wk with 2 wk for transition to the DG level of the diets, 1 wk for adaptation to CT, and 2 wk for measurements. Feed offered and refused were measured daily. Total urine and fecal output were collected daily for 4 d consecutively. Data were analyzed using a mixed linear model with diet and period as fixed effects and square and animal within square as random effects. There was no effect (P ≥ 0.22) of CT on DM intake, but 40% DG in the diet (40DG and 40DGCT) decreased (P ≤ 0.015) DM intake compared with 20DG. As a result, nitrogen (N) intake was not different (P > 0.15) among heifers fed 20DG, 40DG, and 40DGCT (313 g N/d) and was less (P ≤ 0.001) for heifers fed 0DG (220 ± 18 g N/d). Apparent total tract N digestibility was less (P ≤ 0.001) in heifers fed 40DGCT (70.6 ± 1.07%) compared with to 0DG, 20DG, and 40DG (78.4%). There was no effect (P = 0.84) of CT (40DGCT vs. 40DG) on the total N output, however, feeding 40DGCT decreased (P ≤ 0.001) the excretion of total urinary N and urea N in urine by 17 and 21%, respectively, compared with heifers fed 40DG and was equivalent (P ≥ 0.12) to the amount excreted by heifers fed 20DG. The reduction of N digestibility reflected the protein binding effects of CT within the gastrointestinal tract and the shift in excess N excretion from labile urea N in urine to bound NDIN and ADIN in feces (P ≤ 0.001) in heifers fed 40DGCT compared with 40DG. Supplementation of CT in high protein diets fed to feedlot cattle reduced urinary N and increased the capture of N in manure to potentially lesson the loss of N as ammonia and provide opportunities for improved nutrient management of beef production.