Feeding condensed tannins to mitigate ammonia emissions from beef feedlot cattle fed high-protein finishing diets containing distillers grains
Koenig, K.M., Beauchemin, K.A., McGinn, S.M. (2018). Feeding condensed tannins to mitigate ammonia emissions from beef feedlot cattle fed high-protein finishing diets containing distillers grains. Journal of Animal Science, [online] 96(10), 4414-4430. http://dx.doi.org/10.1093/jas/sky274
Plain language summary
Livestock production plays a critical role in achieving food security, however, livestock farming systems are major emitters of ammonia. Ammonia is of concern because it can form secondary products in the atmosphere contributing to fine particulate matter and reduced air quality and when deposited can damage natural ecosystems. Distillers grains, the major by-product feeds from grain-based ethanol production, are an economical energy source and are replacing 15 to 40% of traditional grains in the diets of beef cattle. However, the protein concentration is 3 times that of the parent grain, and as a result protein requirements of cattle are routinely exceeded. Protein (nitrogen) fed in excess of requirements is excreted largely as urea which is rapidly converted to ammonia. Condensed tannins are present in a variety of plants species and are well known for their affinity to bind protein. We found that feeding small quantities of a condensed tannin extract to growing beef feedlot cattle fed high protein diets containing distillers grains lowered ammonia emissions by 23% and had no negative impacts on growth performance and carcass traits. In addition, plasma urea concentration in the cattle fed the condensed tannin extract was lower indicating that protein digestion in the gastrointestinal tract and excretion of urea in urine was reduced. Development of plant tannins as natural feed additives to modify protein digestion and reduce the excretion and loss of labile urea nitrogen will enable beef cattle producers to take advantage of the economics of existing and new by-product feeds in environmentally sustainable production systems.
Two experiments were conducted to determine the effects of feeding a condensed tannin extract (CT) on dry matter intake (DMI), growth performance, carcass traits, and NH3-N emissions of beef feedlot cattle fed high-protein barley-based finishing diets. In Exp. 1, 36 crossbred steers (346 ± 4.2 kg) were individually fed 4 diets with 20% corn dried distillers grains (DG) and increasing concentrations of a CT extract from Acacia mearnsii (black wattle) at 0%, 1.2%, 2.4%, and 3.5% of DM (9 steers per diet) for 52 d. The DMI was not affected at 1.2% and 2.4% but tended (P = 0.08, quadratic effect) to decrease at 3.5% CT extract. There was no effect (P ≥ 0.12) of increasing CT extract on ADG, but G:F tended (P = 0.09) to decrease linearly. In Exp. 2, 148 crossbred steers (457 ± 3.8 kg) were allocated to 16 pens with 4 pens per treatment in a completely randomized design and fed for 83 d. The 4 dietary treatments included 0% corn DG (0DG), 20% DG (20DG), 40% DG (40DG), and 40% DG with 2.5% CT extract (40DGCT) and contained 13.3, 15.9, 20.4, and 19.4% CP, respectively. All cattle were weighed, and blood was collected from 5 steers per pen every 3 wk. Ammonia emissions were measured in four 3-wk periods using the integrated horizontal flux technique with passive NH3 samplers from 2 pens of cattle fed 0DG and 20DG (Period 1), 40DG and 40DGCT (Period 2), 0DG and 40DG (Period 3), and 0DG and 40DGCT (Period 4). There was no effect (P ≥ 0.15) of diet on final body weight (621 ± 7.1 kg), DMI (11.9 ± 0.25 kg/d), ADG (1.98 ± 0.07 kg/d), G:F (166 ± 5.4 g/kg), and carcass traits. Plasma urea N (PUN) increased (P < 0.001) from 0DG to 40DG (113 to 170 ± 6.0 mg N/L) and was reduced (P < 0.001) by 40DGCT (146 mg N/L) compared with 40DG and tended (P = 0.09) to be reduced compared with steers fed 20DG (153 mg N/L). Ammonia-N emissions were greater from cattle fed 40DG [113.7 vs. 70.8 ± 4.57 g N/(steer·d), P = 0.003] and tended to be greater from cattle fed 20DG [51.3 vs. 26.3 ± 11.2 g N/(steer·d), P = 0.11] compared with 0DG. Cattle fed 40DGCT tended to have lower NH3-N emissions compared with cattle fed 40DG [72.7 vs. 95.1 ± 9.3 g N/(steer·d), P = 0.09 and 20.5 vs. 26.5 ± 2.64% N intake, P = 0.11]. Feeding 2.5% CT to beef feedlot cattle fed a high-protein diet had no detrimental effect on performance, reduced PUN indicating lower urinary urea N excretion, and lowered NH3-N emissions by 23%.