Intakes and excretion route of nitrogen, phosphorous and sulfur by finishing beef heifers fed increasing levels of wheat dried distillers grains with solubles to substitute for barley grain and barley silage.

Li, Y.L., Beauchemin, K.A., McAllister, T.A., and Yang, W.-Z. (2014). "Intakes and excretion route of nitrogen, phosphorous and sulfur by finishing beef heifers fed increasing levels of wheat dried distillers grains with solubles to substitute for barley grain and barley silage.", Livestock Science, 170, pp. 43-52. doi : 10.1016/j.livsci.2014.09.020  Access to full text

Abstract

A study was conducted to determine the fecal and urinary excretion of N, P and S with increasing inclusion of wheat dried distillers grains with solubles (DDGS) to substitute for barley grain and barley silage in finishing diet fed to growing beef heifers. Eight ruminally fistulated Angus heifers were assigned to a replicated 4×4 Latin square design with 21 d periods using diets consisting of barley silage, barley concentrate, and wheat DDGS in ratios of 150:850:0, 100:650:250, 50:650:300 and 0:650:350 (DM basis), respectively, for control (CON), low (DDGS25), medium (DDGS30) and high (DDGS35) DDGS diets. Heifers were fed a total mixed ration for ad libitum intake. Total collection of feces and urine were conducted for 5 d in each experimental period. Intake of N was higher for heifers fed DDGS diets than heifers fed CON diet with no differences among DDGS diets. The increased N intake resulted in an increase in N retention as well as increased N excretion. The N was primarily excreted in urine (~700 g/kg N excreted) with less in feces (~300 g/kg N excreted). Urinary N excretion linearly increased, whereas fecal N excretion linearly decreased, with increasing dietary DDGS inclusion. Intake of P was higher for DDGS than CON, but linearly decreased with increasing DDGS inclusion in the diets due to decreased DMI. Total P excretion was higher whereas P retention was lower in heifers fed DDGS than heifers fed CON diets. The majority of P was excreted by feces (from 897 to 634 g/kg P excreted) and linearly decreased with increasing dietary DDGS inclusion; conversely, the urinary P excretion linearly increased. Feeding DDGS diets considerably increased S intake with no differences among DDGS diets. Only a small part of S consumed was retained and the excretion of S via feces was lower, but the excretion via urine was higher, for heifers fed DDGS compared with heifers fed CON diet. Results indicate that inclusion 250 to 350 g/kg wheat DDGS in finishing diets substantially increased the intakes and excretion of N, P, and S. Increasing the excretion of N, P, and S is a primary environmental concern when using DDGS in feedlot cattle. Developing nutrient management programs that minimize N, P and S losses to the environment and maximize plant use need to be considered.

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