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Nutrient Digestibility and Mass Balance in Laying Hens Fed a Commercial or Acidifying Diet¹

W. Wu-Haan^*, W. J. Powers^*,2, C. R. Angel, C. E. Hale, III and T. J. Applegate

^* Department of Animal Science, Iowa State University, Ames 50011; Animal and Avian Sciences, University of Maryland, College Park 20742; Rose Acre Farms, Seymour, IN 47274; and Department of Animal Sciences, Purdue University, West Lafayette, IN 47907

² Corresponding author: wpowers{at}msu.edu

The objectives of the current study were to evaluate the effect of an acidifying diet (gypsum) combined with zeolite and slightly reduced crude protein (R) vs. a control diet (C) on nutrient retention in laying hens and compare 3 approaches to estimating nutrient excretion from hens: 1) mass balance calculation (feed nutrients – egg nutrient), 2) use of an indigestible marker with analyzed feed and excreta nutrient content, and 3) an environmental chamber that allowed for capturing all excreted and volatilized nutrients. Hens (n = 640) were allocated randomly to 8 environmental chambers for 3-wk periods. Excreta samples were collected at the end of each trial to estimate apparent retention of N, S, P, and Ca. No diet effects on apparent retention of N were observed (53.44%, P > 0.05). Apparent retention of S, P, and Ca decreased in hens fed R diet (18.7, – 11.4, and 22.6%, respectively) compared with hens fed the C diet (40.7, 0.3, and 28.6%, respectively; P < 0.05). Total N excretion from hens fed the C and R diet was not different (1.16 g/hen/d); however, mass of chamber N remaining in excreta following the 3-wk period was less from hens fed the C diet (1.27 kg) than from hens fed the R diet (1.43 kg). Gaseous emissions of NH₃ over the 3-wk period from hens fed the C diet (0.74 kg per chamber) were greater than emissions from hens fed the R diet (0.45 kg). The 3-wk S excretion mass (estimated using the calculation, indigestible marker, and environmental chamber methods, respectively) was greater from hens fed the R diet (1.85, 1.54, and 1.27 kg, respectively) compared with hens fed the C diet (0.24, 0.20, and 0.14 kg, respectively). The 3-wk P excretion was similar between diets (0.68 kg). Results demonstrate that feeding the acidified diet resulted in decreased N emissions, but because of the acidulant fed, greatly increased S excretion and emissions.

Key Words: laying hen • nitrogen • sulfur • mass balance • retention

¹ This material is based upon work supported by the National Research Initiative Air Quality Program of the Cooperative State Research, Education, and Extension Service, USDA, under agreement No. 2005-35112-15356 and funding received by the Iowa Egg Council. The authors would also like to thank Sarah Zamzow and Martha Jeffrey for their laboratory assistance during the course of this project.