Effects of Temperature during Moist Heat Treatment on Ruminal Degradability and Intestinal Digestibility of Protein and Amino Acids in Hempseed Cake

1559 Asian-Aust. J. Anim. Sci. Vol. 25, No. 11 : 1559-1567 November 2012 http://dx.doi.org/10.5713/ajas.2012.12213 www.ajas.info pISSN 1011-2367 eISSN 1976-5517 Effects of Temperature during Moist Heat Treatment on Ruminal Degradability and Intestinal Digestibility of Protein and Amino Acids in Hempseed Cake L. Karlsson1,2,*, M. Ruiz-Moreno1, M. D. Stern1 and K. Martinsson2 1 Department of Animal Science, University of Minnesota, St. Paul, MN 55108-6118, USA ABSTRACT: The objective of this study was to evaluate ruminal degradability and intestinal digestibility of crude protein (CP) and amino acids (AA) in hempseed cake (HC) that were moist heat treated at different temperatures. Samples of cold-pressed HC were autoclaved for 30 min at 110, 120 or 130C, and a sample of untreated HC was used as the control. Ruminal degradability of CP was estimated, using the in situ Dacron bag technique; intestinal CP digestibility was estimated for the 16 h in situ residue using a three-step in vitro procedure. AA content was determined for the HC samples (heat treated and untreated) of the intact feed, the 16 h in situ residue and the residue after the three-step procedure. There was a linear increase in RUP (p = 0.001) and intestinal digestibility of RUP (p = 0.003) with increasing temperature during heat treatment. The 130C treatment increased RUP from 259 to 629 g/kg CP, while intestinal digestibility increased from 176 to 730 g/kg RUP, compared to the control. Hence, the intestinal available dietary CP increased more than eight times. Increasing temperatures during heat treatment resulted in linear decreases in ruminal degradability of total AA (p = 0.006) and individual AA (p<0.05) and an increase in intestinal digestibility that could be explained both by a linear and a quadratic model for total AA and most individual AA (p<0.05). The 130C treatment decreased ruminal degradability of total AA from 837 to 471 g/kg, while intestinal digestibility increased from 267 to 813 g/kg of rumen undegradable AA, compared with the control. There were differences between ruminal AA degradability and between intestinal AA digestibility within all individual HC treatments (p<0.001). It is concluded that moist heat treatment at 130C did not overprotect the CP of HC and could be used to shift the site of CP and AA digestion from the rumen to the small intestine. This may increase the value of HC as a protein supplement for ruminants. (Key Words: Cannabis sativa, Heat Treatment, Amino Acids, Ruminal Degradability, Intestinal Digestibility) INTRODUCTION Proteins fed to ruminants are broken down by microbes in the rumen and used for microbial protein synthesis. Although some feed proteins escape the rumen without being degraded. Amino acids (AA) that are required by the ruminant originate from both microbial protein and rumen undegradable protein (RUP) and, to a lesser extent, from endogenous protein (NRC, 2001). Strategies that are used to increase conversion of feed N into meat or milk include feeding to achieve greater microbial protein synthesis, to balance the supply of rumen degradable protein (RDP) and RUP, and to improve the supply of essential AA (Schwab et * Corresponding Author: Linda Karlsson. Tel: +47-916-49895, Fax: +47-739-14134, E-mail: 2 Department of Agricultural Research for Northern Sweden, Swedish University of Agricultural Sciences (SLU), SE-90183 Umeå, Sweden. Submitted Apr. 22, 2012; Accepted Jun. 1, 2012; Revised Aug. 9, 2012 al., 2005). Accurate determination of the amount of RDP and the intestinal digestibility of RUP is required to estimate feed protein available to ruminants by nutritional models. Individual AA have been shown to differ with respect to their rumen degradability (Weisbjerg et al., 1996; Harstad and Prestløkken, 2001), so the RUP AA profile in a feed may differ from the feed AA profile. Hence, it may be incorrect to use the AA composition of the feed when predicting the supply of individual dietary AA to the small intestine. A range of feed processing methods are applied to protect supplemented feed protein from microbial degradation in the rumen and thereby increase the amount of AA available for digestion in the small intestine. Heat treatment is a common method that can be performed in a number of ways, including moist heat treatment of feed, using an autoclave with a positive relationship between steam pressure and temperature (Van der Poel et al., 2005). Several in situ and in vitro studies demonstrated that it is Copyright © 2012 by Asian-Australasian Journal of Animal Sciences 1560 Karlsson et al. (2012) Asian-Aust. J. Anim. Sci. 25:1559-1567 possible to shift protein digestion in different oilseed feedstuffs from the rumen to the small intestine by heat treatment, without decreasing total digestibility (McKinnon et al., 1995; Dakowski et al., 1996; Mustafa et al., 1999a). However, temperatures that are too high may overprotect the protein, resulting in a decrease in post-ruminal availability (McKinnon et al., 1995; Dakowski et al., 1996). In recent years, there has been increasing interest in using alternative protein crops in livestock production. Hemp (Cannabis sativa L.) is an ancient crop, cultivated for fiber and oil, that has received renewed attention during the last decade. The residue left after mechanical or solvent extraction of the oil from hempseed is a cake or a meal rich in protein and fiber (Callaway, 2004). A few studies have been published investigating the use of hempseed as a protein feed. These studies included hempseed in diets for lambs (Mustafa et al., 1999b ; Karlsson and Martinsson, 2011), growing cattle (Gibb et al., 2005; Hessle et al., 2008; Turner et al., 2008) and dairy cows (Karlsson et al., 2010). Mustafa et al. (1999b) found a low effective protein degradation (EPD) of 394 g/kg CP in hempseed meal estimated in situ. An in vitro study by Karlsson et al. (2009) showed that cold pressed hempseed cake (HC) had an EPD value of 330 g/kg CP. Contrary to these observations, the estimated EPD value of HC was 709 g/kg CP in an in situ study (Karlsson and Martinsson, 2011). In addition, a low intestinal RUP digestibility was found, resulting in a much lower value for intestinally available CP of HC (90 g/kg CP) than the value for hempseed meal (654 g/kg CP) reported by Mustafa et al. (1999b). Heat treatment may be an option to decrease EPD in HC and thereby increase RUP and supply of AA to the post-ruminal tract. A high intestinal digestibility of RUP is required to ensure that there is no decrease in total available CP from feed. To the authors’ knowledge, there are no published studies investigating possibilities for altering site of protein digestion of HC. The objective of this study was to evaluate ruminal degradability and intestinal digestibility of CP and AA in HC, exposed to moist heat treatment at various temperatures. (Consolidated Stills and Sterilizers, Boston, MA, USA). Different temperatures we (...truncated)