| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
* Department of Biological Sciences, University of New Hampshire, Durham 03824
Facultad de Veterinaria, Universitat Autònoma de Barcelona, Bellaterra, Spain 08193
Department of Animal Sciences, University of Illinois, Champaign 61801
Department of Animal Science, University of Minnesota, St. Paul 55108
3 Corresponding author: charles.schwab{at}unh.edu
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
Key Words: amino acid digestibility • rumen-undegradable protein • soybean meal
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
In the Institut National de la Recherche Agronomique (Vérité and Peyraud, 1989) and the Scandinavia AAT-PBV models (AAT = AA absorbed from small intestine; PBV = protein balance in the rumen; Madsen et al., 1995), digestibility of RUP is adjusted for changes in ruminal degradability of feed protein. In these models, it is assumed that feedstuffs contain a constant protein fraction that is totally indigestible in the small intestine and also completely undegradable in the rumen. Therefore, true digestibility of RUP is calculated according to the following equation:
 |
The mobile bag technique (MBT) has been the most common method used to estimate intestinal digestibility of RUP and RUP-AA in individual feeds in ruminants (NRC, 2001). However, the MBT is an invasive procedure that requires the animals to be fitted with ruminal, duodenal, and sometimes ileal cannula. This procedure is also very time-consuming, and currently there is no standardized protocol for conducting this procedure. The precision-fed cecectomized rooster assay may be a viable alternative for estimating small intestinal RUP-AA digestibility (Titgemeyer et al., 1990). Titgemeyer et al. (1990) observed a high correlation between estimates of intestinal dietary RUP-AA digestibility made in steers fitted with duodenal and ileal cannulas and estimates from cecectomized roosters in which birds were crop intubated with duodenal digesta collected from the steers.
The objectives of this experiment were 1) to determine digestibility of RUP-AA in SBM and SoyPlus (SP; expeller SBM, West Central, Ralston, IA) using the precision-fed cecectomized rooster assay and 2) to determine if these feedstuffs contained a constant protein fraction that was both undegradable in the rumen and indigestible in the small intestine.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
Ruminal Incubation
Procedures for the ruminal cannulation surgery and experimental protocol were approved by the Institutional Animal Care and Use Committee at the University of New Hampshire. To provide RUR for use in the precision-fed cecectomized rooster assay and for use in experiments reported previously (Boucher et al., 2009a,b) to evaluate in vitro methods for estimating RUP-AA digestibility, 1.2 kg of sample (ground to 2 mm) was weighed equally into 150 polyester bags so that each bag contained 8 g of sample. The bags had a mean pore size of 50 µm and dimensions of 10 x 20 cm (Ankom Technologies, Macedon, NY). Bags were tied with plastic fastening ties 2 cm below the top of the bag, soaked in 39°C water for 15 min, and placed inside 4 mesh laundry bags (46 x 56 cm; Whitney Design Inc., St. Louis, MO) for ruminal incubation. The mesh laundry bags were filled with 38 polyester in situ bags of 2 different samples so that 76 bags were in each laundry bag during each incubation. Nine metal washers (diameter = 4.3 cm; total weight = 115 g) were tied inside each mesh laundry bag, and a 60-cm string was tied to one end of the bag. The mesh laundry bags were inserted into the rumen of 4 ruminally cannulated lactating cows averaging (mean ± SD) 48 ± 4 DIM, and cows were fed a 55% forage, 45% concentrate diet. Three separate ruminal incubations with 4 ruminally cannulated cows were required to incubate the 6 samples. One-week intervals were allotted between each incubation.
Samples were ruminally incubated for 16 h. One time point was selected to be representative of total RUP. The 16-h ruminal incubation time was selected for several reasons. First, in a literature search, 16 studies were identified that determined RUP digestibility of SBM using a single time point for ruminal incubation. Of the 16 studies, 11 used a 16-h ruminal incubation, 1 used a 14-h ruminal incubation, 3 used a 12-h ruminal incubation, and 1 used an 8-h ruminal incubation. To compare estimates obtained in this experiment with those previously reported in the literature, the 16-h ruminal incubation was selected as the most appropriate. In addition, Calsamiglia and Stern (1995) determined there was no difference in RUP digestibility measured in vitro when concentrate ingredients were ruminally incubated in situ for 12 h compared with 16 h.
After the 16-h ruminal in situ incubation, bags were removed from the rumen and submerged in cold water within 5 min. Polyester bags were removed from the laundry bags and processed according to the procedure of Gargallo et al. (2006), with some modifications. Bags were rinsed 3 times for 5 min in an automatic washing machine with a final spin and then suspended in a 0.1% methylcellulose (M-0262, Sigma, St. Louis, MO) solution and shaken in a water bath (50 rpm; Precision Scientific, Chicago, IL) at 37°C for 30 min to help in the detachment of particle-associated bacteria (Whitehouse et al., 1994). Bags were then rinsed again 3 times for 5 min in an automatic washing machine, followed by a final spin, and then frozen. In the procedure of Gargallo et al. (2006), samples were oven-dried at 55°C for 48 h. In the current experiment, samples were lyophilized (Labconco, Kansas City, MO) for 48 h to ensure that additional heat damage was not imposed on the residual feed. Once lyophilized, residues were composited by sample, weighed, and ground to pass a 1-mm screen for the precision-fed cecectomized rooster assay (Aldrich et al., 1997).
Precision-Fed Cecectomized Rooster Assay
Procedures for the cecectomy of roosters and the experimental protocol were approved by the Institutional Animal Care and Use Committee at the University of Illinois. The cecectomized rooster digestibility assay used in this experiment was described by Parsons (1985) and Aldrich et al. (1997). Thirty grams of each feed was ground to pass a 1-mm screen and was crop intubated to 4 cecectomized Single Comb White Leghorn roosters. For crop intubation, the beak of the bird was opened and the stem of a funnel was inserted into the crop. Feed was then poured into the funnel and pushed with a plunger (Sibbald, 1983). The ground RUR were also crop intubated to cecectomized roosters, but 30 g of RUR sample could not be intubated to the roosters because of the bulkiness of the sample. Therefore, the amount of RUR sample intubated was adjusted to the maximum amount that could be comfortably intubated, which was (mean ± SD) 23.7 ± 1.4 and 23.6 ± 1.3 g for the SP and SBM RUR samples, respectively. The experiments were conducted from June 2006 to January 2008. In each experiment, feed was withheld from the roosters for 24 h before and 48 h after intubation of samples, and the birds had access to water at all times. Roosters were housed individually in wire mesh cages fitted with excreta collection trays, and total excreta were collected for 48 h and lyophilized (Sibbald, 1983). The same group of birds was used to determine the digestibility of feeds and RUR. Basal endogenous AA excretion was previously determined by 48-h collection of excreta from fasted birds (Parsons, 1985; NRC, 1994), and the basal endogenous AA loss values were used to calculate standardized feed-AA and RUP-AA digestibility. Standardized digestibility is defined as digestibility estimates calculated by subtracting only basal endogenous AA losses from the outflow of AA (Stein et al., 2007).
Chemical Analysis
Portions of the RUR, feed, and excreta were ground to pass a 40-µm screen (Arthur H. Thomas Co., Philadelphia, PA) for analysis of the complete AA profile via cation-exchange chromatography coupled with postcolumn ninhydrin derivatization and quantification [AOAC, 2000; method 982.30 E(a,b,c); Experimental Station Chemical Laboratories, University of Missouri, Columbia]. For determination of all AA except Met, Cys, and Trp, samples were hydrolyzed with 6 M HCl before analysis. For determination of Met and Cys content, samples were oxidized with performic acid before acid hydrolysis to convert Met to methionine sulfone and Cys to cysteic acid, and for analysis of Trp content, samples were subjected to alkaline hydrolysis before acid hydrolysis. Intact feeds and RUR were also analyzed for DM, NDF, ADF, neutral detergent-insoluble CP (NDICP), acid detergent-insoluble CP (ADICP), CP, fat, starch, ash, and minerals by using wet chemistry (Dairy One DHI Forage Testing Laboratory, Ithaca, NY). Neutral detergent fiber was analyzed according to the procedure of Van Soest et al. (1991), using the Ankom A200 filter bag technique (Ankom Technology, Fairport, NY). Briefly, samples were digested for 75 min in NDF solution with 4 mL of 
-amylase and 20 g of sodium sulfite added at the beginning of digestion. Samples were then rinsed 2 times in boiling water with -amylase, followed by rinses with boiling water and acetone. Crude protein was analyzed using a combustion analyzer (AOAC, 2000; method 990.03; Leco FP-528, Leco, St. Joseph, MI). For starch analysis, sugar was preextracted from the samples, and starch was determined using a YSI 2700 Select biochemistry analyzer (YSI application note number 319, YSI Incorporated, Yellow Springs, OH). Minerals were analyzed using a Thermo Jarrell Ash IRIS Advantage HX Inductively Coupled Plasma Radial Spectrometer (Thermo Jarrell Ash Corporation, Franklin, MA), and fat was determined by ether extraction (AOAC, 2000; method 2003.05). Nonfiber carbohydrate was calculated as 100 – [CP + (NDF – NDICP) + fat + ash].
Calculations and Statistical Analysis
Standardized AA digestibility for the intact feeds and standardized RUP-AA digestibility for the RUR were calculated as follows (Stein et al., 2007):
 |
Indigestibility of the intact feed samples was calculated as follows:
 |
Indigestibility of AA in the ruminally incubated feeds was calculated according to the equation of Prestløkken and Rise (2003):
 |
Data were analyzed as a completely randomized design according to the following model:
 |
2)]. The MIXED procedure (SAS Institute, 2002) was used to solve the above model for each feed type. Tukey’s Studentized range test was used to compare least squares means among samples. Significance was declared at P < 0.05 and tendencies are reported at 0.05 < P < 0.10. The MEANS procedure of SAS was used to evaluate the difference between digestibility of individual AA and total AA. The absolute value of the difference between digestibility of individual AA and total AA within each rooster was calculated, and these values were used in the MEANS procedure. |
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
Chemical Composition and AA Profile of Feeds and RUR
The chemical composition of the intact feed and RUR of SP and SBM samples is presented in Table 1. The concentrations of CP, NDF, ADF, lignin, NDICP, and ADICP increased in the RUR compared with the intact samples, whereas the concentrations of fat, NFC, and ash decreased in the RUR compared with the intact samples. Similar results have been reported in the literature (Frydrych, 1992; Susmel et al., 1994; Vanhatalo and Ketoja, 1995). Frydrych (1992) reported that the N concentration in the 16-h RUR of SBM was greater than in the intact feed, but the author did not report changes in the composition of other components. Vanhatalo and Ketoja (1995) reported that the concentrations of CP, ADF, NDF, and NDF-N were greater in the 12-h RUR of SBM compared with those in the intact feed, and Susmel et al. (1994) reported an increase in CP and crude fiber and a decrease in ash and lipids in the 14-h RUR of SBM. The decrease in the NFC concentration in the RUR of SBM and SP observed in the present experiment was expected because NFC are degraded at a faster rate than CP and fiber components (Sniffen et al., 1992; NRC, 2001). The CP increase in the RUR compared with the intact feed for SP and SBM may also be partly attributed to microbial contamination of the RUR. Although methylcellulose was used to detach particle-associated bacteria, the procedure does not remove all the bacteria from the undegraded feedstuff (Whitehouse et al., 1994). Heat-treated SP and SBM samples had greater concentrations of NDF, ADF, lignin, NDICP, and ADICP than nonheated samples. This observation was also expected because fiber concentration and CP associated with fiber increase when feeds are heated (Van Soest and Mason, 1991).
|
náková et al. (2002) also reported increases in the profile of Phe and the BCAA in the RUR of SBM after samples were ruminally incubated in situ for 16 h. Together, these results support the concept that the AA composition of RUP is different from that of intact feed protein. Two factors can contribute to a difference in the AA profile of the RUR compared with the feed: 1) AA are not degraded at the same rate in the rumen (Prestløkken and Rise, 2003; Borucki-Castro et al., 2007), and 2) microbial contamination of the RUR can result in a different AA profile of feeds after ruminal incubation.
Standardized Digestibility of AA and RUP-AA
Standardized intestinal AA and RUP-AA digestibility estimates of SP and SBM samples are presented in Table 2. Heating the SBM and SP samples at 150°C for 90 min depressed digestibility of total AA compared with the unheated samples. This effect was likely due to protein cross-linking reactions that occur in the more advanced stages of the Maillard reaction, which can depress digestibility of total protein (Mauron, 1990). Heating the SBM and SP samples particularly depressed Lys digestibility. This was expected because the Maillard reaction decreases Lys digestibility and bioavailability (Mauron, 1990; Faldet et al., 1992). To determine the bioavailability of Lys in roasted soybeans, Faldet et al. (1992) fed rats soybeans roasted at various temperatures for various periods in combination with a basal diet in which Lys was limiting for growth. Growth of rats fed the experimental diets was compared with growth of rats fed a Lys-adequate diet. Soybeans that were roasted at 150°C for 90 min (same heat treatment as used in the present study) caused a depression in rat growth compared with rats fed soybeans that were heated at lower temperatures, for shorter periods, or both.
|
Digestibility of RUP-AA in SBM has been measured in several experiments (Griffin et al., 1993; Masoero et al., 1994; O’Mara et al., 1997; Van Straalen et al., 1997; Cerenáková et al., 2002; Prestløkken and Rise, 2003; Taghizadeh et al., 2005; Borucki-Castro et al., 2007). From these studies, 11 RUP-AA digestibility estimates of SBM were obtained. The MBT with collection of bags from the feces was used for 9 estimates (Masoero et al., 1994; O’Mara et al., 1997; Van Straalen et al., 1997; Cerenáková et al., 2002; Prestløkken and Rise, 2003; Taghizadeh et al., 2005; Borucki-Castro et al., 2007), the MBT with collection of bags from the ileum was used for 2 estimates (Prestløkken and Rise, 2003), and the precision-fed rooster assay was used for 1 estimate (Griffin et al., 1993). Average estimates for RUP-total AA, RUP-total essential AA, RUP-Lys, and RUP-Met digestibility reported in these studies were (mean ± SD) 96 ± 5, 96 ± 5, 96 ± 4, and 97 ± 3%, respectively. In the present study, average estimates for RUP-total AA, RUP-total essential AA, RUP-Lys, and RUP-Met in the SP and SBM samples were (mean ± SD) 94 ± 1, 94 ± 1, 89 ± 2, and 95 ± 1%, respectively. Average RUP-AA digestibility estimates reported in the current experiment generally fell within reported ranges. However, for RUP-Lys, the digestibility estimate of 89% observed in the present experiment was lower than the average value of 96%. This discrepancy may be due to differences among samples, but may also be attributed to differences in the techniques used. With the MBT, collection of bags from the ileum is preferred to collection of bags from the feces because microbial fermentation in the large intestine can influence digestibility estimates. Another concern with the MBT is that AA that disappear from the bag are assumed to be absorbed in the small intestine. However, this assumption does not account for nutrient antagonism and competition for AA transport systems in the small intestine.
Standardized AA digestibility was similar to standardized RUP-AA digestibility, which is in agreement with several observations reported in the literature (de Boer et al., 1987; Vanhatalo et al., 1995; Beckers et al., 1996). However, some authors have reported differences in CP and AA digestibility between intact and ruminally incubated SBM (Vanhatalo and Ketoja, 1995; Prestløkken and Rise, 2003). Vanhatalo and Ketoja (1995) reported that CP digestibility of intact SBM (88.9%) was higher than RUP digestibility (82.5%). Prestløkken and Rise (2003) also reported that 16-h ruminal incubation of feeds increased CP and AA digestibility, with digestibility of CP in intact SBM equal to 96.7% and RUP digestibility equal to 99.2%. Although these authors reported differences in CP and AA digestibility between intact and ruminally incubated SBM, the reported differences were small. Therefore, based on results reported in this experiment and those reported by others (de Boer et al., 1987; Vanhatalo et al., 1995; Beckers et al., 1996), it was concluded that intestinal AA digestibility could be determined using intact SBM and SP. However, to predict the metabolizable AA supply accurately, SBM and SP would need to be ruminally incubated to determine changes in AA profile after ruminal incubation because differential rates of AA degradation may result in a different AA profile for RUP compared with the original feedstuff.
Indigestibility of Intact and Ruminally Incubated Feeds
Indigestibility coefficients of intact feed and ruminally incubated samples of SP and SBM are presented in Table 3. For unheated SP and SBM samples, indigestibility of AA in ruminally incubated samples was lower compared with intact feeds, suggesting that SP and SBM do not contain a constant protein fraction that is neither degradable in the rumen nor digestible in the small intestine, as assumed in the Institut National de la Recherche Agronomique and AAT-PBV systems.
|
Prestløkken and Rise (2003) also observed that total AA indigestibility of intact SBM and SoyPass was higher than total AA indigestibility of ruminally incubated SBM and SoyPass. Indigestibility estimates for the intact SBM and SoyPass were 3.3 and 3.5%, respectively, and indigestibility estimates of ruminally incubated SBM and SoyPass were 0.7 and 1.6%, respectively. Indigestibility coefficients of intact SBM and SP samples in the present study were higher than those observed by Volden and Harstad (1995) and Prestløkken and Rise (2003), but indigestibility estimates of ruminally incubated SBM and SP samples were similar among studies. Although indigestibility estimates of intact SP and SBM samples were higher than the values these authors reported, digestibility estimates of SBM concurred with NRC (1994) reference AA digestibility values. The difference in indigestibility estimates may also be attributed to the different techniques used to determine intestinal AA digestibility (i.e., the MBT vs. the precision-fed rooster assay).
Because indigestibility values were lower for ruminally incubated samples compared with intact feeds, as reported by Prestløkken and Rise (2003) and in the present experiment, SBM and SP appeared to contain a protein fraction that was indigestible in the small intestine but partly degraded in the rumen, digested in the small intestine after ruminal incubation, or both. Because few studies to date have tested this hypothesis, and to our knowledge, no other studies have used the precision-fed rooster assay, more research is needed to clarify reported discrepancies regarding indigestibility estimates of SBM.
Digestibility of Individual AA Versus Total AA
In NRC (2001), RUP digestibility coefficients are assigned to individual feedstuffs, which is an improvement compared with NRC (1989), which assumed 80% RUP digestibility for all feeds. However, both the swine (NRC, 1998) and poultry (NRC, 1994) NRC models assign intestinal digestibility coefficients to individual AA within feeds. Therefore, in the advancement of ruminant nutrition models, it may be beneficial to assign intestinal digestibility coefficients to individual RUP-AA within feeds.
To evaluate the difference between digestibility of individual AA and total AA, the absolute value of the difference between digestibility of individual AA and total AA in intact and ruminally incubated SP and SBM samples was calculated (Table 4). The absolute value of the difference between digestibility of individual AA and total AA was greater than zero for all AA. The mean difference for the ruminally incubated samples ranged from (mean ± SD) 1.02 ± 0.9 for Val to 11.4 ± 9.5 for Lys. When the heat-treated samples were removed from the analysis, the difference between Lys digestibility and total AA digestibility within the ruminally incubated SP and SBM samples was smaller (5.14 ± 1.7; data not shown), but it was still different from zero. Because the absolute value of the difference between digestibility of individual RUP-AA and total RUP-AA in SP and SBM samples was greater than zero for all AA, if digestibility coefficients are assigned to individual RUP-AA within these feedstuffs, predictions of the metabolizable AA supply may be improved.
|
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
|
ACKNOWLEDGMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
|
FOOTNOTES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
2 Present address: William H. Miner Agricultural Research Institute, Chazy, NY 12921.
Received for publication November 10, 2008. Accepted for publication May 28, 2009.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSFOOTNOTESACKNOWLEDGMENTSREFERENCES |
|---|
náková, Z., A. Sommer, M. Chrenková, and P. Doleová. 2002. Amino acid profile of escaped feed protein after rumen incubation and their intestinal digestibility. Arch. Anim. Nutr. 56:409–418.[CrossRef]This article has been cited by other articles:
|
|
 |
|
  S. E. Boucher, S. Calsamiglia, C. M. Parsons, H. H. Stein, M. D. Stern, P. S. Erickson, P. L. Utterback, and C. G. Schwab Intestinal digestibility of amino acids in rumen-undegraded protein estimated using a precision-fed cecectomized rooster bioassay: II. Distillers dried grains with solubles and fish meal J Dairy Sci, December 1, 2009; 92(12): 6056 - 6067. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
