Effects of type of canola protein supplement on

Published December 5, 2014

Effects of type of canola protein supplement on ruminal fermentation and nutrient flow to the duodenum in beef heifers1 G. N. Gozho, J. J. McKinnon, D. A. Christensen, V. Racz, and T. Mutsvangwa2 Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Canada S7N 5A8

ABSTRACT: Ruminal fermentation, nutrient digestion, and flows to the duodenum in growing cattle fed differently produced canola protein supplements were studied in a 4 × 4 Latin square design using Speckle Park heifers (initial BW = 451 ± 26 kg). Canola protein supplement treatments consisted of the following: 1) 8.78% regular canola meal (RCM); 2) 9.25% RCM plus 1.80% canola oil (RCMO); 3) 11.1% canola presscake from biodiesel oil extraction (CPC); and 4) 8.14% high ruminally undegradable protein (RUP) canola meal (RUCM) plus 1.32% canola oil (RUCMO). Experimental diets also contained 39.9, 40.2, 39.9, and 39.9% barley grain; 31.7, 31.4, 31.2, and 31.4% barley silage; and 17.5, 15.2, 15.6, and 16.5% oat hulls for the RCM, RCMO, CPC, and RUCMO diets, respectively. Feeding the CPC, RCMO, and RUCMO diets decreased (P ≤ 0.05) ruminal NH3-N concentration compared with feeding the RCM diet. Compared with the RCM diet, adding canola oil in the RCMO diet or residual oil in the CPC diet resulted in greater ruminal concentrations of propionate (P ≤ 0.09). Additionally, feeding the RCMO

diet also resulted in greater ruminal concentrations of acetate (P = 0.07), valerate (P = 0.06), and total VFA (P = 0.07) compared with the RCM diet. Also, compared with the RCM diet, heifers on the RUCMO diet had decreased acetate (P = 0.02) concentrations. The changes in ruminal concentrations of acetate and propionate resulted in reduced acetate:propionate ratios in the RCMO (P = 0.08), CPC (P = 0.02), and RUCMO (P < 0.01) diets. Ruminal digestion and flows of nutrients to the duodenum were not affected by dietary treatment. However, adding canola oil to the RCMO and RUCMO dietary treatments decreased the digestibility of ADF (P ≤ 0.08) and NDF (P ≤ 0.08) in the total tract compared with the RCM diet. Total tract digestibility of OM was also decreased (P = 0.02) in heifers fed the RUCMO compared with the RCM diet. Notwithstanding the different processing methods employed in making RCM, CPC, or RUCM, there were no differences among the diets for ruminally degraded protein, ruminal microbial protein synthesis, and the flow of N fractions to the duodenum.

Key words: amino acid, beef heifer, canola protein, microbial N ©2009 American Society of Animal Science. All rights reserved.

INTRODUCTION Canola meal is a readily available protein supplement that is used extensively in ruminant rations in Canada (Christensen and McKinnon, 1989). Despite an excellent AA profile, canola meal is a poor source of metabolizable AA because it is extensively degraded in the rumen (Kendall et al., 1991; McAllister et al., 1993). In Canada, pre-press solvent extraction is the

1 This research was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canola Council of Canada, and the Saskatchewan Canola Development Commission. The authors thank A. Olkowski (Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, Canada) for assistance with AA analysis. 2 Corresponding author: [email protected] Received January 27, 2009. Accepted June 16, 2009.

J. Anim. Sci. 2009. 87:3363–3371 doi:10.2527/jas.2009-1841

predominant method of oil extraction from canola seed (Newkirk, 2002). However, mechanical crush method is also used in oil extraction in biodiesel production (Kemp, 2006). Mechanical crush results in the formation of canola presscake (CPC), which has greater oil and reduced CP contents than canola meal (Keith and Bell, 1991; Mustafa et al., 2000). The greater oil content makes CPC an effective energy source in ruminant diets; however, this increased oil content can potentially have a negative impact on ruminal fiber fermentation (Jouany, 1994) and, consequently, on ruminal digestion and nutrient availability. The oil extraction processes involved in the production of canola meal and CPC differ in that pre-press solvent extraction uses a solvent extraction step and that canola meal is subjected to greater temperatures compared with CPC from the mechanical crush method. Heat decreases solubility of proteins by creating cross-linkages within and among peptides chains and

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to carbohydrates (Deacon et al., 1988). Thus, heat exposure can increase the ruminally undegraded protein (RUP) value of the meal (Mustafa et al., 2000; Jones et al., 2001) and potentially increase the contribution of such protein supplements to MP. Therefore, we hypothesized that canola protein supplements produced as byproducts from different oil extraction procedures have different RUP values and different abilities to supply MP. Our objective was to investigate the effect of using differently produced canola protein supplements on ruminal fermentation, ruminal digestion, and duodenal protein supply in beef heifers fed barley-based diets.

MATERIALS AND METHODS All experimental procedures and animal use were approved by the University of Saskatchewan Animal Care Committee based on the current guidelines of the Canadian Council on Animal Care (1993).

Animals and Experimental Design Four Speckle Park heifers (initial BW = 451 ± 26 kg) that were fitted with 10-cm ruminal (Bar Diamond, Parma, ID) and simple T-type duodenal cannulae were used in a 4 × 4 Latin square design with 21-d periods. Duodenal cannulae were inserted proximal to the common bile and pancreatic duct, approximately 10 cm distal to the pylorus. Each experimental period consisted of 14 d of dietary adaptation and 7 d of data collection. Throughout the experiment, animals were housed indoors in individual stalls equipped with large feed bunks, automatic water dispensers, and rubber floor mats.

Experimental Diets The main ingredients of the experimental diets were barley grain, barley silage, and pelleted concentrate. The protein in the concentrate was supplied by regular canola meal (RCM; Federated Cooperatives, Saskatoon, Saskatchewan, Canada), CPC from biodiesel oil extraction that is marketed as Milligan meal (Milligan Biotech, Foam Lake, Saskatchewan, Canada), or a proprietary high RUP canola meal that is marketed as Alberta Gold (RUCM; Canbra Foods Ltd., Lethbridge, Alberta, Canada). According to the manufacturer, Alberta Gold is produced using a patented manufacturing process that results in a meal with 55% of CP as RUP (assuming a ruminal outflow rate of 4%). This would be greater than the RUP content of RCM as indicated by previous work that showed effective ruminal degradabilities of RCM ranging from 62.5 to 74% (Boila and Ingalls, 1992; McAllister et al., 1993). In Canada, RCM is produced by the pre-press solvent extraction process. Generally, this process involves seed conditioning at 75 to 78°C, flaking and cooking at 90°C for 20 to 30 min, followed by solvent extraction in hexane. The resultant presscake is then desolventized-toasted at 100 to

110°C for approximately 60 min, dried, and then cooled (Newkirk et al., 2003). Biodiesel oil extraction uses a cold press system without the use of a solvent or heat. Seeds are pressed once, subjected to extrusion under pressure, and then pressed a second time to remove remaining oil, and the presscake is dried in a cooler. The protein sources for the experimental diets (DM basis) were 1) 8.78% RCM, 2) 9.25% RCM plus 1.80% canola oil (RCMO), 3) 11.10% CPC, or 4) 8.14% RUCM plus 1.32% canola oil (RUCMO). Canola oil was added to the RCMO and RUCMO treatments to simulate the greater residual oil content of CPC. The composition and chemical analysis of the 4 diets are presented in Table 1. Diets were fed as total mixed rations that were offered in 2 equal portions at 0800 and 1600 h. The diets were fed at approximately 1.5 × NEm requirements with an expected ADG of 0.84 kg/d. The respective DM, CP (DM basis), and ether extract (DM basis) were 87.8, 39.2, and 3.34% for RCM; 91.7, 33.0, and 15.2% for CPC; and 92.9, 42.8, and 4.68% for RUCM.

Sample Collection Digesta flow and nutrient digestibility were determined using Yb and Cr as markers for the solid and liquid fractions, respectively. Microbial protein synthesis was measured using 15N as the ruminal microbial marker. Marker solution prepared by dissolving 4.88 g of YbCl3·6H2O (2.2 g of Yb; Cambridge Isotope Laboratories, Andover, MA) and 9 g of (15NH4)2SO4 (243 mg 15 N/d; 10% atom percentage of 15N; Cambridge Isotope Laboratories) in 2 L of deionized water was made up daily for each animal. For the Cr complex of EDTA, marker solution was prepared in bulk using the method described by Binnerts et al. (1968) and infused at a rate of 2.7 g/d of Cr-EDTA. Whole ruminal contents were taken from each animal to determine background 15 N natural abundance (15NB) before marker infusion. Marker solutions were then continuously infused into the rumen using an automatic peristaltic pump (model 205U, Watson Marlow, Cornwall, UK) starting on d 15. On d 1 of infusion, one-half of the daily dose of each marker was placed into the rumen via ruminal cannula as a priming dose. From d 16 to 19, spot urine samples were collected from each heifer before morning and afternoon feeding by vulva stimulation to initiate urination. During the same time, blood samples were collected via coccygeal venipuncture using 10 mL of evacuated serum tubes (Becton, Dickinson and Company, Franklin Lakes, NJ). Urine and blood samples were cooled on ice and transported to the laboratory. Blood samples were centrifuged for 15 min at 1,800 × g and 4°C to harvest serum, which was then stored frozen at −21°C until analysis. Urine was acidified with concentrated HCl to achieve urine pH less than 3. Specific gravity of urine was measured, and 50-mL aliquots from daily sampling were composited for each cow and period and stored at

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Table 1. Ingredient composition and chemical analysis of experimental diets Treatment1 Item Total mixed ration, % of DM Barley silage Concentrate Dry-rolled barley Concentrate, % of DM Barley grain Oat hulls Regular canola meal Canola presscake High RUP canola meal Canola oil Rumensin premix2 Limestone Trace mineral salt3 Vitamin A and D premix4 Chemical composition of total mixed ration DM, % CP, % of DM OM, % of DM NDF, % of DM ADF, % of DM Ether extract, % of DM Energy content,5 DM basis Diet ME, Mcal/kg of DM NEm, Mcal/kg of DM NEg, Mcal/kg of DM

RCM

RCMO

CPC

RUCMO

18.2 44.2 37.6

18.2 44.2 37.5

18.2 44.4 37.5

18.3 44.1 37.6

36.4 38.0 19.0 — — — 1.05 3.02 1.12 1.41

36.3 34.1 18.9 — — 4.07 1.05 3.01 1.11 1.41

35.3 34.8 — 23.3 — — 1.04 2.99 1.10 1.39

38.3 35.3 — — 16.8 2.99 1.05 3.03 1.12 1.41

64.2 12.1 94.9 28.9 13.8 2.29

63.5 12.1 95.0 28.1 13.4 3.88

64.5 12.1 95.1 28.2 13.3 3.53

63.1 12.1 95.1 28.1 13.3 4.15

2.48 1.56 0.97

2.53 1.63 1.03

2.56 1.63 1.03

2.50 1.62 1.02

1 RCM = 8.78% regular canola meal, RCMO = 9.25% RCM plus 1.80% canola oil, CPC = 11.10% canola presscake, RUCMO = 8.14% high ruminally undegraded protein canola meal plus 1.32% canola oil. 2 Provided 27.85 mg of monensin (Elanco Division, Eli Lilly Canada Inc, Guelph, Ontario, Canada)/kg of diet DM. 3 Trace mineral salt: 95% sodium chloride, 1.2% zinc, 1.0% manganese, 0.4% copper, 400 mg/kg of iodine, 60 mg/kg of cobalt, and 30 mg/kg of added selenium. 4 440,500 IU of vitamin A/kg, and 88,000 IU of vitamin D3/kg. 5 Calculated based on NRC (1996) level 2 model.

–20°C until analyzed for total N. Diluted samples from spot urine samples (2 mL of urine in 8 mL of distilled water) were also composited for each cow and period and stored at –20°C for later determination of urea-N and purine derivatives. Starting on d 20, a 1-L composite sample of whole ruminal digesta (taken from the cranial ventral, caudal ventral, central, and cranial dorsal rumen), 300 mL of duodenal digesta, and grab fecal samples were taken at 0800, 1100, 1400, 1700, 2000, and 2300 h and at 0200 and 0500 h on d 21, to represent a 24-h feeding cycle. Duodenal digesta and fecal samples from each of these sampling times were stored at –20°C. A portion of the ruminal contents (500 mL) collected at each sampling time was squeezed through 4 layers of cheesecloth, and both the filtrate and particulate portions were retained. Ruminal fluid pH was immediately determined using a Model 265A portable pH meter (Orion Research Inc., Beverly, MA). Two 5-mL aliquots of ruminal fluid were mixed with 1 mL of metaphosphoric acid (25% wt/vol) and 1 mL of 1% H2SO4 and stored at −20°C for later determination of ruminal VFA and NH3-N, respectively. The solid digesta that remained after filtration were mixed with 300 mL of 0.15 M sterile saline solution and homogenized in a blender for 60 s to dislodge particle-

associated bacteria. The blended mixture was squeezed through 4 layers of cheesecloth to obtain a second filtrate. The 2 filtrates were mixed, and 300 mL of the mixture was used to isolate mixed ruminal bacteria by differential centrifugation. Filtrates were initially centrifuged at 1,000 × g for 5 min at 4°C to remove protozoa and residual feed particles. The supernatant was subsequently centrifuged at 20,000 × g for 30 min at 4°C to obtain a mixed ruminal bacteria pellet. Bacteria pellets were pooled by period for each cow, freeze-dried, and ground to a fine powder using a ball mill. Also, during the 7-d data collection period, samples of dryrolled barley grain, barley silage, and protein concentrate were collected on alternate days, composited, and stored at −20°C for later analysis.

Sample Analyses Duodenal digesta samples were thawed at room temperature and pooled per cow per period to provide a representative duodenal sample (1.5 L) that accounted for diurnal variation. A subsample (1.0 L) of the composited sample was filtered through a Dacron polyester bag with a pore size of 52 ± 5 µm (mean ± SD) to separate digesta into liquid and solid fractions. The

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remaining 0.5 L was processed as whole duodenal digesta. Duodenal digesta, solid, and liquid fractions were freeze-dried and ground through a 1-mm screen using a Christy-Norris mill (Christy and Norris Ltd., Chelmsford, UK). Grab fecal samples were oven-dried at 60°C, ground through a 1-mm screen using a Christy-Norris mill, and 10 g from each sampling time was combined to form 1 representative sample for each animal in each period. Marker concentrations were determined in feces and duodenal digesta fractions after sample combustion at 550°C for 8 h in a muffle furnace (AOAC, 1990) followed by nitric acid digestion as described by Vicente et al. (2004). Concentration of Cr was determined by atomic absorption spectrophotometry (Perkin Elmer 2300, Perkin-Elmer Corp, Norwalk, CT), and Yb concentration in the same sample was determined by atomic emission spectroscopy (Varian Spectra 220, Varian, Mulgrave, Australia). Concentrations of Yb and Cr were used to determine correct proportions of fractions needed to reconstitute true duodenal digesta (TDD) based on the method of France and Siddons (1986). Feed samples were composited by diet and period and dried at 60°C for 48 h (AOAC, 1990) and ground through a 1-mm screen as described previously. Analytical DM content of feed, feces, TDD, and bacteria pellet was determined by drying at 135°C for 3 h (AOAC, 1990). Ash was determined by combustion in a furnace as described previously. Subsequently, OM content was calculated as the difference between analytical DM and ash content. Feed samples were also analyzed for ether extract. Kjeldahl N (AOAC, 1990), ADF, and NDF with heat-stable α-amylase and sodium sulfite (Van Soest et al., 1991) were determined in feed, feces, and TDD samples. Total N in bacteria pellet samples was determined using a combustion assay (Leco FP-528 Analyzer, Leco Corporation, St. Joseph, MI). To determine NH3-N in TDD, 10 mL of sodium citrate (0.07 M, pH 2.2) was added to 0.5 g of TDD sample, mixed thoroughly, and held at 39°C for 30 min. Samples were subsequently centrifuged at 18,000 × g for 15 min at 4°C, and NH3-N concentration was determined in the supernatant using a phenol-hypochlorite assay (Broderick and Kang, 1980). The nonammonia N (NAN) content of TDD was determined as the difference between total N of TDD and NH3-N in TDD. Frozen samples for ruminal 15NB determination were freeze-dried and ground through a 1-mm screen (Christy and Norris Ltd.) and, subsequently, ground to a fine powder using a ball mill. To volatilize NH3-N from the mixed ruminal bacteria pellet, TDD and 15NB ruminal digesta samples (containing 100 µg of N) were weighed into 5 × 9-mm tin capsules and 50 µL of 72 mM K2CO3 were added, and samples were then incubated in an oven at 60°C for 24 h. Enrichment of 15N in NAN of TDD, 15NB ruminal digesta, and mixed ruminal bacteria samples was determined by combustion to N2 gas in an elemental analyzer and continuous flow isotope ratio-mass spectrometry.

The TDD samples for AA analyses were oxidized with performic acid and hydrolyzed with 6 M HCl as described by Llames and Fontaine (1994). Amino acid analysis was performed using an analytical ion exchange column AA911 (Transgenomic, Omaha, NE) and HPLC system (Agilent 1100 series, Hewlett Packard, Germany). Amino acids were postcolumn derivatized with ninhydrin reagent, and detection was performed at 570 nm using a diode array detector. Samples for ruminal VFA were thawed at room temperature, centrifuged at 18,000 × g for 15 min at 4°C, and filtered through a 0.45-µm membrane. A 0.9-mL portion of the filtered supernatant was mixed with 0.1 mL of 10 mg/mL of crotonic acid as an internal standard. Ruminal VFA were separated and quantified by gas chromatography (Agilent 6890, Mississauga, Ontario, Canada) as described by Erwin et al. (1961). Similarly, ruminal fluid samples for NH3-N were thawed, centrifuged for 10 min at 18,000 × g at 4°C to obtain a clear supernatant, and then analyzed using a phenolhypochlorite assay described previously. Urine samples were analyzed for total N by the macro-Kjeldahl procedure, uric acid (Stanbio Uric Acid Liquicolor, Stanbio Laboratory, Boerne, TX), creatinine (Kit 420, Stanbio Laboratory), and allantoin according to the method described by Chen and Gomes (1992). Serum and urinary urea-N was determined by the diacetyl monoxime method (Stanbio Urea Nitrogen Kit, Stanbio Laboratory). Total purine derivative (PD; i.e., allantoin + uric acid):creatinine (CR) ratio was used as an indicator of relative changes in rumen microbial flows to the intestinal tract (Loy et al., 2008).

Nutrient Flow Calculations Nutrients flowing to the duodenum were calculated as described by Reynal and Broderick (2005) with some modifications. Background of 15N enrichment in bacteria and digesta were assumed to be similar based on observations by Ahvenjärvi et al. (2002). Therefore, 15NB was used for computing 15N enrichment in bacterial and digesta fractions. The mean 15NB was 0.36903 atom percent N (16 background samples, averaged across animals and periods). The atom percent 15N above background enrichment was calculated for digesta and bacterial samples for each cow in each period as 15N enrichment = 15N-atom % in sample − 0.36903. Assuming that isolated mixed ruminal bacteria were representative of the bacterial biomass flowing out of the rumen, total microbial N flowing to the duodenum was calculated using the 15N microbial marker as total microbial N flow = NAN flow to the duodenum × (duodenal 15N enrichment of NAN ÷ rumen bacteria 15N enrichment), where flows are expressed in grams per day. Apparent digestion of nutrients in the rumen was calculated as nutrient apparently digested in the rumen = nutrient intake – duodenal flow of nutrient, where nutrient intake, digestion, and flow to the duodenum are expressed


in kilograms per day. Organic matter truly digested in the rumen (OMTDR) was determined after correcting for microbial OM flowing to the duodenum as OMTDR = OM intake – (duodenal OM flow – microbial OM flow), where OMTDR, OM intake, duodenal OM flow, and microbial OM flow are expressed in kilograms per day. Nonammonia nonmicrobial nitrogen (NANMN) fraction, assumed to comprise dietary and endogenous NAN, was calculated as NANMN flow = total NAN flow – microbial N flow, where NANMN flow, total NAN flow, and microbial N flow are expressed in grams per day. Flows of DM excreted in feces were calculated by dividing Yb infused (Yb, g/d) by Yb concentration (Yb, g/kg of DM) in the feces. Outputs of OM, ADF, and NDF in feces were calculated by multiplying DM flow by their concentration in fecal DM.

Statistical Analysis Data were analyzed as a 4 × 4 Latin square using the Proc Mixed procedure (SAS Inst. Inc., Cary, NC) with the following model: Yijk = µ + Ci + Pj + Tk + εijk, where Yijk = the dependent variable, µ = overall mean, Ci = random effect of cow, Pj = fixed effect of period, Tk = fixed effect of dietary treatment, and εijk = random residual error. Ruminal pH and NH3-N data were analyzed accounting for repeated measures as recommended by Wang and Goonewardene (2004) for the analysis of animal experiments. Data for these measurements were analyzed by including the variable time in the repeated statement, as well as terms for time (hour), and interaction (diet × time) in the model described previously. Significance was declared at P < 0.10, and least square means were separated using Bonferroni’s procedure.

RESULTS AND DISCUSSION All diets had similar concentrations of DM, ADF, NDF, and CP (Table 1). Because the same batches of concentrates were used throughout the experiment, no statistical analyses were conducted on feed chemical composition. However, ether extract analysis showed that fat content was numerically greater by 1.59, 1.24, and 1.86 percentage points for the RCMO, CPC, and RUCMO diets, respectively, compared with the RCM diet (Table 1). Canola oil was added to the RCMO and RUCMO diets so that dietary fat content would be similar to the CPC diet. The CPC diet was formulated to contain 3.6% dietary fat. According to the ether extract analysis, fat content was more variable in dietary treatments to which canola oil had been added (SD = 0.37, 0.27, 0.04, and 0.04 for the RCMO, RUCMO, CPC, and RCM diets, respectively). This variation could be a result of insufficient feed mixing during pelleting. The main reason for supplementing diets with fat is to increase the energy density of ruminant rations (Hess et al., 2008). Generally, adding fat to ruminant diets can disrupt ruminal fermentation and depress digestion of

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structural carbohydrates (Jenkins, 1993). Diets in the present study contained on average 2.52 Mcal of ME/ kg of DM as predicted by the NRC (1996), but energy density for the RCM diet was 0.04 Mcal of ME/kg of DM less than in the other 3 diets because of its slightly less lipid content (Table 1). The effects of dietary treatment on ruminal pH, ammonia, VFA, PD, and urea N concentrations are shown in Table 2. There was no dietary effect on ruminal pH, and this was expected because diets were formulated to provide rumen fermentable carbohydrates from the same sources with the only different feed ingredient among the 4 treatments being the source of protein. Averaged across treatments ruminal pH was 6.29. Compared with feeding the RCM diet, ruminal NH3-N concentrations were less by 24% (P = 0.03), 20% (P = 0.05), and 33% (P = 0.005) in heifers fed the RCMO, CPC, and RUCMO diets, respectively. Considering that dietary fat content of the RCM treatment was on average 1.56 percentage points less than the other 3 treatments, reduction in ruminal NH3-N concentration could have been a result of the deleterious effects of dietary fat on ruminal protozoa that have been observed with fat-supplemented diets (Oldick and Firkins, 2000; Beauchemin et al., 2009). Such decreases in rumen protozoa could be a result of greater NH3-N incorporation into microbial protein caused by less intraruminal recycling of N (Oldick and Firkins, 2000; Onetti et al., 2001) and a decrease in dietary protein degradation by rumen microbes as a consequence of reduced ruminal protozoa (Petit et al., 2004). Despite the observed treatment effect on ruminal NH3-N concentrations, we did not detect treatment effects on the supply of ruminally degraded protein (RDP) or blood and urinary urea-N (Table 2). Compared with the RCM diet, heifers fed the RCMO diet had greater ruminal concentrations of acetate (P = 0.07), propionate (P = 0.09), valerate (P = 0.06), and total VFA (P = 0.07). Similarly, heifers fed the CPC diet had greater concentrations of propionate (P = 0.02) compared with the RCM diet. On the other hand, feeding the RUCMO diet resulted in decreased ruminal concentrations of acetate (P = 0.02) compared with the RCM diet. These changes in ruminal fermentation resulted in reduced acetate:propionate ratio in heifers fed the RCMO (P = 0.08), CPC (P = 0.02) and RUCMO (P < 0.01) diets compared with the RCM diet. In general, response to feeding greater dietary fat content on ruminal VFA proportions have been mixed with reports of no effect (Zinn and Shen, 1996) or decreased acetate and increased propionate concentrations (Boggs et al., 1987; Zinn, 1988). The PD:CR ratio, urinary urea N as a proportion of urinary N, and blood urea N were not affected by dietary treatment. Intakes, ruminal outflows, and total tract digestibilities for OM, NDF, and ADF are presented in Table 3. Because DMI was restricted, intakes of OM, NDF, and ADF were not affected by dietary treatment. Despite acetate:propionate ratios that are consistent with

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Table 2. Effects of feeding different types of canola protein supplements on characteristics of ruminal fermentation, urine, and blood in growing beef heifers Treatment1 Item Ruminal pH Ruminal NH3-N, mg/dL VFA concentration, mM Acetate Propionate Butyrate Isobutyrate Valerate Isovalerate Total VFA Acetate:propionate ratio PD:CR2 Urinary urea N, % of urine N Blood urea N, mg/dL

RCM

RCMO

6.27 9.4

CPC

6.27 7.2a

6.32 7.5a

84.7a 29.2a 17.4 1.58 1.81a 2.68 137.4a 3.04a 0.59 42.1 15.3

75.2 23.3 15.6 1.49 1.51 2.19 119.3 3.47 0.71 41.1 14.9

80.4 31.6a 15.6 1.58 1.76 2.50 133.7 2.84a 0.73 46.7 16.5

RUCMO 6.31 6.3a 62.8a 25.6 11.4 1.29 1.35 1.84 103.4 2.49a 0.69 49.9 15.9

SEM 0.12 0.75 3.36 2.54 1.42 0.09 0.11 0.20 6.30 0.20 0.05 4.02 0.40

a

Values differ from RCM (P < 0.10). RCM = 8.78% regular canola meal; RCMO = 9.25% RCM plus 1.80% canola oil; CPC = 11.10% canola presscake; RUCMO = 8.14% high ruminally undegraded protein canola meal plus 1.32% canola oil. 2 PD:CR = purine derivative:creatinine ratio in urine. 1

changes in ruminal fermentation patterns, we did not detect differences among treatments in the ruminal digestibility of OM, NDF, and ADF (Table 3). Oldick and Firkins (2000) observed a decrease (P = 0.10) in acetate:propionate ratio and ruminal NDF digestibility in heifers fed fat-supplemented diets. Similar to our results, feeding steam-flaked corn-based diets supplemented with 4% fat from tallow, full fat corn germ, corn oil, and flax oil had no effect on ruminal digestion of OM and NDF (Montgomery et al., 2008). The rela-

tively large variation inherent in flow studies often limits the ability to detect differences (Titgemeyer, 1997). Ruminal digestibility coefficients for OM, NDF, and ADF obtained from the current study were generally low. A possible explanation is that experimental diets contained between 15.2 and 17.5% (on DM basis) oat hulls, which could have led to low nutrient digestion in the rumen observed in our study. Previous in vitro studies showed a decreased rate and extent of DM disappearance of oat hulls compared with corn fiber

Table 3. Effects of feeding different types of canola protein supplements on intake, flow to the duodenum, and ruminal digestibility of DM, OM, NDF, and ADF in growing beef heifers Treatment1 Item Intake, kg/d DM OM NDF ADF Ruminal digestibilities, kg/d OM, apparent NDF ADF Ruminal digestibilities, % of intake OM, apparent NDF ADF Total tract digestibilities, % of intake OM NDF ADF a

RCM

RCMO

CPC

RUCMO

SEM

8.72 8.16 3.00 1.53

8.57 8.03 2.79 1.41

8.83 8.28 2.93 1.48

8.60 8.08 2.80 1.41

0.27 0.28 0.11 0.06

3.19 0.82 0.39

3.29 0.62 0.31

3.15 0.90 0.41

3.51 0.71 0.33

0.43 0.19 0.11

38.9 26.7 24.1

41.6 22.7 22.2

38.1 30.4 27.5

43.2 25.0 23.4

5.11 6.18 7.18

76.3 50.5 48.1

75.7 48.6a 44.6a

76.5 50.6 46.2

74.9a 46.3a 42.7a

0.46 0.78 1.24

Values differ from RCM (P < 0.10). RCM = 8.78% regular canola meal; RCMO = 9.25% RCM plus 1.80% canola oil; CPC = 11.10% canola presscake; RUCMO = 8.14% high ruminally undegraded protein canola meal plus 1.32% canola oil. 1

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Table 4. Effects of feeding different types of canola protein supplements on flow of N fractions to the duodenum in growing beef heifers Treatment1 Item

RCM

RCMO

CPC

RUCMO

SEM

N intake, g/d CP Intake, g/d Flow at the duodenum, g/d Truly digested in the rumen g/d % of CP intake RDP2 supply g/d % of DMI RUP3 flow g/d % of DMI Flow to the duodenum Total N, g/d Total N, % of N intake Ammonia N, g/d NAN,4 g/d NAN, % of N intake Microbial N, g/d Microbial N, % of N intake NANMN,5 g/d NANMN, % of NAN NANMN, % of N intake Microbial efficiency OMTDR,6 g of microbial N/kg

169

165

171

167

5.6

1,057 845

1,033 816

1,066 833

1,042 830

31 61

833 78.8

891 85.8

921 86.4

870 83.1

63 4.4

848 9.7

901 10.5

932 10.6

882 10.2

63 0.51

208 2.4

132 1.6

134 1.5

161 1.9

44 0.53

138 81.5 2.40 135 80.1 102 60.4 33.3 23.0 19.7

132 80.3 1.65 131 79.3 110 66.2 21.3 16.1 13.2

135 79.0 1.76 133 78.0 112 65.5 21.5 15.6 12.5

135 80.7 1.79 133 79.7 107 63.8 25.3 20.0 15.7

9.8 6.0 0.35 9.7 5.9 8.2 4.2 7.1 4.9 4.4

35.1

34.4

37.9

30.9

5.2

1

RCM = 8.78% regular canola meal; RCMO = 9.25% RCM plus 1.80% canola oil; CPC = 11.10% canola presscake; RUCMO = 8.14% high ruminally undegraded protein canola meal plus 1.32% canola oil. 2 Ruminally degraded protein. 3 Ruminally undegraded protein. 4 NAN = nonammonia N. 5 NANMN = nonammonia nonmicrobial N. 6 OMTDR = OM truly digested in the rumen.

and soybean hulls (Hsu et al., 1987). Oat hulls have increased lignin content, and ruminal digestion is impaired by hydroxycinnamic cross-linked complex cell wall structure (Yu et al., 2005). Surprisingly, digestibility of OM, NDF, and ADF in the total tract was affected by dietary treatment. Compared with the RCM diet, feeding the RCMO diet decreased the digestibility of ADF (P = 0.08) and NDF (P = 0.08) in the total tract. Additionally, feeding the RUCMO diet decreased the digestibility of OM (P = 0.02), NDF (P < 0.01), and ADF (P = 0.02) compared with the RCM diet (Table 3). These data suggest that adding canola oil to the RCMO and RUCMO diets affected fiber digestion in the hindgut. Feeding fat to ruminants can cause a shift in fiber digestion from the rumen to the hindgut (Boggs et al., 1987; Jenkins and Fotouhi, 1990). As observed for other nutrients, N intake and flow of N fractions to the duodenum were similar across diets (Table 4). Averaged across diets, duodenal flow of total N, NAN, NANMN, and microbial N was 135, 133, 25, and 108 g/d, respectively. Similarly, the flow of these N fractions as a percentage of N intake was unaffected by dietary treatment. Microbial efficiency also was not affected by dietary treatment and averaged 34.6 g of

microbial N/kg of OM truly digested in the rumen (Table 4). Preexperiment diet evaluation using the NRC (1996, level 2) model revealed that, on average, these diets were expected to provide 636 and 170 g/d of MP from bacteria and RUP, respectively. These values were similar to 673 and 158 g/d calculated from microbial N and NANMN in our study. Surprisingly, the RDP fractions were similar among the 4 treatments. Reduced rumen degradable fractions were expected for heifers fed the RUCMO and RCM diets compared with the CPC diet. This is because RCM and RUCM protein supplements are exposed to heat in the desolventizertoaster step during oil extraction. Also, according to the manufacturer, RUCM contains 55% of CP as RUP. The data from in vivo measurements of RDP in the current experiment revealed no dietary treatment effect and averaged across treatments were 891 g/d or 10.3% of DMI (Table 4). Previous in situ studies with RCM and CPC have shown that the effective ruminal degradability of CP from CPC is greater than that from RCM (Mustafa et al., 1997; Jones et al., 2001). Flows of individual AA to the duodenum are presented in Table 5. Flows of individual AA were not affected by diet. These results were expected considering that

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Table 5. Effects of feeding different types of canola protein supplements on flow of AA (g/d) to the duodenum in growing beef heifers Treatment1 AA

RCM

RCMO

CPC

RUCMO

SEM

Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Valine Alanine Aspartic acid Cystine Glutamic acid Glycine Proline Serine

35.5 26.1 33.0 59.1 54.9 11.3 37.7 37.7 37.8 48.5 81.2 16.7 126.2 47.2 44.1 37.9

33.3 22.6 30.4 54.8 50.4 11.1 34.0 35.1 34.3 44.2 72.9 15.5 113.5 41.9 36.8 34.5

33.4 27.2 33.1 60.7 56.0 12.3 39.3 39.8 38.0 49.8 81.9 17.0 124.0 47.9 47.2 39.5

36.7 25.8 32.5 60.2 56.0 13.2 38.3 39.6 36.7 49.8 83.4 16.9 122.3 48.2 47.6 39.5

2.9 3.4 3.1 4.9 5.2 1.3 3.2 3.4 3.5 4.2 6.9 1.3 9.8 3.6 4.5 2.9

1 RCM = 8.78% regular canola meal; RCMO = 9.25% RCM plus 1.80% canola oil; CPC = 11.10% canola presscake; RUCMO = 8.14% high ruminally undegraded protein canola meal plus 1.32% canola oil.

the contribution of RUP to AA reaching the duodenum could have been minimal because less than 20% of dietary protein escaped rumen degradation. In summary, feeding differently produced canola protein supplements to growing heifers had no effect on ruminal digestion or nutrient flows to per se, but changes in ruminal fermentation patterns consistent with fat supplementation were observed. Compared with the RCM diet, feeding the RCMO and RUCMO diets reduced the digestibility of ADF, NDF, and OM in the total tract. There were decreases in ruminal NH3-N and changes in the concentrations of ruminal VFA associated with adding canola oil or having greater residual oil in the protein supplement. Notwithstanding these changes, lipid content in the meal did not have an impact on microbial protein synthesis or N fractions reaching the duodenum. Considering that ruminal digestion or N metabolism was not affected, the biological significance of these changes in ruminal fermentation patterns appear to be minor. Results from the current study show that rumen degradability of protein from canola meal types is very high and could limit its ability to supply metabolizable AA. These results suggest that, apart from minor changes in ruminal fermentation as a result of the greater residual oil compared with RCM, CPC seems to be as good a protein source as either of the canola protein supplements used in this study.

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