Effect of Thermal Processing on Estimated Metabolizable Protein

Jul 21, 2014 - ABSTRACT: This study evaluated the effect of thermal processing on the estimated metabolizable protein (MP) supply to dairy cattle from...
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Effect of Thermal Processing on Estimated Metabolizable Protein Supply to Dairy Cattle from Camelina Seeds: Relationship with Protein Molecular Structural Changes Quanhui Peng,†,‡ Nazir A. Khan,†,⊥ Zhisheng Wang,‡ Xuewei Zhang,§ and Peiqiang Yu*,†,§ †

Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada Animal Nutrition Institute, Sichuan Agriculture University, Sichuan 625014, China § Tianjin Agricultural University, Tianjin 300384, China ‡

S Supporting Information *

ABSTRACT: This study evaluated the effect of thermal processing on the estimated metabolizable protein (MP) supply to dairy cattle from camelina seeds (Camelina sativa L. Crantz) and determined the relationship between heat-induced changes in protein molecular structural characteristics and the MP supply. Seeds from two camelina varieties were sampled in two consecutive years and were either kept raw or were heated in an autoclave (moist heating) or in an air-draft oven (dry heating) at 120 °C for 1 h. The MP supply to dairy cattle was modeled by three commonly used protein evaluation systems. The protein molecular structures were analyzed by Fourier transform/infrared-attenuated total reflectance molecular spectroscopy. The results showed that both the dry and moist heating increased the contents of truly absorbable rumen-undegraded protein (ARUP) and total MP and decreased the degraded protein balance (DPB). However, the moist-heated camelina seeds had a significantly higher (P < 0.05) content of ARUP and total MP and a significantly lower (P < 0.05) content of DPB than did the dry-heated camelina seeds. The regression equations showed that intensities of the protein molecular structural bands can be used to estimate the contents of ARUP, MP, and DPB with high accuracy (R2 > 0.70). These results show that protein molecular structural characteristics can be used to rapidly assess the MP supply to dairy cattle from raw and heat-treated camelina seeds. KEYWORDS: camelina seed, protein metabolic characteristics, protein molecular structure, protein evaluation system

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INTRODUCTION Camelina (Camelina sativa L. Crantz), commonly known as gold-of-pleasure or false flax, is an unexploited, short-seasoned oilseed crop in the family of Brassicaceae. Over the past few years, the demand for camelina seeds has increased because of its increased use in biodiesel and bio-oil production, and in animal feed.1,2 Moreover, because of its early maturity and adaptability to diverse soil and environmental conditions, the crop grows well in the cold, semiarid, and marginal lands of North America. As a result, the cultivated area of camelina was estimated to reach 0.607 million hectares by 2013 in North America.3 Camelina seeds contain over 35% oil,3 with a remarkably high content (>37%) of C18:3n-3,2,4 which makes it a valuable alternative source of omega-3 fatty acids in human and animal diets.5 Moreover, it is well-known that camelina seeds are relatively rich in crude protein (CP, >25%) and essential amino acids,3,6 indicating the potential of this oilseed as a high quality protein and oil supplement for dairy cattle, particularly during early lactation. The beneficial effects of feeding camelinaderived oil on animal health and the fatty acid profiles of meat and milk have been extensively evaluated;7−13 however, to the author’s knowledge, the metabolizable protein (MP) supply to dairy cattle from camelina seeds has not been evaluated. Excessive degradation of oilseed-derived protein in the rumen decreases the efficiency of protein utilization and increases feed cost and N losses to the environment.14,15 Thermal processing has been used widely to decrease the rumen degradation of protein; however, the establishment of optimal heating conditions © 2014 American Chemical Society

is vital to optimize protein utilization in ruminants. Recent research has demonstrated that thermal processing alters protein digestive behavior by changing protein molecular structures.16 Therefore, quantifying the heat-induced changes in protein molecular structures in relation to changes in protein digestive behavior in the rumen and intestines of dairy cattle can help to establish optimal heating conditions.17,18 However, such studies are extremely rare, partly because of the lack of appropriate analytical techniques. Recent research has revealed that Fourier transform/infrared-attenuated total reflectance (FT/IR-ATR) molecular spectroscopy can be used as a fast, nondestructive, and noninvasive bioanalytical technique to detect protein molecular structural changes in feed tissues.16,18,19 Over the past few decades, various protein evaluation models such as the National Research Council (NRC)-2001 model,20 the DVE/OEB system21 (DVE, truly absorbed protein in the small intestine; OEB, degraded protein balance), and the PDI22 (protein truly digestible in the small intestine) system have been developed, which estimate the MP supply to dairy cattle using in situ ruminal and intestinal protein digestibility data. So far, the MP content and feed milk value (FMV) of camelina seeds have not been investigated by employing and comparing different protein evaluation models. Therefore, the first objective Received: Revised: Accepted: Published: 8263

March 18, 2014 July 21, 2014 July 21, 2014 July 21, 2014 dx.doi.org/10.1021/jf5013049 | J. Agric. Food Chem. 2014, 62, 8263−8273

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kinetics equation of Ørskov and McDonald25 with a modification for lag time by Robinson et al:26

of the present study was to evaluate the metabolic characteristics of the protein in the rumen and intestines of dairy cattle and to estimate the MP supply to dairy cattle from raw and heat-treated camelina seeds. The second objective was to establish the relationship between the protein molecular structural characteristics and the MP supply to dairy cattle as predicted by three evaluation systems in order to provide a new tool for the rapid evaluation of protein nutritive value. We hypothesized that some specific protein structural characteristics can be used to estimate the MP content, degraded protein balance (DPB), and FMV of camelina seeds.

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CP (t ) = U + (100 − S − U ) × e−Kd(t − T0) where CP (t) is the CP (g/kg) present in the residues at time h incubation; S is the soluble CP fraction (g/kg); U is the rumen nondegradable CP fraction (g/kg); Kd is the degradation rate/h; and T0 is the lag time (h). The results were analyzed using the PROC NLIN (nonlinear) procedure of Statistical Analysis System (SAS, 2009)27 with an iterative least-squares regression (Gauss−Newton method). Rumen-degraded feed protein (RDP) and rumen-undegraded protein (RUP) were calculated according to the NRC-200120 model as

⎡ ⎤ Kd ⎥ RDP (g/kg) = S + D⎢ ⎢⎣ (Kd + K p) ⎥⎦

MATERIALS AND METHODS

Camelina Seeds, Heat Treatment and Processing. Seeds of Blaine Creek and Celine varieties of camelina were sampled from three replicate plots in two different years (2010 and 2011) by the Feeds Innovation Institute (FII), University of Saskatchewan (Saskatoon, Canada). The seeds were used as a model for camelina-derived feed protein. The seeds (1 kg) of each camelina variety were spread (2 cm thin layer) in aluminum pans (23 cm × 33 cm × 5 cm high) and heated in an air-draft oven (dry heating) or an autoclave (Amsco Eagle SG-3031, Steris Corp., Mentor, OH) under 15 pounds per square inch pressure (moist heating) for 1 h at 120 °C. The heat processing was carried out in two replicate runs. After heat treatment, the seeds were immediately removed from the oven or autoclave, cooled at room temperature (22 ± 2 °C), and stored at 4 °C for further processing and analysis. The raw seeds were used as a control. The seeds were ground through a 2 mm screen (Retsch ZM-1, Brinkmann Instruments Ltd., Mississauga, ON, Canada) for in situ incubation studies. For chemical analysis, the seeds were ground through a 1 mm screen, whereas for molecular spectral analyses, the seeds were finely ground through a 0.25 mm screen. For the fine grinding, the seeds were kept cool and were slowly fed into the grinder to avoid extrusion. Molecular Spectroscopy. The protein molecular structural bands of the raw and heat-treated camelina seeds were analyzed using FT/ IR-ATR microspectroscopy (Jasco-4200, Jasco Inc., Easton, MD) at the molecular spectroscopy laboratory of the Department of Animal and Poultry Science, University of Saskatchewan (Saskatoon, Canada). The FT/IR-ATR was equipped with a deuterated L-alanine-doped triglycine sulfate detector (JASCO Corp., Tokyo, Japan) and a ceramic infrared light source, and was outfitted with a MIRacle ATR accessory module and a ZnSe crystal and pressure clamp (Pike Technologies, Madison, WI, U.S.A.). For each sample, 128 scans were generated in the mid-infrared (ca. 4000−800 cm−1) and fingerprint (ca. 1800− 800 cm−1) regions in a transmission mode at a spectral resolution of 4 cm−1. Each sample was run five times. The spectra were collected with Jasco Spectra Manager II software, and the molecular structural features were quantified by Ominic 7.2 software (Spectra-Tech Inc., Madison, WI, U.S.A.). The specific spectral bands associated with protein functional groups, such as amide I and amide II, and protein secondary structures, such as α-helix and β-sheet, were identified and quantified as reported by Peng et al.3 In Situ Rumen Incubation. Four nonlactating Holstein cows, fitted with flexible rumen cannula with an internal diameter of 10 cm (Bar Diamond Inc., Parma, ID, U.S.A.), were used for the in situ incubation. The cows were handled and cared for according to the guidelines of the Canadian Council on Animal Care.23 The cows had free access to fresh drinking water and were individually fed twice each day with a balanced total mixed ration, containing 805 g barley silage and 195 g concentrate per kg DM, according to NRC maintenance requirements.20 The detailed chemical composition of the concentrate and barley silage is reported earlier.19 The rumen degradation kinetics of raw and heat-treated camelina seeds were determined according to the standard in situ method as described by Yan et al.24 Rumen Degradation Characteristics. The rumen degradation characteristics of protein were computed according to the first-order

⎡ ⎤ Kp ⎥ RUP (g/kg) = U + D⎢ ⎢⎣ (Kd + K p) ⎥⎦ where D is the potential degradable protein (g/kg) and was calculated as D = 100 − S − U, and Kp is the estimated outflow rate of digesta from rumen, which was assumed to be 6%/h for the three evaluation systems. Intestinal Protein Digestion Determination. The intestinal digestibility of RUP was determined using the three-steps in vitro method of Calsamiglia and Stern28 with slight modifications as described in our previous study by Peng et al.3 Estimating Metabolizable Protein Supply to Dairy Cattle: NRC-2001 Model. The detailed framework, concepts, and formulas of the NRC-2001 dairy model are provided by the NRC.20 Briefly, the MP supply from raw and heat-treated camelina seeds to the small intestine of dairy cattle was calculated from (1) truly absorbable RUP (ARUPNRC), (2) truly absorbable ruminally synthesized microbial protein (microbial protein, MCP) (AMCPNRC), and (3) truly absorbable rumen endogenous protein (AECPNRC). The MP was calculated as follows:

MP (g/kg DM) = ARUPNRC (g/kg) + AMCPNRC (g/kg) + AECPNRC (g/kg) The ARUPNRC content was estimated as follows:

ARUPNRC (g/kg DM) =

dRUP (%RUP) × RUPNRC (g/kg DM) 100

where, dRUP was the intestinal digestibility of RUP, determined according to the three-step in vitro procedure of Calsamiglia and Stern.28 The RUP content was calculated as

RUPNRC (g/kg DM) = CP (g/kg DM) ×

RUP (%CP) 100

The AMCPNRC was estimated from the predicted MCP synthesized in the rumen. The NRC (2001) assumes that the MCP contributed by bacteria and protozoa contains 80% true protein while the other 20% CP is contributed by nucleic acids, which are not available to dairy cattle. Moreover, it also assumes that the digestibility of true MCP is 80%. Thus, AMCPNRC = MCP × 0.8 × 0.8 According to the NRC-2001 model, the MCP was estimated from the total digestible nutrients (TDN). The model assumes that the yield of MCP from 1 kg TDN is 130 g. The MCPTDN was calculated as follows:

MCPTDN (g/kg DM) = 0.130 × TDN However, if RDP in the feed is less than 1.18 × MCPTDN, then MCP is calculated from RDP as follows:

MCPRDP (g/kg DM) = 0.85 × RDP (g/kg DM) 8264

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where the NRC (2001) assumes that 85% of the RDP is converted to MCP, and 1.18 results from 1.00/0.85. The supply of endogenous crude protein (ECP) to the small intestine was calculated as

The degraded protein balance (DPBDVE) was calculated from the difference between the MCPRDP and the potential MCP based on the energy extracted during the anaerobic fermentation of FOM (MCPFOM) in the rumen:

DPPDVE = MCPRDP − MCPFOM

ECPNRC (g/kg DM) = 6.25 × 1.9 × DM

where MCPRDP was determined as follows:

The number 6.25 represents the protein−N conversion factor, and 1.9 indicates that 1.9 g of endogenous N was originated from 1 kg of DM. The NRC assumes that 50% of the ECPNRC passes to the duodenum, and 80% of the rumen ECP is true protein. The truly absorbed ECP in the small intestine (AECPNRC) was estimated as

⎡ ⎛ RUP (%CP) ⎞⎤ ⎟⎥ MCPRDP = CP (g/kg DM) × ⎢1 − ⎜1.11 × ⎣ ⎝ ⎠⎦ 100 Nutrient Supply Evaluated Using PDI System. The principles and calculations of the PDI system22,30 were used to calculate the supply of truly digestible protein (PDI) to the small intestine of dairy cattle from the raw and heat-treated camelina seeds. The PDI of feed comprises the truly absorbable RUP (ARUPPDI) and the truly absorbable rumen-synthesized MCP (AMCPPDI):

AECPNRC = 0.50 × 0.80 × ECPNRC The DPBNRC was calculated as the difference between the potential MCPRDP and MCPTDN, as follows: DPB NRC (g/kg DM) = MCPRDP (g/kg DM)

PDI (g/kg DM) = ARUPPDI + AMCPPDI

− 1.18 × MCPTDN (g/kg DM)

The ARUPPDI was calculated from the RDPPDI as

Nutrient Supply Evaluated Using DVE/OEB System. The calculation for estimating the MP supply using the DVE/OEB system21 is summarized here. The MP (DVE) value of feed comprises truly absorbable RUP (ARUPDVE), truly absorbable rumen-synthesized MCP (AMCPDVE), and a correction for endogenous ECPDVE losses (ENDPDVE). The MPDVE value was calculated as

ARUPPDI (g/kg DM) = CP (g/kg DM) × (1.11 × (1 − RDP)) × TId

The PDI system assumes that 1.11 is a correction factor for the rumen bypass protein (RUPPDI = 1.11 × (1 − RDPPDI) based on in vivo experiments. The RDP was calculated from the disappearance of protein from nylon bags during 48 h, assuming a rumen particle outflow rate of 6%/h. The TId is the true intestinal digestibility of RUP. TId was calculated as

MPDVE (g/kg DM) = ARUPDVE + AMCPDVE − ENDPDVE The ARUPDVE was calculated on the basis of the content and digestibility of RUPDVE. The ARUPDVE was calculated as

ARUPDVE (g/kg DM) =

TId (g/kg DM) = 88.3 + 0.371 × CP − 0.0037 × CP2

dRUP (%RUP) × RUPDVE (g/kg DM) 100

− 1.07 × ADL − 0.313 × UDOM where CP, acid detergent lignin (ADL), and undigested OM (UDOM) are expressed in (g/kg DM). The AMCPPDI was calculated from (1) the MCP synthesized based on the available energy (MCPME), assuming that the degraded CP and other nutrients are not limiting, and (2) the MCP synthesized based on RDP (MCPRDP), assuming that energy and other nutrients are not limiting. The MCPME was estimated from the FOM and was calculated as follows:

where dRUP was determined according to Calsamiglia and Stern.28 The content of RUPDVE was calculated from the CP content of the feeds and RUP contents of the CP as follows:

⎡ RUP (%CP) ⎤ RUPDVE (g/kg DM) = 1.11 × ⎢CP (g/kg DM) × ⎥ ⎣ ⎦ 100 where 1.11 is the correction of the in situ data from the in vivo results.21 The AMCPDVE was calculated as follows:

MCPME = FOM × 0.145 × 0.8 × 0.8

AMCPDVE (g/kg DM) = 0.75 × 0.85 × MCPFOM (g/kg DM)

where 0.145 represents the yield of MCP that is assumed to be 145 g CP/kg FOM, and its true protein content and true digestibility in the small intestine are assumed to be 0.80 each. The FOM was calculated as follows:

where 0.75 is the assumed amount of true protein in the MCP, and 0.85 is the digestibility of MCPFOM. The MCPFOM was calculated as

MCPFOM = 0.15 × FOM

FOM = DOM − EE − RUPPDI

where the factor 0.15 represents the assumption of the DVE system that for 1 kg of fermentable organic matter (FOM), 150 g of MCPFOM is synthesized in the rumen. The FOM was calculated as

The DOM was calculated as

DOM = 87.75 − 0.314 × CF (%of DM) + α where α = 6.2 for oilseeds. The MCPRDP was calculated as

FOM (g/kg DM) = DOM − Cfat − RUP − RUST − FP

MCPRDP = 0.80 × 0.80 × RDPPDI

where DOM is the digestible organic matter (OM); Cfat is the ether extract; RUST is the ruminally undegraded feed starch; and FP is fermentation products for conserved forages. For camelina seeds, FP and RUST were assumed to be zero. The DVE/OEB system assumes that the ECP losses (ENDPDVE) in the digestive tract are associated with the passage of the undigested DM (UDM). The ECPDVE was calculated as

as mentioned before, the true protein content of MCP and the true digestibility in the small intestine are 0.80 each. The RDPPDI was calculated as RDPPDI (g/kg DM) = 0.90 × CP (g/kg DM) × (1.11(1 − RDP))

where 0.90 is the efficiency of conversion of degraded N to rumen microbial N. The truly absorbable rumen-synthesized MCP in the small intestine (AMCPPDI) was calculated as

ENDPDVE (g/kg DM) = 0.075 × UDM (g/kg DM) where the DVE/OEB system assumed that 75 g of protein would be excreted per kilogram of UDM. The UDM was calculated as

AMCPPDI (g/kgDM) = CP ×

⎡ OM × dOM ⎤ UDM (g/kg DM) = (0.35 × ash) + OM − ⎢ ⎥⎦ ⎣ 100

RDPPDI DOM

The degraded protein balance (DPBPDI) was calculated as

where 0.35 is the constant utilized by CVB,29 which indicates that 35% of the ash is not digested, and dOM is the degradability of OM after 120 h of rumen incubation.

DPBPDI (g/kg DM) = (ARUPPDI + MCPRDP) − (ARUPPDI + MCPME) 8265

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Feed Milk Value. The FMVs of raw and heat-treated camelina seeds were calculated using the estimated MP supply as obtained with the NRC-2001, DVE/OEB, and PDI systems. The FMV was calculated as

Table 1. Dry and Moist Heat-Induced Changes in Protein Supply to Dairy Cattle from Camelina Seeds: Estimated by NRC-2001 Modela heat treatments (HT)b

FMV = MP × 0.67 × 0.033 Where, 0.67 is the efficiency of MP for milk production, and 0.033 is the protein content (g/g) of milk. Statistical Analysis. The PROC MIXED procedure of the Statistical Analysis System (SAS)27 was used to analyze the data on modeled protein supply, DPB, and FMV. The model used for analysis was

item (g/kg DM)

control

HT-1

HT-2

contrast SEMc P value

Absorbable Microbial Protein Synthesized in the Rumend MCPTDN 147.13b 151.40a 149.68ab 0.540 0.025 MCPRDP 152.01a 122.71b 131.46ab 2.304 0.010 AMCPNRC 94.16b 96.90a 95.80ab 0.344 0.025 Absorbable Endogenous True Protein in the Small Intestinee ECPNRC 11.09 10.98 11.59 0.042 0.052 AECPNRC 4.44 4.39 4.64 0.107 0.051 Truly Absorbable Rumen-Undegraded Protein in Small Intestinef RUPNRC 68.29c 111.93a 88.39b 1.514 0.002 ARUPNRC 33.41b 78.64a 46.52b 3.021 0.002 Total Metabolizable Proteing MPNRC 132.03b 179.92a 146.95b 2.893 0.002 Degraded Protein Balanceh DPBNRC 36.88a 3.31c 15.23b 2.133 0.001 FMVNRC 2.92c 3.98a 3.25b 0.146 0.001

Yij = μ + Ti + eij where Yij is an observation on the dependent variable ij; μ is the overall population mean; Ti is the fixed effect of heat treatment (i = control, moist heating, and dry heating), and eij is the random error associated with the observation ij. The plots were used as experimental replicates. Comparisons among the three protein evaluation models were performed using the PROC MIXED procedure of SAS,27 using the following model: Yij = μ + M i + eij where Yij is an observation on the dependent variable ij; μ is the overall population mean; Mi is the fixed effect of the protein evaluation model (i = NRC-2001, DVE/OEB, PDI); and eij is the random error associated with the observation ij. The different treatments (control, dry heating, and moist heating) were used as replications. For variables with significant (P < 0.05) differences, posthoc analyses were carried out using the Tukey Test to compute pairwise differences in the means. Stepwise, multiple-regression analyses were performed using the PROC REG procedure of SAS27 to determine which of the protein molecular structural features can be used to estimate the modeled protein nutrient supply to dairy cattle from raw and heat-treated camelina seeds. The independent variables tested in the model were the α-helix height, β-sheet height, amide-I area, amide-II area, ratio of the α-helix to β-sheet height, and ratio of the amide I to amide II area. Only variables contributing significantly (P < 0·05) to the estimation of the dependent variable were left in the final model. Collinearity among the independent variables was detected and avoided by the use of the variance inflation factor (VIF) option of SAS.27

control vs HT 0.014 0.005 0.014 0.242 0.241 0.001 0.003 0.002 0.001 0.002

a

Means within a row with different letters differ at the P < 0.05 level. HT-1, moist-heated in an autoclave at 120 °C for 1 h; HT-2, dryheated in an air-draft oven at 120 °C for 1 h. cSEM, standard error of mean. dMCPTDN, MCP synthesized in the rumen based on available energy; MCPRDP, MCP synthesized in the rumen based on available protein, calculated as 0.85 of rumen-degraded protein; AMCPNRC, truly absorbable rumen-synthesized MCP in the small intestine. eECP, rumen endogenous crude protein; AECP, truly absorbable endogenous protein in the small intestine. fRUPNRC, ruminally undegraded crude protein; ARUPNRC, truly absorbable rumen-undegraded feed protein in the small intestine. gMP, total metabolizable protein contributed by ARUPNRC, AMCPNRC, and AECP. hDPBNRC, degraded protein balance, which reflects the difference between the potential MCP synthesis based on ruminally degraded feed protein and that based on energy (TDN) available for microbial fermentation in the rumen. FMVNRC, feed milk value. The efficiency of use of the metabolizable protein for lactation is assumed to be 0.67,19 and the protein content of milk is assumed to be 33 g/kg milk. b

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RESULTS Estimating Protein Supply to Dairy Cattle Using the NRC-2001 Model. Heat processing increased the contents of MCPTDN, AMCPNRC, ARUPNRC, and total MP, with the increase being significant (P < 0.05) for moist heating (Table 1). The FMV and RUPNRC contents increased (P < 0.05) with both dry and moist heating, and the highest (P < 0.05) values were estimated for moist heating. In contrast, the MCPRDP and DPBNRC contents decreased (P = 0.01) with heat processing, and the lowest value was computed for moist heating. Protein Supply to Dairy Cattle Using the DVE/OEB System. Heat processing decreased the contents of MCPFOM and DPBDVE, and the decrease was significant (P < 0.05) for moist heating (Table 2). Both the dry and moist heating significantly (P < 0.05) decreased the contents of MCPRDP and AMCPDVE, and the lowest values were estimated for moist heating. In contrast, the contents of RUPDVE, ARUPDVE, MPDVE, and FMVDVE increased (P < 0.05) with both dry and moist heating; however, the highest (P < 0.05) values were obtained with moist heating. Protein Supply to Dairy Cattle Using the PDI System. Both dry and moist heating decreased (P < 0.01) the contents of MCPME, MCPRDP, AMCPPDI and DPBPDI, and the lowest values (P < 0.05) were obtained with moist heating (Table 3).

The contents of RUPPDI and FMV increased (P < 0.05) for both dry and moist heating; however, the highest (P < 0.05) values were obtained with moist heating. The contents of PDIE (ARUPPDI + MCPME) and PDIN (ARUPPDI + MCPRDP) increased with heat processing with significant (P < 0.05) increase being observed with moist heating. Comparison of Estimated Protein Supply to Dairy Cattle by the NRC-2001 Model, DVE/OEB System, and PDI System. Comparison of the estimated contents of protein nutrient supply and FMV of camelina seeds by the NRC-2001 model, DVE/OEB system, and PDI system are presented in Table 4. The estimated content (g/kg DM) of rumen-synthesized MCP on the basis of available energy was significantly higher (P < 0.05) in the NRC-2001 model (149.40) than that estimated by the DVE/OEB (59.51) and PDI (37.32) systems. Subsequently, the estimated content of truly absorbable rumensynthesized MCP was substantially higher (P < 0.05) in the NRC-2001 model than those obtained with the DVE/OEB and PDI systems. In contrast, the rumen-synthesized MCP based on RDP was higher (P < 0.05) in the DVE/OEB and PDI systems than that in the NRC-2001 model. Moreover, the estimated content of truly absorbed rumen-synthesized MCP was higher (P < 0.05) in the DVE/OEB system than that in the PDI system. 8266

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Table 2. Dry and Moist Heat-Induced Changes in Metabolizable Protein Supply to Dairy Cattle from Camelina Seeds: Estimated by DVE/OEB Systema heat treatments (HT)b item (g/kg DM)

control

HT-1

Absorbable Microbial Protein Synthesis in the Rumend MCPFOM 66.65a 54.04b MCPRDP 179.94a 143.792c AMCPDVE 42.49a 34.54b Absorbable Endogenous True Protein in the Small Intestinee ECPDVE 11.43 12.63 Truly Absorbable Rumen-Undegraded Protein in Small Intestinef RUPDVE 65.19c 111.93a ARUPDVE 37.11c 87.29a Total Metabolizable Proteing MPDVE 68.17c 109.48a Degraded Protein Balanceh DPBDVE 109.10a 89.75b FMVDVE 1.40c 2.53a

contrast

HT-2

SEMc

P value

control vs HT

57.83ab 154.36b 36.87b

2.120 2.761 1.351

0.035 0.002 0.041

0.046 0.003 0.025

13.09

1.14

0.623

0.384

88.68b 51.64b

1.52 1.44

0.001 0.011

0.000 0.014

75.42b

4.663

0.008

0.015

96.52ab 1.53b

6.388 0.103

0.035 0.008

0.028 0.015

Means within a row with different letters differ at the P < 0.05 level. bHT-1, moist-heated in an autoclave at 120 °C for 1 h; HT-2, dry-heated in an air-draft oven at 120 °C for 1 h. cSEM, standard error of mean. dMCPFOM, MCP synthesized in the rumen based on available energy; MCPDVE, MCP synthesized in the rumen based on rumen-degraded crude protein; AMCPDVE, truly absorbable rumen-synthesized MCP in the small intestine. e ECPDVE, endogenous protein losses in the digestive tract. fRUPDVE, ruminally undegraded feed protein calculated according to the DVE/OEB model; ARUPDVE, truly absorbable rumen-undegraded feed protein in the small intestine. gDVE, truly absorbable protein in the small intestine contributed by RUP DVE, MCPFOM, and a correction for ENDP. hDPBDVE, reflects the difference between the potential MCP synthesis based on rumen-degraded feed crude protein and that based on energy (FOM) available for microbial fermentation in the rumen. FMVNRC, feed milk value. The efficiency of use of the metabolizable protein for lactation is assumed to be 0.67,19 and the protein content of milk is assumed to be 33 g/kg milk. a

Table 3. Dry and Moist Heat Induced Changes in Protein Supply to Dairy Cattle from Camelina Seeds: Estimated by PDI Systema heat treatments (HT)b item (g/kg DM)

Control

HT-1

Absorbable Microbial Protein Synthesis in the Rumend MCPME 40.49a 33.43c MCPRDP 117.26a 92.04c AMCPPDI 35.41a 27.44c Truly Absorbable Rumen-Undegraded Protein in Small Intestinee RUPPDI 65.89c 111.88a ARUPPDI 37.11b 87.29a Degraded Protein Balancef PDIN (ARUPPDI + MCPRDP) 138.46b 170.11a PDIE (ARUPPDI + MCPME) 77.45b 121.63a DPBPDI (PDIN − PDIE) 61.55a 48.48c FMVPDI 2.26c 3.03a

contrast

HT-2

SEMc

P value

control vs HT

37.61b 100.55b 32.14b

0.519 1.432 0.480

0.005 0.002 0.003

0.003 0.001 0.002

88.21b 51.64ab

1.599 3.352

0.001 0.002

0.000 0.003

140.55ab 88.49ab 52.06b 2.66b

2.451 7.365 1.694 0.060

0.004 0.098 0.006 0.001

0.009 0.232 0.005 0.001

Means within a row with different letters differ at the P < 0.05 level. bHT-1, moist-heated in an autoclave at 120 °C for 1 h; HT-2, dry-heated in an air-draft oven at 120 °C for 1 h. cSEM, standard error of mean. dMCPME, amount of MCP that could be synthesized from the available energy in the rumen, when degraded nitrogen (N) is not limiting; MCPRDP, amount of MCP that could be synthesized in the rumen from the degraded dietary N when energy is not limiting; AMCPPDI, truly absorbable rumen-synthesized MCP in the small intestine. eRUPPDI, ruminally undegraded feed protein; ARUPPDI, truly absorbable ruminally undegraded feed protein. fPDIN, digestible proteins in the small intestine where N is the limiting factor for rumen microbial activity; PDIE, digestible proteins in the small intestine where energy is the limiting factor for rumen microbial activity; DPBPDI, the difference between MCP synthesis based on rumen-degraded feed crude protein and that based on energy from anaerobic fermentation in the rumen. The efficiency of use of the metabolizable protein for lactation is assumed to be 0.67,19 and the protein content of milk is assumed to be 33 g/kg milk. a

the three protein evaluation systems, and the highest (P < 0.05) value was recorded for the NRC-2001 model, followed by the PDI and DVE/OEB systems, respectively. Using Protein Molecular Structural Spectra to Predict the Estimated Protein Supply to Dairy Cattle. The multipleregression equations in Table 5 show that the protein secondary structure (α-helix height) can be used to predict ECPNRC (R2 = 0.73), AECPNRC (R2 = 0.75), ARUPNRC (R2 = 0.84),

The contents of ARUP did not differ significantly among the three evaluation systems. The MP content obtained with the NRC-2001 model was higher (P < 0.05; 152.97 vs 84.33) than that of the DVE/OEB system. The DPB was different (P < 0.01) among the three evaluation systems, and the highest (P < 0.05) value was obtained with the DVE/OEB system. The PDI system had a higher (P < 0.05) DPB value than did the NRC-2001 model. The FMV of camelina seeds differed among 8267

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Table 4. Comparison of the NRC-2001 Model, DVE/OEB System, and PDI System in the Prediction of Metabolizable Protein Supply to Dairy Cattle from Camelina Seeds meana item (g/kg DM)

NRC-2001

PDI

SEMb

P value

37.32c

0.691

89 g/kg DM; 60%) and MCPME (>112 g/kg DM; 75%). With the recent advances in fat metabolism in the rumen and on the basis of previous recommendations of other studies,38 the concept of energy inputs adopted by the three models needs to be further standardized for different feed types. The RUP does not provide energy for MCP synthesis, which is taken into account by the DVE/OEB and PDI systems. However, the TDN used for MCP synthesis in the NRC-2001 model needs to be corrected for this RUP content. Fermented protein provides much less energy to rumen microbes than do

the in situ method, which could be related to the over estimation of RUP by the in situ method.36 The NRC-2001 model showed that heat processing caused a small increase ( 0.70).

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REFERENCES

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ASSOCIATED CONTENT

* Supporting Information S

Dry and moist heat-induced changes in in situ ruminal CP degradation kinetics of camelina seeds. Dry and moist heatinduced changes in the protein molecular spectral characteristics of of camelina seeds as revealed by FT/IR-ATR molecular spectroscopy. This material is available free of charge via the Internet at http://pubs.acs.org.

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Article

AUTHOR INFORMATION

Corresponding Author

*Phone: +1 306 966 4132. Fax: + 1 306 966 4151. E-mail: [email protected]. Present Address ⊥

N.A.K.: Department of Animal Nutrition, the University of Agriculture Peshawar, Pakistan. Funding

The research projects of the (Professor Dr. Peiqiang Yu) chair group were supported by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC), SaskCanola, Saskatchewan Agricultural Development Fund (ADF), Ministry of Agriculture Strategic Research Chair Program, and ThousandTalent-People Program in Tianjin. Quanhui Peng (Ph.D. student scholarship) was financially supported by the China Scholarship Council. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors wish to thank Zhiyuan Niu, research assistant in the Department of Animal and Poultry Science, University of Saskatchewan, for providing assistance with the chemical analyses. We thank Colleen Christensen at Feed Innovation Institute for the collection of samples. 8272

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