18th Annual Colorado Dairy Nutrition Conference, January 23, 2007

Union Colony Civic Center, Hensel Phelps Theatre, 701 10th Ave., Greeley, CO 80631

Dianah Ngonyamo-Majee, PhD
Animal Scientist
Chemistry and Animal Agriculture Technology

Monsanto Company, 3302 SE Convenience Blvd, Ankeny, IA 50021

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The negative correlation between corn vitreousness vs. starch availability and milk production potential has been widely reported in US and Europe. This presentation covers some of these recent findings, and how this will influence the amount of energy available for milk production as it is applied in the MILK2006 model and adopted in our Monsanto corn hybrid selection programs. Monsanto scientists drive our Research and Development pipeline starting from discovering new corn traits, to advanced quality trait analytics and converting the seed germplasm into highly nutritive animal feed products. In our work we understand that our trait discovery and advancement programs should satisfy the needs of both the corn growers and dairy producers who may have different perspectives of the corn crop. For the corn growers yield is the most important trait when evaluating the productivity of our seed germplasm, whereas, the dairy producer looks for not just high yield, but most importantly nutritive quality (i.e. nutrient content and nutrient availability) that determine milk productivity per cow and/or per acre. Hence, the processes we follow at Monsanto to determine the nutritional value of our corn germplasm will be highlighted, with supporting data showing the variability of some of our corn germplasm on vitreousness, hardness and starch availability, and how we use this data in corn hybrid selection programs to support sales of our Monsanto (Branded and Non-branded) corn products.

Key words: corn starch, vitreousness, starch digestibility

Abbreviations Key: A-fraction = zero hour disappearance or bag wash loss; BL = black layer harvest stage; C/F ratio = height ratio of course to fine particles; CH = total column height; GEM = Germplasm Enhancement of Maize project, Iowa; ML = half milk line harvest stage; MT = 21d post BL harvest stage NIRS = near infrared reflectance spectroscopy; pRDMD = post-ruminal dry matter degradability; RDMD = ruminal dry matter degradability; T = time (s) to collect ground sample to a set receptacle height; TDMD = total dry matter degradability; RSTARCHD = ruminal starch degradability; and TSTARCHD = total tract starch degradability.

Introduction

Corn, in the form of silage, dry or high moisture grain is used as the main source of energy in dairy diets around the world. This energy largely comes from the starch component of the kernel, contributing about half the energy value of corn silage (Schwab et al., 2003). In dry and high-moisture corn grain, starch contributes about three-fourths of the kernel dry weight (Schwab et al., 2003; Watson, 2003) and thus most of the energy supplied. Kernel starch is stored in the endosperm as starch granules. The starch granules located in the corneous or vitreous part of the endosperm are surrounded by protein storage bodies and imbedded in a dense protein matrix, whereas those located in the floury part of the endosperm have little cellular structure (Figures 1 and 2). Hence, the floury endosperm has the highest density of starch granules (Watson, 2003) as shown by the Scanning Electron Micrograph (SEM) in Figure 2. Recent findings from around the world have reported differences in corn hybrids on the proportion of vitreous and floury endosperm, and hence endosperm texture, thus influencing starch availability (Ngonyamo-Majee, 2004, 2005; Michalet-Doreau and Doreau, 1999). As a result there has been a worldwide realization of the importance of looking more into kernel endosperm starch properties influencing starch availability to ensure there is more accurate prediction of feed energy values from corn based dairy diets.

Unfortunately, the prediction of total digestible nutrients (TDN) using the 2001 Requirements for Dairy Animals (NRC, 2001) [i.e TDN (maintenance) = tdCP + (tdFA*2.25) + tdNDF + tdNFC - 7; where; tdCP = total digestible crude protein, tdFA= total digestible fatty acids, tdNDF = total digestible neutral detergent fiber, and tdNFC= total digestible non-NDF carbohydrates] fails to directly account for these differences in starch availability in corn based diets. This is because the value for tdNFC is predicted from the equation from Weiss et al. (1996) [i.e tdNFC% (at maintenance) = 0.98 * (100 - NDF+NDFCP- CP - ash - FA +1)]. The 0.98 factor is based on the assumption that NFC is uniformly digested. The NRC (2001) acknowledged that this assumption is not correct by implementing processing adjustments factors (PAF) in their summative equations, but the PAF were arbitrary assignments.

Schwab et al. (2003) introduced the MILK2000 equation for corn silage that accounts for differences in the proportion of starch in the NFC fraction and attempts to account for differences in starch availability as affected by whole-plant corn silage DM content and kernel processing. The MILK2000 corn silage equation is shown below;

TDN (maintenance) = tdCP + (tdFA*2.25) + tdNDF + tdSTARCH + tdNSTNFC - 7;

Where tdNSTNFC = total digestible non-starch total NFC

In this equation separation of tdSTARCH attempts to account for effects of whole-plant DM content (Bal et al., 1997) and kernel processing (Bal et al., 2000a, b, c) on starch availability rather than the NRC (2001) PAF. However, the MILK2000 (Schwab et al., 2003) and NRC (2001) equations ignore that starch digestibility may be influenced by corn hybrid as related primarily to kernel vitreousness and hardness properties as discussed earlier. Hence MILK2006 model was recently introduced by Shaver et al. (2006), as an improvement on the MILK2000 model with more flexibility on input parameters in addition to trying to account for the hybrid differences in starch availability. Hence, the primary objectives of this paper is to review these corn endosperm characteristics that influence starch digestibility in dairy cows and how we are using this knowledge at Monsanto to improve on our corn hybrid selection programs for the branded and non-branded corn markets.

Review of Current Research Findings

Several studies conducted in different parts of the world confirm the negative relationship between kernel vitreousness, hardness and density vs. starch digestibility.

US and South American Studies

An experiment was conducted at the University of Wisconsin, Madison by Correa et al. (2002), using 14 US and five Brazilian corn hybrids with the objective of determining the relationship between corn kernel vitreousness vs. ruminal in-situ starch degradation. The corn plants were grown in their respective countries and harvested at different growth stages i.e. half milk-line (ML), black layer (BL), and 21d post BL (MT) for US hybrids and the Brazilian flint hybrids were harvested at only the MT stage. Results from this study showed strong negative correlations between both kernel vitreousness (-0.93; P<0.001) (Figure 3) and density (-0.87; P<0.001) with starch degradability. Vitreousness and density were found to have a strong positive correlation of 0.87 (P<0.001). Another important finding from this study was that vitreousness increased with advancing maturity.

A series of follow-up studies to Correa et al. (2002) were conducted at University of Wisconsin West Madison and Marshfield Research Stations to further evaluate effects of vitreousness, density and kernel hardness properties on starch availability in the whole digestion tract (rumen and post-ruminal) (Majee et al., 2003; Ngonyamo-Majee et al., 2004a, b, 2005a, b). In addition test runs were conducted on how this knowledge may be used in a breeding program from screening of inbred lines, hybrid development and final selection of hybrids with high starch availability. In all the studies, samples were processed by grinding using the Wiley 6mm screen size which was recommended by Sapienza (2002) to target a particle size distribution that ensures increased sensitivity of the in-situ rumen assay to detect differences in degradation as influenced by maturity and germplasm differences.

The initial experiments by Majee et al. (2003) and Ngonyamo-Majee et al. (2004b) included 33 corn inbred lines originating from the Germplasm Enhancement of Maize (GEM) project at Iowa State University (17); flint-lines from North Carolina State University and the International Maize and Wheat Improvement Center (6); near-isogenic variants of Ohio-43 (Oh43) carrying opaque-2 (o2), floury-2 (fl2), sugary-2 (su2), amylose-extender-1 (ae1), soft-endosperm-1 (h1) and waxy-1-sugary-2 (wx1su2) alleles affecting endosperm composition (6); Wisconsin Quality Synthetic (WQS C2) and three check inbreds; B73 (Iowa Stiff Stalk Synthetic); Oh43 (Ohio State University), and W64A (University of Wisconsin). The inbreds were harvested at two growth stages (ML and BL stages) and kernel physical traits evaluated included vitreousness, density and grinding hardness measures determined using a Stenvert micro hammer-cutter mill that measures time to collect ground sample to a set receptacle height (T); total column height (CH); and height ratio of course to fine (C/F) particles. Results from this study showed that correlations between vitreousness and hardness factors were higher for BL than ML; C/F ratio (r = 0.898 vs. 0.645); CH (r = -0.844 vs. -0.501); and T (r = 0.710 vs. 0.532), thus showing same effects of increasing vitreousness with advancing maturity as found by Correa et al. (2002). The 33 corn germplasm sources evaluated in this study exhibited tremendous diversity in endosperm properties, suggesting that potential exists for improving corn starch digestion by ruminants through germplasm selection.

They followed up this study with a hybrid evaluation experiment involving 13 new hybrids from crosses of selected inbreds from the above experiment covering low (0-30 %), medium (30-70 %) and high (70-100 %) vitreousness classifications and test lines (Mo17Ht and B73). Six check hybrids, W64AxOh43 carrying opaque-2 (o2), floury-2 (fl2), sugary-2 (su2) and amylose-extender (ae1) mutant genes, straight W64AxOh43, and B73xMo17Ht were included. The hybrids were harvested at three maturity stages (ML; BL and MT). Kernel endosperm properties evaluated included vitreousness, density, Stenvert hardness measurements and compositional data on crude ptotein (CP), starch, and oil content. In-situ ruminal (RDMD) and total tract DM degradabilities (TDMD i.e. RDMD plus in vitro enzymatic method on ruminal in situ residue) were also determined. Dry matter degradability was used instead of starch degradability because strong (P<0.0001) correlations were found in earlier studies between RDMD and ruminal starch degradability (RSTARCHD) (r = 0.98) Correa et al (2002) and between TDMD and total tract starch degradability (TSTARCHD) (0.90) (Ngonyamo-Majee et al., 2004a). Results from this experiment showed all kernel hardness parameters and CP content were negatively correlated (P<0.001) with degradability measurements. This agrees with findings from several authors who found that starch granule accessibility was affected by the presence of an extensive protein matrix in the endosperm (McAllister et al., 1993; Philippeau et al., 1998; Watson, 2003) which may have been reflected by the increased kernel CP content in the more vitreous corn germplasm. Data from a selection of these hybrids on endosperm properties and resultant degradabilities is presented in Tables 1 and 2, respectively. Vitreous grain type was found to shift the primary site of starch degradability from the rumen to the small intestines. However, despite the compensatory digestion in the post-rumen, germplasm differences still existed on TDMD and TSTARCHD. The results also showed potential for using the NIRS calibrations to select corn germplasm with endosperm characteristics related to starch availability. Hence, NIRS calibrations for kernel vitreousness and hardness factors were developed and tested for their potential use in large scale corn breeding programs. Although the NIRS calibrations developed were found capable of ranking inbreds and developing hybrids of high starch degradability, it was found that a more direct NIRS calibration based for starch degradability would be a better screening tool. This led to the 3^rd set of experiments which targeted development of NIRS calibrations using digestibility data from corn germplasm of diverse background.

These NIRS calibrations were developed for predicting degradability parameters from a total of 547 samples originating from US, South America and Zimbabwe (Africa) (Ngonyamo-Majee et al., 2005a). The analytical data used was collected during the period 2003 - 2005. Data on the developed NIRS calibration statistics showed high R² values (P<0.001) and low standard error of calibration (SEC) and standard error of cross validation (SECV). These are key statistical factors used as indicators of a good NIRS calibration. There was also strong positive correlations (r = 0.90; 0.92; and 0.95) found between laboratory generated data and NIR predicted values for 0-hr disappearance, RDMD and TDMD, respectively. These results demonstrated that there is good potential for using NIRS calibrations for screening corn germplasm recommended for silage, high moisture corn and grain using digestibility data to promote hybrids of high starch availability.

All these Wisconsin studies confirmed the strong influence of vitreousness and other kernel physical traits on starch and DM degradability, however, there was still need to confirm the in-situ, in-vitro, and NIRS results with animal feeding trials. The next series of experiments conducted by Taylor and Allen (2005a, b, c) at Michigan State University covered this and other questions relating to possible interactions of corn grain endosperm type and the brown midrib 3 (bmr3) mutation in corn silage on feeding behavior, rumen fermentation, N partitioning, site of starch digestion and milk yield in lactating dairy cows. They used two corn hybrids (6208FQ and 657) (Cargill Hybrid Seeds, Minneapolis, MN) grown for the silage treatment. These are isogenic hybrids except that Cargill 657 has the bmr3 mutation (Taylor and Allen, 2005a, b, c). For the endosperm type treatment, they used two corn hybrids of low vitreousness (SL53; Crow's Hybrid Corn Company, Kentland, IN) and high vitreousness (Z75W; Wilson Genetics, Harlan, IA). These hybrids had vitreousness ratings of 3.0 % for the floury or low vitreousness hybrid and 67.2 % for the high vitreousness treatment. The animal feeding trial was conducted using 8 multiparous Holstein cows at the Michigan State University Dairy Cattle Teaching and Research Center using a 4 x 4 Latin square design balanced for crossover effects.

Results from these studies showed no interaction of corn endosperm type and bmr3 mutation corn silage on all production parameters. Both RSTARCHD and TSTARCHD were greater for floury vs. vitreous endosperm based diets. The compensatory digestion in the intestines from the vitreous corn endosperm type reduced hybrid differences but not significantly enough to eliminate them from the TSTARCHD hybrid comparisons, as was also reported in Wisconsin studies (Ngonyamo-Majee et al., 2004a, b, 2005a, b). There was also no clear benefit found on milk production from shifting starch digestion from the rumen to the intestines. There have been conflicting arguments about the benefits of ruminal vs. post-ruminal starch digestion from different sources (Krause et al., 2002; Hall, 2002; Knowlton et al. 1998; Huntington, 1997; Freetly and Klindt, 1996; Eisemann et al., 1994; McAllister et al. 1990; Owen et al., 1986). However, I agree with the recommendation made by Hall (2002) and Huntington (1997) who stressed the importance of rumen fermentation of starch as a means of maximizing both microbial protein synthesis and energy supply.

European Studies

Several studies were conducted in France, mostly at the experimental site in Limagne with the main objective of evaluating the influence of vitreousness on starch availability from corn germplasm of flint and dent genetic background (Philippeau and Michalet-Doreau, 1997 and 1998). These studies also looked at the effect of vitreousness with advancing maturity (Philippeau and Michalet-Doreau, 1997) and an evaluation on whether the ensiling process may reduce the effects of vitreousness (Philippeau and Michalet-Doreau, 1998). Results from these studies agree with US findings on the negative correlation of vitreousness with starch availability (Figure 4). They also found that the difference between flint vs. dent germplasm was more marked on RSTARCHD than TSTARCHD (Philippeau and Michalet-Doreau, 1997 and 1998). Ensiling had the effect of increasing ruminal DM and starch degradabilities by +5.6 and +5.9 percentage units, respectively (Philippeau and Michalet-Doreau, 1998). This was found to have been caused by the partial solubilization of the endosperm proteins during the silage fermentation process, thus exposing the starch granules to rumen microbial attack (Philippeau and Michalet-Doreau, 1998). Ensiling induced the same increase in RSTARCHD regardless of corn genotype, hence the difference between flint vs. dent on starch availability remained the same before and after ensiling (Philippeau and Michalet-Doreau, 1998).

Another European study was conducted by Remond et al. (2004), evaluating effects of vitreousness from germplasm of semi-flint vs. dent as expressed by differences in particle size. What is unique and most interesting about this study is that they processed the corn samples differently to produce different mean particle sizes (0.7; 1.8 and 3.7 mm mean particle size) with the objective of assessing how corn processing may be used to manipulate site of starch digestion.

The results show that site of digestion was shifted from the rumen to the intestines through coarse processing (Figure 5 and Table 4). This shift was however found to cause a quantitatively small effect on glucose supply to the animals and hence milk yield remained higher for the finely ground samples which achieved high RSTARCHD values (Table 5). This agrees with our US findings that maintaining high ruminal starch availability is key to achieving greater nutrient utilization and milk productivity from our corn hybrids. However, this study showed that flint corn germplasm of high vitreousness may be manipulated to achieve high ruminal starch availability through more fine processing. It is however important to consider the costs involved in fine processing vs. the option of ensuring our corn breeding and hybrid selection programs select for low vitreousness and high starch availability.

Application in Monsanto Company

Pilot study: Evaluation of vitreousness and ruminal starch availability of selected Monsanto hybrids harvested in 2005 from different US sites. (Ngonyamo-Majee, J. Hinen and P. Feng. 2006. Monsanto TCM, St Louis, MO).

This involved a set of 30 corn hybrids (with 10 replications each) selected to cover the current Monsanto genetic base. The corn grain samples were all harvested at the BL maturity stage. The samples were ground through a Wiley mill (6 mm screen, Arthur H. Thomas, Philadelphia, PA) and used for measurement of in-vitro ruminal starch degradability RSTARCHD) using Daisy II incubators after 12 h of incubation. Rumen fluid was collected from four steers at Sapienza Analytica research farm (Slater, IA) and composited for use in this study. At end of incubation, the bags were put in mesh bags and placed in a washing machine filled with tepid water and allowed to agitate on a gentle cycle with the lid open to prevent spinning (Cherney et al., 1990). After rinsing, the samples were dried at 62^o C for 48 h and DM and starch contents determined to provide estimates of ruminal dry matter degradability (RDMD) and starch degradability (RSTARCHD).

Grain density was determined by water displacement procedure (Correa et al, 2002). Kernel vitreousness as determined by visual rating method. This involved randomly selecting 20 kernels which are placed on a light box with the germ facing upwards. The proportion of the endosperm that is translucent (i.e. allowing light to pass through) is considered as the horny portion of the endosperm. This is rated vs. the opaque portions which do not allow light to pass through (floury portion of the endosperm) and given a score as a percentage of the total endosperm. Compositional properties, such as crude protein, oil and extractable starch were determined by near infrared transmittance (NIT). Corn starch was determined by both wet chemistry procedure (CRA method) and NIT.

Results and Discussion

Data from this study showed wide genetic variability from our germplasm (Table 6). Kernel physical characteristics showed density ranging from 1.156 - 1.406 with mean 1.244 g/cm³; % vitreousness had a range of 62 - 90 with mean 79% (Figure 6); 1000 kernel weight ranged from 206 - 396 with mean 322g; and RSTARCHD showed a range from 46.4 - 69.6 % with mean 57.8% (Figure 7). Relationship between starch availability and kernel physico-chemical properties showed a strong negative correlation for kernel protein with RSTARCHD of - 0.79 (Figure 8). The strong negative correlation with kernel protein could be related to the negative effects of the endosperm proteins, particularly the matrix proteins hindering easy access of starch granules to enzymatic degradation. Two distinct clusters (Figure 9) appeared on density with low (<1.250 g/cm³) and high density (>1.350 g/cm³). This is a reflection of our past breeding and hybrid selection efforts that targeted two distinct market demands for hard vs. relatively softer endosperm.

Relationship with Extractable Starch

Extractable starch refers to the amount of starch that can be recovered through the wet milling process, and hence is lower than starch content. There was a positive correlation between RSTARCHD and Extractable starch (r = 0.76: P<0.001) (Figure 10). The high extractable starch (HES) hybrids tend to mill more easily and give wet millers greater starch recovery, thus, explaining the good correlation with rumen degradability which is also highly influenced by grind particle size (Remond et al., 2004). A combination of wet harvest moistures and kernel-drying temperatures over 140°F are reported to be very detrimental to extractable starch (Paulsen et al., 1999) and the same was reported for RSTARCHD from Wisconsin studies (Ngonyamo-Majee et al., 2004a). These findings show how RSTARCHD and Extractable starch are strongly influenced by the similar intrinsic and extrinsic factors which could make it easy for us to select for both in our corn hybrid selection programs.

Conclusions

At Monsanto we have therefore realized that there is need to investigate endosperm properties that influence starch digestibility and use this information to rank our corn hybrids that are targeted for the dairy industry. This allows us to meet the demands from;

• Our corn growers for corn hybrids of high yield per acre and high nutrient yield per acre.

• Our dairy producers for corn silage and grain hybrids that produce high milk yield per acre grown of the corn crop and per tonnage of the corn fed (as predicted through the MILK2006 model).

• Our communities for improved nutrition by providing high quality milk that can be targeted for specific products (raw milk, cheese, yoghurt and other milk products)

Because we are a global company our Monsanto products target all parts of the world. Hence we utilize the knowledge from these research reviews from US, South America, Europe and Africa and combine that with our own research findings to make decisions on commercial corn germplasm recommendations. It is however important to note that how we apply these research findings for our US industry may differ from European, South American and African industry needs for corn hybrid advancement and commercial seed sales due to differences in total diet formulations amongst other reasons.

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Figure 1: Corn Vitreousness illustration

Diagram Source: Hoseney, 1986. Principles of Cereal Science and Technology. Am Assoc of Cereal Chemists, St. Paul, MN

Figure 2: Scanning electron micrograph of fractured endosperm showing how horny endosperm breaks along cell walls because of the strength of the protein matrix, whereas the floury endosperm fractures across cells, exposing round starch granules not completely surrounded by a protein matrix. (Adapted from Watson, 2003)

NB: the floury part of the endosperm is at the bottom right hand corner where the starch granules are exposed

Figure 3: Effect of vitreousness on starch availability adapted from Correa et al, 2002.

US corn hybrids

Brazilian corn hybrids

Figure 4: Kernel vitreousness vs. ruminal in-situ starch availability for dent vs. flint genotype with advancing maturity (Philippeau & Michalet-Doreau, AFST, 1997)

Figure 5: Effect of corn particle size on site and extent of starch digestion in lactating dairy cows (Remond et al., 2004).

a, b, c Means differ (P < 0.05)

Figure 6: The range of vitreousness from a selection of 30 Monsanto corn hybrids harvested in 2005 from different US sites. ( Ngonyamo-Majee D., J. Hinen and P. Feng, 2006.

Figure 7: Ruminal starch availability from a selection of 30 Monsanto corn hybrids harvested in 2005 from different US sites. ( Ngonyamo-Majee D., J. Hinen and P. Feng, 2006.

Figure 8: Correlation between RSTARCHD vs. protein

Figure 9: Correlation between RSTARCHD vs. density/p>

Figure 10: Correlation between RSTARCHD vs. Ext Starch

Table 1: Kernel endosperm properties for a selection of hybrids selected from Ngonyamo-Majee et al. (2004b).

a,b,c,…Different superscripts in each column within each comparison differ (P<0.05).

MPS = the geometric mean particle size (mm).

Table 2: Hybrid differences on ruminal dry matter degradability (RDMD), total tract dry matter degradability (TDMD) and total tract starch degradability (TSTARCHD) from a selection of hybrids from Ngonyamo-Majee et al. (2004b).

a,b,c,…Different superscripts in each column within each comparison differ (P<0.05).

Table 3: Interactions of endosperm type and NDF digestibility from bmr mutation (Taylor and Allen, 2005a, b and c)

Floury = 3.0% Vitreousnesss and 1.377mm Mean Particle Size

Vitreous = 67.2% Vitreousnesss and 1.594 mm Mean Particle Size

Table 4: Effect of corn particle size on site and extent of starch digestion in lactating dairy cows (adapted from Remond et al., 2004).

Table 5: Effect of corn particle size on DM intake, milk yield and composition in lactating dairy cows (adapted from Remond et al., 2004).

Table 6: Vitreousness Classification from 30 Selected Monsanto Corn Hybrids

(Ngonyamo-Majee, J. Hinen and P. Feng, 2006. Monsanto TCM, St Louis, MO.)