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Variation in nutritional value of sorghum hybrids with contrasting seed weight characteristics and comparisons with maize in broiler chicks.

SORGHUM GRAIN primarily is used as an animal feed in the USA and is the second most important feed grain following maize. Physical seed characteristics, variation in composition due to production in diverse environments, and processing methods used before feeding are a few of the major aspects known to affect variation in feed quality of sorghum grain. In feed lot cattle, the feeding value of sorghum grain is considered to be 85 to 100% that of maize, depending on the type and degree of physical processing implemented before feeding. For swine and poultry, sorghum grain has been suggested to have a relative feeding value of 90 to 95% that of maize (Cousins, 1979; Hulan and Proudfoot, 1982). More recent studies have shown that grain sorghum can be used as a complete replacement for maize in broiler diets without sacrificing animal performance (Sharma et al., 1979; Gualtieri and Rapaccini, 1990; Dean, 2000). Others have argued that addition of 1 to 2.5 % fat is needed in sorghum-based broiler diets to raise the ME content for the replacement of yellow maize (Douglas et al., 1990a).

The feed value of sorghum can be improved through breeding programs that genetically manipulate the physical or chemical characteristics that govern digestibility (Samford et al., 1971, p. 7-9). Gene sources that contribute to higher seed weight via increased grain-fill rate and duration of sorghum have been publicly released and currently are being used to produce hybrids with improved performance characteristics (Tuinstra et al., 2001b). Hicks et al. (2002) evaluated the feed quality components of sorghum lines and hybrids varying in seed weight. The large-seeded hybrids with high seed weight generally had increased crude protein (CP) and fat content and lower starch values than conventional hybrids. Additional research is needed to determine how these changes in chemical composition of the kernel (i.e., CP, fat, and starch) impact the feeding value of sorghum grain. The objectives of the experiment reported here were to evaluate ME content of grain sorghum hybrids varying in seed weight and composition and to compare these values with ME of hybrid maize produced in the same environments.


Hybrid Grain Production

Two female and four male parent lines were intercrossed to produce eight sorghum hybrids. AWheatland and ASA3042 were used as seed parents and the males included two conventional pollinator lines (RTx2737 and RTx435) and two lines with high seed weight (Eastin-1 and KS115). AWheatland, ASA3042, RTx2737, and RTx435 are conventional seed and pollinator parents used by the private sorghum seed industry in hybrid seed production in the USA. Eastin-1 is a large-seeded breeding line developed at the University of Nebraska and was provided courtesy of Dr. Jerry Eastin. KS115 is a large-seeded germplasm source developed at Kansas State University (Tuinstra et al., 2001b).

Grain samples representing the eight hybrid sorghum entries and hybrid maize were produced under dryland conditions at Kansas State University experiment stations in Ottawa and Manhattan during 2000 and in Belleville and Manhattan in 2001. Each sorghum hybrid was planted in a single-row plot approximately 50 m in length with 0.76 m between rows to allow for the production of a minimum of 14 kg of bulked hybrid grain. Seed were treated with N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide (captan) at the label rate. Cultural practices for field experiments included application of 110 kg N [ha.sup.-1] before planting and 0.24 L quinclorac [ha.sup.-1] plus 0.68 kg atrazine [ha.sup.-1] applied postemergence for weed control. The hybrid maize sample was collected from adjacent commercial grain production fields at each experiment site. Plots at each location were harvested and bulked by pedigree at physiological maturity.

Grain Characteristics

The grain sorghum hybrids in this study were characterized as normal for endosperm type and hetero-yellow for endosperm color. The pericarp color for each sorghum hybrid was red and these hybrids did not have a pigmented testa (i.e., nontannin type). The commercial maize samples were no. 2 yellow dent with normal endosperm type. Seed were sampled from bulked grain harvested at each of the four locations.

Seed weight was used as a measure for comparing seed size by averaging three replicates of 100 seed. The average hardness index (AHI) of maize and sorghum kernels was assessed using a Venables Tangential Abrasive Dehulling Device (TADD) model 4E-220 (Oomah et al., 1981; Reichert et al., 1986). A sample weight of 10 g was placed in the decorticator with the exterior of the seed being removed and weighed at 1, 2, and 4 min for sorghum grain samples and 1, 2, 4, and 10 min for maize samples (Almeida-Dominguez et al., 1997). The percentage of the kernel removed by this procedure at the respective time intervals was plotted and AHI was calculated by taking the inverse of the slope and multiplying it by 60. These values were defined as the time (s) to remove 1% of the kernel weight as ground fines. The larger the AHI value, the harder the sample.

Analyses of crude fat, crude fiber, moisture, N, ash, and gross energy were determined by AOAC (2000) methods. Crude protein was determined using the N combustion method proposed by Leco CN-2000 (Leco Corporation, St. Joseph, MI). Nitrogen-free extract (NFE) was calculated by subtracting moisture, CP, crude fiber, crude fat, and ash from 100. Analyses of amino acid concentrations were conducted using high performance liquid chromatography.

Determination of Metabolizable Energy

Cobb x Cobb male boiler chicks (1-d-old, average initial body wt. of 47 g) were used in 21-d ME assays. The first assay was conducted during the spring of 2001 and the second assay was completed during the spring of 2002. The cereals were ground through a 30-horsepower hammermill (Jacobson Model P-240) equipped with a screen having 2.4-mm openings.

The chicks were housed in brooder batteries with six chicks per pen and six pens per treatment. Feed and water were consumed on an ad libitum basis. The batteries had six tiers with four pens for a total of 24 total pens per battery. Treatments were blocked by tier and randomly assigned to pens across four batteries. The chicks were fed a common diet (Table 1) for 14 d before being changed over to the experimental diets for ME determination as described by Scott et al. (1982).

To calculate the ME content of the experimental cereal grains, a reference diet with equal quantities of sucrose and corn starch was used (Table 1). The blend of sucrose and corn starch was replaced on an equal weight basis with the ground cereal grains. Using a known ME value of 3.985 Mcal [kg.sup.-1] for the sucrose-starch blend (National Research Council, 1994), the ME content of the cereals were calculated as described by Scott et al. (1982). The reference diet and the individual replacement diets had chromic oxide (0.25%) added as an indigestible marker to calculate the ME of an ingredient.

Chicks were allowed 5 d for adjustment to the treatment diets, followed by 2 d of fecal collections. Feed and fecal samples were dried at 50[degrees]C in an oven, ground, analyzed for dry matter, N, gross energy (AOAC, 2000), and chromium (Williams et al., 1962) to calculate the nutrient digestibility of the grains (Scott et al., 1982).

Weight of the chicks was recorded at the beginning (15 d) and end (21 d) of the replacement diet phase. Finally, average daily gain, average daily feed intake, and gain/feed were calculated for the 7-d replacement phase.

Statistical Analyses

A combined ANOVA was conducted for all characters using the PROC MIXED procedure of SAS (SAS Institute, 1999). For the combined analysis of seed weight and composition, locations and location interactions were considered random effects, with hybrids examined as fixed effects. The combined analysis of the feeding trials was performed with location and replication as random effects and hybrid examined as a fixed effect. Pen was the experimental unit.


Mean seed weight and AHI of the hybrid grains are given in Table 2. Maize hybrids averaged 28.35 g 100 [seed.sup.-1] (data not shown) and were nearly 10 times larger than the average seed weights of the sorghum hybrids. A combined analysis of seed weight across the four locations revealed differences (P [less than or equal to] 0.05) among sorghum hybrids. Hybrids produced using KS115 had by far the largest seed weights, averaging 3.76 and 4.14 g 100 [seed.sup.-1]. Hybrids produced from crosses with Eastin-1 were considerably smaller, averaging 2.69 to 2.93 g 100 seed-1. These hybrids were significantly greater in seed weight than conventional hybrids produced using RTx435 and RTx2737, whose seed weights ranged from 2.25 to 2.53 g 100 [seed.sup.-1].

The AHI is a measure of the endosperm texture and refers to the relative proportion of hard (corneous) to soft (floury) endosperm. The KS115 hybrids had a mean AHI of 15.2, which was the lowest among the sorghum entries and was comparable with that of maize with an AHI of 15.0 (Table 2). Hybrids produced from crosses with Eastin-1 had a mean AHI of 15.4 and hybrids with normal seed size averaged 15.7.

The CP values of the sorghum samples (Table 3) ranged from 12.1 to 14.1% and were greater than maize (average value of 10.2%). Several of the large-seeded hybrids had higher CP concentrations than the normal hybrids, although some exceptions were apparent. Maize had more crude fat (P [less than or equal to] 0.05) than the Eastin-1 and normal hybrids (Table 3). The KS115 hybrids were not different from maize in regards to fat content. Few notable differences or trends among grain samples were apparent for fiber, ash, NFE, or gross energy content.

Maize samples contained the highest lysine content, but overall had the lowest amino acid content for seven of the 11 essential amino acids (Table 4). Among the sorghum samples, ASA3042 x Eastin-1 ranked the highest for every essential amino acid. Large-seeded hybrids were, in general, greater in total essential amino acid content than the normal-seeded hybrids.

No significant differences were noted among the replacement diets for average daily gain (Table 5). There were some differences for average daily feed intake and gain/feed during the replacement diet phase, yet no clear trends were apparent. Overall, pen performance data were consistent with poultry performance values reported by the National Research Council (NRC, 1994). These results suggest that unbiased comparisons of the metabolizable energy content of the hybrid treatments were possible.

Significant environment, hybrid, and hybrid x environment interaction effects were noted for ME (Table 6). Given the significant hybrid by environment (H x E) interaction, ME values were reported on an individual and combined environment basis (Table 7).

Individual hybrid ME values across the four environments ranged from 3.12 to 3.74 Mcal [kg.sup.-1]. The ASA3042 x KS115 hybrid had the highest average ME content (3.59 Mcal [kg.sup.-1]) followed by hybrid maize (3.51 Mcal [kg.sup.-1]). The average ME content of the KS115 hybrids was greater than the other male hybrid groups with a ME value of 3.48 Mcal [kg.sup.-1]. The RTx2737 hybrids had an average ME content of 3.39 Mcal [kg.sup.-1] followed closely by the RTx435 hybrids with an average ME of 3.36 Mcal [kg.sup.-1]. The Eastin-1 hybrids had the lowest average ME value of 3.31 Mcal [kg.sup.-1].

Contrasts among hybrid samples were performed to assess differences in ME content among different classes of the cereal grains (Table 8). The average ME value for maize was higher (P [less than or equal to] 0.05) than the average for all sorghums, and the same was true for the comparison of maize and conventional sorghum. However, the ME content of maize did not differ significantly from the KS115 hybrids. The ME value for the KS115 hybrids was higher (P [less than or equal to] 0.05) than the conventional sorghum.

Phenotypic correlations indicated that seed weight was highly correlated with crude fat, and crude fat was correlated with ME content (Table 9). Crude protein and AHI were not correlated with variation in the feed quality traits.


Significant genetic variation for seed weight and feeding value were detected among sorghum genotypes evaluated in this study. KS115 and, to a lesser extent, Eastin-1 produced hybrids with high seed weights. Results from chemical analyses of the sorghum grain samples were consistent with previous studies. Hicks et al. (2002) showed CP levels ranging from 10.5 to 12.5%, and crude fat values ranging from 3.2 to 3.7% in large-seeded hybrids. The fat content values reported in this study were similar and CP values were slightly higher than those previously reported. The maize samples were considerably lower in CP content than the sorghum hybrids. This agrees with reports by Douglas et al. (1990b) and Hulan and Proudfoot (1982) that indicated higher protein levels for sorghum than maize. Grain sorghum produced in Kansas typically averages 3.1% fat (Kansas Grain Sorghum Commission, 1997). The conventional sorghum hybrids evaluated in this study were consistent with those estimates. The fat contents of the KS115 hybrids were higher than those observed in the conventional sorghum hybrids, and consistent with reports by Hicks et al. (2002). Total essential amino acid content was highest in Eastin-1 hybrids followed closely by KS115 hybrids, while conventional sorghum hybrids and hybrid maize expressed lower values.

Significant hybrid and environment effects and hybrid x environment interactions were detected for ME in the chick assay. As a group, KS115 hybrids had the greatest ME content, followed by the conventional hybrids with normal seed size. Hybrids produced from crosses with the female line ASA3042 had greater average ME content than crosses made with AWheatland. The highest average hybrid ME value was for ASA3042 x KS115, followed by hybrid maize. Although relatively large-seeded, the Eastin-1 hybrids had lower ME content than the other hybrids in this study.

Hicks et al. (2002) demonstrated that large-seeded lines and their hybrids generally express higher CP and fat content and lower starch concentrations than conventional hybrids. The impact of these differences in seed size and composition on poultry feed value was not determined. To address this question, our study focused on an analysis of a smaller subset of entries with grain produced in multiple environments. Correlation analyses and evaluation of mean performance of hybrids indicated that seed weight was correlated with variation in fat content, and fat content was correlated with ME value. These findings are consistent with recommendations by Douglas et al. (1990a), who concluded that additional fat content would improve the feed value of sorghum for replacement of yellow maize in feed rations.

Tuinstra et al. (2001a) demonstrated in multilocation field trials that hybrids produced using KS115 were competitive for grain yield when compared with conventional hybrid sorghum varieties. In these experiments, variation in grain yield was positively correlated with increased seed weight. Given similar or improved yield potential, it seems clear that efforts to breed for increased seed size and fat content using KS115 or a similar germplasm source should represent an effective strategy for improving feed value of sorghum, at least for monogastric animals.

One factor that might ultimately limit the use of these germplasm sources in development of improved hybrid varieties is low tolerance for weathering. KS115 is highly susceptible to grain molds; however, anecdotal evidence suggests that this problem may be overcome in F1 hybrids through use of red-seeded female parent lines that have high levels of grain mold resistance. Alternately, research efforts could focus on incorporating genes for increased seed weight characteristics from KS115 into genetic backgrounds with improved grain mold resistance.


Results from this study indicate that the use of KS115 as a means of increasing seed size and yield potential in grain sorghum improvement programs may also contribute to enhanced feed quality. Comparisons of sorghum hybrids indicated that KS115 hybrids produced grain with exceptionally high seed weight and increased fat content. These seed characteristics appear to be beneficial to sorghum-based poultry diets, resulting in increased animal performance that is comparable with that of maize.

Abbreviations: AHI, average hardness index; CP, crude protein; ME, metabolizable energy; NFE, nitrogen-free extract.


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Travis D. Kriegshauser, Mitchell R. Tuinstra, * and Joe D. Hancock

T.D. Kriegshauser and M.R. Tuinstra, Dep. of Agronomy; J.D. Hancock, Dep. of Animal Sciences and Industry, Kansas State Univ., Manhattan, KS, 66506. Contribution No 05-103-J from the Kansas Agric. Exp. Stn. Received 27 July 2005. * Corresponding author (drmitch@
Table 1. Common, replacement, and reference diet composition
(% feed basis).

                                  Common    Replacement    Reference
Item ([dagger])                    diet        diet          diet

                                              % ration

Sorghum                             --         50.00          --
Corn starch                       25.00         --           25.00
Sucrose                           25.00         --           25.00
Soybean meal                      37.57        37.57         37.57
Corn gluten meal                   6.33         6.33          6.33
Monocalcium phosphate              2.00         2.00          2.00
Limestone                          1.76         1.76          1.76
Soybean oil                        1.00         1.00          1.00
Salt                               0.53         0.53          0.53
Methionine                         0.32         0.32          0.32
Vitamins and minerals ([double
  dagger])                         0.25         0.25          0.25
Threonine                          0.13         0.13          0.13
Lysine                             0.06         0.06          0.06
Chromic oxide ([section])          0.00          --            --
Tylosin (antibiotic)               0.05         0.05          0.05

([dagger]) Diets were formulated to 1.21% lysine, 1.10% Ca, and 0.90%

([double dagger]) Provided 6621 IU (international units) of vitamin A,
0.03 g of vitamin B12, 992 IU of vitamin D3, 30 IU of vitamin E, 2.6 mg
of vitamin K, 7.45 mg of riboflavin, 69 mg of niacin, 32 mg of
pantothenic acid, 1950 mg of choline,130 mg of Zn, 171 mg of Fe, 44 mg
of Mn, 18 mg of Cu, 0.84 mg of I, and 0.4 mg of Se per kilogram of

([section]) Replacement and reference diets were top-dressed with 0.25%
chromic oxide for metabolizable energy determinations.

Table 2. Mean physical characteristics of maize and sorghum
hybrid grain samples.

Hybrid                        Seed wt.          AHI ([dagger])

                         g 100 [seed.sup.-1]          s

ASA3042 x KS115                 3.76                 15.2
AWheatland x KS115              4.14                 15.1
ASA3042 x Eastin-1              2.69                 14.9
AWheatland x Eastin-1           2.93                 16.0
ASA3042 x RTx435                2.39                 16.0
AWheatland x RTx435             2.53                 16.7
ASA3042 x RTx2737               2.25                 15.6
AWheatland x RTx2737            2.36                 14.7
Maize                            --                  15.0
Mean                            2.88                 15.5
LSD (0.05)                      0.26                  1.73

([dagger]) AHI = average hardness index.

Table 3. Mean proximate analysis components of maize and
sorghum hybrid grain samples (% dry-matter basis).

                            Chemical composition ([dagger])

Hybrid         Protein   Fat   Fiber   Ash   dagger])     Gross energy

                                 %                     Mcal [kg.sup.-1]

ASA3042 x       13.5     3.6    2.7    1.6     70.8           4525
AWheatland x    12.9     3.8    2.3    1.5     71.5           4553
ASA3042 x       14.1     3.4    2.1    1.5     70.9           4577
AWheatland x    13.3     3.5    2.1    1.6     71.4           4513
ASA3042 x       13.2     3.4    2.1    1.6     71.9           4506
AWheatland x    12.1     3.1    2.0    1.6     73.3           4520
ASA3042 x       12.7     3.4    2.3    1.6     72.1           4525
AWheatland x    12.3     3.4    2.3    1.6     72.6           4538
Maize           10.2     3.8    2.2    1.4     73.8           4498
Mean            12.7     3.5    2.2    1.5     72.0           4528
LSD (0.05)       1.1     0.3    0.6    0.2      1.3            124

([dagger]) AOAC method (2000).

([double dagger]) NFE = nitrogen-free extract.

Table 4. Average essential amino acid content of cereal grains (%
dry-matter basis).

                                  Essential amino acids

Hybrid                  ARG     GLY + SER    HIS     ILE     LEU


ASA3042 x KS115         0.46      0.87       0.30    0.46    1.66
AWheatland x KS115      0.46      0.83       0.29    0.46    1.57
ASA3042 x Eastin-1      0.47      0.90       0.31    0.49    1.75
AWheatland x Eastin-1   0.44      0.85       0.29    0.47    1.63
ASA3042 x RTx435        0.45      0.85       0.30    0.46    1.60
AWheatland x RTx435     0.43      0.82       0.28    0.43    1.49
ASA3042 x RTx2737       0.44      0.85       0.30    0.44    1.50
AWheatland x RTx2737    0.44      0.83       0.29    0.43    1.47
Maize                   0.46      0.79       0.30    0.32    1.17
Mean                    0.45      0.84       0.29    0.44    1.54
LSD (0.05)              0.06      0.13       0.04    0.09    0.30

                                      Essential amino acids

Hybrid                  LYS     MET + CYS    PHY + TYR    THR     TRP


ASA3042 x KS115         0.26      0.46         1.04       0.39    0.10
AWheatland x KS115      0.26      0.44         0.99       0.37    0.10
ASA3042 x Eastin-1      0.26      0.47         1.10       0.40    0.10
AWheatland x Eastin-1   0.25      0.45         1.02       0.38    0.09
ASA3042 x RTx435        0.25      0.47         1.03       0.38    0.10
AWheatland x RTx435     0.25      0.47         0.96       0.37    0.09
ASA3042 x RTx2737       0.26      0.43         0.98       0.37    0.09
AWheatland x RTx2737    0.26      0.45         0.95       0.36    0.09
Maize                   0.30      0.47         0.77       0.34    0.07
Mean                    0.26      0.46         0.98       0.37    0.09
LSD (0.05)              0.03      0.06         0.21       0.07    0.20

                         Essential amino

Hybrid                  VAL       Total


ASA3042 x KS115         0.61      6.59
AWheatland x KS115      0.61      6.38
ASA3042 x Eastin-1      0.65      6.90
AWheatland x Eastin-1   0.61      6.47
ASA3042 x RTx435        0.60      6.47
AWheatland x RTx435     0.57      6.13
ASA3042 x RTx2737       0.57      6.23
AWheatland x RTx2737    0.58      6.13
Maize                   0.46      5.42
Mean                    0.58      6.30
LSD (0.05)              0.10      1.05

Table 5. Mean pen performance of six chicks during the replacement
diet phase.

                           Average       Average daily      Gain-feed
Hybrid                    daily gain      feed intake         ratio

                         g [d.sup.-1]    g [d.sup.-1]     g [kg.sup.-1]

ASA3042 x KS115              278              372              749
AWheatland x KS115           265              360              730
ASA3042 x Eastin-1           273              371              735
AWheatland x Eastin-1        278              377              737
ASA3042 x RTx435             277              375              737
AWheatland x RTx435          267              369              723
ASA3042 x RTx2737            265              361              733
AWheatland x RTx2737         280              371              756
Maize                        271              353              767
Mean                         273              368              741
LSD (0.05)                    19               16               36

Table 6. Mean squares from the combined analysis of variance for
metabolizable energy (ME) content.

Source             d.f.    MS for ME

Environment (E)      3     0.1431 *
Hybrid (H)           8     0.2494 **
H x E               24     0.1084 **
Error              175     0.0417

* Statistically significant at the 0.05 probability level.

** Statistically significant at the 0.01 probability level.

Table 7. Average metabolizable energy (ME) values of hybrid sorghum and
maize grain sample (dry-matter basis).

                                        ME content

Hybrid                  Ottawa 2000   Manhattan 2000   Belleville 2001

                                       Mcal [kg.sup.-1]

ASA3042 x KS115            3.62            3.74             3.42
AWheatland x KS115         3.52            3.48             3.20
ASA3042 x Eastin-1         3.43            3.33             3.20
AWheatland x Eastin-1      3.42            3.37             3.34
ASA3042 x RTx435           3.15            3.62             3.40
AWheatland x RTx435        3.12            3.27             3.51
ASA3042 x RTx2737          3.45            3.59             3.46
AWheatland x RTx2737       3.28            3.32             3.27
Maize                      3.32            3.50             3.73
Mean                       3.37            3.47             3.39
LSD (0.05)                 0.12            0.12             0.12

                               ME content

Hybrid                  Manhattan 2001    Average

                             Mcal [kg.sup.-1]

ASA3042 x KS115            3.58             3.59
AWheatland x KS115         3.31             3.37
ASA3042 x Eastin-1         3.19             3.29
AWheatland x Eastin-1      3.23             3.34
ASA3042 x RTx435           3.28             3.36
AWheatland x RTx435        3.36             3.32
ASA3042 x RTx2737          3.32             3.46
AWheatland x RTx2737       3.41             3.32
Maize                      3.49             3.51
Mean                       3.35             3.39
LSD (0.05)                 0.12             0.20

Table 8. Mean squares from statistical contrasts comparing classes
of hybrid sorghum and maize for differences in metabolizable
energy (ME) content.

Contrast comparisons of ME content among grain classes       MS

Maize vs. all sorghum                                     0.351 **
Maize vs. conventional sorghum                            0.410 **
Maize vs. KS115 hybrids                                   0.659
Conventional sorghum vs. KS115 hybrids                    0.472 **

** Statistically significant at the 0.01 probability level.

Table 9. Phenotypic correlations among feed quality traits of sorghum
hybrids. ([dagger])

                          Crude                             ME ([double
Trait                    protein    Crude fat    Seed wt.     dagger])

Crude fat                 -0.13
Seed wt.                   0.24      0.47 **
ME                        -0.05      0.64 **       0.23
AHI ([double dagger])      0.11     -0.26         -0.11         -0.14

** Statistically significant at the 0.01 probability level.

([dagger]) Data from hybrid maize not included in the analysis.

([double dagger]) ME = metabolizable energy.

([section]) AHI =average hardness index.
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Author:Kriegshauer, Travis D.; Tuinstra, Mitchell R.; Hancock, Joe D.
Publication:Crop Science
Date:Mar 1, 2006
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