J. Anim Sci. 2007. 85:196-203. doi:10.2527/jas.2006-116
© 2007 American Society of Animal Science
Nutritional evaluation of high-digestible sorghum for pigs and broiler chicks1
E. K. D. Nyannor*,
S. A. Adedokun*,
B. R. Hamaker
,
G. Ejeta
and
O. Adeola*,2
* Departments of Animal Science,
and
Food Science, and
and
Agronomy, Purdue University, West Lafayette, IN 47907-2054
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Abstract
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Two experiments were conducted to evaluate the nutritional quality of 2 varieties of Purdue high-digestible sorghum (PHD1 and PHD2) and a normal sorghum, compared with corn, in diets of pigs and broiler chicks. In Exp. 1, 12 pigs (average BW, 55 kg) fitted with ileal T-cannula were fed 4 diets containing 946 g of corn or sorghum (PHD1, PHD2, and normal) per kg in a 2-period crossover design (i.e., each pig received 2 diets over a 2-wk period with 6 pigs per dietary treatment) to determine apparent ileal or total tract digestibility of nutrients and energy. There was no difference in the ileal or total tract digestibility of DM, energy, P, Ca, or N among dietary treatments. In Exp. 2, a total of 192 broiler chicks were grouped by weight into 8 blocks of 4 cages each with 6 chicks per cage, and cages were assigned randomly to 1 of the 4 dietary treatments within each block. Chicks were fed corn-soybean meal (SBM) or sorghum-SBM diets for 21 d to determine apparent total tract retention and then switched to diets containing 935 g of the corresponding corn or 1 of the 3 sorghum varieties per kg for 7 d to determine apparent ileal digestibility and total tract retention. Apparent ileal digestibilities of DM and P, as well as energy, were not different in chicks fed diets containing 935 g of corn or 1 of the 3 sorghum varieties per kg. However, apparent total tract retention of DM, energy, and N in chicks fed corn was greater (P < 0.05) than those fed 1 of the 3 sorghum varieties. Although the apparent ME content of corn was greater than PHD1 and normal sorghum (P < 0.01), it was not different from PHD2 sorghum. There was no difference in apparent total tract retention of DM between chicks fed the corn-SBM and PHD-SBM diets, but it was greater (P < 0.05) in chicks fed the corn-SBM diet than those fed the normal sorghum-SBM diet. Apparent total tract retention of N in chicks fed the PHD1-SBM diet was lower (P < 0.05) than in those fed the corn-SBM diet but greater (P < 0.05) than in chicks fed the normal sorghum-SBM meal diet. No difference in the apparent ME content between the corn-SBM and PHD2-SBM diets was observed, but it was greater (P < 0.05) for the corn-SBM diet than the PHD1- or normal sorghum-SBM diet. Weight gain, feed intake, and feed efficiency were not different in chicks fed the corn-SBM or sorghum-SBM diets. Sorghum could serve as a substitute for corn in cereal grain-SBM diets for pigs and broiler chicks.
Key Words: broiler chick • pig • protein digestibility • sorghum
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INTRODUCTION
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Dietary energy ingredients represent the major items in terms of quantity and cost of feed for livestock. The use of corn in livestock diets and its use as an alternative fuel in ethanol production has increased demand for corn, necessitating the exploration of other energy sources for livestock diets. To reduce the overdependence on corn, several researchers have explored, for instance, sorghum (Louis et al., 1991
; Mitzner et al., 1994; Elkin et al., 2002) or pearl millet (Adeola and Orban, 1995) as an alternative to corn in diets for various livestock species.
Sorghum is a drought-tolerant crop and can be grown under a wider range of environmental conditions than corn. However, when used as a feedstuff in nonruminant diets, sorghum is often lower than corn in both energy and nutrient digestibility, in part due to the tannin content of some sorghum varieties. The discovery of cultivars of sorghum with high in vitro protein digestibility (Oria et al., 1995), which may be comparable or superior to that of other cereal grains, can provide a viable alternative or complement to corn as the source of energy for swine and poultry diets. In addition, the nutritional quality of the highly digestible mutant cultivars of sorghum may not be negatively affected by cooking or environmental factors (Oria et al., 2000). However, there is a dearth of information on the use of these highly digestible sorghum cultivars in diets of pigs and poultry.
The objectives of the studies were to determine the nutrient and energy utilization of Purdue high digestibility sorghum (PHD) in growing pigs and broiler chicks and to evaluate growth performance of boiler chicks fed corn, normal sorghum, and PHD sorghum diets containing soybean meal (SBM) as a source of supplemental AA.
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MATERIALS AND METHODS
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Two mutant sorghum cultivars selected for their high protein quality and digestibility from a cross between highly digestible and hard endosperm lines of sorghum varieties were evaluated in 2 studies. It was hypothesized that N digestibility of PHD would be greater than that of normal sorghum in pigs and broiler chicks. It was expected that broilers fed tannin-free sorghum-SBM diets adequate in all nutrients and energy would perform equally as well as those birds fed corn-SBM diets. All procedures involving animals were approved by the Purdue Animal Care and Use Committee.
Experiment 1
Dietary Treatments.
Four diets were formulated to contain 946 g of corn or 1 of the 3 varieties of tannin-free sorghum per kg (as-fed basis; Table 1). The 3 cultivars of sorghum were the Purdue high digestibility mutants PHD 024789 and PHD 024790 (herein referred to as PHD1 and PHD2, respectively) and the normal sorghum (P721N). The PHD1 and PHD2 were selected for protein quality, high digestibility, and hard endosperm characteristics from a cross between the P850115 (a high-digestible line) and MR 732 (a high-yielding, good grain-quality line). Chromic oxide was included in the diets at 3 g/kg as an indigestible marker for the estimation of apparent ileal and total tract nutrient digestibilities and retention.
Animals.
Twelve crossbred (Hampshire x Duroc x Yorkshire x Landrace) barrows, with an average BW of 55 kg, were surgically implanted with a plastic T-cannula approximately 6 cm anterior to the ileocecal junction according to procedures described by Dilger et al. (2004). They were divided into 3 blocks of 4 pigs each using weight as a blocking factor. They were fed 4 diets in a 2-period crossover design so that each pig received 2 different diets over a period of 2 wk rotation with 6 pigs per dietary treatment. Pigs were housed individually in stainless-steel metabolism crates with continuous lighting. Each feeding period was 7 d in duration. On d 1 of each period, pigs were weighed, and the daily feed allotment was determined based on the average BW of all pigs at a rate of 50 g/kg of BW or 4 times the maintenance requirement. The daily allotment was divided into 2 equal portions and offered at 0700 and 1700. Fecal grab samples were collected once on d 5 and stored at –20°C until analyses. Ileal digesta were collected from 0800 to 2000 on d 6 and 7 by attaching a plastic bag to the cannula via a rubber Oring. The plastic bag was changed every 2 h or sooner, if necessary, and stored at –20°C until analyses.
Experiment 2
As in Exp. 1, all of the procedures involving animals were approved by the Purdue Animal Care and Use Committee. One-hundred ninety-two 1-d-old (Ross-308) male broiler chicks obtained from a commercial hatchery were wing-banded and grouped by BW into 8 blocks of 4 cages each with 6 chicks per cage, The cages were assigned randomly to 4 dietary treatments within each block. In the first phase of the study, the chicks were fed 1 of 4 corn- or sorghum-SBM diets (Table 2) ad libitum for 21 d in environmentally controlled battery cages with a lighting cycle of 23 h light and 1 h of darkness. On d 22, the first day of the second phase, the chicks were switched to diets containing 935 g of the respective cereal grain, 50 g of corn oil, 4.0 g of salt, 2.4 g of DL-Met, and 3.0 g of vitamin-trace mineral premix and containing 80 g of CP, 9.2 g of Ca, and 6.5 g of P per kg (as-fed basis) for 7 d.
The room temperatures for the battery cages were 35, 32, and 27°C for d 1 to 8, 8 to 15, and 15 to 29, respectively. Chicks were allowed unrestricted access to adjustable nipple drinkers throughout the study. Individual BW and feed consumption on a cage basis were recorded weekly. During d 17 to 21 and 25 to 28, excreta were collected daily from underneath the cages and kept frozen until analyses. On d 29, birds were weighed and euthanized by CO2 asphyxiation, and ileal digesta were collected and frozen at –20°C until analyses.
Chemical Analyses and Calculations
The sorghum cultivars used in the animal studies were evaluated for their in vitro protein digestibility using the turbidity assay described by Aboubacar et al. (2003). Because the turbidity measurements are indicative of the extent of undigested kafirin in solutions, greater turbidity readings indicate poorer protein digestibility.
Ileal digesta was lyophilized and analyzed for DM, Cr, N, GE, Ca, and P. Fecal samples were dried at 55°C in a forced-draft oven for 5 d. Before chemical analyses, feed, fecal, and ileal digesta samples were ground to pass through a 1-mm screen. The DM content of samples was determined by oven drying at 105°C for 24 h. The N content of diets, feces, and digesta samples was determined by the combustion method (AOAC, 2000; Model FP200, Leco Corp., St. Joseph, MI) and GE by an adiabatic bomb calorimetry (Model 1261, Parr Instrument Co., Moline, IL).
For the determination of Cr, P, and Ca concentrations, feed, digesta, and fecal samples were prepared by a wet-ash digestion with nitric and perchloric acids (AOAC, 2000). The concentration of P was determined using a colorimetric assay where acid molybdate and Fiske’s SubbaRow reducer solution were added to the wet-ash of digesta to form a phospho-molybdenum complex. Color intensity, determined with a spectrophotometer using absorbance at 620 nm (AOAC, 2000; SpectraCount, model No. AS1000, Packard, Meriden, CT), was proportional to P concentration. Calcium was determined by atomic absorption spectrophotometry (AAnalyst 30, Perkin Elmer, Norwalk, CT) and Cr (Spectronic 21D, Milton Roy Co., Rochester, NY) was determined at a wavelength of 440 nm.
Apparent ileal total tract digestibilities were calculated using the index method as described previously by Dilger et al. (2004). Apparent total tract digestibility and the apparent DE or ME content of sorghum- or corn-based diets and sorghum- or corn-SBM diets were estimated as described by Adeola (2001).
Statistical Analysis
A 2-period crossover in a randomized complete block design was used for the analysis of data from the pig experiment. The data collected from the broiler chick study were analyzed as a randomized complete block design using the GLM procedure (SAS Inst. Inc., Cary, NC). Individual pigs served as experimental units, but cages were the experimental units in the broiler chick experiment. Means were separated by least significant difference using the PDIFF option of SAS, and differences were considered significant at an alpha value of 0.05.
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RESULTS
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In Vitro Protein Digestibility
The chemical composition and in vitro protein digestibility of the sorghum grains used in both experiments are presented in Tables 3 and 4, respectively. The turbidity values for the PHD sorghum varieties were lower than the normal sorghum (P721N).
Apparent Digestibility of Nutrients and Energy
There was no difference in apparent ileal or total tract digestibility of DM, energy, N, P, or Ca in pigs fed 946 g of corn/kg, PHD1, PHD2, or normal sorghum (Table 5). Similarly, the estimated DE content based on ileal digesta or feces was not different among dietary treatments.
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Table 5. Apparent digestibility of nutrients and energy in pigs fed diets containing 946 g of corn or sorghum per kg (DM basis)1
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In the broiler chick study, there was no difference in apparent ileal digestibility of DM or any of the nutrients and energy in chicks fed diets containing 935 g of corn or sorghum varieties/kg (Table 6). Apparent total tract retention of DM, N, and energy in chicks fed corn was better (P < 0.05) than those fed sorghum diets. Apparent energy retention in chicks fed the PHD1 sorghum was lower (P < 0.05) than those fed the PHD2 or normal sorghum. There was no difference in N retention between chicks fed the PHD sorghum diets, but chicks fed the PHD1 and 2 diets had better (P < 0.05) N retention than those fed the normal sorghum. Calcium retention did not differ among chicks fed sorghum varieties or corn. The ME content of corn and PHD2 was greater (P < 0.05) than PHD1 or normal sorghum, and PHD1 sorghum contained less ME (P < 0.05) than normal sorghum.
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Table 6. Digestibility values of nutrients and energy in chicks fed diets containing 935 g of corn or sorghum per kg (DM basis)
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Apparent total tract digestibility of DM was not different in chicks fed corn- or PHD sorghum-SBM diets, but it was lower (P < 0.05) in chicks fed the normal sorghum-SBM diet than those fed the corn- or PHD1 sorghum-SBM diet (Table 7). Apparent energy digestibility was greater (P < 0.05) in chicks fed the corn-SBM diet than those fed the normal sorghum-SBM diet. Apparent nitrogen digestibility in chicks fed PHD1 sorghum-SBM diet was greater (P < 0.05) than those fed the normal sorghum-SBM diet but lower (P < 0.05) than those fed the corn-SBM diet. Apparent total tract digestibility of P and Ca did not differ among the 4 dietary treatments. There was no difference in the apparent ME content among the sorghum-SBM diets, but it was lower (P < 0.05) than the corn-SBM diet, except the PHD2-SBM diet.
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Table 7. Apparent total tract digestibility of nutrients and energy in broilers fed corn or sorghum-soybean meal diets (DM basis)
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Growth Performance
The results of the comparative evaluation of PHD sorghum-SBM diets for broiler chicks with corn and a normal sorghum cultivar (P721N) are shown in Table 8. Body weight gain, feed intake, and feed efficiency were not affected by the dietary treatments during the 21-d growth period.
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DISCUSSION
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The prolamin storage proteins, kafirins, are the main form of protein storage bodies in sorghum. The ß- and 
-kafirins are known to contain a significant amount of cysteine (Weaver et al., 1998) forming disulfide bonds in mature grains (Oria et al., 1995). The formation of disulfide-bound complexes has been implicated in the reduction of protein digestibility in mature sorghum grain. The highly digestible sorghum cultivars, unlike the normal sorghum, however, have numerous invaginations in the endosperm, which can increase the accessibility of proteases to the highly digestible 
-kafirins (Oria et al., 2000). The PHD cultivars of sorghum had lower turbidity readings than the normal sorghum, indicating superior in vitro protein digestibility.
Poor digestibility of protein and starch of sorghum has been considered as being partly responsible for about 5% lower in the feeding value compared with corn (Rooney and Pflugfelder, 1986). The N digestibility for pigs fed normal sorghum (P721N) was expected to be poorer than pigs fed corn or PHD sorghum due to the superior in vitro protein digestibility of the PHD cultivars of sorghum. The high variability in apparent ileal N, P, and Ca digestibility is attributable to the rather large variation within dietary treatments values, resulting in a high standard deviation. Dietary treatment differences were, therefore, not detected, de-spite the large numerical differences. Larger sample size, within experimental constraints, might have enabled the detection of difference in the apparent digestibility of N, P, and Ca.
The total tract digestibility of DM and energy for pigs fed sorghum diets in this study are consistent with the observations of Louis et al. (1991), who reported that sorghum-SBM and corn-SBM diets have comparable value for lactating sows. This finding was also corroborated by the report of Shelton et al. (2004), who found no difference in growth performance or carcass traits in finishing pigs fed corn-SBM or sorghum-SBM diets. However, Louis et al. (1991) observed better N digestibility in corn-fed lactating sows compared with those fed sorghum, which was not observed in growing pigs fed corn or sorghum in the current study. In a study with nursery pigs, Healy et al. (1994) reported that corn-fed starter pigs gained 23% faster, consumed more feed, and more efficiently converted feed than sorghum-fed pigs. They also reported better N and DM apparent digestibilities for corn- than sorghum-fed pigs. The endosperm characteristics of sorghum may affect the feeding value of the grain. Healy et al. (1994) observed that pigs fed diets with soft endosperm sorghum outperformed those pigs fed sorghum with hard endosperm.
In an earlier study with growing pigs (BW between 39 and 55 kg), Lin et al. (1987) reported similar ileal N digestibility for pigs fed corn, sorghum, oat groats, and barley, which was greater than wheat middlings. They, however, reported lower N retention for pigs fed sorghum compared with those fed corn or oat groats, which can be attributable to the lower lysine content of the sorghum type used in that study. The mutant PHD cultivars have been shown to contain highly digestible lysine (Elkin et al., 2002). The nutrient digestibility values obtained in the pig experiment compare favorably with other cereal grains. The DM and energy digestibility values in pigs fed corn or sorghum in the current study are similar to that reported by Lawrence et al. (1995) for 20-kg barrows fed corn but are greater than those pigs fed pearl millet. However, the total tract N digestibility values in pigs fed sorghum (69 to 74%) in the current study were similar to 20-kg barrows fed pearl millet (67 to 71%; Lawrence et al., 1995). Adeola and Orban (1995) also reported similar digestibility values for growing pigs fed pearl millet. Goodband and Hines (1988) reported comparable growth performance and nutrient digestibility for starter pigs fed sorghum or barley. In a comparative study of nutrient and energy digestibility of sorghum, pearl millet, and corn in growing pigs, Yin et al. (2002) reported similar DM, CP, and energy digestibility values for pigs fed sorghum, pearl millet, and regular corn.
Elkin et al. (2002) demonstrated the superiority of a highly digestible sorghum cultivar over the normal sorghum, P721N, in broilers chicks in terms of total AA digestibility (93 vs. 74%). In an earlier study, Elkin et al. (1996) reported better protein efficiency ratio and net protein retention for broiler chicks fed the PHD sorghum-based diet than chicks fed corn or normal sorghum. However, the superiority of the protein in the highly digestible sorghum over corn was not confirmed by Elkin et al. (2002), even though chicks fed the PHD sorghum-based diets outperformed those fed normal P721N diets.
The proportion of crude fat in sorghum is about 1% lower than that in corn (NRC, 1998). Additionally, sorghum has lower starch digestibility than corn due to the nature of the peripheral endosperm of sorghum, which may provide physical and enzymatic resistance to starch digestion (Rooney and Pflugfelder, 1986). Weurding et al. (2001) estimated the potential sorghum starch digestibility in broiler chicks to be about 1.5% lower than corn, resulting in a lower digestible energy of sorghum grains relative to corn. This could partially account for the lower ME and energy digestibility for broilers fed the sorghum-based diets.
The better apparent total tract N digestibility in birds fed the PHD sorghum cultivars might have contributed to the improvement in apparent DM digestibility in chicks fed the PHD sorghum cultivars compared with those fed the normal sorghum. Poor N utilization could account for rather low N retention in the second phase of the broiler study (34%) compared with the total tract digestibility on chicks fed SBM-supplemented diets (63%). Evidently, feeding corn or sorghum as the sole source of protein would lead to N imbalance, resulting in a greater uric acid production and subsequently greater N output. This is supported by a greater apparent ileal N digestibility (81%) in chicks fed the PHD sorghum diets but rather low apparent N retention (35 to 39%) in chicks fed the PHD sorghum diets.
There are fundamental differences between the digestive system of the pig and the avian species; therefore, the difference in the nutrient digestibilities is expected. For nonfibrous dietary ingredients, however, birds normally have similar digestibility values as other nonruminants (Pond et al., 1995). The PHD sorghum cultivars used in this study are devoid of tannin, a known antinutritive substance in sorghum. The similarities in the DM and energy digestibilities were therefore expected, but apparent ileal N digestibility seemed to be greater in broilers than in pigs. The digestibility of Ca and P in broilers fed corn or sorghum seemed to be lower than pigs fed corn or sorghum diets. Unlike in the chick study, where total N retention was lower than apparent ileal N digestibility, the total tract N digestibility for pigs was rather high, perhaps because of the hindgut microbial activity in pigs. Obviously, the apparent N retention in the pig study should have been the criterion for a valid comparison.
With such high in vitro protein digestibility of the PHD sorghum cultivars, as indicated by turbidity values, it was expected that the N digestibility in broilers or pigs fed the PHD would surpass those fed the P721N sorghum diets. The greater N retention in broilers fed the PHD sorghum diets was therefore expected, but there was no improvement in apparent ileal N digestibility in broilers fed the PHD sorghum diets. This observation indicates the problem in relying on in vitro nutrient digestibility values as the sole indicator in evaluating feed ingredients. However, the better N retention in broiler chicks fed PHD sorghum-SBM diets compared with those fed the normal sorghum-SBM diet closely agrees with the results of the in vitro protein digestibility.
The apparent total tract N digestibility of the PHD sorghum was found to be lower than corn but greater than the normal sorghum (P721N) in broiler chicks, but such a difference was not detected in the pig study. Growth performance of broiler chicks was equally supported by corn or sorghum. Sorghum grain compares quite favorably with corn in terms of the nutritional quality, and with the added advantage of tolerance to inclement weather, it could be economically incorporated into diets of nonruminants and ease the demand pressure on corn if favorably priced.
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Footnotes
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1 Journal paper No. 2006-17884 of the Purdue University Agricultural Research Programs. The authors thank the staff of Purdue University Swine Research Unit and Animal House for care of experimental animals and P. Jaynes for able technical assistance. 
2 Corresponding author: ladeola{at}purdue.edu
Received for publication February 28, 2006.
Accepted for publication August 1, 2006.
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Abstract
INTRODUCTION
