Strategies to enhance the performance of pigs and poultry on sorghum-based diets

Animal Feed Science and Technology 181 (2013) 1–14

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Animal Feed Science and Technology journal homepage: www.elsevier.com/locate/anifeedsci

Review

Strategies to enhance the performance of pigs and poultry on sorghum-based diets Sonia Y. Liu ∗ , Peter H. Selle, Aaron J. Cowieson Poultry Research Foundation within the University of Sydney, 425 Werombi Road, Camden, NSW 2570, Australia

a r t i c l e

i n f o

Article history: Received 5 October 2012 Received in revised form 21 November 2012 Accepted 16 January 2013

Keywords: Sorghum Pig Poultry Steam-pelleting Technologies Particle size

a b s t r a c t Grain sorghum is grown for consumption by both human and animals; sorghum-based diets are offered to ruminants, pigs and poultry. Sorghum is included in animal diets primarily as an energy source, being largely derived from starch. However, the efficiency of utilisation of energy from sorghum is variable and this may be problematic for animal production. Starch granules are surrounded by kafirin protein bodies and both are embedded in the glutelin protein matrix in the sorghum endosperm. Protein–starch interactions in the sorghum endosperm may limit starch hydrolysis and its availability. The digestibility of protein/amino acids in sorghum is usually inferior to the other cereal grains. Kafirin, which is the dominant protein fraction in sorghum, is poorly digested and deficient in basic amino acids, especially lysine. Sorghum contains more phenolic compounds and phytate than the other cereal grains and both phenolics and phytate may impede digestion by directly or indirectly binding with protein and starch. As considered in this review, various feed processing technologies have been evaluated to improve sorghum utilisation in pigs and poultry. Sorghum varieties with a hard endosperm tend to be more popular in breeding programmes due to their insect resistance and high yield. The texture of sorghum grains varies with the proportions of corneous and floury endosperm. The extent of particle size reduction and its uniformity following grinding is critical to growth performance in pigs and poultry. Sorghum is especially vulnerable to hydrothermal processes which markedly reduce the in vitro pepsin digestibility of sorghum proteins. Thus steampelleting, steam-flaking and wet-extrusion, which involve heat and moisture, may lead to undesirable physico-chemical changes in sorghum including disulphide linkage formation in kafirin protein bodies. Dry-extrusion where heat is generated by friction may enhance starch digestibility by gelatinising starch and disrupting sorghum structures without the addition of moisture. Combining reducing agents with hydrothermal processes may enhance the solubility and digestibility of sorghum protein by either cleaving disulphide linkages or preventing their formation. The inclusion of exogenous enzymes in pig and poultry diets is an established practice to improve performance of monogastric species and phytate-degrading enzymes are of particular relevance due to the relatively high phytate contents in sorghum. Additional strategies including irradiation may also have potential to enhance nutrient utilisation in sorghum. Pigs and poultry may respond differently to any strategy due to fundamental differences in gastrointestinal structure and physiology, which is particularly true of grain particle size. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.

Abbreviations: AME, apparent metabolisable energy; AMEn, nitrogen corrected AME; DM, dry matter; FCR, feed conversion ratio; GE, gross energy; N, nitrogen; NSP, non-starch polysaccharide; PDI, pellet durability index. ∗ Corresponding author. Tel.: +61 2 93511638; fax: +61 2 93511693. E-mail address: [email protected] (S.Y. Liu). 0377-8401/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.anifeedsci.2013.01.008

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Contents 1. 2. 3. 4.

5.

6. 7.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Particle size reduction of sorghum grain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steam-pelleting sorghum-based diets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other processing technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1. Steam-flaking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2. Extrusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3. Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feed additives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Exogenous enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Reducing agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Additional approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 3 6 7 7 7 8 9 9 10 10 10 11 11

1. Introduction The performance of pigs and poultry on sorghum-based diets may not always be comparable to diets based on maize and other cereals. This may be due to, in part, the possibility that sorghum contains condensed tannin although tannin-free crops are becoming increasingly available on a global basis. Nevertheless, any strategies that can be developed to enhance the performance of pigs and poultry on sorghum-based diets would be beneficial. Sorghum (Sorghum bicolor (L.)) is an important cereal that can be grown under drier conditions than those suitable for maize, and its annual global production in 2011 was 63 million tonnes (Swick, 2011). Sorghum is used as part, or sometimes as the entire, cereal grain base in diets for pigs and poultry (Kopinski and Willis, 1996; Selle et al., 2010a). Sorghum, like other cereals, is rich in starch (∼700 g/kg) and has a protein concentration from 115 to 137 g/kg; sorghum has a nitrogen corrected apparent metabolisable energy (AMEn) ranging from 13.5 to 17.7 MJ/kg (Hughes and Choct, 1999). In 17 sorghum samples, Bryden et al. (2009a) reported a range of 71–118 g/kg crude protein with a digestibility coefficient range of 0.69–0.84. Nevertheless, sorghum is potentially an attractive energy source for the livestock and poultry industry. Although the chemical composition of sorghum is similar to maize, sorghum has been associated with sub-optimal, or inconsistent poultry performance (Black et al., 2005; Bryden et al., 2009b). One limitation to the nutritional value of sorghum in non-ruminant species may be kafirin, which is the dominant protein in sorghum with an approximate concentration of 544 g/kg grain protein (Paulis and Wall, 1979). The poor digestibility of kafirin is due to its low solubility and structure of protein bodies and it has an unfavourable amino acid profile as it contains a paucity of basic amino acids, especially lysine (1.5 g/kg protein) (Mosse et al., 1988). As reviewed by Duodu et al. (2003), the poor protein digestibility in sorghum is due to an array of exogenous (grain structure, polyphenols, phytate and cell wall components) and endogenous (disulphide crosslinking, kafirin hydrophobicity and protein secondary structure) factors. Grain sorghum contains relatively high concentrations of phytate or phytic acid (Doherty et al., 1982). In addition to chelating minerals, phytate binds protein through binary or ternary complexes; moreover, it may bind starch directly or indirectly through starch-granule associated protein (Baldwin, 2001; Oatway et al., 2001). In sorghum endosperm, starch granules are surrounded by numerous kafirin protein bodies and both are embedded in the glutelin protein matrix. Starch and protein interactions may affect starch gelatinisation and enzyme hydrolysis (Rooney and Pflugfelder, 1986). Due to relationships between phytate, starch and protein in sorghum, it is likely that the enzymatic degradation of phytate would contribute to enhanced starch and protein utilisation. Some sorghum varieties may contain condensed tannin which has pronounced anti-nutritive properties. However, a number of countries, including USA and Australia, are now producing ‘tannin-free’ sorghums. Vitreousness of sorghum endosperms vary from 100 to 880 g/kg (Cagampang and Kirleis, 1984), but sorghum with a hard texture, and a higher proportion of vitreous endosperm, are widely planted because they are more resistant to fungal infection and insect attack during development than soft grains (Chandrashekar and Mazhar, 1999). However, sorghum with harder endosperms is associated with higher kafirin concentrations (Chandrashekar and Kirleis, 1988; Selle, 2011). Moreover, starch granules in vitreous endosperm are embedded in a firm protein matrix, while starch granules are loosely associated with papery sheets of protein in floury endosperm (Palmer, 1972; Hoseney et al., 1974). Beta et al. (2001) reported a significant correlation between sorghum endosperm textures and pasting temperatures; pasting temperatures increased with the hardness of sorghum grains. Cagampang and Kirleis (1984) showed that amylose concentrations increased from 249 to 290 g/kg starch when grain hardness (vitreousness) increased from 100 to 880 g/kg. Grinding processes such as hammer-milling physically reduce grain particle size and may disrupt endosperm structures. Feed processing technologies used for sorghum could play a major role in improving its value as an animal feedstuff. One challenge in sorghum processing is the vulnerability of sorghum to ‘moist-heat’ (Selle et al., 2010b). Hamaker et al. (1986) showed an average 20.2% reduction in protein digestibility (0.803 versus 0.641) in sorghum following wet-cooking

S.Y. Liu et al. / Animal Feed Science and Technology 181 (2013) 1–14

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and the indigestible protein consisted mainly of kafirin. Confocal laser scanning microscopy confirmed the formation of disulphide linkages during wet-cooking of sorghum and showed that protein bodies are more closely embedded in the protein matrix than in uncooked sorghums (Choi et al., 2008; Ng’andwe et al., 2008). The negative impact of ‘wet-cooking’ on sorghum protein solubility and digestibility is a challenge for pigs and poultry feed producers to process high quality sorghum-based diets with accepted pellet integrity. However, numerous in vitro studies have shown that reducing agents (e.g. sodium bisulphite and 2-mercaptoethanol) may prevent disulphide linkage formation in sorghum protein during wetcooking (Hamaker et al., 1987; Rom et al., 1992; Oria et al., 1995). The major sorghum-based feed processing methods include milling, steam-flaking, steam-pelleting, expansion, extrusion and irradiation. The majority of sorghum-based pig and poultry diets are steam-pelleted at relatively high temperature to ensure sufficient starch gelatinisation and pellet quality (Selle et al., 2010b). Various factors, such as particle size and its uniformity after milling, the temperature used for steam-pelleting, and extrusion with or without moisture, influence the nutritional value of the end product. Besides, although pigs and poultry are both monogastric species, they may respond differently to dietary treatment. For example, poultry prefer larger particles or even whole grain for stimulating the development of the gizzard and small intestine, while pigs prefer relatively smaller particle size in the feed due to the limited particle size reduction in the pig gastrointestinal tract (Healy et al., 1991; Amerah et al., 2007a). Thus the aim of this review is to consider various strategies including particle size reduction, steam-pelleting, steam-flaking, extrusion, expansion, irradiation and possible feed additives utilisation that may enhance pigs and poultry performance in sorghum-based diets. 2. Particle size reduction of sorghum grain The first stage of preparing pig and poultry diets is the reduction in grain particle size, usually by either hammer-milling or roller-milling. It has been appreciated for some time that particle size can influence growth performance and pellet integrity in pigs and poultry (Amerah et al., 2007d). Hammer-milling reduces particle size by grinding grains under a set of hammers moving at high speed until the particles are able to pass through a certain sieve size, while roller-milling reduces particle size by forcing grain through gaps between one or more pairs of horizontal rollers (Murphy and Harner, 1990). Various endproduct particle sizes can be derived from changing sieve sizes in a hammer-mill or gap distances in a roller-mill. Svihus et al. (2004) showed that roller-milling generated a lower proportion of small particles below 0.5 mm (227 g/kg versus 279 g/kg) and large particles above 1.6 mm (136 g/kg versus 170 g/kg) than hammer milling, indicating that roller-milling provides a more uniform particle size distribution than hammer-milling. The finding that hammer-milling generates considerable variations in particle size is supported by Zhuge et al. (1990), Groesbeck et al. (2003), and Ngamnikom and Songsermpong (2011). Although pigs and poultry are both monogastric animals, responses to various particle sizes are different due to fundamental differences in gut structure and function. For poultry, Svihus (2011) reviewed the influence of diet structure on gizzard function and nutrient availability. The gizzard is capable of reducing coarse particles to a certain critical size (less than 0.1 mm) and it was recommended to include at least 200–300 g/kg cereal particles larger than 1 mm in poultry diets to stimulate gizzard development. Numerous studies including particle size and whole grain feeding have been completed with wheat and maize (Amerah et al., 2007c,d; Biggs and Parsons, 2009); however, sorghum data is scarce. Chickens possess a gizzard, a highly effective grinding organ, which is not the case for pigs; consequently, the impact of particle size in diets for pigs is more pronounced than poultry. An in vitro study by Mahasukhonthachat et al. (2010b) concluded that reducing particle size increased starch digestion rate, water solubility/absorption index and changed starch pasting properties, while Al-Rabadi et al. (2009) found reducing average particle size from 3.78 mm to 0.045 mm increased in vitro starch digestion rates by 60-fold factor. The changes in starch functional properties in these studies may be due to a more open grain endosperm structure by milling and increased available surface area for enzymatic action. Amerah et al. (2007b) reviewed the effects of particle size on digestion and performance in poultry and highlighted that optimum particle sizes for broiler diets based on maize or sorghum lie between 600 and 900 ␮m, and the effects of particle size on performance may be observed even after pelleting. It should be noted that the optimum particle size of sorghum is affected by endosperm hardness with 300 ␮m for hard and 500 ␮m for soft sorghum. Cabrera (1992) demonstrated interactions between sorghum grain hardness and particle size on weight gain in broilers where particle size reduction from 1000 to 400 ␮m increased weight gain in chicken fed hard sorghum by 9.2% but decreased weight gain in chicken fed with soft sorghum by 9.7% from 7 to 21 days post-hatch (Fig. 1). Endosperm texture in this study was scored on a scale of 1–5 and the hard sorghum rated 3 and the soft sorghum 5 (1 = hard endosperm and 5 = soft endosperm). Both sorghums had red pericarps and were tannin-free and the diets were steam-pelleted at 65 ◦ C through 4.8 mm die and then crumbled. Interestingly, the compositions of these two sorghums, including key amino acids, ash and gross energy (GE), were similar although the soft sorghum contained more crude protein (105 g/kg versus 95 g/kg). The observation that particle size interacts with grain texture indicated that optimum sorghum particle size in chickens varies with grain hardness. Small particle size may increase nutrient utilisation by increasing surface area for enzymatic hydrolysis; however, particle size reduction should not compromise the development of gastrointestinal tract in chickens. In theory, according to two regression equations in Fig. 1, chickens fed hard and soft sorghum-based diets should achieve the same weight gain (43.4 g) when particle size equals 576 ␮m.

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Daily weight gain (g/bird)

47 y = 0.0063x + 39.73 R² = 0.77

46 45 44

Hard sorghum Soft sorghum

43 42 41

y = -0.0069x + 47.33 R² = 0.86

40 39 300

500

700

900

1100

Particle size (µm) Fig. 1. Effects of sorghum grain hardness and particle size on daily weight gain of broilers from 7 to 21 days post-hatch (Cabrera, 1992).

Healy et al. (1991) found that feed efficiency of pigs is usually improved by fine grinding more in sorghum than maize. Feoli et al. (2007) found that feed conversion ratio (FCR) of broilers was improved by 10.1% (1.52 versus 1.69) when sorghum grain was ground through 4 mm as opposed to 6.4 mm screens. Both studies suggested that sorghum grain was equal to maize in nutritional value when ground to an appropriate particle size. Subsequently, Rodgers et al. (2012) found that from 11 to 35 days in broilers, changing from hammer-milling to roller-milling of sorghum improved feed efficiency by 4% which may be due to a more uniform particle size. These differences in feed efficiency in whole, hammer-milled and roller-milled sorghum-based diets may be the result of variations in the balance between starch and protein digestion and glucose and amino acids absorption, which may influence N retention and deposition (Black et al., 2005). There is considerable complexity in the relationships between grain particle size and feed form (mash versus pellet). Lack of uniform particle size in mash diet reduces feed efficiency because of the increased time and energy for chicks to select larger particles (Nir et al., 1994), though this may be overcome by feeding pelleted or crumbled diets. Nir et al. (1990) emphasised the beneficial effects of coarseness of ground sorghum in mash diet, where feed intake and body weight gain were positively related to the coarseness of the feed although feed efficiency did not differ among treatments. Nir et al. (1995) showed interactions between grinding method and feed form on body weight and feed intake from day 1 to day 28 post-hatch, where the beneficial effect of pelleting the hammer-milled diet was more pronounced than the roller-milled diets. The reasons for these differences may be explained by larger geometric mean diameter of particles obtained by the roller mill than that by the hammer mill (1.413 mm versus 0.628 mm). This is consistent with relative gizzard weights in the same study where larger particles in the roller milled diet stimulated gizzard development. However, in pelleted diets smaller particles may provide better pellet quality (hardness and integrity) and enhance feed intake and weight gain. In conclusion, particle size reduction is critical to enhance utilisation of sorghum in poultry feed where both mean diameter and uniformity of particle size are important. The importance of grain particle size in a steam-pelleted diet is not as pronounced as in mash diets (Amerah et al., 2007c). However, in a series of three studies completed in our laboratory, white sorghum (Liberty) was ground through hammermill sieve-sizes of 6.0, 3.2 and 2.0 mm (Selle et al., 2012, in press, in preparation). The impact of particle size on growth performance remained in evidence in steam-pelleted diets fed to broilers as shown in Table 1. There was a quadratic effect of hammermill sieve size on broiler feed efficiency (P<0.001) which suggested an optimal sieve size of 3.73 mm (Fig. 2) for grinding this white sorghum prior to steam-pelleting complete diets. In theory, the particle size generated from a 3.73 mm 1.750 1.700

FCR (g/g)

1.650

y = 0.0266x2 - 0.1984x + 1.8477 R² = 0.62

1.600 1.550 1.500 1.450 1.400 1.5

2.5

3.5

4.5

5.5

6.5

Hammer-mill sieve (mm) Fig. 2. Particle size effects on feed conversion ratio (FCR) in white sorghum-based broiler diets from 7 to 28 days post-hatch (Selle et al., 2012, in press, in preparation).

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Table 1 The impact of hammer-milling white sorghum (Liberty) through different sieve sizes prior to incorporation into diets steam-pelleted at conditioning temperatures of 90–95 ◦ C on broiler performance from 7 to 28 days post-hatch. Sieve size Conditioning temperature Item

6.0 mma 95 ◦ C

3.2 mmb 95 ◦ C

2.0 mmc 90 ◦ C

Weight gain (g/bird) Feed intake (g/bird) FCRd

1462 2359 1.614

1540 2285 1.485

1529 2382 1.557

Relative gizzard weight (g/kg) e

AME (MJ/kg DM) N retention (%) AMEn (MJ/kg DM)f

19.35

17.79

16.90

13.39 56.8 11.25

12.79 60.3 11.80

13.31 64.5 11.68

Starch digestibility coefficients Proximal jejunum Distal jejunum Proximal ileum Distal ileum

0.606 – 0.844 0.869

0.759 0.838 0.902 0.910

0.721 0.783 0.847 0.889

Nitrogen digestibility coefficients Proximal jejunum Distal jejunum Proximal ileum Distal ileum

0.488 – 0.844 0.869

0.540 0.681 0.793 0.795

0.522 0.642 0.741 0.781

a b c d e f

Selle et al. (2012). Selle et al. (in press). Selle et al. (in preparation). Feed conversion ratio. Apparent metabolisable energy. Nitrogen corrected AME.

hammer mill sieve will result in the best FCR for this particular sorghum variety but will almost certainly vary between varieties depending on grain texture. In this series of feeding studies, it is noticeable that the diets passed through a 4 mm die in the pellet press. Thus the steam-pelleting process will influence particle size of the coarsely (6.0 mm) ground sorghum. There is a lack of research on milling technique and particle size of sorghum-based diets in layer hens. Deaton et al. (1989) found differing particle sizes derived from hammer-mills (0.814–0.873 mm) and roller-mills (1.343–1.501 mm) in maizebased diets did not influence the performance of laying hens as assessed by body weight, egg production, feed efficiency and egg quality. In contrast, Cabrera et al. (1994a) showed reducing particle size in sorghum-based diets from 1.0 to 0.4 mm increased egg production by 7% for soft sorghum and 3% for hard sorghum and, overall, increased egg weight by 2% and improved feed efficiency by 9%. There was no significant effect of particle size reduction in maize-based diet in the same study and it can be concluded that layers responded more to particle size reductions in sorghum than maize. However, it was also noted that particle size reduction in this study reduced feed production rates and increased energy consumption, thus the extra cost of feed production needs to be taken into consideration. Particle size reduction of sorghum is also crucial in pig diets; however, the outcomes of observations are quite different from poultry. Similar to poultry, optimal particle size for pigs depends on grain type (Healy et al., 1994; Laurinen et al., 2000), texture (Healy et al., 1991), feeding system (Choct et al., 2004) and the age of animals (Ngoc et al., 2011). Guillou and Landeau (2000) reviewed 23 scientific papers and concluded that every 100 ␮m increase in particle size will induce a 0.6% reduction in faecal energy digestibility, 0.8% reduction in faecal N digestibility and 0.03% increase in FCR in growing swine. Increasing the fineness of sorghum improved nutrient digestibility and feed efficiency in weaned and grower-finisher pigs due to increased surface area for enzymatic hydrolysis (Carter, 1996). However, particle sizes lower than 400 ␮m (mash or pellet) may increase the risk of gastric ulceration (Morel, 2005). Finely ground sorghum reduced the ratio of starch and protein digestibility coefficients in distal ileum and changed the balance of digestion in growing-finishing pigs (Owsley et al., 1981). The synchronicity of starch and protein digestion and absorption is important in pigs and poultry for efficient protein deposition (Li et al., 2007; Yin et al., 2010; Drew et al., 2012). When comparing the two methods of particle size reduction, roller-milling holds advantages over hammer-milling in preparing pig diets. Thacker (2006) found pig performance and carcass traits were unaffected by processing method, but roller-mills had lower energy requirements, lower maintenance costs, quieter operation and more accurate control of particle size than hammer-mills. This is consistent with a previous study where the method of particle size reduction did not affect growth performance, but feeding pigs with roller milled diets increased apparent digestibility of DM, N and GE, while noticeably decreasing faecal excretion of DM and N (Wondra et al., 1993). Hence, particle size uniformity is critical to enhance nutrient digestibility in pigs. Furthermore, Costa et al. (2007) showed that dustiness caused by fine particulate matters may reduce the quality of air inside piggeries, however, this should be controlled by optimum grinding size, proper feed formulation and pellet quality.

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As discussed, smaller particle size may improve pig performance but the extra cost of feed production should be taken into account. For roller-milling, reducing sorghum particle size from 800 to 400 ␮m increased energy consumption by nearly 3-fold, and decreased production rate by 63% (Cabrera et al., 1993). Similarly, reducing sorghum particle size increased hammer-milling energy by 5.7 times, and decreased production rate by 75% (Cabrera et al., 1994b). Double hammer-milling could be a solution to gain more uniform particle size, however, proper methodology and remixing of fines is important. Moreover, finding a balance between increased feed production costs with decreasing sorghum particle size is influenced by improved feed efficiency in growing pigs. However, escalating feed ingredient prices increase the value of any advantages generated by feed processing technologies.

3. Steam-pelleting sorghum-based diets The majority of pig and poultry diets are steam-pelleted because diets with high pellet integrity offer advantages over mash diets. As outlined by Behnke (1996), these advantages include decreased feed wastage, reduced selective feeding, decreased ingredient segregation, destruction of pathogenic organisms, thermal modification of starch and protein and improved palatability. Importantly, poultry spend less time and energy consuming pelleted feed because prehension is facilitated which increases voluntary feed intakes (Jensen et al., 1962). In comparison to mash diets, pelleting has been shown to improve performance in both pigs (Medel et al., 2004; Lahaye et al., 2007) and poultry consistently (Engberg et al., 2002; Svihus et al., 2004; Zang et al., 2009). Vanschoubroek et al. (1971) summarised the effects of pelleting diets in 117 trials on pig performance where pelleting increased growth rate by 6.6%, feed efficiency by 7.9% and reduced feed intake by 2.1%. Cerrate and Waldroup (2010) reviewed 18 boiler trials where pelleted diets generated 14.4% higher weight gains, 10.5% higher feed intakes with a 3.4% improvement in feed efficiency. The preparation of a pelleted diet involves mixing, steam-conditioning, pelleting and cooling; mash feed passes through a conditioner where heat is introduced by the injection of steam and then enters a chamber where the conditioned meal is forced through the die to produce the pellet. Sorghum starch normally has higher gelatinisation temperatures (68–78 ◦ C) than maize (62–72 ◦ C) and wheat (58–64 ◦ C) (Taylor and Dewar, 2001); and it consequently requires high steam-pelleting temperatures to achieve adequate starch gelatinisation and pellet integrity. However, high steam-pelleting temperatures may compromise the nutrient value of sorghum, especially protein, due to its vulnerability to moist-heat and possible disulphide linkages formation following hydrothermal processes (Taylor, 2005). Pellet integrity is important to maximise the beneficial effects of pelleted diets. Factors influencing pellet quality (hardness and durability) include the overall dietary composition, cereal type, particle size, production rate, die thickness, addition of binders and conditioning temperatures (Thomas and van der Poel, 1996; Thomas et al., 1997, 1998; Loar and Corzo, 2011). The extent of starch gelatinisation appears to be low following pelleting, varying between 50 and 300 g/kg starch and the partial gelatinisation of starch following steam-pelleting does not greatly influence starch digestibility (Svihus and Zimonja, 2011). Alternative methods to assess starch gelatinisation, including differential scanning calorimetry, rapid viscosity analyser or other wet chemistry methods, may be contributing to this variability. Sorghum is vulnerable to wet-cooking or hydrothermal processing and steam-pelleting sorghum-based diet has the capacity to reduce protein solubility in part by increasing concentrations of disulphide linkages. Selle et al. (2012) reported that steam-pelleting sorghum-based broiler diets increased disulfide linkages (33.88 ␮mol/g protein versus 34.95 ␮mol/g protein) and reduced protein solubility (56.3% versus 38.3%). Moreover, in this study, N retention was positively correlated with protein solubility (r = 0.659; P<0.001), indicating steam-pelleting sorghum-based diets reduced both in vitro protein solubility and in vivo N retention in tandem. Selle et al. (in preparation) increasing conditioning temperatures from 70 ◦ C to 80 ◦ C and 90 ◦ C in finely-ground (2.0 mm) sorghum-based broiler diets linearly increased average starch digestibility coefficients in four segments of small intestine by 8.7% (0.766 at 70 ◦ C versus 0.833 at 90 ◦ C). Similarly, average N digestibility coefficients were increased by 11.7% (0.666 at 70 ◦ C versus 0.744 at 90 ◦ C). Curiously, these improvements in starch and N digestibility were not reflected in broiler performance. However, improvements of starch digestibility by increasing pelleting temperature from 65 ◦ C to 95 ◦ C in intermediatelyground (3.2 mm) sorghum-based broiler diets were less pronounced (Selle et al., in press). This suggests that grain particle size interacts with steam-pelleting temperatures to influence starch digestibility. In contrast, Abdollahi et al. (2010) showed that increasing pelleting temperatures from 60 to 90 ◦ C significantly decreased ileal starch and protein (N) digestibility by 2.5% and 3.0%, respectively. Again, these depressions in starch and protein digestion did not significantly influence weight gain and feed efficiency in broilers. The authors suggested that the poor ileal protein digestibility of the diet conditioned at 90 ◦ C may be explained by the formation of disulphide-bonded oligomeric proteins that are resistant to enzymatic hydrolysis. This is supported by the recent finding by Selle et al. (2012) where steam-pelleting was shown to increase disulphide linkages. However, sorghum proteins contribute a relatively small proportion of total protein in complete broiler diets which dilutes the negative impact of reduced protein solubility following steam-pelleting. The lack of correlation between improved digestibility and broiler performance may indicate that the dynamics of starch and protein digestion are more important performance determinants than static apparent digestibility assessments, including those made in the distal ileum. Indeed, it seems likely that broiler growth performance parameters correlate with starch and protein digestion kinetics more so than with digestibility coefficients.

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4. Other processing technologies As discussed, the majority of sorghum-based pig and poultry diets are steam-pelleted; however, different processing technologies are used in other target species. The prime example is steam-flaking of sorghum for incorporation into diets for feedlot beef cattle. Also, extrusion technology is widely used in the production of aquaculture diets, pet foods and human snacks. Potentially, these technologies could have relevance to the processing of sorghum for pig and poultry diets. 4.1. Steam-flaking Steam flaking includes conditioning/tempering, flaking, drying and cooling where grain kernels are compressed between two counter-rotating rolls and driers and coolers are used to reduce moisture and increase shelf life (Speetjens, 2002). Steamflaked sorghum is more often used in intensive beef and dairy cattle production. Kim et al. (1994) compared steam-flaked and extruded sorghum in lactating sows. In comparison to unprocessed sorghum, both processes increased DM, N and GE digestibility and decreased N excretion. In 21 day broiler study, steam-flaked sorghum diets significantly increased weight gain by 11.1%, DM digestibility by 1.6% and GE digestibility by 2.3% in comparison to diets based on extruded sorghum (Cao et al., 1998a). Contrary results were obtained by the same authors in another broiler study where steam-flaked sorghum diets reduced digestibility of DM, GE and N (Cao et al., 1998b). Moisture, the degree of heating and retention time during conditioning are the major variables influencing starch gelatinisation. Optimum moisture content (180–200 g/kg) improved flake quality and reduced broken or fine flakes; however, increasing moisture did not affect the degree of starch gelatinisation because starch is not heated during tempering (McDonough et al., 1997). Subsequently, it was shown that steam-flaking generated higher concentrations of whole flakes (r2 = 0.509), larger flake diameter (r2 = 0.846), more enzyme-susceptible starches (r2 = 0.564) and less flake breakage (r2 = 0.560) in sorghum grains with lower amylose contents (McDonough et al., 1998b). Osman et al. (1970) showed that the thickness of flakes was related to the extent of in vitro starch digestion, where intermediate (31.3%) and thin (41.0%) flakes increased digested starch by 2- and 3-fold factors. This was due to longer retention time and more moisture penetration into the sorghum endosperm when thinner flakes were produced. Similar results from other studies have been reviewed by Kim et al. (2000) where, interestingly, sorghum-based diets, with steaming only but without flaking, depressed starch digestion when compared to unprocessed samples; this may be caused by the formation of disulphide linkages in sorghum protein. McDonough et al. (1998a) showed that in the end product, tempering sorghum with a reducing agent (␤-mercaptoethanol) increased enzyme susceptible starch by 7.3% and decreased pasting temperatures by 14.8%. Scanning electron microscopy showed that reducing agents partially solubilised and weakened the protein matrix within endosperm, which allowed additional expansion of starch granules until the partially damaged pericarp cracked open (McDonough et al., 1998a). However, ␤-mercaptoethanol cannot be used in feed or food, and more research should be completed to examine the effects of other reducing agents that may be used in food and feedstuffs. 4.2. Extrusion Extrusion is a relatively complex process in which food materials are heated by shear friction and forced to flow through a die which is designed to form and/or puff-dry the ingredients (Riaz, 2000) and extrusion is widely used in processing aquaculture feed and dry pet-foods. Compared with steam-pelleting and flaking, extrusion generates more starch gelatinisation and reduces heat-labile antinutritive factors to a greater extent. Alternatively, extrusion may compromise protein solubility and digestibility (Dahlin and Lorenz, 1993a,b; Ismail and Zahran, 2002; Brennan et al., 2011). There are numerous in vitro investigations into extrusion on sorghum starch digestibility. An early study by Glennie (1987) showed extrusion increased water solubility indices, reduced amylose content and molecular weight of starch and made starch more susceptible to enzyme degradation. Phenolic compounds, especially condensed tannin, may interact with starch during extrusion. Dahlin and Lorenz (1993b) reported that extruding high tannin sorghum at low-moistures (15 g/kg) and low-temperatures (80–100 ◦ C) had significantly lower carbohydrate digestibility, however, there was no significant effect of any extrusion conditions on carbohydrate digestibility in low tannin sorghum. Thus the tannin content of sorghum will adversely affect starch digestibility following extrusion; however, tannin free sorghum is increasingly available, but other phenolic compounds may influence starch and protein digestibility (Beta and Corke, 2004; Wu et al., 2011) as shown by Beta and Corke (2004) where ferulic acid influenced sorghum starch pasting properties. Extrusion has been used in processing soybeans to reduce trypsin inhibitor levels and extruding sorghum and soybeans in tandem may benefit pig performance. For example, Hines et al. (1990) reported improvements of 4.8% feed efficiency and 15.7% N digestibility in finishing pigs fed with extruded sorghum–soybean blends. For nursery pigs to 28 day of age, extruded sorghum alone improved feed conversion by 9.7% (Richert et al., 1992a). Also Richert et al. (1992b) found extruded sorghum increased N digestibility by 2.8% and similar results have been reported (Hancock and Bramel-Cox, 1991; Hancock et al., 1992). There are extremely few studies in poultry regarding the effects of extruding sorghum on bird performance. In a 5week feeding study, Zhuge et al. (1990) found that increasing wet-extrusion temperature of sorghum from 100/110 ◦ C to 130/135 ◦ C prior to incorporation into broiler diets adversely affected growth performance. The negative impact of wetextrusion on bird performance may be avoided by using dry extrusion, which not require an external source of heat or

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Pepsin digestibility

0.5

y = -0.0003x + 0.5299 R² = 0.93, P < 0.001 0.45

0.4

0.35 100

200

300

400

500

Extrusion moisture content (g/kg) Fig. 3. Effects of extrusion moisture content on pepsin digestibility of protein. Adapted from Gomez et al. (1988).

steam and heat is generated solely from friction (Riaz, 2000). Fapojuwo et al. (1987) showed that increasing dry extrusion temperature of sorghum from 50 to 200 ◦ C significantly increased protein digestibility by 59% (0.449 versus 0.714). However, heating extruded sorghum (200 ◦ C) with boiling water for 5 min depressed protein digestibility by 23% (0.714 versus 0.549). The marked reduction in protein digestibility following ‘wet-cooking’ was probably due to the induction of disulphide cross-linkages. This outcome shows that dry extrusion can enhance sorghum protein digestibility by mechanically disrupting structural organisation within the grain. Clearly, these advantages are compromised by heating in the presence of water as opposed to dry extrusion where the heat is generated by friction. Dahlin and Lorenz (1993a) found wet extrusion depressed N solubility in low-tannin sorghum and importantly, Gomez et al. (1988) showed that increasing extrusion moisture significantly decreased pepsin digestibility in sorghums with various amylose contents (Fig. 3). Moreover, as starch and protein may interact in sorghum endosperm, wet extrusion may also influence starch digestion. Mahasukhonthachat et al. (2010a) reported that increasing extrusion moisture from 250 to 400 g/kg decreased starch digestion rates by 31% (0.045 h−1 versus 0.031 h−1 ). Thus dry extrusion may be advantageous for processing sorghum. However, extrusion of sorghum is associated with higher energy costs than steam-pelleting but extrusion has the potential to increase starch gelatinisation and improve animal performance. Dry extrusion of sorghum holds appeal because it gelatinises starch and physically disrupts structures within the grain without exposing sorghum to moist-heat as would be the case with conventional ‘wet’ extrusion. The pronounced increase in protein digestibility followed dry extrusion of sorghum reported by Fapojuwo et al. (1987) does suggest that investigations into dry extruded sorghum are justified particularly in view of escalating grain prices. 4.3. Expansion Although extrusion is associated with greater starch gelatinisation, it represents an increase in the cost of production; alternatively, attention has been given to the use of expanders. The annular gap expander is similar in design to a singlescrew extruder, but differs by discharging material over an annular gap outlet design instead of forcing it through a fixed die (Fancher et al., 1996). The operating conditioning temperature for expanders ranges from 93 to 127 ◦ C, and retention time ranges from 10 to 25 s, which is lower and shorter than extruders. However, expansion could reduce energy consumption by 70–98%, and increase production rate by 100–1100% when compared to extrusion (Fancher et al., 1996). Froeschner et al. (1997) compared the effects of expanded and standard pellets for growing pigs in sorghum-based diets containing different genotypes and found pellet durability index (PDI) increased from 92.5 to 96.7% as the amylopectin concentrations increased from 250 to 750 g/kg starch, and expanded growing pig diets had 30% higher PDI (94.2 units versus 72.6 units) and 15% improvement in FCR (1.358 versus 1.598) compared to steam-pelleted diets. In support of this, Johnston et al. (1999) showed that expansion markedly increased PDI in sorghum-based diets for finishing pigs (93.4% versus 83.7%) and lactating sows (90.4% versus 71.7%) in comparison to steam-pelleted diet. In finisher pig diets, expansion increased starch gelatinisation from 328 g/kg starch in a steam-pelleted diets to 468 g/kg starch, and increased weight gain by 6.3% (Johnston et al., 1999). In addition, Traylor et al. (1998) showed that apparent digestibility of protein (N) and digestible energy was linearly (P<0.01) correlated to cone pressure during expansion, where protein digestibility increased from 0.783 with nil cone pressure to 0.810 at 2296 kilopascal (extra 14.9 kWh/t energy consumption), and digestible energy increased from 13.97 MJ/kg with nil cone pressure to 14.91 MJ/kg at 1145 kPa (extra 8.9 kWh/t energy consumption). Instructively, it appears that the beneficial effects on digestible energy of increased cone pressure during expansion were more pronounced in sorghum-based diets than wheat and maize-based pig diets (Traylor et al., 1998). Of course, any improvements in performance and nutrient digestibility could offset higher energy costs associated with expansion (Traylor et al., 1999). The effects of expanded broiler diets on performance are inconsistent, which may be due to the various temperatures used in feeding studies. Deyoe et al. (1967) found there was no significant difference in performance of chicks fed expanded

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and unexpanded sorghum-based diets. In support of this, steam pelleted and expanded sorghum showed no differences in broiler performance in a two-phase broiler study (Cramer et al., 2003). However, in a wheat-based diet study, comparisons between mash, steam pelleting, expansion and extrusion, showed that the extent of positive effects of processing on broiler performance followed the order: extrusion > expansion > steam pelleting > mash (Lundblad et al., 2011). 5. Feed additives A variety of feed additives may be included in sorghum-based diets; however, this review will cover only exogenous enzymes and reducing agents. The inclusion of non-starch polysaccharide (NSP) degrading enzymes in poultry diets based on viscous grains (wheat, barley) is common place but sorghum is not as responsive because it contains less soluble NSP (Choct, 2006). Alternatively, the inclusion of phytate-degrading enzymes in sorghum-based pig and poultry diets is routine. Alternatively, proteases have the potential to improve sorghum protein digestibility and enhance growth performance. Given the likely importance of disulphide bond formation in hydrothermally processed sorghum-based diets, consideration should be given to the inclusion of reducing agents with the capacity to cleave disulphide bonds. 5.1. Exogenous enzymes The inclusion of exogenous enzymes in pig and poultry diets has risen dramatically, particularly the inclusion of NSP degrading enzymes in barley- and wheat-based diets and supplementation of phytase in the majority of pig and poultry diets. Sorghum is a ‘non-viscous’ grain due to its low concentrations of soluble NSP (Selle et al., 2010a). The studies that have evaluated NSP degrading enzymes in sorghum-based pig and poultry diets have been inconclusive because combinations or enzyme cocktails were used in most of these studies, so that the beneficial effects, if any, could not be distinguished. However, Flores et al. (2009) reported that addition of an enzyme combination of phytase, pectinases, ␤-glucanases and hemicellulases to sorghum–canola based pelleted diets significantly improved Ca and P digestibility and increased metabolisable energy in grower pigs. Park et al. (2003) found that inclusion of ␣-amylase and cellulase in finisher pig diets tended to increase average daily weight gain, but did not affect feed efficiency and N digestibility and carcass characteristics. Also, Kim et al. (1998) found that adding cellulolytic enzymes (0.5 g/kg) to sorghum–soybean based diets for finisher pigs did not influence growth performance, carcass merit, or nutrient utilisation. For broilers, Cadogan et al. (2005) found that a combination of protease (4000 U/kg), amylase (400 U/kg) and xylanase (300 U/kg) significantly increased weight gain (3.7%) and feed intake (4.9%) to 21 days but similar improvements were not found at 42 days post-hatch. Sorghum contains about 2.92 g/kg total phosphorus (P) and 82.7% of total P is phytate bond P (2.41 g/kg phytate-P). Moreover, natural phytase activity in sorghum is extremely low (35 FTU/kg) when compared to wheat (503 FTU/kg) and barley (348 FTU/kg) (Selle et al., 2003). In diets for pigs between 51 and 99 kg live weight, substituting monocalcium phosphate completely with phytase (750 FTU/kg) reduced phosphorus excretion by more than 30% in sorghum-soybean based diet without affecting pig performance (Bernal et al., 2006). Phytate may bind protein through binary or ternary complexes depending on gut pH and iso-electric point of protein, furthermore, phytate has the potential to bind starch through hydrogen bonds, phosphate linkages or starch granule associated protein (Yoon et al., 1983; Oatway et al., 2001). Thus apart from increasing P retention, the ‘extra-phosphoric’ effects of enhanced protein and energy utilisation may be evident when phytase is included in pig and poultry diets. However, Cervantes et al. (2004) found that phytase (500 or 1000 FTU/kg) supplementation did not improve amino acids digestibility and pig performance in sorghum–soybean meal based diets. This was later confirmed when phytase (1050 FTU/kg) and pancreatin (126 USP protease activity/kg) combination did not affect AID of amino acids in growing pigs fed with sorghum-based diet (Cervantes et al., 2011). The lack of response in amino acid digestibility with phytase supplementation may have been a consequence of the analyses being completed in cannulated pigs. As discussed by Selle and Ravindran (2008), most phytase and amino acids digestibility assays in cannulated pigs generate poor responses in comparison to studies which ileal digesta samples are taken by slaughter techniques. Nevertheless, there is a lack of basic amino acids in kafirin and the extent of phytate-protein complex may be small resulting less response to phytase in the Cervantes et al. (2004, 2011) studies. However, Ravindran et al. (1999) showed that addition of phytase (1200 FTU/kg) in sorghum-only broiler diets significantly increased amino acid digestibility by an average of 6.3% (0.743 versus 0.791). Subsequently, Ravindran et al. (2000) found a 3% improvement (P<0.001) on ileal N digestibility in wheat–sorghum-based broiler diets with phytase supplementation (400 FTU/kg), and significant interactions of phytase inclusion levels and non-phytate-P content on AME and ileal P digestibility, suggesting that response of broiler chickens to microbial phytase supplementation is influenced by dietary phytic acid and non-phytate phosphorous levels. The inclusion of phytase is critical in lysine-deficient broiler diets, as demonstrated by Ravindran et al. (2001), increasing phytase inclusion levels from 0 to 1000 FTU/kg linearly increased ileal lysine digestibility from 0.794 to 0.841 in a lysine-deficient wheat–sorghum–soybean meal diet. Interestingly, a recent study done by Poultry Research Foundation showed that phytase inclusion (1000 FTU/kg) increased starch digestibility in proximal jejunum, distal ileal and total small intestinal tract by 26%, 5% (P<0.05) and 7% (P<0.05), respectively, and improved AMEn by 5% (P<0.05) in sorghum-based broiler diets (Selle et al., in preparation). Therefore, phytase additions in sorghum-based broiler diets hold appeals for improving energy utilisation and broiler performance. Studies with a keratinase in sorghum-based broiler diets completed in our laboratory have been encouraging (Selle et al., in press). This Bacillus lichenformis derived protease (300 U/g) significantly improved apparent starch digestibility in distal jejunum and proximal ileum by 14% (0.678 versus 0.770) and 5% (0.812 versus 0.851), respectively, and significantly

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increased apparent N digestibility in distal jejunum, distal ileum and total small intestinal tract by 17% (0.538 versus 0.627), 7% (0.719 versus 0.770) and 12% (0.579 versus 0.647), respectively. However, these improvements were not reflected in growth performance which may have been due to more than adequate concentrations of protein/amino acids in basal diet. In contrast, other studies found small responses to proteases in sorghum-based pig and poultry diets (Leite et al., 2011; Zamora et al., 2011). One challenge of including proteases in sorghum-based diets is disulphide linkages formation in sorghum grains following wet-cooking. Keratin is an indigestible protein source with high cystine contents and substantial disulphide linkages, intuitively, a protease with the capacity to degrade keratin would also degrade kafirin (Selle et al., 2010a). However, this hypothesis remains to be confirmed and the likelihood is that the majority of proteases do not have the capacity to reduce disulphide linkages. There is a lack of evaluations of enzyme efficacy under various feed processing conditions where recovery of enzyme activity under high-temperature process is crucial. Due to its hard grain texture, sorghum-based diet may benefit from using exogenous enzyme with particle size reduction, moreover, the vulnerability of sorghum to ‘moist-heat’ may be overcome by dry extrusion and the inclusion of selected proteases and/or reducing agents. 5.2. Reducing agents Wet cooking sorghum with reducing agents, such as sodium bisulphite, 2-mercaptoethanol and dithiothreitol, has the capacity to cleave the disulphide bonds between cysteine residues. Moreover, it has been shown to improve in vitro starch and protein digestibility (Hamaker et al., 1987; Rom et al., 1992; Choi et al., 2008). Apart from improving protein digestibility, Chandrashekar and Kirleis (1988) showed that cooking sorghum with 2-mercaptoethanol (0.5 g/kg) increased the degree of starch gelatinisation from 791 to 952 g/kg starch. Also, Zhang and Hamaker (1999) showed sodium dodecyl sulphate (30 g/kg) treatment increased enzymatic hydrolysis of starch. This may be explained by a reduction in the integrity of the protein matrix from breaking disulphide linkages and allowing starch granules more access for water penetration and gelatinisation. Moreover, although reducing agents are not usually included in sorghum-based diets, they have been used with full fat soybeans for chicks and improved growth performance (Herkelman et al., 1991). Sulphide ions are able to cleave the disulphide bonds and change the protein structure of trypsin inhibitors in soybean (Wang et al., 2009). Sorghum plays an important role as an energy source in pig and poultry diets, and any improvement in starch digestibility by using reducing agent will be encouraging and as it would increase the value of sorghum as a feedstuff. Both kafirin and glutelin may negatively impact on starch digestibility and the use of a reducing agent may indirectly improve starch digestibility by impacting on these proteins in sorghum endosperm. Thus reducing agents may provide higher starch gelatinisation and better protein digestion in sorghum, and ultimately improve animal performance. Future research into the effects of reducing agents in sorghum-based diets, and the interaction with processing conditions and other additives, especially feed enzymes, are necessary. 6. Additional approaches Disulphide linkage formation during wet-cooking sorghum is a challenge for properly preparing sorghum-based pig and poultry diets. However, irradiation, a rapid and clean method to prevent disulphide linkages, has the potential to enhance the value of sorghum. Siddhuraju et al. (2002) reviewed the effect of ionising radiation on antinutritive factors and the nutritional value of plant materials and concluded that ionising radiation may be a possible method to counter certain antinutritive factors. Duodu et al. (1999) reported that cooking irradiated sorghum reduced phytic acid content in porridge and Abu-Tarboush (1998) showed that irradiation reduced tannin content in sorghum. Also, it has been shown that electron beam irradiation reduced tannin content of sorghum by up to 86% and the phytate content by up to 90% (Shawrang et al., 2011). Moreover, in the same study, at doses higher than 15 kilogray, digestibility of DM, protein and energy were significantly enhanced in poultry. Irradiation can modify bonds involved in secondary structure of sorghum protein and irradiation following wet cooking sorghum alleviated adverse effects in sorghum protein digestibility (Fombang et al., 2005). However, high doses of irradiation may cause Maillard reaction and protein aggregation, which would negatively affect protein digestibility (Fombang et al., 2005). Apart from confirming reductions in phyate and tannin content after irradiation, Hassan et al. (2009) indicated that irradiated sorghum increased globulin, prolamin and albumin fractions but decreased in vitro protein digestibility by 9.9%. There is lack of in vivo studies on animal performance with irradiated sorghum-based diets; however, irradiation is a clean and rapid way of processing sorghum with potential to protect against micro-organisms, mycotoxins and insects. 7. Conclusions The processing of sorghum alters the physiochemical properties of protein and starch and the nutritional value of sorghum for pigs and poultry. Processing technologies probably have more potential to enhance the nutritive value of sorghum in comparison to maize and wheat and sorghum particle size in particular is critical for optimising growth performance in pigs and poultry. Generally, poultry require larger particles to stimulate the gizzard development, while smaller particles facilitate maximum nutrient utilisation in pigs. Fundamentally, pelleted diets improve growth performance in pigs and poultry in comparison to mash diets. Various processing techniques, such as steam-pelleting, expansion and extrusion, have different impacts on starch and protein utilisation. Importantly, dry extrusion may improve starch gelatinisation and

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digestibility without compromising protein digestibility. To avoid the inimical effect of ‘moist-heat’ on sorghum protein digestibility, inclusion of reducing agents during processing may prevent disulphide bond formation and maximise the benefits of hydrothermal treatments. Inclusion of exogenous enzymes in sorghum-based diets, especially phytase and protease, may play critical roles in enhancing the value of sorghum as a feedstuff. Clearly, a number of strategies to enhance the performance of pigs and poultry offered sorghum-based diet may be considered. Therefore, further research into such strategies, individually and in combinations, is merited to improve the value of sorghum as a feedstuff for livestock and poultry. Acknowledgment The authors acknowledge the financial support of a post-graduate scholarship for Ms. Sonia Yun Liu awarded by Poultry CRC. References Abdollahi, M.R., Ravindran, V., Wester, T.J., Ravindran, G., Thomas, D.V., 2010. Influence of conditioning temperature on performance, apparent metabolisable energy, ileal digestibility of starch and nitrogen and the quality of pellets, in broiler starters fed maize- and sorghum-based diets. Anim. Feed Sci. Technol. 162, 106–115. Abu-Tarboush, H.M., 1998. Irradiation inactivation of some antinutritional factors in plant seeds. J. Agric. Food Chem. 46, 2698–2702. Al-Rabadi, G.J.S., Gilbert, R.G., Gidley, M.J., 2009. Effect of particle size on kinetics of starch digestion in milled barley and sorghum grains by porcine alpha-amylase. J. Cereal Sci. 50, 198–204. Amerah, A.M., Lentle, R.G., Ravindran, V., 2007a. Influence of feed form on gizzard morphology and particle size spectra of duodenal digesta in broiler chickens. J. Poult. Sci. 44, 175–181. Amerah, A.M., Ravindran, V., Lentle, R.G., Thomas, D.G., 2007b. Feed particle size: implications on the digestion and performance of poultry. Worlds Poult. Sci. J. 63, 439–455. Amerah, A.M., Ravindran, V., Lentle, R.G., Thomas, D.G., 2007c. Influence of feed particle size and feed form on the performance, energy utilization, digestive tract development, and digesta parameters of broiler starters. Poult. Sci. 86, 2615–2623. Amerah, A.M., Ravindran, V., Lentle, R.G., Thomas, D.G., 2007d. Influence of particle size on the performance, digesta characteristics and energy utilisation of broilers fed maize and wheat based diets. Proc. Aust. Poult. Sci. Symp. 19, 89–92. Baldwin, P.M., 2001. Starch granule-associated proteins and polypeptides: a review. Starch-Starke 53, 475–503. Behnke, K.C., 1996. Feed manufacturing technology: current issues and challenges. Anim. Feed Sci. Technol. 62, 49–57. Bernal, H., Ruiz, E.A., Meza, Z., Valdivie, M., Colin, J., Gutierrez, E., Morales, H., 2006. Substitution of monocalcium phosphate by the enzyme phytase in diets for fattening pigs. Cuba J. Agric. Sci. 40, 181–188. Beta, T., Corke, H., Rooney, L.W., Taylor, J.R.N., 2001. Starch properties as affected by sorghum grain chemistry. J. Sci. Food Agric. 81, 245–251. Beta, T., Corke, H., 2004. Effect of ferulic acid and catechin on sorghum and maize starch pasting properties. Cereal Chem. 81, 418–422. Biggs, P., Parsons, C.M., 2009. The effects of whole grains on nutrient digestibilities, growth performance, and cecal short-chain fatty acid concentrations in young chicks fed ground corn–soybean meal diets. Poult. Sci. 88, 1893–1905. Black, J.L., Hughes, R.J., Nielsen, S.G., Tredrea, A.M., MacAlpine, R., Van Barneveld, R.J., 2005. The energy value of cereal grains, particularly wheat and sorghum, for poultry. Proc. Aust. Poult. Sci. Symp. 17, 21–29. Brennan, C., Brennan, M., Derbyshire, E., Tiwari, B.K., 2011. Effects of extrusion on the polyphenols, vitamins and antioxidant activity of foods. Trends Food Sci. Technol. 22, 570–575. Bryden, W.L., Li, X., Ravindran, G., Hew, L.I., Ravindran, V., 2009. Ileal Digestible Amino Acids in Feedstuffs for Poultry. RIRDC Publication 09/71, Rural Industries Research and Development Corporation, Barton, ACT. Bryden, W.L., Selle, P.H., Cadogan, D.J., Liu, X., Muller, N.D., Jordan, D.R., Gidley, M.J., Hamilton, W.D., 2009. A Review of the Nutritive Value of Sorghum for Broilers. RIRDC Publication No. 09/007, Rural Industries Research and Development Corporation, Barton, ACT. Cabrera, M.R., 1992. Effects of sorghum genotype and particle size on milling characteristics and performance of finishing pigs, broiler chicks, and laying hens. M.Sc. Thesis, Kansas State University, Kansas, USA. Cabrera, M.R., Hancock, J.D., Behnke, K.C., Bramel-Cox, P.J., Hines, R.H., 1993. Sorghum genotype and particle size affect growth performance, nutrient digestibility, and stomach morphology in finishing pigs. Kansas State University Swine Day 1993, Report of Progress 695, Kansas, USA, pp. 134–139. Cabrera, M.R., Hancock, J.D., Behnke, K.C., Hines, R.H., Bramel-Cox, P.J., 1994a. Corn, sorghum genotype, and particle size affect milling characteristics and productivity of commercial egg-type hens. Poult. Sci. 73, 11. Cabrera, M.R., Hancock, J.D., Bramel-Cox, P.J., Hines, R.H., Behnke, K.C., 1994b. Effects of corn, sorghum genotype, and particle size on milling characteristics and growth performance in broiler chicks. Poult. Sci. 73, 11. Cadogan, D.J., Selle, P.H., Creswell, D., Partridge, G., 2005. Phytate Limits Broiler Performance and Nutrient Digestibility in Sorghum-Based Diets. Poultry Research Foundation. Cagampang, G.B., Kirleis, A.W., 1984. Relationship of sorghum grain hardness to selected physical and chemical measurements of grain quality. Cereal Chem. 61, 100–105. Cao, H., Hancock, J.D., Hines, R.H., Behnke, K.C., Park, J.S., Senne, B.W., Jiang, J.M., Froetschner, J.R., Sorrell, P., 1998. Effects of sorghum endosperm hardness and processing on growth performance and nutrient digestibility in pigs and broiler chicks. Kansas State University Swine Day 1998, Report of Progress 819, Kansas, USA, pp. 251–255. Cao, H., Hancock, J.D., Hines, R.H., Behnke, K.C., Senne, B.W., Froetschner, J.R., Jiang, J.M., Johnston, S.L., 1998. Effects of sorghum starch type, endosperm hardness, and processing on digestibility and growth performance in finishing pigs and chicks. Kansas State University Swine Day 1998, Report of Progress 819, Kansas, USA, pp. 256–260. Carter, R.R., 1996. Effects of feedmill processes on the nutritional value of grain sorghum for livestock. In: Third Australian Sorghum Conference, Melbourne, Vic, pp. 251-260. Cerrate, S., Waldroup, P., 2010. Maximum profit feed formulation. 4. Interaction between energy content and feed form. Int. J. Poult. Sci. 9, 641–647. Cervantes, M., Yanez, J., Barrera, M.A., Figueroa, J.L., Torrentera, N., Sauer, W., 2004. Ileal amino acid digestibility and performance of pigs fed grain sorghumbased diets supplemented with phytase. Interciencia 29, 527–531. Cervantes, M., Gomez, R., Fierro, S., Barrera, M.A., Morales, A., Araiza, B.A., Zijlstra, R.T., Sanchez, J.E., Sauer, W.C., 2011. Ileal digestibility of amino acids, phosphorus, phytate and energy in pigs fed sorghum-based diets supplemented with phytase and Pancreatin (R). J. Anim. Physiol. Anim. Nutr. 95, 179–186. Chandrashekar, A., Kirleis, A.W., 1988. Influence of protein on starch gelatinization in sorghum. Cereal Chem. 65, 457–462. Chandrashekar, A., Mazhar, H., 1999. The biochemical basis and implications of grain strength in sorghum and maize. J. Cereal Sci. 30, 193–207. Choct, M., Selby, E.A.D., Cadogan, D.J., Campbell, R.G., 2004. Effects of particle size, processing, and dry or liquid feeding on performance of piglets. Aust. J. Agr. Res. 55, 237–245. Choct, M., 2006. Enzymes for the feed industry: past, present and future. Worlds Poult. Sci. J. 62, 5–15.

12

S.Y. Liu et al. / Animal Feed Science and Technology 181 (2013) 1–14

Choi, S.J., Woo, H.D., Ko, S.H., Moon, T.W., 2008. Confocal laser scanning microscopy to investigate the effect of cooking and sodium bisulfate on in vitro digestibility of waxy sorghum flour. Cereal Chem. 85, 65–69. Costa, A., Guarino, A., Navarotto, P., Savoini, G., Berckmans, D., 2007. Effects of corn milling type on physical characteristics and dustiness of swine diets. Trans. ASABE 50, 1759–1764. Cramer, K.R., Wilson, K.J., Moritz, J.S., Beyer, R.S., 2003. Effect of sorghum-based diets subjected to various manufacturing procedures on broiler performance. J. Appl. Poult. Res. 12, 404–410. Dahlin, K., Lorenz, K., 1993a. Nitrogen solubility of extruded cereal grains. Lebensm. Wiss. Technol. 26, 49–53. Dahlin, K.M., Lorenz, K.J., 1993b. Carbohydrate digestibility of laboratory-extruded cereal-grains. Cereal Chem. 70, 329–333. Deaton, J.W., Lott, B.D., Simmons, J.D., 1989. Hammer mill versus roller mill grinding of corn for commercial egg layers. Poult. Sci. 68, 1342–1344. Deyoe, C.W., Sanford, P.E., Waggle, D.H., 1967. Feeding expanded corn and sorghum grain in broiler diets. Poult. Sci. 46, 1252. Doherty, C., Faubion, J.M., Rooney, L.W., 1982. Semiautomated determination of phytate in sorghum and sorghum products. Cereal Chem. 59, 373–378. Drew, M.D., Schafer, T.C., Zijlstra, R.T., 2012. Glycemic index of starch affects nitrogen retention in grower pigs. J. Anim. Sci. 90, 1233-U1213. Duodu, K.G., Minnaar, A., Taylor, J.R.N., 1999. Effect of cooking and irradiation on the labile vitamins and antinutrient content of a traditional African sorghum porridge and spinach relish. Food Chem. 66, 21–27. Duodu, K.G., Taylor, J.R.N., Belton, P.S., Hamaker, B.R., 2003. Factors affecting sorghum protein digestibility. J. Cereal Sci. 38, 117–131. Engberg, R.M., Hedemann, M.S., Jensen, B.B., 2002. The influence of grinding and pelleting of feed on the microbial composition and activity in the digestive tract of broiler chickens. Br. Poult. Sci. 43, 569–579. Fancher, B.I., Rollins, D., Trimbee, B., 1996. Feed processing using the annular gap expander and its impact on poultry performance. J. Appl. Poult. Res. 5, 386–394. Fapojuwo, O.O., Maga, J.A., Jansen, G.R., 1987. Effect of ectrusion cooking on in vitro protein digestibility of sorghum. J. Food Sci. 52, 218–219. Feoli, C., Hancock, J.D., Herrera, M.C., Herrera, G.M., Rios, M.J., Vargas, F., Mason, S.C., 2007. Nutritional value of corn versus sorghum when ground through different screen sizes and used in diets for broiler chicks. J. Anim. Sci. 85, 399. Flores, A.I.S., Landin, G.M., Rosales, S.G., Ibarguengoytia, J.A.C., 2009. Effect of fibrolytic enzymes and phytase on nutrient digestibility in sorghum–canola based feeds for growing pigs. Tec. Pecu. Mex. 47, 1–14. Fombang, E.N., Taylor, J.R.N., Mbofung, C.M.F., Minnaar, A., 2005. Use of gamma-irradiation to alleviate the poor protein digestibility of sorghum porridge. Food Chem. 91, 695–703. Froeschner, J.R., Cheng, Z.J., Hancock, J.D., Behnke, K.C., 1997. Effects of sorghum genotype and processing method on production characteristics and growth performance of nursery pigs. Kansas State University Swine Day 1997, Report of Progress 795, Kansas, USA, pp. 75–78. Glennie, C.W., 1987. Physicochemical properties of sorghum starch thermally treated by different methods. Starch-Starke 39, 273–276. Gomez, M.H., Waniska, R.D., Rooney, L.W., Lusas, E.W., 1988. Extrusion-cooking of sorghum containing different amounts of amylose. J. Food Sci. 53, 1818–1822. Groesbeck, C.N., Goodband, R.D., Dritz, S.S., Tokach, M.D., Nelssen, J.L., Hastad, C.W., 2003. Particle size, mill type, and added soy oil influence flowability of ground corn. J. Anim. Sci. 81, 80. Guillou, D., Landeau, E., 2000. Feed particle size and pig nutrition. Prod. Anim. 13, 137–145. Hamaker, B.R., Kirleis, A.W., Mertz, E.T., Axtell, J.D., 1986. Effect of cooking on the protein profiles and in vitro digestibility of sorghum and maize. J. Agric. Food Chem. 34, 647–649. Hamaker, B.R., Kirleis, A.W., Butler, L.G., Axtell, J.D., Mertz, E.T., 1987. Improving the in vitro protein digestibility of sorghum with reduing agents. Proc. Natl. Acad. Sci. U.S.A. 84, 626–628. Hancock, J.D., Bramel-Cox, P.J., 1991. Use of agronomic conditions, genetics, and processing to improve utilization of sorghum grain. Kansas State University Swine Day 1991, Report of Progress 641, pp. 15–20. Hancock, J.D., Hines, R.H., Gugle, T.L., 1992. Extrusion of sorghum soybean meal and whole soybean improves growth performance and nutrient digestibility in finishing pigs. J. Anim. Sci. 70, 64. Hassan, A.B., Osman, G.A.M., Rushdi, M.A.H., Eltayeb, M.M., Diab, E.E., 2009. Effect of gamma irradiation on the nutritional quality of maize cultivars (Zea mays) and sorghum (Sorghum bicolor) grains. Pak. J. Nutr. 8, 167–171. Healy, B.J., Hancock, J.D., Bramel-Cox, P.J., Behnke, K.C., Kennedy, G.A., 1991. Optimum particle size of corn and hard and soft sorghum grain for nursery pigs and broiler chicks. Kansas State University Swine Day 1991, Report of Progress 641, Kansas, USA, pp. 66–72. Healy, B.J., Hancock, J.D., Kennedy, G.A., Bramelcox, P.J., Behnke, K.C., Hines, R.H., 1994. Optimum particle-size of corn and hard and soft sorghum for nursery pigs. J. Anim. Sci. 72, 2227–2236. Herkelman, K.L., Cromwell, G.L., Stahly, T.S., 1991. Effects of heating time and sodium metabisulfite on the nutritional-value of full-fat soybeans for chicks. J. Anim. Sci. 69, 4477–4486. Hines, R.H., Hancock, J.D., Fitzner, G.E., Weeden, T.L., Gugle, T.L., 1990. Effect of extrusion on the nutritional value of soybeans and sorghum grain in finishing pigs. Kansas State University Swine Day 1990, Report of Progress 610, Kansas, USA, pp. 76–78. Hoseney, R.C., Davis, A.B., Harbers, L.H., 1974. Pericarp and endosperm structure of sorghum grain shown by scanning electron-microscopy. Cereal Chem. 51, 552–558. Hughes, R.J., Choct, M., 1999. Chemical and physical characteristics of grains related to variability in energy and amino acid availability in poultry. Aust. J. Agr. Res. 50, 689–701. Ismail, F.A., Zahran, G.H., 2002. Studies on extrusion conditions of some cereals and legumes. Egypt J. Food Sci. 30, 59–76. Jensen, L.S., McGinnis, J., Reddy, C.V., Merrill, L.H., 1962. Observations on eating patterns and rate of food passage of birds fed pelleted and unpelleted diets. Poult. Sci. 41, 1414. Johnston, S.L., Hancock, J.D., Hines, R.H., Kennedy, G.A., Traylor, S.L., Chae, B.J., Han, I.K., 1999. Effects of expander conditioning of corn- and sorghum-based diets on pellet quality and performance in finishing pigs and lactating sows. Asian Aust. J. Anim. Sci. 12, 565–572. Kim, I.H., Hancock, J.D., Burnham, L.L., Kennedy, G.A., Hines, R.H., Nichols, D.A., 1994. Processing procedures and feeding systems for sorghum-based diets given to lactating sows. Kansas State University Swine Day 1994, Report of Progress 717, Kansas, USA, pp. 31–34. Kim, I.H., Hancock, J.D., Hines, R.H., Kim, C.S., 1998. Effects of cellulase enzymes and bacterial feed additives on the nutritional value of sorghum grain for finishing pigs. Asian Aust. J. Anim. Sci. 11, 538–544. Kim, I.H., Cao, H., Hancock, J.D., Park, J.S., Li, D.F., 2000. Effects of processing and genetics on the nutritional value of sorghum in chicks and pigs – review. Asian Aust. J. Anim. Sci. 13, 1337–1344. Kopinski, J.S., Willis, S., 1996. Recent Advances in Utilisation of Sorghum for Growing Pigs. AIAS Occasional Publication, Australian Institute of Agricultural Science, Sydney, Australia, 235–250. Lahaye, L., Riou, Y., Seve, B., 2007. The effect of grinding and pelleting of wheat and maize on amino acids true ileal digestibility and endogenous losses in growing pigs. Livest. Sci. 109, 138–140. Laurinen, P., Siljander-Rasi, H., Karhunen, J., Alaviuhkola, T., Nasi, M., Tuppi, K., 2000. Effects of different grinding methods and particle size of barley and wheat on pig performance and digestibility. Anim. Feed Sci. Technol. 83, 1–16. Leite, P., Leandro, N.S.M., Stringhini, J.H., Cafe, M.B., Gomes, N.A., Jardim, R.D., 2011. Broiler performance and digestibility of sorghum or millet diets with enzymatic complexes. Pesq. Agropec. Bras. 46, 280–286. Li, T.J., Huang, R.L., Wu, G.Y., Lin, Y.C., Jiang, Z.Y., Kong, X.F., Chu, W.Y., Zhang, Y.M., Kang, P., Hou, Z.P., Fan, M.Z., Liao, Y.P., Yin, Y.L., 2007. Growth performance and nitrogen metabolism in weaned pigs fed diets containing different sources of starch. Livest. Sci. 109, 73–76. Loar, R.E., Corzo, A., 2011. Effects of feed formulation on feed manufacturing and pellet quality characteristics of poultry diets. Worlds Poult. Sci. J. 67, 19–27.

S.Y. Liu et al. / Animal Feed Science and Technology 181 (2013) 1–14

13

Lundblad, K.K., Issa, S., Hancock, J.D., Behnke, K.C., McKinney, L.J., Alavi, S., Prestløkken, E., Fledderus, J., Sørensen, M., 2011. Effects of steam conditioning at low and high temperature, expander conditioning and extruder processing prior to pelleting on growth performance and nutrient digestibility in nursery pigs and broiler chickens. Anim. Feed Sci. Technol. 169, 208–217. Mahasukhonthachat, K., Sopade, P.A., Gidley, M.J., 2010a. Kinetics of starch digestion and functional properties of twin-screw extruded sorghum. J. Cereal Sci. 51, 392–401. Mahasukhonthachat, K., Sopade, P.A., Gidley, M.J., 2010b. Kinetics of starch digestion in sorghum as affected by particle size. J. Food Eng. 96, 18–28. McDonough, C., Anderson, B.J., Acosta-Zuleta, H., Rooney, L.W., 1998a. Effect of conditioning agents on the structure of tempered and steam-flaked sorghum. Cereal Chem. 75, 58–63. McDonough, C.M., Anderson, B.J., Rooney, L.W., 1997. Structural characteristics of steam-flaked sorghum. Cereal Chem. 74, 542–547. McDonough, C.M., Anderson, B.J., Acosta-Zuleta, H., Rooney, L.W., 1998b. Steam flaking characteristics of sorghum hybrids and lines with differing endosperm characteristics. Cereal Chem. 75, 634–638. Medel, P., Latorre, M.A., de Blas, C., Lazaro, R., Mateos, G.G., 2004. Heat processing of cereals in mash or pellet diets for young pigs. Anim. Feed Sci. Technol. 113, 127–140. Morel, P.C.H., 2005. Particle size influences the incidence of stomach ulcers but has no effect on performance in barley-based diets for pigs. In: Manipulating Pig Production X. Proceedings of the Conference of the Australasian Pig Science Association, vol. 10, Werribee, Australia, p. 147. Mosse, J., Huet, J.C., Baudet, J., 1988. The amino-acid composition of whole sorghum grain in relation to its nitrogen-content. Cereal Chem. 65, 271–277. Murphy, J.P., Harner, J.P., 1990. Feed mills for on-farm feed manufacturing. Kansas State University Swine Day 1990, Report of Progress 610, Kansas, USA, pp. 19–23. Ng’andwe, C.C., Hall, A.N., Taylor, J.R.N., 2008. Proteolysis of sorghum endosperm proteins when mashing with raw grain plus exogenous protease and potassium metabisulphite. J. inst. Brew. 114, 343–348. Ngamnikom, P., Songsermpong, S., 2011. The effects of freeze, dry, and wet grinding processes on rice flour properties and their energy consumption. J. Food Eng. 104, 632–638. Ngoc, T.T.B., Len, N.T., Ogle, B., Lindbergh, J.E., 2011. Influence of particle size and multi-enzyme supplementation of fibrous diets on total tract digestibility and performance of weaning (8–20 kg) and growing (20–40 kg) pigs. Anim. Feed Sci. Technol. 169, 86–95. Nir, I., Melcion, J.P., Picard, M., 1990. Effect of particle-size of sorghum grains on feed-intake and performance of young broilers. Poult. Sci. 69, 2177–2184. Nir, I., Hillel, R., Shefet, G., Nitsan, Z., 1994. Effect of grain particle-size on performance.2. grain texture interactions. Poult. Sci. 73, 781–791. Nir, I., Hillel, R., Ptichi, I., Shefet, G., 1995. Effect of particle-size on performance.3. grinding pelleting interactions. Poult. Sci. 74, 771–783. Oatway, L., Vasanthan, T., Helm, J.H., 2001. Phytic acid. Food Rev. Int. 17, 419–431. Oria, M.P., Hamaker, B.R., Shull, J.M., 1995. Resistance of sorghum alpha-kafirins, beta-kafirins, and gamma-kafirins to pepsin digestion. J. Agric. Food Chem. 43, 2148–2153. Osman, H.F., Theurer, B., Hale, W.H., Mehen, S.M., 1970. Influence of grain processing on in vitro enzymatic starch digestion of barley and sorg-hum grain. J. Nutr. 100, 1133–1139. Owsley, W.F., Knabe, D.A., Tanksley, T.D., 1981. Effect of sorghum particle-size on digestibility of nutrients at the terminal ileum and over the total digestivetract of growing-finishing pigs. J. Anim. Sci. 52, 557–566. Palmer, G.H., 1972. Morphology of starch granules in cereal grains and malts. J. inst. Brew. 78, 326–330. Park, J.S., Kim, I.H., Hancock, J.D., Hines, R.H., Cobb, C., Cao, H., Hong, J.W., Kwon, O.S., 2003. Effects of amylase and cellulase supplementation in sorghum-based diets for finishing pigs. Asian Aust. J. Anim. Sci. 16, 70–76. Paulis, J.W., Wall, J.S., 1979. Distribution and electrophoretic properties of alcohol-soluble proteins in normal and high-lysine sorghums. Cereal Chem. 56, 20–23. Ravindran, V., Cabahug, S., Ravindran, G., Bryden, W.L., 1999. Influence of microbial phytase on apparent ileal amino acid digestibility of feedstuffs for broilers. Poult. Sci. 78, 699–706. Ravindran, V., Cabahug, S., Ravindran, G., Selle, P.H., Bryden, W.L., 2000. Response of broiler chickens to microbial phytase supplementation as influenced by dietary phytic acid and non-phytate phosphorous levels. II. Effects on apparent metabolisable energy, nutrient digestibility and nutrient retention. Br. Poult. Sci. 41, 193–200. Ravindran, V., Selle, P.H., Ravindran, G., Morel, P.C.H., Kies, A.K., Bryden, W.L., 2001. Microbial phytase improves performance, apparent metabolizable energy, and ileal amino acid digestibility of broilers fed a lysine-deficient diet. Poult. Sci. 80, 338–344. Riaz, M.N., 2000. Extruders in Food Applications. CRC Press, Florida, ISBN: 9781566767798. Richert, B.T., Hancock, J.D., Hines, R.H., 1992. Extruded sorghum and soybeans for nursery pigs. Kansas State University Swine Day 1992, Report of Progress 667, Kansas, USA, pp. 70–73. Richert, B.T., Hancock, J.D., Hines, R.H., Gugle, T.L., 1992. Extruded corn, sorghum, and soybean meal for nursery pigs. Kansas State University Swine Day 1992, Report of Progress 667, Kansas, USA, pp. 74–78. Rodgers, N.J., Choct, M., Hetland, H., Sundby, F., Svihus, B., 2012. Extent and method of grinding of sorghum prior to inclusion in complete pelleted broiler chicken diets affects broiler gut development and performance. Anim. Feed Sci. Technol. 171, 60–67. Rom, D.L., Shull, J.M., Chandrashekar, A., Kirleis, A.W., 1992. Effects of cooking and treatment with sodium bisulfite on in vitro protein digestibility and microstructure of sorghum flour. Cereal Chem. 69, 178–181. Rooney, L.W., Pflugfelder, R.L., 1986. Factors affecting starch digestibility with special emphasis on sorghum and corn. J. Anim. Sci. 63, 1607–1623. Selle, P.H., Walker, A.R., Bryden, W.L., 2003. Total and phytate-phosphorus contents and phytase activity of Australian-sourced feed ingredients for pigs and poultry. Aust. J. Exp. Agric. 43, 475–479. Selle, P.H., Ravindran, V., 2008. Phytate-degrading enzymes in pig nutrition. Livest. Sci. 113, 99–122. Selle, P.H., Cadogan, D.J., Li, X., Bryden, W.L., 2010a. Implications of sorghum in broiler chicken nutrition. Anim. Feed Sci. Technol. 156, 57–74. Selle, P.H., Gill, R.J., Downing, J.A., 2010b. The vulnerability of sorghum to ‘moist-heat’. Proc. Aust. Poult. Sci. Symp. 21, 68–71. Selle, P.H., 2011. The protein quality of sorghum. Proc. Aust. Poult. Sci. Symp. 22, 147–160. Selle, P.H., Liu, S.Y., Cai, J., Cowieson, A.J., 2012. Steam-pelleting and feed form of broiler diets based on three coarsely ground sorghums influences growth performance, nutrient utilisation, starch and nitrogen digestibility. Anim. Prod. Sci. 52, 842–852. Selle, P.H., Liu, S.Y., Cai, J., Cowieson, A.J., in press. Steam-pelleting temperatures, grain variety, feed form and protease supplementation of mediumly-ground, sorghum-based broiler diets. I. Influence on growth performance, relative gizzard weights, nutrient utilisation, starch and nitrogen digestibility. Anim. Prod. Sci., AN12363. Selle, P. H., Liu, S. Y., Cai, J., Cowieson, A.J., in preparation. Steam-pelleting temperatures and grain variety of finely-ground, sorghum-based broiler diets. I. Influence on growth performance, relative gizzard weights, nutrient utilisation, starch and nitrogen digestibility. Anim. Prod. Sci. Shawrang, P., Sadeghi, A.A., Behgar, M., Zareshahi, H., Shahhoseini, G., 2011. Study of chemical compositions, anti-nutritional contents and digestibility of electron beam irradiated sorghum grains. Food Chem. 125, 376–379. Siddhuraju, P., Makkar, H.P.S., Becker, K., 2002. The effect of ionising radiation on antinutritional factors and the nutritional value of plant materials with reference to human and animal food. Food Chem. 78, 187–205. Speetjens, J., 2002. Steam flaked grain. World Grain 48, 26–28. Svihus, B., Klovstad, K.H., Perez, V., Zimonja, O., Sahlstrom, S., Schuller, R.B., Jeksrud, W.K., Prestlokken, E., 2004. Physical and nutritional effects of pelleting of broiler chicken diets made from wheat ground to different coarsenesses by the use of roller mill and hammer mill. Anim. Feed Sci. Technol. 117, 281–293. Svihus, B., 2011. The gizzard: function, influence of diet structure and effects on nutrient availability. Worlds Poult. Sci. J. 67, 207–223. Svihus, B., Zimonja, O., 2011. Chemical alterations with nutritional consequences due to pelleting animal feeds: a review. Anim. Prod. Sci. 51, 590–596.

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Swick, R.A., 2011. Global feed supply and demand. In: Recent Advances in Animal Nutrition Australia. University of New England, Armidale, Australia, 18, 1–8. Taylor, J.R., Dewar, J., 2001. Developments in sorghum food technologies. Adv. Food Nutr. Res. 43, 217–264. Taylor, J.R.N., 2005. Non-starch polysaccharides, protein and starch: form function and feed – highlight on sorghum. Proc. Aust. Poult. Sci. Symp. 17, 9–16. Thacker, P.A., 2006. Performance of growing-finishing pigs fed diets containing normal or low lignin-high fat oat processed using a hammer mill or roller mill. J. Anim. Vet. Adv. 5, 662–669. Thomas, M., van der Poel, A.F.B., 1996. Physical quality of pelleted animal feed.1. Criteria for pellet quality. Anim. Feed Sci. Technol. 61, 89–112. Thomas, M., vanZuilichem, D.J., vanderPoel, A.F.B., 1997. Physical quality of pelleted animal feed.2. Contribution of processes and its conditions. Anim. Feed Sci. Technol. 64, 173–192. Thomas, M., van Vliet, T., van der Poel, A.F.B., 1998. Physical quality of pelleted animal feed 3. Contribution of feedstuff components. Anim. Feed Sci. Technol. 70, 59–78. Traylor, S.L., Hancock, J.D., Behnke, K.C., Hines, R.H., Lee, D.J., Johnston, S.L., Sorrell, P., 1998. Expander processing conditions affect nutrient digestibility in finishing pigs fed corn-, sorghum-, wheat-, and wheat midds-based diets. Kansas State University Swine Day 1998, Report of Progress 819, Kansas, USA, pp. 228–232. Traylor, S.L., Behnke, K.C., Hancock, J.D., Hines, R.H., Johnston, S.L., Chae, B.J., Han, I.K., 1999. Effects of expander operating conditions on nutrient digestibility in finishing pigs. Asian Aust. J. Anim. Sci. 12, 400–410. Vanschoubroek, F., Coucke, L., Van Spaendonck, R., 1971. The quantitative effect of pelleting feed on the performance of piglets and fattening pigs. Nutr. Abstr. Rev. 41, 1–9. Wang, H., Faris, R.J., Wang, T., Spurlock, M.E., Gabler, N., 2009. Increased in vitro and in vivo digestibility of soy proteins by chemical modification of disulfide bonds. J. Am. Oil Chem. Soc. 86, 1093–1099. Wondra, K.J., Hancock, J.D., Behnke, K.C., Hines, R.H., Stark, C.R., 1993. Effects of hammermills and roller mills on growth performance, nutrient digestibility, and stomach morphology in finishing pigs. Kansas State University Swine Day 1993, Report of Progress 695, Kansas, USA, pp. 140–143. Wu, Y., Lin, Q.L., Chen, Z.X., Xiao, H.X., 2011. The interaction between tea polyphenols and rice starch during gelatinization. Food Sci. Technol. Int. 17, 569–577. Yin, F., Zhang, Z., Huang, J., Yin, Y., 2010. Digestion rate of dietary starch affects systemic circulation of amino acids in weaned pigs. Br. J. Nutr. 103, 1404–1412. Yoon, J.H., Thompson, L.U., Jenkins, D.J.A., 1983. The effect of phytic acid on in vitro rate of starch digestibility and blood–glucose response. Am. J. Clin. Nutr. 38, 835–842. Zamora, V., Figueroa, J.L., Reyna, L., Cordero, J.L., Sanchez-Torres, M.T., Martinez, M., 2011. Growth performance, carcass characteristics and plasma urea nitrogen concentration of nursery pigs fed low-protein diets supplemented with glucomannans or protease. J. Appl. Anim. Res. 39, 53–56. Zang, J.J., Piao, X.S., Huang, D.S., Wang, J.J., Ma, X., Ma, Y.X., 2009. Effects of feed particle size and feed form on growth performance, nutrient metabolizability and intestinal morphology in broiler chickens. Asian Aust. J. Anim. Sci. 22, 107–112. Zhang, G.Y., Hamaker, B.R., 1999. SDS-sulfite increases enzymatic hydrolysis of native sorghum starches. Starch-Starke 51, 21–25. Zhuge, Q., Yan, Z., Klopfenstein, C.F., Behnke, K.C., 1990. Nutritional value of sorghum grain depends on processing. Feedstuffs 62 (18), 55.