Feed potential of small cereal grains in poultry production in semi-arid areas: A review

Abstract

A review of available literature shows that small grains are widely used across the globe for human and livestock feed. Sustainable chicken production can significantly contribute to dietary needs and resolve food insecurity in the smallholder sector. It is estimated that local chickens constitute 80% of poultry production in sub-Saharan countries, 28% in America, 15% in Europe, and 60% in Asia. The success of production of small grains such as sorghum (Sorghum bicolor), finger millet (Eleusine coracana), and pearl millet (Pennisetum glaucum) has been attributed to their drought resilience and adaptability to climate change. Sorghum, in particular, is the fifth most important global cereal crop after maize. Chicken producers use local small grains as major components for inclusion in poultry diets in order to decrease the cost of production and increase the profits. The potential use of small grain as a major source of native chicken is attributed to their richness in the composition of diverse nutrients. Small grains contain diverse amino acids and energy levels. Millets, in particular, are high in minerals such as calcium, iron, and pyridoxine (vitamin B₆). Sorghum has metabolizable energy, calcium, and phosphorus for supporting chicken growth and production. Studies reviewed on on the performance of broilers on varying degrees of small grain inclusion have been made using broiler chickens fed on varying degrees of small grain inclusion in various diets. Studies showed that a diet containing 12.34 MJ ME/kg dry matter (DM) to 12.91 MJ ME/kg DM is recommended for growth performance during the starter and grower phases of Venda spotted breed chicks. Furthermore, indigenous naked neck chickens aged between 1 and 6 weeks were reported to require a diet containing an energy level of 14 MJ ME/kg DM for optimal growth and carcass quality. Chicken feed formulation through least cost feed formulation recommended small grain inclusion at 13.9 ME (MJ/kg) to obtain diets with 11.8% crude protein. Physical (such as grain germination, soaking, and grinding) and chemical (such as fermentation, urea treatment, and use of alkali substance) strategies can enhance the utilization of small grains by chickens. There is a greater scope for improving small grain utilization by chickens by establishing convenient and accurate levels of inclusion in the diets and adding their value through biofortification interventions.

Keywords:

• chicken feed
• crude protein
• Gallus domesticus
• small grains
• total digestible nutrients

PUBLIC INTEREST STATEMENT

“Small grains,” normally called traditional grains, such as sorghum, pearl millet, and finger millet, are widely grown by low-resource communal farmers to improve resilience in food security. They play vital multipurpose functions of providing nutrition to humans and are basic sources of chicken feed. Due to their tolerance to harsh climatic conditions, they often thrive well in marginal rainfall areas and soils with poor fertility. Moreover, they are rich in essential nutrients such as carbohydrates, zinc, calcium, iron, and phosphorus. This makes them a good source of chicken feed for supporting growth and production. This review article seeks to chronicle nutritional composition, feeding standards, and economic impact of using small grains as key ingredients for chicken feed. This study comes at a time when the global crop production dynamics is shifting towards promotion of the production of climate- and nutrition-smart crops for provision of livestock feed.

1. Introduction

Traditional grains, also known as small grains, are cereals such as pearl millet [(Pennisetum glaucum (L)], finger millet (Eleusine coracana), and sorghum [Sorghum bicolor (L) Moench] widely grown by smallholder farmers mainly in marginal rainfall regions. The production trends of small grains and in particular sorghum have been increasing by approximately 14% and 40% at World and Africa levels, respectively, over the years (Table 1). Small grains production has a significant presence in sub-Saharan countries such as Nigeria, Sudan, and Tanzania (Clara et al., 2019). In Asia, the major growing countries are China, Pakistan, India, South Korea, and Thailand (Bhagavatula et al., 2013). Small grains are also grown in United States, Mexico, Argentina, Peru, Honduras, Brazil, Argentina, and Venezuela as well as in the European countries such as France, Italy, Spain, Romania, and Albania. More than 90% of total global sorghum harvested areas are in Africa and Asia (FAO, 2021), with Africa accounting for 61% of the area and 41% of the production and Asia accounting for one-quarter of global production (Table 1). Zimbabwe’s yearly small grain production stands at 347, 9 metric tonnes (Ministry of Lands, Agriculture, Fisheries, Water and Rural Settlement, 2021).

Table 1. Global sorghum production by tonnage (in millions) per region at five time intervals

Region	2000	2005	2010	2013	2015
World	55.8	59.6	60	61.3	63.5
Africa	18.4	24.8	24.7	25/7	24.8
North Central America	18.0	15.7	15.9	16.4	17.2
South America	4.9	5.3	6.2	6.8	5.5
Asia	11.3	18.2	10.5	8.7	8.0
Europe	0.7	0.5	0.7	1.1	0.9
Oceania incl. Australia	2.1	2.0	1.6	2.2	2.1

Source: USDA (2016).

Small grains are hardy and resilient to harsh climatic conditions (Hadebe et al., 2017; International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), 2015) and are adaptable to a wide range of environments in semi-arid areas. Sorghum, in particular, is the fifth most important global cereal crop after maize, rice, wheat, and barley (FAOSTAT, 2021). The most grown millet varieties are forage-grain types and hybrids suitable for both human consumption and stock feed. Red sorghum, albeit its high flavonoids, is preferred as it is less susceptible to bird damage. High production of sorghum and finger millet in smallholder farming communities indicates the importance of small grains in rural livelihoods and food security (Muchineripi, 2014; FAO, ICRISAT, 2008; FAO, 2021). In the present context of global climate change, small grains in sub-Saharan Africa and Asia stand as the most resilient semi-arid tropical crop due to their adaptability to high temperatures, water scarcity, saline conditions, and erratic rainfall.

2. Use of small grains to enhance the chicken livelihood asset

The ability of domesticated chickens (Gallus domesticus) to adapt to a wide range of areas, short production cycle, and efficient utilization of limited space makes them a preferred farming enterprise for developed and developing countries. Sustainable native chicken production can significantly contribute to dietary needs and resolve food insecurity in the smallholder sector. It is estimated that local (native) chickens constitute 80% of poultry production in sub-Saharan countries (Desha et al., 2016), 28% in America, 15% in Europe, and 60% in Asia. Many farmers depend on native chicken production for their livelihood, especially as a source of protein (Bidi et al., 2019); however, scarcity and high cost of feed are the major constraints. Louw (2011) postulated that 70–80% of the variable costs of chicken production are feed related. Maize grain is the major ingredient for chicken feeds (Hafeni, 2013). Maize grain, however, faces stiff competition from food for human beings, biofuels, and beverages. This ultimately reduces the ability of smallholder farmers to supplement their livestock using maize. Hence, there is a need to find an alternative energy base for chicken feed. Accordingly, maize is more expensive as feed source for livestock which reduces its use as a supplement. The adverse effect of climate change has resulted in the focus of more resilient, hardy, and nutritious small grains than maize for chicken feed. Their drought-tolerant nature enables small grains to thrive in marginal areas, making their production an appropriate strategy in responding to climate change (Muzerengi & Tirivangasi, 2019). Small scale farmers have therefore relied on pearl millet, finger millet, and sorghum as prime feed for chicken in marginal areas.

Chicken producers can use local small grains as major components for inclusion in chicken diets in order to decrease the cost of production and bring in lowly resourced farmers in the mainstream of chicken production value chain (Hafeni, 2013). Several studies have shown interest in using small grains as alternatives to maize (Masenya et al., 2021; Ravindran, 2013; Singh et al., 2012). There is a considerable opportunity to increase the use of these feedstuffs in native chicken diets without sacrificing animal performance or product quality (Afsharmanesh et al., 2016). Native chickens typically require their diet to contain a large percentage of cereal grains to provide protein and energy for optimal performance. Small grains are concentrated sources of readily digestible polysaccharides carbohydrates (like starch) but also contain variable levels of low-digestible carbohydrates (like cellulose). The volatility and changes in the availability of maize have spurred interest in the use of small grains as alternative ingredients for chicken feed (Banton-Alavo et al., 2015). With the escalation of poultry feed prices revealed in this review, and the real prospect of declining availability of grains for chicken, it is opportune that research efforts be directed to finding alternatives to wheat/maize-based diets. In view of these advantages found in small grains, this discourse seeks to dig deeper and contribute to understanding of the potential of small grains as an option to native chicken feeds by smallholder farmers in Asia and sub-Saharan Africa.

3. Nutritional value of small grains

Cereal grains are concentrated sources of readily digestible carbohydrates (like starch) and also contain variable levels of low-digestible carbohydrates (like cellulose). Finger millet has relatively higher carbohydrate content than pearl millet and sorghum. Small grains contain diverse amino acids (lysine, tryptophan, methionine, valine, etc.) most of which are essential. Millets are high in minerals and contain folate, thiamin, niacin, riboflavin, pantothenic acid, and pyridoxine (vitamin B₆) (Taylor, 2017). In contrast with maize, most small grains have on average 2,664 kcal/kg ME compared to 2,883 kcal/kg for maize but with relatively high levels of amino acids such as lysine (3.41 g/kg dry matter (DM)), tryptophan (3.15 g/kg DM), leucine (11.53 g/kg DM), and methionine (2.66 g/kg DM) content (Kumarh et al., 2015). The indispensable amino acids contained in small grains are important for chicken growth, production, and immunity. It is important that diets given to chickens meet these production requirements. The significance of small grains as chicken feed is essentially dependent upon the nature and the concentration of different carbohydrate and amino acids fractions found in the grain and the animal’s physiological ability to utilize those fractions. Protein requirement in chicken is a function of the amino acid profile, not just the crude protein (CP) content, as birds cannot synthesize essential amino acids (Bidi et al., 2019). Feed rations formulated for chicken diets should be rich in essential amino acids to stimulate growth and reproduction. Unfortunately, this cannot be true for maize-based diets since lysine is the major limiting amino acid. Evaluation of the nutritional value of small grains has been done over years with diverse outcomes. However, due to hybridization, biofortification, and genetic engineering, grain composition for sorghum, finger millet, and pearl millets continues to change drastically. Generally, most small grains approximately contain 89–90% DM, 5.44–15% CP, 2.8% ether extract, 1.5–1.7% ash, 2.1–2.3% crude fibre (CF), and 71.7–72.3% nitrogen-free extract on an as normally fed to animals (Ebadi et al., 2005; Taylor, 2017). Recent changes in genetic composition (probably as a result of hybridization) of small grain varieties have prompted many researchers to review their nutritional value (Table 2).

Table 2. Nutritional composition of small grain (pearl millet, finger millet and sorghum)

Nutrient	Grain type
	Sorghum	Pearl millet	Finger millet
Protein (g)	10.4	11.8	7.7
Fat (g)	3.1	4.8	1.5
CF (g)	2.0	2.3	3.8
Carbohydrates (g)	70.7	67.0	72.6
Energy (kcal)	329	363	336
Iron (g)	5.4	11.0	3.9
Mineral matter (g)	1.6	2.3	2.7
Ca (mg)	25	42	344
P (mg)	222	296	283

Source: Muui (2014).

Finger millet has 81.5% carbohydrates, 9.8% protein content, 4.3% CF, and 2.7% minerals. Its protein contains more lysine, threonine, and valine than pearl millet. In addition, Lauriault et al. (2021) reported average values for neutral detergent fibre (NDF) and acid detergent fibre (ADF) to be 140 g/kg DM and 62 g/kg DM, respectively, for pearl millet types. Balasubramanian et al. (2014), Moreau et al. (2016), and Patekar et al. (2017) have reported fat levels of 1.8–4.3% in sorghum and finger millet, respectively. Different factors contribute to these variations, with soil type being the main determinant in mineral content (Wafula et al., 2018). According to Anitha et al. (2019) and Food and Agriculture Organization, millets can be an important source of essential nutrients such as amino acids, mineral, and trace elements. However, there are wide variations evident in the chemical composition of pearl and finger millets (Mallet & Plessis, 2001; National Academy Press Washington DC, 1994). Ramashiaa et al. (2018) reported that pearl millet contains higher energy compared to other cereal grains like rice and wheat, and it is an important source of thiamine, niacin, and riboflavin (Amato & Forrester, 1995; Mustafa et al., 2008; Taylor, 2004). Moreover, the content of minerals such as calcium, iron, and phosphorus in pearl millet compares well to those found in other cereals (Adeola & Orban, 1995). Furthermore, Ali et al. (2003) reported nutritional value of pearl millet of about 92.5% DM, 2.1% ash, 2.8% CF, 7.8% crude fat, 13.6% CP, and 63.2% starch. In addition, the starch content of millet was recorded by Krishnakumari and Thayumanavan (1995) to be in the range of 64–79%. Studies by Hassan et al. (2014) have shown that pearl millet contains 11.6% protein which is higher than barley (11%), maize (10.4%), and sorghum (2.5%). The CP for millets is 8–60% higher than that of maize. In contrast, finger millet has 11.8% protein. The presence of protein in millets defines its richness in amino acids (Table 3). In particular, finger millet is comparatively balanced in essential amino acid levels such as leucine, phenylalanine, threonine, and valine (Ravindran, 1991). This gives small grains a relatively better advantage than maize for its inclusion in chicken diets.

Table 3. Amino acid profile of pearl and finger millets

Amino acids (g/100 g)	Pearl millet	Finger millet
Essential amino acids
Isoleucine	5.1	4.3
Leucine	14.1	10.8
Lysine	0.5	2.2
Methionine	1.0	2.9
Phenylalanine	7.6	6.0
Threonine	3.3	4.3
Valine	4.2	6.3
Histidine	1.7	NA
Non-essential amino acids
Alanine	8.1	6.1
Arginine	0.9	3.4
Aspartic acid	6.2	5.7
Glutamic acid	22.8	23.4
Cystine	0.8	NA
Proline	8.2	9.9

Source: Hassan et al. (2021).

Nyoni et al. (2020) have noted the chemical composition of small grain diversity as a subject to different genotypic diversity. Based on their studies, white-grained sorghum varieties are more degradable than red tannin containing types. However, no consensus has been recommended for the level of substitution of these ingredients in commercial meat chicken breeds (broiler) feeds (Banton-Alavo et al., 2015; Kalinda & Tanganyika, 2017; Tandiang et al., 2014). Metabolizable energy (ME) and protein composition in sorghum and millet grains are essential in supporting native chicken growth and production. Results from poultry feeding experiments in the USA using pearl millet with maize or sorghum indicate that pearl millet is at least equivalent to maize and generally superior to sorghum and finger millet in protein content and quality, protein efficiency ratio values, and ME levels (Singh & Perez-Maldonado, 2010). Both the gross energy and ME values of pearl millet tend to be higher than those of maize (Banton-Alavo et al., 2015). The absence of condensed polyphenols in pearl millet makes it more efficiently digestible than sorghum and finger millet. Chicken performance is enhanced if chickens are fed with feed stuffs rich in protein, vitamins, and energy. None waxy sorghum has 60–70% starch that comprises 70% amylopectin and 30% amylose. The dominant protein (42.4–57.6%) in sorghum grain is kafrin (Salinas et al., 2006). In cereal-based diets, more than 30% of CP is contributed by proteins, meaning that the quantity and nutritional quality of the protein play significant roles in chicken diets (Khalil et al., 2021). Pearl millet contains on average 6% of essential amino acids whereas finger millet has 3.2%. In particular, glutamic acid is 22.8% and 23.2% for pearl millet and finger millet, respectively (Amadou et al., 2013).

4. General ration formulation for chicken production

Livestock, in general, require a balanced diet that will supply the appropriate amount of proportions of nutrients (protein and energy) needed for different physiological metabolisms (Table 4). Chicken growth and production, in particular, are dependent on diets which have adequate total digestible nutrients (TDN). Ration formulation is therefore designed to compute diets that are able to meet the nutrient requirements for chickens in the best way in order to maximize productivity (Ncobela & Chimonyo, 2015). The technique of ration formulation involves mixing different nutrient ingredients together to produce a balanced diet. The idea is to ensure that feed rations given to chickens are not deficient of macro- and micro-nutrients such as energy, proteins, vitamins, phosphorus, iron, and calcium for growth and reproduction (Patil et al., 2016). Normally, computations of feeding standards for chicken utilize models that balance for CP, TDN, phosphorus, and calcium. The objective being provision of necessary and adequate nutrients for maintenance and production at minimum cost. For successful chicken ration formulation, essential information such as type and quantity of feed resources available, concentration of TDN and CP in each feed material type, price of the feed resource, nutrient requirements for production, reproduction, and growth, normal maximum intake levels of the animal in question, and desirable production levels are considered (Samuel Olugbenga et al., 2015). Ration formulation for native chicken production should take into cognizance requirements of dietary nutrient for each age. The general requirements recognize more CP levels for young birds.

Table 4. Protein and energy for improved productivity of native chickens

Nutrient level	Improved production parameter	Chicken age (weeks)	Research
Protein
18–19%	Improved growth and productivity	1–6	Mbajiorgu (2010)
18%	Improved weight gain	1–13	Kalinda and Tanganyika (2017)
15.53%	Improved carcass weight and DOP	14	Charles et al. (2017)
Energy
14 MJ ME/kg	Improved growth and productivity	1–6	Mbajiorgu (2010)
12.91 MJ ME/kg	Improved feed intake and FCR	8–13	Alabi et al. (2013)
2,750 kcal/kgME	Improved growth performance	9–20	Mohammad and Sohail (2008)

MJ—Mega Joules, ME—Metabolizable Energy, DOP—Dressing out Percentage, FCR—Food Conversion Efficiency.

5. Relevance of good chicken rations and feeding standards

The objectives in chicken production are to maximize production and efficient utilization of feed resources. The poor productivity of native chickens is often attributed to poor quality and quantity of feeds and furthermore compounded by poor management practices in smallholder farmers (Ayssiwede et al., 2011; Mapiye et al., 2008). Poor-quality feeds and incorrect mixing of dietary nutrient levels such as energy and protein can potentially cause nutritional stress and health concerns and reduce productive potential of chickens. Studies by Bregendahl and Zimmerman (2002) have recorded below-minimal slaughter weights of 1.5 kg at 6 weeks for Hubbard broilers, and high mortality and low giblets weight by using finishing diets containing 14.5% CP. Diets containing low calcium and phosphorus have resulted in poor egg shell formation and improperly developed egg yolk in Hyaline layers (Leeson et al., 2008). Tang et al. (2017) and Mohammad and Sohail (2008) posit that performance and productivity of broiler chickens can be improved by manipulating their diets especially for energy and protein. Studies by Mbajiorgu (2010), Kalinda and Tanganyika (2017), and Alabi et al. (2013) and Jha and Mishra (2021) reported that 18–19% CP content levels showed improved growth and productivity in indigenous Venda, Naked Neck, and Barred Rock chickens (Table 4). The chicken feeding program affects the profitability more than any other single factor. Chicken feeding regimes and standards are premised on the assessment of nutritive value of feed stuff, description of nutrient requirements and diagnosis, and prognosis and prevention of nutritional disorders and metabolism (Sebastian et al., 2008). In particular, chicken feed is composed of 60–65% energy-giving materials, 30–35% protein, and 2–8% minerals (Samuel Olugbenga et al., 2015). The small grains have the potential to provide these energy levels. Whole grain feed intake was reported by Esatu et al. (2022) to be 15–55 g/day for chicks and 60–95 g/day for growers and mature birds. Feed intake is affected by the level of energy available in the diet, which results in chickens consuming a lot of food to meet their energy requirements. Dietary levels of 130 g/kg protein are adequate for 14–21-day growth phase. Mbajiorgu (2010) reported that indigenous chickens aged between 1 and 6 weeks require a diet containing an energy level of 14 MJ ME/kg DM for optimal growth. Studies by Alabi et al. (2013) showed that a diet containing 12.34 MJ ME/kg DM to 12.91 MJ ME/kg DM is recommended for growth performance during the starter and grower phases of Venda chicks. Yang et al. (2022) reported improved gizzard development of broiler chickens fed with whole grain of sorghum and millet. Any standard rations must have adequate nutrient levels of energy (13.7 MJ ME/kg), proteins (21% CP), fats, and vitamins (1,500 IU). The major sources of energy for smallholder farmers have been millet, sorghum, and maize. Minerals and vitamins are normally incorporated in the diets as pre-mixes. Both Esatu et al. (2022) and Mbajiorgu (2010) reported that native indigenous chickens of various ecotype survive fluctuations in feed availability with insignificant impact on their production.

6. Chicken feed formulation

Energy is very critical in chicken feed, and in fact, the more the energy loaded in the ration, the less feed the birds would consume. Suitable quantities of fat may be added to increase dietary energy concentrations and palatability. Precisely, chickens lack physiological ability to synthesize amino acids and require feed rations with an abundant digestible crude protein (DCP). Under commercial production systems, deficiency of this amino acid is offset by the addition of synthetic amino acids or the addition of conventional protein sources such as soybean or fishmeal (Bidi et al., 2019). Chickens need feed ration that are high in CP to improve their growth rate, feather development, and carcass weight. The principles of chicken feed formulation should take into account the provision of essential nutrients at specific stages of growth, the efficiency of feed digestion, and gut motility (Gunasekar, 2007). Least-cost formulation of diets optimizes the combination of feed ingredients that supplies the required levels of nutrients at least cost (Rossi, 2004). The concept of feeding monogastric based on locally available feed resources requires the understanding of the relative roles and nutrient needs of the two-compartment system represented by pre-proventriculus digestion and post-duodenal enzymatic and microbial digestion (Xiao et al., 2021). While digestibility, nutrient retention, and gut fill are major determinants of the choice of feed for chicken, it should be noted that diet formulation and feeding standards hinge on maize as the main source of energy (Hafeni etal 2013). Maize has 13.9 ME (MJ/kg) vs 12.6 ME (MJ/kg) for sorghum but is low in lysine and tryptophan (Dei, 2015). Conversely, millets including finger millet have 9.08ME MJ/kg (Hassan et al., 2021). Therefore, rations made from small grains such as sorghum and millets should offer a richer CP since grain DCP for protein is 11.8% compared to 9.4% for maize (Rurinda et al., 2014). This advantage makes traditional grains more suitable for chicken feed at early weeks of life and during egg production. Studies by Iji et al. (2018)) and Okitoi et al. (2009) have shown significant and positive effects of growth on chickens supplemented with feed containing high CP. It then makes sense that smallholder farmers should utilize the presence of high amino acid profiles on small grain as feed stuff and feed ration for chickens since its CP profile is higher compared to that of maize.

7. Feed formulation models

Mathematical models have been exploited in animal feed formulation to identify the set and quality of nutrient ingredients to maximize animal weight gain and yields. Feed formulation models such as Pearson square method (Sebastian et al., 2008), linear programming and nonlinear programming (Mpofu et al., 2006; Mudiwa et al., 2021), trial and error method (Gunasekar, 2007), and least cost formulation software (Rossi, 2004; Thomson & Nolan, 2001) have been computed. The objective being the maximization of live bird profitability, minimizing feed cost per kg live weight, and optimizing nutrient diet required of chickens at minimal cost (Samuel Olugbenga et al., 2015; Thirumalaisamy et al., 2016). Chicken feeds are currently formulated based on the quantity of metabolizable energy (ME) within each constituent ingredient. ME is the energy that is digested, absorbed, and not excreted in urine (Noblet at al., 2022). Linear programming models have been adopted by using the most popular feedstuffs used in ration formulation for local farms and broiler feed factories which include yellow maize, soybean, fish meal, premix, vitamin/mineral, salt, lysine, oyster shell, bone meal, methionine, wheat bran, sorghum, and calcium di-phosphate (Priyaranjan et al., 2020). Studies by Banerjee (2010), (Table 5) have shown specific nutrient requirements for broiler starter and finisher diets. As such, the model designed and tested for starter and finisher ration is shown (Table 5).

Table 5. Dietary nutrient requirements for broiler starter and finisher diets

	Starter diets		Finisher diets
Nutrient requirements	Max value	Min value	Max value	Min value
ME (kcal/kg)	3.500	2.800	4.000	3.050
Protein (%)	40	15	22	13
Fat (%)	2.5	1.0	6.0	1.0
Calcium (%)	1.5	0.5	1.0	0.3
Phosphorus (%)	0.7	0.1	0.6	0.1
Lysine (%)	2.5	0.5	2.0	0.5
Methionine (%)	0.7	0.2	0.7	0.2
Sodium (%)	0.3	0.02	0.3	0.02
Chloride (%)	0.5	0.05	0.5	0.05
Viatmin A (IU/kg)	13.500	-	10.000	-
Vitamin D3 (IU/kg)	4.950	-	3.900	-
Vitamin E (IU/kg)	73	-	48	-

Source: Banerjee (2010).

The resolved feed ingredients for starter and finisher rations are designed to concentrate high levels of essential amino acids to increase growth rate and maturity in hybrid chickens (Sebastian et al., 2008). The ration formulated to provide these nutrients consists of 31.27 kg maize or 28.65 kg sorghum, 30.52 kg soybean, 29.03 kg wheat bran, 8.36 kg oyster shell, 0.16 kg lysine, 0.06 kg methionine, 0.3 kg salt, and 0.3 kg premix mix (Samuel Olugbenga et al., 2015). The energy provision for millets has been estimated to be 70% of maize (it is apparent from the model that if energy base is from sorghum, the energy level is higher by ±2.62 kg (31.27 kg vs 28.65 kg)), further asserting the richness of sorghum as a carbohydrate feed. In addition, the proposed optimal ration formulation results produced by linear programming model in the case of the finisher ration consist of 25.09 kg maize (yellow), 24.16 kg soybean, 39.95 kg wheat bran, 23.1 kg sorghum, 9.97 kg oyster shell, 0.18 kg lysine, 0.04 kg methionine, 0.3 kg salt, and 0.3 kg premix mix, which is the proposed optimal ration for finisher broilers according to the local feedstuffs availability. This ration provides for 21% CP (Oladokun & Johnson, 2012; Rossi, 2004).

8. Development and field evaluation of small grains as chicken feed ration

Inadequate nutrition is one of the major constraints limiting livestock production in developing countries. Chicken require balanced diets for their survival, growth, reproduction, and production (Zaefarian et al., 2022). The development of cost-effective and sustainable feed which is based on locally available feed resources is necessary for sustainable native chicken production (IAEA, 2000). There are clear agronomic practices that farmers should follow to develop a quality crop with adequate carbohydrates for chicken feed (Mengesitu et al., 2018). This is because energy plays a significant role in feed intake and nutrient retention, hence affects production. The value of small grains as chicken feed is essentially dependent upon the nature and the concentration of different carbohydrate and amino acid fractions found in the grain and the animal’s ability to utilize those fractions. The ability to improve the nutritional quality (defined as the content of essential amino acids) of small grain protein by classical plant breeding is limited by the low level of variation in the gene pool available for crossing (Kennedy et al., 2016). This calls for genetic engineering with wild ecotypes (Zhao et al., 2002) to improve nutrition, yields, and pest and diseases resistance Wide variability has been observed in the essential amino acid composition of sorghum protein and millets, probably because the crops are grown under diverse agro-climatic conditions which affect the grain composition (FAO, 2013). The concentration of digestible nutrients is dependent on the genotype, soil fertility status, crop management, and seed colouration. The cellulose and endosperm size define the structural carbohydrates contained in small grains and hence their inherent energy reservoirs. It has been observed that the application of nitrogen- and phosphorus-based inorganic fertilizers such as diammonium phosphate and calcium ammonium nitrate increases sorghum vigor, maturation, and chemical composition (Rashid et al., 2008). This in turn improves the quality of the crop in terms of its nitrogen and carbohydrate content (Mativavarira et al., 2013). On farm small, grain development protocols should enhance the crop’s propensity to ensure a full physiological maturity especially at the soft-to-hard dough stages. At these stages, maximum grain filling is essential to ensure a complete carbohydrate synthesis process. Feedstuffs that are ingested by chickens do not undergo microbial fermentation prior to the small intestine where feed is enzymatically digested. Thus, chickens are fundamentally less able to achieve peak levels of muscle growth, egg production, and reproduction when fed diets rich in fermentable carbohydrates or nonstarch polysaccharides (Reaves, 2017). High NDF and ADF that measure high CF and hemicelluloses are the signs of poor grain quality attributed to poor agronomic field practices and crop development throughout its growth cycle. Non-starch polysaccharides are considered antinutritional compounds that should be minimized in chicken diets.

Biofortification of sorghum grain through genetic strategies is a powerful approach for changing the nutrient balance in the native chicken diet on a large scale. In the context of developing fortified foods for low-income consumers, different studies have revealed a narrow range of genetic diversity for sorghum grain micronutrient contents, with Fe and Zn contents from the wild (Abdelhalim et al ., 2019; Ashok Kuma et al., 2015). The narrow genetic diversity for grain minerals in modern cultivars could be attributed to eroded genetic diversity by domestication and breeding processes. Therefore, efforts must be devoted to identifying valuable alleles which are deficient in the wild ancestors of crop plants and to reintroduce them into cultivated crops (Tanksley & McCouch, 1997). This is meant to improve the grain quality to sustain high level of ME provision to chickens. Biofortification of millets enhances the accumulation of nutrients (especially essential amino acids lysine) and reduces the antinutrients to increase the bioavailability of minerals such as iron, calcium, and magnesium (Tumbare & Maphosa, 2023; Vinoth & Ravindhran, 2017). These genetically modified sorghum and millets have both improved lysine content and protein digestibility due to the suppression of synthesis of specific kafirin storage proteins. Nutrient degradability and digestibility in chickens are greatly affected by the presence of polyphenols and tannins. Biofortified waxy grain sorghum and millets (0% amylose and 100% amylopectin) are easily digestible and recommended for inclusion in chicken diets. Zaefarian et al. (2022) reported an inverse correlation of total protein and kafrin among diverse sorghum ecotypes. The lower concentration of kafrin affects the release of starch and conversely improves grain digestibility.

9. Enhancement of small grain usability in native chicken diets

Adequate feed intake is crucial to ensure the sufficient nutrient supply for animals. Appropriate feeding will ensure that chickens reach slaughter weights at the correct time. Tannin-containing sorghums can be toxic and impair feed efficiency in chickens (Qianqian et al., 2018). Tannins encapsulate nutrients and render them inaccessible by digestible enzymes (Zaefarian et al., 2022). Tannins are usually subdivided into hydrolyzable tannins and proanthocyanidins or condensed tannins (Sugiharto et al., 2019). Polyphenols can affect the utilization of sorghum protein and metabolizable energy for poultry, and this has caused sorghum to suffer from misconceptions and concerns about these toxic compounds (Lasisi et al. (2018). They have the ability to bind proteins and form insoluble or soluble tannin-protein complexes and also complex with starch, cellulose, and minerals. Tannins can be toxic and affect the growth and development of chickens. They are present in sorghums and finger millet with a pigmented seed coat or testa between the pericarp and endosperm (Walker et al., 1999). The content of tannins, lectins, saponins, and trypsin inhibitors in small grains may be attributed to the depressed chicken growth as they can limit the acceptability and utilization by the chickens. In addition, grains are also often contaminated with several toxins including deoxynivalenol and mycotoxins (Escriva et al., 2015), which can exert lethal effect on chickens. Reports show that proanthocyanidins inhibit digestive enzymes, including amylases, cellulases, pectinases, lipases, and proteases, and have a major antinutritive effect that can influence the nutrient digestibility of lipids, starch, and amino acids negatively (Brestenský et al., 2012; Garcia et al., 2004). The presence of anti-nutritive compounds in seeds or cereal grains has been accounted to poor nutritive values and digestibility.

Germinated grains can be used as the alternative to the conventional energy or protein-rich feed ingredients in chicken diets. The germinated feed grains can also be used to promote the intake and growth performance of native chicken. Tarasevičienė et al. (2019) and Falcinelli et al. (2020) reported that germination can trigger the accumulation or increase in bioactive components such as vitamins, γ-aminobutyric acid, polyphenols, and trace elements that function as antioxidants as well as increasing polyphenol content and antioxidant capacity of grains. Studies by Kim et al. (2018), Lien et al. (2017), Rao et al. (2018) and Rico et al. (2020) confirm a significant increase in vitamins, caffeic acid, ferulic acid, and p‐coumaric acid and activity of enzyme (L-galactono-γ-lactone dehydrogenase) by sprouting. The ultimate benefit in small grain germination is improved degradability and digestibility (Chowdhury & Koh, 2017; Mustafa et al., 2008). Other physical strategies to improve utilizability of small grains include cooking, roasting, soaking, and grinding. According to Rozewicz (2022), extrusion is one strategy that can improve digestibility of small grain. It has been reported that heat processing interventions such as autoclaving, steam cooking, steam conditioning, expansion, and micronization have been evaluated to enhance feed value of millets and sorghum. (Megudu et al., 2012) Chemical methods could also be applied, including the use of alkaline substances, addition of tallow (fat), application of tannin-binding agents (such as polyvinylpolypyrrolidone, activated charcoal, and compound polyethylene glycol), enzyme administration, fermentation, and urea treatment (Nkhata et al., 2018). Germination has been reported to improve feed digestibility (Malomo et al., 2013), biological value of proteins (Nkhata et al., 2018), availability of amino acids, vitamin, and trace minerals (Rao et al., 2018), and mineral retention/utilization (Chowdhury & Koh, 2017), and thereby increased nutrient supply for the growth of native chickens. These improved attributes have been confirmed by studies by Malama et al. (2020), Mdzimure et al. (2017), and Rao et al. (2018) who posit a relatively improved growth performance of broilers fed on sprouted sorghum grains. Afsharmanesh et al. (2016) reported that dietary sprouted pearl millet improved the development of intestinal villi, thereby increasing nutrient absorption within the intestinal lacteals.

10. Economic impact of using small grains as ingredients for native chicken feed

Stock feed is a major cost driver in the poultry production value chain. This is because feed accounts for 75–80% of total cost of production and is one essential variable cost that should be monitored to sustain chicken production enterprise (Samuel Olugbenga et al., 2015). Feed is acknowledged to be an important input in native chicken production. Its cost, however, is a major constraint to profitability and can render chicken enterprises unprofitable. The use of sorghum to replace maize in feeds is economically attractive to arrest increases in maize price that occur periodically. It is important that farmers are aware of inputs price dynamics so that rations are formulated at bare minimum cost to improve profitability. Millets are gluten-free, low-cost cereals which are estimated to cost 40% than maize (Hassan et al., 2021). Similar studies by Silva et al. (2015) have estimated cost of 77.8% less in use of small grain as chicken feed ingredients than maize. The lower cost is attributed to high protein percentage in millets than maize grain. This makes small grain inclusion in rations lower than maize if compared volume by volume. Sorghum grain has 95% of the protein digestibility than maize, and it is priced less in most markets (Olomu, 1995). The scientific knowledge for utilization of low-cost, small grain to reduce feed cost is a perquisite in any viable poultry business. Finger millet, pearl millet, and sorghum offer basic nutrient requirements (protein and energy) at a cheaper cost. Small grains like sorghum and millets have adequate energy levels averaging 18 MJ/kg DM and ME of 13 MJ/kg DM and have proven to equate maize grain as a major source of carbohydrate for poultry rations. Studies by Wilson et al. (2007) have estimated that total net profit from the use of pearl millet was 6% more than maize-based feed. This places one of finger millet as the best alternative source of energy base in chicken feed ration formulation.

Economics deals largely with maximization (profit) or minimization (cost or resources outlay) of quantities important in value framework of production chain. In this respect, it is important to evaluate the cost–benefit analysis of alternative feed resources to chicken rations that maximize profits. Native chicken production enterprises should be driven by cost reduction technological innovations and economies of scale. Studies related to development of least cost feed mix have utilized derivation of isoquants, marginal rate of substitution and isoclines equations as well as application of quadratic programming (Hassam Mohammed, 1970). In providing and managing recommendations to farmers, nutritionists have overlooked and paid little attention between physical and economic efficiency. The later determines the optimum feeding program for profitability at minimum cost. Production function equation developed by Hassam Mohammed (1970) of Y = M − AR^x (where Y = total body live weight of animal corresponding to x units of feed consumption; M = maximum total weight at maturity; A = constant; R = ratio of successive gain) has been developed to produce a profitable ration of 20% CP with 1.45 kcal of ME fed to broilers at 10 weeks. It has been proven that to maximize profit, the marginal value product should be equated to the marginal factor cost plus opportunity cost at a time (Thirumalaisamy et al., 2016). More careful approaches to sustain native chicken production in the competitive market should address feed cost reduction while sustaining the nutritional needs of chickens as well. This requires well-calculated balance of chicken ratios by optimizing nutrient requirements (especially amino acids) using locally available and cheap small grains. Maize-based rations are more expensive than sorghum/millet diets, yet the outcome of growth performance from millet/sorghum diets is the same. Studies by Thirumalaisamy et al. (2016) showed that 80% white sorghum inclusion to chicken rations produced the same performance in weight gain as 100% maize-based ration. While this is true, studies by FAO (2011) have shown more than 30% reduction in broiler production cost by using sorghum and millets instead of maize as the energy base.

11. Post-slaughter performance of native chickens fed on millet-based diets

Meat colour is a major quality in consumer product preference. The development of dietary manipulation of skin/meat colour is vital to chicken producers to attract more consumers. Different shades of skin and shank pigmentations are major factors that determine the selling price of live chickens among live chicken buyers. A darker shank colour is preferred to one having a lighter shade of yellow. Colour can be assessed by the DSM Broiler Fan, expressed in a 101–110 scale, or by a colorimeter (Garcia et al., 2013; Sirriet et al., 2009). Skin colour is a result of the type of feed eaten by the chicken. Other parameters such as nutritional value, flavor, tenderness, or fat content have insignificant influence on skin colour (Shelton, 2014). Consumers have different perceptions in terms of the quality of the product based on their visual assessment. Naturally yellow-skinned chickens are preferred than light or pale shades. The carotenoids belong to a group of more than 500 pigments, and chickens use these compounds for skin pigmentation (Garcia et al., 2013). The skin pigmentation is more relevant in chicken meat production. Millets contain low levels of carotenoids and xanthophylls, resulting in pale meat colour which is less preferred by consumers. (Obzberk et al. (2020) observed that broiler meat luminosity depends on the complement of pigment proportional to its amount. On the other hand, low-tannin white sorghum varieties contain high zeaxanthin that enhances colouration of egg yolk and skin (Zaefarian et al., 2022). It has been observed that inclusion of sorghum and millet at 50% and 100% in all-mixed diets increased the level of skin pigmentation. These results are consistent with studies by Farahat et al. (2020), Tandiang et al. (2014), and Issa (2009) who reported no significant difference in pigment colouration at more than 50% white sorghum substitution for maize. In contrary, chickens fed on finger millet whole grain have shown a better meat colouration against DSM (Palmer, 2015) diets.

12. Future recommendations

To improve the precision of feed formulations and production efficiency, there is a need to seriously consider the apparent metabolizable energy and apparent metabolizable net energy values of various small grains when formulating chicken diets. Studies to improve both energy and CP values for small grains through biofortification interventions have potential to improve the quality of cereal grains as feed for chickens. Sorghum and millets may in the future be bred for better feed value for poultry. Their inherent drought tolerance characteristics may extend cultivation area and use for poultry in the world and contribute to ensuring better access to cheaper poultry products such as meat and eggs.

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No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Boat Sibanda

Boat Sibanda is a lecturer at Lupane State University. He is a PhD student researching on chicken production value chain, chicken feed nutrition and feeding standards. He has published a number of journal articles related to livestock production.

Mlamuleli Mhlanga

Dr. Mlamuleli Mhlanga is a senior lecturer and Dean at Lupane State University. He holds a PhD in Ecological Sciences. His research interest is on wildlife and human-wildlife interaction.

Mcebisi Maphosa

Professor Maphosa is a senior lecturer, seasoned breeder and consultant at Midlands State University. He holds a PhD in plant breeding and biotechnology. His research interest is in small grain breeding, genetics and biotechnology.

Ronny Sibanda

Dr. Ronny Sibanda is a consultant and agriculture economist in animal production economics and marketing at the Institute of Rural Technology, Bulawayo. He holds a PhD in Agriculture Economics and his research interest is in livestock value chains and value chain end market analysis.