Cassava, characterized by a high productivity per unit area, is one of the three major tuber crops cultivated worldwide, and is considered an effective source of energy for livestock production (Rolland-Sabaté et al. 2012, Li et al. 2017). However, the widespread use of cassava in livestock feed has been limited on account of its low levels of certain essential amino acids and high hydrocyanic acid content (Tiwari and Jha 2016). However, Falade and Akingbala (2010) have confirmed that adequate drying can reduce the concentrations of hydrocyanic acid in cassava to acceptable levels. In this study, we used the SC9 variety of cassava, which has been established to be a low cyanogenic glycoside (0.9 mg/kg) variety. The levels of cyanogenic glycoside in the feed formulae calculated in this study ranged from 0.14 to 0.41 mg/kg, which meet the requirements for cyanogenic glycoside contents outlined in the feed hygiene standards of China (< 100 mg/kg) (MAC 2017).
The performance of broilers fed cassava diets varied depending on the level of cassava content in their diet. Gomez et al. (1984) have reported that supplementation of broiler diets with 30% CRM had no appreciable adverse effects on the body weights of birds. Similarly, weight gain was not affected in chickens fed 10% cassava leaf meal (Bakare et al. 2020), 20% cassava peel meal (Oyebimpeet al. 2006), 60% composite cassava meal (Ukachukwu 2008). Contrastingly, in the present study, we detected significant reductions in the BW, ADG, and ADFI of broilers during the initial period (1–21 day) of feeding on CRM-supplemented diets. Compared to corn with a crude protein level of 8%-9% (Koehler and Wieser 2013), dried cassava is characterized by low protein contents (4.45%) and high levels of fiber (4.63%), which would limit nutrient digestion in the small intestines of poultry (Aro et al. 2008, Raphaël et al. 2012). These observations reflect the relatively the poor ability of chicks to digest cassava early in life, as at this stage their digestive tract have yet fully develop.
However, during the latter stages of the trial (22–42 days), these detrimental effects became increasingly less apparent in the CRM15 broilers. Similarly, Yadav also observed a linear reduction in the BW of chicks fed diets supplemented with 37.5% and 50% cassava during the starter periods, whereas these high levels of cassava had little effect on ADG and ADFI during the latter phase of growth (Yadav et al. 2019). Throughout the 42 d feeding period in this study, we found that the FCR of birds in the CRM15 was similar to that of CT birds, although supplementation with CRM had an negative influence on the weight gain of broilers. A well-developed gut is essential for the efficient utilization of cassava, as high levels of starch and fiber evades digestion in the small intestine and passes to the large intestine, wherein it is fermented by the gut microbiota (Oladunmoye et al. 2014, Jha and Berrocoso 2015). These high fiber and starch contents of cassava may play a prebiotic role in the fully developed hindgut segment. However, birds in the CRM30 and CRM45 were characterized by lower values for BW and body measurements, which would accordingly lead to longer rearing times and higher feed consumption. Previous studies have also found that supplementation with higher levels of CRM in broilers delayed weight gain (Ochetim 1991, Ru et al. 2012). Similar to this study, dietary CRM supplementation was observed to retard the growth of broilers during the early stage (1–21 days) of the feeding trial, whereas the body measurements of CRM15 birds were not significantly different from those of CT birds during the latter stage of the trial (22–42 days), thereby indicating that the growth of CRM15 broilers substantially improved with a prolongation of the period during which they fed on a CRM-supplemented diet. Despite the fact that body measurements closely reflect poultry growth, development, and flock uniformity, particularly in intensive poultry production systems, the effects of CRM on the body measurements of broilers has rarely been reported (He et al. 2021). In the present study, we established that whereas supplementing broiler diets with CRM15 had no appreciable adverse effects on the growth or development of broilers, the use of high levels of CRM (30% and 45%) had negative effects on broiler growth and body measurements.
Study have shown that apparent digestibility is reduced when corn is substituted with more than 30% cassava, and that feeding dried potato pulp at 25% also reduces nutrients apparent digestibility and retention (Khempaka et al. 2016). In the present study, we found that replacing corn with 30% and 45% cassava contributed to significant reductions in the apparent digestibility of dry matter, crude protein, and ether extract in broilers. However, substitution ratio of 15% showed no significant difference compared to the CT broilers. This effect could be attributable to the fact that cassava is rich in non-starch polysaccharides (NSP), which are mostly insoluble. In this regard, the concentration of water-soluble NSP in cassava root was lower (0.078% ~ 1.64%) than that in maize (8.4%) and soybean (9.8%) (Meng and Slominski 2005, Chauynarong et al. 2015, Uthumporn et al. 2017). Insoluble NSP reduces the efficient digestion of nutrients by interfering with the action of amylase and protease (Morgan et al. 2016). Nevertheless, these SNP in cassava can serve as a substrate for microbial fermentation, which influences the production of short-chain fatty acids (Canfora and Blaak 2017), which, along with glucose, are essential nutrients for metabolic conversions in the body. The main amino acids found in cassava root are glutamine, alanine, and asparagine, while the content of methionine and cysteine, which are key essential amino acids in poultry diet, is relatively low (Morgan et al. 2016). The low protein content of cassava root makes it a significant disadvantage for its use in poultry feed. Furthermore, the co-ingestion of glucose and amino acids has been shown to have a synergistic effect in potentiating insulin secretion and subsequently stimulating muscle protein synthesis (Van Loon et al. 2000). Accordingly, supplementing feed with amino acids or subjecting cassava to fermentation are considered effective approaches to enhancing the nutritional value of supplemental cassava, as has been confirmed by some studies (Aladi et al. 2021, Chang'a et al. 2020, Diarra and Anand 2020).
Dietary constituents can influence the structure of the digestive tract and the passage of digesta through the gastrointestinal tract. For example, the intake of roughage has the effect of promoting increased muscle activity in the gizzard, thereby contributing to a gain in weight, and maximizing the grinding ability of the gastrointestinal tract (Jacobs and Parsons, 2013). Indeed, it has been demonstrated that the gizzards of broilers fed coarse diets were 15% heavier than those of birds fed fine diets. Furthermore, high-protein diets have been found to reduce intestinal villus height/crypt depth and butyric acid production. Guo et al. (2018) has also reported that the digestive tract weight indices of the gizzard and rectum increased in birds fed a diet supplemented with pine needle powder. Similarly, svihus (2011) found that consumption of feed containing structural components, such as hulls, wood shavings, or large cereal particles, can contribute to a rapid and significant enlargement in the size of the gizzard. In the present study, we found that supplementing diets with CRM had no significant effects on the indices of the proventriculus and gizzard of broilers at 42 days of age, although contributed to reduction in the indices of the jejunum and ileum, which could plausibly be attributed to the crude fiber content of the cassava (4.63%) used to supplement the diets, which was not sufficient to alter the weight of the gastrointestinal tract.
Similar to the findings of previous studies that have reported that supplementing the diet of slow-growing broilers with 10% cassava had no significant effects on carcass or growth performance (da Silva et al. 2019, Almeida et al. 2020), we found that when broilers were fed a diet in which corn was replaced with 15% cassava, there was no significant differences in the rates of semi-evisceration and evisceration in the broilers compared with the controls, and no significant difference in the organ indices of groups. However, differences in the other slaughter indices were mainly reflected in the proportions of breast and thigh muscles. It can thus be speculated that the observed differences in carcass yield may be associated with the balance of amino acids in the diet. It has, for example, been established that the amounts and proportions of methionine and lysine are directly linked to carcass and slaughter yields, particularly with respect to muscle tissue, which accounts for approximately 50% of total carcass protein. Similarly, the findings of previous studies have indicated that substitution with 10–16% cassava had no appreciable effects on the muscle mass of poultry, whereas substituting maize with 40% CRM had the effect of reducing breast yield (Omede et al. 2018, Khempaka et al. 2016). Given that rapid protein deposition is dependent on efficient nutrient conversion, low-protein cassava supplementation may be more appropriate for the growth of slow-growing broilers. Further studies are required to examine the synergistic promotion effect of the proportional composition of nutrient.
In this study, we found that replacing corn in the diets of yellow-feather broilers with 15% cassava root meal did not significantly influence the production performance, rate of nutrient digestibility, slaughter performance, or gastrointestinal tract indices of broilers chicks compared with control birds. In addition, the substitution is best done at a later stage. In contrast, high levels of dietary cassava can inhibit the production performance, nutrient digestibility, and slaughter performance of these broilers. Accordingly, our findings indicate that when supplemented at appropriate levels, cassava root meal, as an alternative high-yield inexpensive energy feed source, may be feasible and effective in broiler production.