Abstract

Ensiling maniçoba (Manihot pseudoglaziovii) is essential to preserve the nutrients of this forage plant. However, the plant moisture content may generate undesirable fermentations. The objective of this study was to evaluate the effects of different cornmeal inclusion levels (0%, 10%, 20%, and 30%) on the chemical composition and fermentation parameters of maniçoba silage, in addition to identifying the variables most affected by cornmeal. The concentrations of dry matter (DM), non-fiber carbohydrates (NFC), total digestible nutrients (TDN), and propionic acid increased with cornmeal inclusion levels (P < 0.05). Crude protein (CP), lignin, and butyric acid contents, as well as pH, were reduced by the additive (P < 0.05). Principal component analysis resulted in two main groups. Group I was formed by variables positively affected by cornmeal inclusion, namely DM, hemicellulose, NFC, and TDN. Group II contained variables that were negatively affected by cornmeal, namely CP, lignin, mineral matter, and butyric acid. Regardless of the addition of cornmeal, maniçoba silage displays an adequate chemical composition and a good fermentation profile for ruminant feeding. Dry matter and total digestible nutrients are the chemical variables most influenced by cornmeal inclusion, whereas pH and butyric acid are the fermentative parameters most affected by the moisture-absorbent additive. Including moderate levels of cornmeal in maniçoba silage is recommended to achieve the best fermentation profile and the highest concentration of digestible nutrients without mischaracterizing it as a roughage feed.

Keywords:
Chemical composition; Ensilage of Euphorbiaceae; Manihot pseudoglaziovii ; Organic acids; Principal components

Resumo

A ensilagem da maniçoba (Manihot pseudoglaziovii) é importante para preservar os nutrientes dessa planta forrageira. Todavia, o teor de umidade da planta pode gerar fermentações indesejáveis. Objetivou-se avaliar efeito de níveis de fubá de milho (0, 10, 20 e 30%) sobre a composição bromatológica e parâmetros fermentativos da silagem de maniçoba, além de identificar as variáveis mais afetada pelo aditivo. As concentrações de matéria seca (MS), carboidratos não-fibrosos (CNF), nutrientes digestíveis totais (NDT) e ácido propiônico aumentaram em função dos níveis de fubá de milho (P<0,05). Os teores de proteína bruta (PB), lignina e ácido butírico, além do pH, foram reduzidos pelo aditivo (P<0,05). Dois grupos foram formados na análise de componentes principais. O grupo I foi formado por variáveis afetadas positivamente pela inclusão do fubá de milho: MS, hemicelulose, CNF e NDT. O grupo II foi formado por variáveis que tiveram seus valores reduzidos pela inclusão do aditivo: PB, lignina, matéria mineral e ácido butírico. A silagem de maniçoba, com ou sem fubá de milho, apresenta bom perfil fermentativo e composição bromatológica adequada para a alimentação de ruminantes. Os teores de MS e NDT são as variáveis da composição químico-bromatológica mais influenciadas pela inclusão do fubá de milho, enquanto pH e ácido butírico são as variáveis do perfil fermentativo mais afeadas pelo aditivo absorvente. Sugere-se a inclusão de níveis moderados de fubá na silagem de maniçoba para obter melhor perfil de fermentação e a maior concentração de nutrientes digestíveis, sem descaracterizar o alimento como volumoso.

Palavras-chave:
Ácidos orgânicos; Componentes principais; Composição bromatológica; Ensilagem de euforbiáceas; Manihot pseudoglaziovii

1. Introduction

The Caatinga rangelands have been used as forage support for livestock over centuries(¹1 Jamelli D, Bernard E, Melo FP. Habitat use and feeding behavior of domestic free-ranging goats in a seasonal tropical dry forest. J. Arid Environ. 2021; 190:e104532. DOI: https://doi.org/10.1016/j.jaridenv.2021.104532.
https://doi.org/10.1016/j.jaridenv.2021.... ). However, the carrying capacity of these natural pastures oscillates throughout the year, drastically diminishing in the dry seasons(²2 Dubeux Jr JCB, Santos MVF, Cunha MV, Santos DC, Almeida RTS, Mello ACL, Souza TC. Cactus (Opuntia and Nopalea) nutritive value: A review. Anim. Feed Sci. Technol. 2021; 275:e114890. DOI: https://doi.org/10.1016/j.anifeedsci.2021.114890.
https://doi.org/10.1016/j.anifeedsci.202... ). Therefore, farmers from this region often adopt strategies to conserve forage to ensure feeding security and herd performance. Ensilaging is a technology employed for the conservation of the nutritional value of forage plants via anaerobic fermentation, achieved by rapidly removing O₂ from the environment to reduce the pH(³3 Muck RE, Nadeau EMG, McAllister TA, Contreras-Govea FE, Santos MC, Kung Jr, L. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 2018; 101(5):3980-4000. DOI: https://doi.org/10.3168/jds.2017-13839.
https://doi.org/10.3168/jds.2017-13839... ,⁴4 Costa ER, Mello ACL, Guim A, Costa SBM, Abreu BS, Silva PHF, Neto DS. Adding corn meal into mixed elephant grass–butterfly pea legume silages improves nutritive value and dry matter recovery. J. Agric. Sci. 2022; 160(3-4):185-193. DOI: https://doi.org/10.1017/S0021859622000284.
https://doi.org/10.1017/S002185962200028... ).

Maize (Zea mays L.) and sorghum (Sorghum bicolor L.) are the most ensiled crops because they have essential traits such as high contents of soluble carbohydrates and dry matter. These characteristics allow good fermentation processes and the maintenance of a high nutritional forage quality after ensilaging(⁵5 Lemos MF, Andrade AP, Silva PHF, Santos CO, Souza CFB, Silva MAV, Oliveira Neto PM. Nutritional value, fermentation losses and aerobic stability of elephant grass (Pennisetum purpureum Schum.) silage treated with exogenous fibrolytic enzymes. Acta Sci. - Anim. Sci. 2020; 42:e48272. DOI: https://doi.org/10.4025/actascianimsci.v42i1.48272.
https://doi.org/10.4025/actascianimsci.v... ). Tropical forage plants are more commonly ensiled compared to traditional crops due to lower soil fertility and tillage requirements. They are also perennial and demand less cultivation labor(⁶6 Bernardes TF, Daniel JLP, Adesogan AT, McAllister TA, Drouin P, Nussio LG, Cai Y. Silage review: Unique challenges of silages made in hot and cold regions. J. Dairy Sci. 2018; 101(5):4001-4019. DOI: https://doi.org/10.3168/jds.2017-13703.
https://doi.org/10.3168/jds.2017-13703... ). Maniçoba (Manihot pseudoglaziovii) is a species native to the Brazilian semiarid region that shows such characteristics. Belonging to the family Euphorbiaceae, it produces tuberous roots rich in starch and water, like other Manihot species, ensuring adaptability to semiarid conditions(⁷7 Alencar FHH, Silva DS, Andrade AP, Carneiro MSS, Feitosa JV. Composição química e digestibilidade da pornunça sob duas fontes de adubação orgânica e cortes. Rev. Caatinga. 2015; 28(1):215-222. DOI: https://doi.org/10.1590/1983-21252015v28n324rc.
https://doi.org/10.1590/1983-21252015v28... ). Maniçoba displays desirable features for forage plants, such as defoliation persistence when managed in fodder banks or Caatinga rangelands, besides excellent crude protein (CP) contents, varying from 140 to 200 g/kg(⁸8 Pinheiro FM, Nair PR. Silvopasture in the Caatinga biome of Brazil: A review of its ecology, management, and development opportunities. For. Syst. 2018; 27(1):eR01S. DOI: https://doi.org/10.5424/fs/2018271-12267.
https://doi.org/10.5424/fs/2018271-12267... ).

Ensiling maniçoba is essential to guarantee forage allowance during the dry season in semiarid regions and ensure its use in animal feeding(⁹9 Costa JHS, Cavalcante ITR, Medeiros GR, Ribeiro NL, Santos SGCG, Nascimento GV, Carvalho CBM. Propagação vegetativa de mudas de Manihot pseudoglaziovii com diferentes diâmetros de estacas. Rev. Inst. Nac. Semi. 2022; 1(3):49-55. Available from: https://editoraverde.org/portal/revistas/index.php/revinsa/article/view/188.
https://editoraverde.org/portal/revistas... ). Maniçoba is a linamarin-rich plant, and hydrocyanic acid (HCN) is released when this amino acid is hydrolyzed in the rumen. However, HCN concentrations over 2.4 mg per kilogram of body weight may lead to animal intoxication or even death(¹⁰10 Gomes MLR, Alves FC, Silva Filho JRV, Souza CMD, Silva MNP, Santana Junior RA, Voltolini TV. Maniçoba for sheep and goats-forage yield, conservation strategies, animal performance and quality of products. Cienc. Rural. 2021; 52(3):e20201096. DOI: https://doi.org/10.1590/0103-8478cr20201096.
https://doi.org/10.1590/0103-8478cr20201... ). Ensiling maniçoba leads to a reduction of up to 65% in the HCN content compared to the fresh plant because the fermentation processes reduce the enzymatic activity of linamarinase(⁹9 Costa JHS, Cavalcante ITR, Medeiros GR, Ribeiro NL, Santos SGCG, Nascimento GV, Carvalho CBM. Propagação vegetativa de mudas de Manihot pseudoglaziovii com diferentes diâmetros de estacas. Rev. Inst. Nac. Semi. 2022; 1(3):49-55. Available from: https://editoraverde.org/portal/revistas/index.php/revinsa/article/view/188.
https://editoraverde.org/portal/revistas... ).

However, the high moisture content in maniçoba may increase undesirable fermentations and impair pH reduction(¹¹11 Kung Jr L, Shaver RD, Grant RJ, Schmidt RJ. Silage review: Interpretation of chemical, microbial, and organoleptic components of silages. J. Dairy Sci. 2018; 101(5):4020-4033. DOI: https://doi.org/10.3168/jds.2017-13909.
https://doi.org/10.3168/jds.2017-13909... ). In recent decades, moisture-absorbent additives such as cornmeal, wheat bran, or molasses have been successfully adopted for ensiling forage plants(³3 Muck RE, Nadeau EMG, McAllister TA, Contreras-Govea FE, Santos MC, Kung Jr, L. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 2018; 101(5):3980-4000. DOI: https://doi.org/10.3168/jds.2017-13839.
https://doi.org/10.3168/jds.2017-13839... ). Absorbent additives can diminish the moisture content because of their hygroscopic potential and high dry matter content. As such, they provide a more suitable environment for lactic acid bacteria (LAB) while inhibiting secondary fermentations performed by other bacteria, fungi, and yeasts. Moreover, these additives can improve the feed value and increase the soluble carbohydrate contents since they are almost always high in energy(³3 Muck RE, Nadeau EMG, McAllister TA, Contreras-Govea FE, Santos MC, Kung Jr, L. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 2018; 101(5):3980-4000. DOI: https://doi.org/10.3168/jds.2017-13839.
https://doi.org/10.3168/jds.2017-13839... ,⁴4 Costa ER, Mello ACL, Guim A, Costa SBM, Abreu BS, Silva PHF, Neto DS. Adding corn meal into mixed elephant grass–butterfly pea legume silages improves nutritive value and dry matter recovery. J. Agric. Sci. 2022; 160(3-4):185-193. DOI: https://doi.org/10.1017/S0021859622000284.
https://doi.org/10.1017/S002185962200028... ). In addition, studies about total mixed ration silages (TMR silages) were conducted successfully, with large proportions of concentrates mixed with the roughage(¹²12 Gusmao JO, Danés MAC, Casagrande DR, Bernardes TF. Total mixed ration silage containing elephant grass for small-scale dairy farms. Grass Forage Sci. 2018; 73(3):717-726. DOI: https://doi.org/10.1111/gfs.12357.
https://doi.org/10.1111/gfs.12357... ).

Based on these premises, the objective of this study was to evaluate the chemical composition, pH reduction, and organic acid profile of maniçoba silage spiked with increasing levels of cornmeal. Moreover, we identified the most relevant variables to characterize these silages via principal component analysis.

2. Material and methods

The experiment was carried out at the Professor Ignacio Salcedo Experimental Station of the Instituto Nacional do Semiárido (INSA), located in the municipality of Campina Grande, state of Paraíba, Brazil (07º14’00” S, 35º57’00” W; 491 m above sea level). The climate is characterized as As’, that is, warm and humid with a rainy season in the autumn and winter(¹³13 Alvares CA, Stape JL, Sentelhas PC, Gonçalves JDM, Sparovek G. Köppen’s climate classification map for Brazil. Meteorol. Z. 2013; 22(6):711-728. DOI: https://doi.org/10.1127/0941-2948/2013/0507.
https://doi.org/10.1127/0941-2948/2013/0... ). The average rainfall is 503 mm annually, and the soil is classified as Solonetz(¹⁴14 IUSS Working Group WRB. World Reference Base for Soil Resources 2014, update 2015 International soil classification system for naming soils and creating legends for soil maps. No. 106. Rome: FAO; 2015. 550p.,¹⁵15 Santos HG. Sistema Brasileiro de Classificação de Solos. 5th ed. Brasília: Embrapa; 2018. 356p. Portuguese.).

The maniçoba forage used for the ensilage was harvested from the natural rangeland of the Caatinga, owned by INSA. Only leaves and thin stems (< 10 mm in diameter) were harvested and mowed into 2–3-cm particles using a stationary machine. The arboreal strata of this site have been managed since 2019, and the plants have already had two reproduction cycles.

The experimental design was completely randomized with six replicates, and experimental silos were made with polyethylene bags proper for ensiling. Each experimental silo had a 6-L capacity, and 5 kg of mass was compacted into the silos. Thus, the silage density was approximately 830 kg/m³ on an as-fed basis. Treatments corresponded to increasing levels of cornmeal (0%, 10%, 20%, and 30%) mixed with the ensiled mass on an as-fed basis. Therefore, 0, 0.5, 1.0, and 1.5 kg of cornmeal were homogenized into maniçoba to compose the additive levels. At the time of harvesting, a 300-g aliquot was separated and identified for chemical analyses of maniçoba and cornmeal before ensiling (Table 1).

The concentrations of dry matter (DM), mineral matter (MM), organic matter (OM), crude protein (CP), and ether extract (EE) were analyzed according to the AOAC(¹⁶16 Horwitz W. Official Methods of Analysis of AOAC International. 18th ed. Gaithersburg: AOAC; 2005. Official Methods: 934.01 (dry matter), 920.39 (ether extract), 942.05 (ashes), and 954.01 (crude protein).). The contents of neutral (NDF) and acid (ADF) detergent fiber were determined using the methodologies proposed by Van Soest et al.(¹⁷17 Van Soest PV, Robertson JB, Lewis BA. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 1991; 74(10):3583-3597. https://doi.org/10.3168/jds.S0022-0302(91)78551-2.
https://doi.org/10.3168/jds.S0022-0302(9... ). The NDF was analyzed without a heat-stable amylase and expressed inclusive of residual ash, protein, and ADF(¹⁷17 Van Soest PV, Robertson JB, Lewis BA. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 1991; 74(10):3583-3597. https://doi.org/10.3168/jds.S0022-0302(91)78551-2.
https://doi.org/10.3168/jds.S0022-0302(9... ). Non-fiber carbohydrates (NFC) were determined according to Sniffen et al.(¹⁸18 Sniffen CJ, O’connor JD, Van Soest PJ, Fox DG, Russell JB. A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availability. J. Anim. Sci. 1992; 70(11):3562-3577. https://doi.org/10.2527/1992.70113562x.
https://doi.org/10.2527/1992.70113562x... ), using the following equation: NFC = 1000 – (NDF + CP + MM + EE). These variables were expressed in grams per kilogram (g/kg).

The silos remained sealed for 35 days, and the pH values were measured according to Bolsen et al.(¹⁹19 Bolsen KK, Lin C, Brent BE, Feyerherm AM, Urban JE, Aimutis WR. Effect of silage additives on the microbial succession and fermentation process of alfalfa and corn silages. J. Dairy Sci. 1992 75(11):3066-3083. https://doi.org/10.3168/jds.S0022-0302(92)78070-9.
https://doi.org/10.3168/jds.S0022-0302(9... ) at seven-day intervals in all silos. For this, the silos were opened, and the ensiled mass samples (25 g) were collected, followed by closing the silos immediately. After definitive opening, the material was collected to determine the silage concentrations of DM, MM, OM, NDF, ADF, CP, NFC, and EE using the methods described above. The lignin content (LIG) was analyzed using the AOAC method(¹⁶16 Horwitz W. Official Methods of Analysis of AOAC International. 18th ed. Gaithersburg: AOAC; 2005. Official Methods: 934.01 (dry matter), 920.39 (ether extract), 942.05 (ashes), and 954.01 (crude protein).), and the total digestible nutrients were calculated using the equation TDN = [889 – (7.99 × ADF)](²⁰20 Patterson T, Klopfenstein TJ, Milton T, Brink DR. Evalua-tion of the 1996 beef cattle NRC model predictions of intake and gain for calves fed low or medium energy density diets. Nebraska Beef Cattle Reports: 2000; 76: 26-29. Available from: https://digitalcommons.unl.edu/animalscinbcr/314/.
https://digitalcommons.unl.edu/animalsci... ). The concentrations of hemicellulose (HEM) and cellulose (CEL) were calculated by subtracting the NDF from the ADF contents and the ADF from the LIG contents, respectively(²¹21 Detmann E. Métodos para análise de alimentos. 2nd ed. Visconde de Rio Branco: Suprema; 2021. 350p. Portuguese.). These variables were also expressed in grams per kilogram (g/kg).

Twenty-five grams (25 g) of fresh silage was weighed, diluted in 225 mL of distilled water, and homogenized in an industrial blender for 1 min to determine the concentrations of organic acids (acetic, butyric, propionic, and lactic acids). The resulting water extract was filtered through filter paper, and 100 mL of the extract was acidified with H₂SO₄ at 50%; subsequently, the extract was filtered through fast filter paper. After filtration, 2 mL of the extract received 1 mL of 20% metaphosphoric acid solution and 0.2 mL of 1% carbolic acid solution, used as an internal standard. The samples were centrifuged for 10 min at 15,000 rpm, and the supernatant was collected in Eppendorf vials and frozen until analysis. The organic acids were detected by high-performance liquid chromatography (HPLC, Ciola and Gregory, Master CG model)(²²22 Kung Jr, L, Ranjit NK. The effect of Lactobacillus buchneri and other additives on the fermentation and aerobic stability of barley silage. J. Dairy Sci. 2000; 84(5):1149-1155. DOI: https://doi.org/10.3168/jds.S0022-0302(01)74575-4.
https://doi.org/10.3168/jds.S0022-0302(0... ).

Data underwent analysis of variance (ANOVA), normality tests of residues, and linear and quadratic regressions using the GLM procedure of SAS^® OnDemand for Academics(²³23 SAS Institute Inc. SAS® OnDemand for Academics: User’s Guide. 1st ed. Cary: SAS Institute Inc.; 2014. 148p.). The pH data were analyzed with the MIXED procedure. Cornmeal inclusion level and seal time (seven-day intervals) were fixed effects, of which the latter was a repeated effect (repeated measurement in time). The variables were subjected to Pearson’s linear correlation analysis using the CORR procedure, also from SAS^® OnDemand for Academics. All statistical results were considered significant at the 5% error probability (P < 0.05).

In principal component analysis, the number of components was selected by eigenvalues using the Mardia criterion(²⁴24 Mardia KV, Kent JT, Bibby JM. Multivariate analysis. 1st ed. London: Academic, 1979. 64p.). Thus, only components with eigenvalues greater than 1.0 were included in the analysis, which was performed using Statistica 8.0.

3. Results and discussion

Fresh maniçoba (Table 1) displayed lower DM and higher CP concentrations than those previously reported(²⁵25 Maciel MDV, Carvalho FFRD, Batista ÂMV, Souza EJOD, Maciel LPAA, Lima DMD. Maniçoba hay or silage replaces Tifton 85 hay in spineless cactus diets for sheep. Acta Sci. - Anim. Sci. 2019; 41:e42553. DOI: https://doi.org/10.4025/actascianimsci.v41i1.42553.
https://doi.org/10.4025/actascianimsci.v... ,²⁶26 Matias AGS, Araújo GGL, Campos FS, Moraes SA, Gois GC, Silva TS, Voltolini TV. Fermentation profile and nutritional quality of silages composed of cactus pear and maniçoba for goat feeding. J. Agric. Sci. 2020; 158(4):304-312. DOI: https://doi.org/10.1017/S0021859620000581.
https://doi.org/10.1017/S002185962000058... ,¹⁰10 Gomes MLR, Alves FC, Silva Filho JRV, Souza CMD, Silva MNP, Santana Junior RA, Voltolini TV. Maniçoba for sheep and goats-forage yield, conservation strategies, animal performance and quality of products. Cienc. Rural. 2021; 52(3):e20201096. DOI: https://doi.org/10.1590/0103-8478cr20201096.
https://doi.org/10.1590/0103-8478cr20201... ). Using leaves and thin stems for ensiling maniçoba contributed to the high moisture and protein concentrations. Regarding the chemical composition of the ensilage, increasing cornmeal inclusion levels had significant effects on all variables assessed (Table 2).

The contents of DM, NFC, and HEM linearly increased with the cornmeal inclusion level. High-energy concentrates such as cornmeal are efficient moisture absorbents for ensiling tropical forage plants(³3 Muck RE, Nadeau EMG, McAllister TA, Contreras-Govea FE, Santos MC, Kung Jr, L. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 2018; 101(5):3980-4000. DOI: https://doi.org/10.3168/jds.2017-13839.
https://doi.org/10.3168/jds.2017-13839... ). Contents of DM over 250 g/kg contribute to a good fermentation process during the seal period(²⁷27 Borreani G, Tabacco E, Schmidt RJ, Holmes BJ, Muck RE. Silage review: Factors affecting dry matter and quality losses in silages. J. Dairy Sci. 2018; 101(5):3952-3979. DOI: https://doi.org/10.3168/jds.2017-13837.
https://doi.org/10.3168/jds.2017-13837... ). Cornmeal inclusion was crucial to achieving this standard since the maniçoba silage without additive had only 200 g/kg of DM. Costa et al.(⁴4 Costa ER, Mello ACL, Guim A, Costa SBM, Abreu BS, Silva PHF, Neto DS. Adding corn meal into mixed elephant grass–butterfly pea legume silages improves nutritive value and dry matter recovery. J. Agric. Sci. 2022; 160(3-4):185-193. DOI: https://doi.org/10.1017/S0021859622000284.
https://doi.org/10.1017/S002185962200028... ) found an increased DM content in elephant grass-butterfly pea silage, from 210 to 221 g/kg, when adding cornmeal to the ensiled mass. Concentrations of DM between 250 and 370 g/kg lead to more desirable (e.g., lactic fermentation) than undesirable fermentations (e.g., butyric fermentation)(²⁸28 Daniel JLP, Bernardes TF, Jobim CC, Schmidt P, Nussio LG. Production and utilization of silages in tropical areas with focus on Brazil. Grass Forage Sci. 2019; 74(2):188-200. DOI: https://doi.org/10.1111/gfs.12417.
https://doi.org/10.1111/gfs.12417... ).

Non-fiber carbohydrates (NFC) comprise starch, saccharose, pectin, and other soluble sugars and are essential to silage fermentation because they enhance the soluble carbohydrate contents mainly degraded by lactic acid bacteria (LAB)(¹⁸18 Sniffen CJ, O’connor JD, Van Soest PJ, Fox DG, Russell JB. A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availability. J. Anim. Sci. 1992; 70(11):3562-3577. https://doi.org/10.2527/1992.70113562x.
https://doi.org/10.2527/1992.70113562x... ). Concentrates such as cornmeal are rich in NFC, whereas the maniçoba shoot is characterized by high concentrations of structural carbohydrates, especially cellulose and lignin(¹⁰10 Gomes MLR, Alves FC, Silva Filho JRV, Souza CMD, Silva MNP, Santana Junior RA, Voltolini TV. Maniçoba for sheep and goats-forage yield, conservation strategies, animal performance and quality of products. Cienc. Rural. 2021; 52(3):e20201096. DOI: https://doi.org/10.1590/0103-8478cr20201096.
https://doi.org/10.1590/0103-8478cr20201... ). Therefore, the increase in cornmeal inclusion levels combined with the reduction of maniçoba in the ensiled mass led to higher NFC and HEM concentrations.

A negative quadratic effect was found in the MM content, which decreased up to a cornmeal inclusion level of 20%, followed by an increase when 30% was added. A minimum MM content of 57 g/kg was reached at 29.3% cornmeal inclusion. The opposite occurred for the OM content, which increased to 20%, diminishing at a cornmeal inclusion level of 30%. A peak OM concentration of 941 g/kg was found with 29.3% cornmeal in the ensiled mass. The fresh maniçoba displayed higher MM values than cornmeal (Table 1), which explains the results, considering that the proportion of maniçoba was reduced as that of cornmeal was increased. High-energy concentrates are often poor in minerals but rich in OM(²⁹29 Marcondes MI, Silva AL, Gionbelli MP, Campos S. Exigências de energia para bovinos de corte. BR-Corte: Tabela Brasileira De Exigências Nutricionais; DZO/UFV: Viçosa, Minas Gerais, Brazil, 163-190. 2016.).

The maniçoba silage concentrations of NDF, ADF, CEL, LIG, and CP linearly decreased (P < 0.05) with increasing cornmeal inclusion levels (Table 2). Plants native to the Brazilian semiarid region, such as maniçoba, are rich in fiber fractions, mainly cellulose and lignin, and often have unique CP contents. However, a significant part of this protein may be bound to lignin or tannins, creating complexes that diminish dry matter digestibility(³⁰30 Muir JP, Santos MVF, Cunha MV, Dubeux Jr. JCB, Lira Jr MA, Souza RT, Souza TC. Value of endemic legumes for livestock production on Caatinga rangelands. Rev. Bras. Cienc. Agr. 2019; 14(2):1-12. DOI: https://doi.org/10.5039/agraria.v14i2a5648.
https://doi.org/10.5039/agraria.v14i2a56... ). In the present study, the TDN concentration was elevated by increasing cornmeal levels because the proportion of maniçoba was reduced in the ensiled mass, which explains the lower EE content (Table 2). Santos et al.(³¹31 Santos F, Charll MDS, Lima Júnior DMD, Cardoso DB, Maciel M, Vale D, Carvalho FFRD. Replacement of Tifton 85 hay with maniçoba hay in the spineless cactus diet of sheep. Rev. Caatinga. 2021; 34:219-227. DOI: https://doi.org/10.1590/1983-21252021v34n122rc.
https://doi.org/10.1590/1983-21252021v34... ) found elevated lignin concentrations (131 g/kg DM) in maniçoba hay used to feed Santa Inês sheep and attributed the reduction in apparent digestibility to the high percentage of maniçoba in the diet.

According to the chemical composition, adding too much cornmeal to the ensiled mass may mischaracterize the maniçoba silage as a roughage feed, considering that the additive linearly reduces the NDF concentration. Thus, the NDF would keep reducing if exaggerated cornmeal levels (e.g., over 30%) were included in the ensiled mass.

Silages made with other forage plants have also been improved by cornmeal as an absorbent additive. Costa et al.(³²32 Costa ER, Mello ACL, Guim A, Costa SBM, Abreu BS, Silva PHF, Neto DS. Adding corn meal into mixed elephant grass–butterfly pea legume silages improves nutritive value and dry matter recovery. J. Agric. Sci. 2022;160(3-4):185-193. DOI: https://doi.org/10.1017/S0021859622000284.
https://doi.org/10.1017/S002185962200028... ) added cornmeal to silages composed of elephant grass genotypes (Cenchrus purpureus Schum.) and the butterfly pea legume (Clitoria ternatea L.). The authors found increased levels of DM (from 210 to 221 g/kg) and the remaining water-soluble carbohydrates (14 to 26 g/kg) when comparing the silage with or without cornmeal.

Isolated effects of cornmeal level (Table 3) and seal time (Fig. 1) were observed on the pH values (P < 0.05), but no interaction was found (P = 0.231). The pH was reduced under a quadratic effect by increasing cornmeal levels at 7, 14, 21, and 28 seal days. At 35 days, the decrease showed a linear behavior in response to increasing cornmeal levels. The pH is a key parameter for indicating good fermentation processes, characterized by more lactic than acetic, propionic, and butyric fermentations(⁶6 Bernardes TF, Daniel JLP, Adesogan AT, McAllister TA, Drouin P, Nussio LG, Cai Y. Silage review: Unique challenges of silages made in hot and cold regions. J. Dairy Sci. 2018; 101(5):4001-4019. DOI: https://doi.org/10.3168/jds.2017-13703.
https://doi.org/10.3168/jds.2017-13703... ).

Cornmeal likely improved the fermentation coefficient of the ensiled mass since high-energy concentrates often have a lower buffering capacity than roughage feeds(³3 Muck RE, Nadeau EMG, McAllister TA, Contreras-Govea FE, Santos MC, Kung Jr, L. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 2018; 101(5):3980-4000. DOI: https://doi.org/10.3168/jds.2017-13839.
https://doi.org/10.3168/jds.2017-13839... ). However, the pH observed in all silages remained below the acceptable values(⁶6 Bernardes TF, Daniel JLP, Adesogan AT, McAllister TA, Drouin P, Nussio LG, Cai Y. Silage review: Unique challenges of silages made in hot and cold regions. J. Dairy Sci. 2018; 101(5):4001-4019. DOI: https://doi.org/10.3168/jds.2017-13703.
https://doi.org/10.3168/jds.2017-13703... ), varying from 3.81 to 4.21. Progressive reductions in pH values were observed in the maniçoba silage (P < 0.05) during the seal period (Fig. 1), with values of 4.08, 4.05, 4.02, 3.96, and 3.90 at 7, 14, 21, 28, and 35 days, respectively. The pH decrease indicates a good fermentation process in all silages(²⁸28 Daniel JLP, Bernardes TF, Jobim CC, Schmidt P, Nussio LG. Production and utilization of silages in tropical areas with focus on Brazil. Grass Forage Sci. 2019; 74(2):188-200. DOI: https://doi.org/10.1111/gfs.12417.
https://doi.org/10.1111/gfs.12417... ), likely because maniçoba is a C4 plant with a lower buffering capacity than other forage plants (e.g., forage legumes)(²⁶26 Matias AGS, Araújo GGL, Campos FS, Moraes SA, Gois GC, Silva TS, Voltolini TV. Fermentation profile and nutritional quality of silages composed of cactus pear and maniçoba for goat feeding. J. Agric. Sci. 2020; 158(4):304-312. DOI: https://doi.org/10.1017/S0021859620000581.
https://doi.org/10.1017/S002185962000058... ,³²32 Costa ER, Mello ACL, Guim A, Costa SBM, Abreu BS, Silva PHF, Neto DS. Adding corn meal into mixed elephant grass–butterfly pea legume silages improves nutritive value and dry matter recovery. J. Agric. Sci. 2022;160(3-4):185-193. DOI: https://doi.org/10.1017/S0021859622000284.
https://doi.org/10.1017/S002185962200028... ,³³33 Ramos JPF, Santos EM, Santos APM, Souza WH, Oliveira JS. Ensiling of forage crops in semiarid regions. Advances in Silage Production and Utilization, 65. 2016.).

The concentrations of lactic and acetic acids were not affected by the increasing levels of cornmeal in the maniçoba silage (Table 4). The proportion of lactic acid was considerably higher than those of the other acids in all tested silages, suggesting good fermentation processes, including in the control treatment(⁴4 Costa ER, Mello ACL, Guim A, Costa SBM, Abreu BS, Silva PHF, Neto DS. Adding corn meal into mixed elephant grass–butterfly pea legume silages improves nutritive value and dry matter recovery. J. Agric. Sci. 2022; 160(3-4):185-193. DOI: https://doi.org/10.1017/S0021859622000284.
https://doi.org/10.1017/S002185962200028... ). The contents of propionic and butyric acids and the acetic-to-propionic ratio (AA/PA) were changed with increasing cornmeal inclusion levels. The propionic acid concentration and AA/PA linearly increased with higher cornmeal levels. Conversely, the butyric acid level was reduced under a quadratic effect.

These changes in the organic acid profile by adding increasing levels of cornmeal into the ensiled mass occurred due to modifications in the roughage-to-concentrate ratio inside the silos. Diets with high percentages of high-energy concentrates, such as cornmeal, favor the proliferation of amylolytic bacteria plus the production of lactic and propionic acids. In contrast, roughage feeds such as maniçoba facilitate the proliferation of cellulolytic bacteria and acetic acid production(³⁴34 Gang G, Chen S, Qiang L, Zhang SL, Tao S, Cong W, Huo W. The effect of lactic acid bacteria inoculums on in vitro rumen fermentation, methane production, ruminal cellulolytic bacteria populations and cellulase activities of corn stover silage. J. Integr. Agric. 2020; 19(3):838-847. DOI: https://doi.org/10.1016/S2095-3119(19)62707-3.
https://doi.org/10.1016/S2095-3119(19)62... ).

Butyric acid production stopped at a cornmeal inclusion level of 30%, whereas a higher butyric acid level was found in the control treatment (Table 4). The population of Clostridium spp. was probably suppressed when cornmeal was added to the ensiled mass. This bacterial genus is sensitive to environments with pH values below 4.5, mainly when the pH decreases sharply. These results are interesting since Clostridium spp. are potentially toxic bacteria(³⁵35 Queiroz OCM, Ogunade IM, Weinberg Z, Adesogan AT. Silage review: Foodborne pathogens in silage and their mitigation by silage additives. J. Dairy Sci. 2018; 101(5):4132-4142. DOI: https://doi.org/10.3168/jds.2017-13901.
https://doi.org/10.3168/jds.2017-13901... ), highlighting the beneficial effect of cornmeal addition (Table 3). Backes et al.(³⁶36 Backes AA, Santos LLD, Fagundes JL, Barbosa LT, Mota M, Vieira JS. Valor nutritivo da silagem de maniçoba (Manihot pseudoglaziovii) com e sem fubá de milho como aditivo. Rev. Bras. Saude Prod. Anim. 2014; 15(1):182-191. Available from: https://www.scielo.br/j/rbspa/a/ZCVkMqsNqXnRTgcxrxLDq9x/abstract/?lang=pt.
https://www.scielo.br/j/rbspa/a/ZCVkMqsN... ) also observed a linear reduction in butyric acid contents when adding cornmeal to maniçoba ensiled mass.

Significant effects were observed on all correlations between chemical composition, pH, and organic acids. Negative correlations were found between DM, pH, and butyric acid (Table 5). As mentioned, moisture reductions in the ensiled mass diminish the pH values and impede undesirable fermentations, such as butyric acid fermentation(³3 Muck RE, Nadeau EMG, McAllister TA, Contreras-Govea FE, Santos MC, Kung Jr, L. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 2018; 101(5):3980-4000. DOI: https://doi.org/10.3168/jds.2017-13839.
https://doi.org/10.3168/jds.2017-13839... ). Conversely, the CP content was positively associated with butyric acid fermentation, likely because silages with high protein contents favor the activity of Clostridium spp., producing butyrate. At the same time, these bacteria contribute considerably to proteolysis during the fermentation process(³⁷37 Anjos ANA, Almeida JCDC, Viegas CR, Silva PHF, Morais LF, Nepomuceno DDD, Soares FA. Protein and carbohydrate profiles of ‘Massai’ grass silage with pelleted citrus pulp and microbial inoculant. Pesqui. Agropecu. Bras. 2022; 57:e02732. DOI: https://doi.org/10.1590/S1678-3921.pab2022.v57.02732.
https://doi.org/10.1590/S1678-3921.pab20... ).

Furthermore, a negative correlation was registered between CP and propionic acid, which indicates that the dietary protein in the silages was rather derived from maniçoba than from cornmeal. Therefore, silages with high proportions of maniçoba in the ensiled mass (e.g., control silage or the silage spiked with 10% cornmeal) had low propionate contents, besides high acetic-to-propionic rates and CP contents(³⁴34 Gang G, Chen S, Qiang L, Zhang SL, Tao S, Cong W, Huo W. The effect of lactic acid bacteria inoculums on in vitro rumen fermentation, methane production, ruminal cellulolytic bacteria populations and cellulase activities of corn stover silage. J. Integr. Agric. 2020; 19(3):838-847. DOI: https://doi.org/10.1016/S2095-3119(19)62707-3.
https://doi.org/10.1016/S2095-3119(19)62... ).

The levels of NDF, ADF, CEL, and LIG displayed high degrees of association with pH and butyric acid (Table 5). The fiber fractions were higher at lower cornmeal inclusion levels. Thus, the silages with little or no additive had more fiber fractions and moisture contents, making them more susceptible to secondary fermentations (e.g., butyric fermentation), plus less marked pH reductions(⁶6 Bernardes TF, Daniel JLP, Adesogan AT, McAllister TA, Drouin P, Nussio LG, Cai Y. Silage review: Unique challenges of silages made in hot and cold regions. J. Dairy Sci. 2018; 101(5):4001-4019. DOI: https://doi.org/10.3168/jds.2017-13703.
https://doi.org/10.3168/jds.2017-13703... ,³⁵35 Queiroz OCM, Ogunade IM, Weinberg Z, Adesogan AT. Silage review: Foodborne pathogens in silage and their mitigation by silage additives. J. Dairy Sci. 2018; 101(5):4132-4142. DOI: https://doi.org/10.3168/jds.2017-13901.
https://doi.org/10.3168/jds.2017-13901... ). Moreover, negative correlations were observed between NDF, ADF, and CEL with propionic acid since fibrolytic bacteria ferment acetic acid rather than propionic acid(³⁴34 Gang G, Chen S, Qiang L, Zhang SL, Tao S, Cong W, Huo W. The effect of lactic acid bacteria inoculums on in vitro rumen fermentation, methane production, ruminal cellulolytic bacteria populations and cellulase activities of corn stover silage. J. Integr. Agric. 2020; 19(3):838-847. DOI: https://doi.org/10.1016/S2095-3119(19)62707-3.
https://doi.org/10.1016/S2095-3119(19)62... ).

The opposite was observed for the NFC, with negative correlations with pH and butyric acid (Table 5). The starch contained in the cornmeal is one of the main components of NFC, contributing positively to lactic and propionic acid fermentation(³3 Muck RE, Nadeau EMG, McAllister TA, Contreras-Govea FE, Santos MC, Kung Jr, L. Silage review: Recent advances and future uses of silage additives. J. Dairy Sci. 2018; 101(5):3980-4000. DOI: https://doi.org/10.3168/jds.2017-13839.
https://doi.org/10.3168/jds.2017-13839... ,¹⁸18 Sniffen CJ, O’connor JD, Van Soest PJ, Fox DG, Russell JB. A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availability. J. Anim. Sci. 1992; 70(11):3562-3577. https://doi.org/10.2527/1992.70113562x.
https://doi.org/10.2527/1992.70113562x... ,³⁵35 Queiroz OCM, Ogunade IM, Weinberg Z, Adesogan AT. Silage review: Foodborne pathogens in silage and their mitigation by silage additives. J. Dairy Sci. 2018; 101(5):4132-4142. DOI: https://doi.org/10.3168/jds.2017-13901.
https://doi.org/10.3168/jds.2017-13901... ). Thus, silages with higher additive inclusions showed higher NFC contents, lower pH values, and less pronounced butyric acid fermentation than those with less or no cornmeal addition.

Principal component analysis (PCA) revealed that 86.59% of the total variation could be explained by the first two PCs, with 80.29% related to PC1 and 6.30% to PC2 (Fig. 2). All variables of Group I (MM, CP, fiber fractions, EE, pH, and butyric acid) were substantially reduced by increasing cornmeal levels. In contrast, variables of Group II (DM, OM, NFC, HEM, and TDN) displayed increasing values when the additive was progressively added. The formation of two well-defined groups indicates the beneficial effects of adding cornmeal into the ensiled mass, both in terms of chemical variables and fermentation parameters(⁴4 Costa ER, Mello ACL, Guim A, Costa SBM, Abreu BS, Silva PHF, Neto DS. Adding corn meal into mixed elephant grass–butterfly pea legume silages improves nutritive value and dry matter recovery. J. Agric. Sci. 2022; 160(3-4):185-193. DOI: https://doi.org/10.1017/S0021859622000284.
https://doi.org/10.1017/S002185962200028... ,²⁸28 Daniel JLP, Bernardes TF, Jobim CC, Schmidt P, Nussio LG. Production and utilization of silages in tropical areas with focus on Brazil. Grass Forage Sci. 2019; 74(2):188-200. DOI: https://doi.org/10.1111/gfs.12417.
https://doi.org/10.1111/gfs.12417... ,³⁵35 Queiroz OCM, Ogunade IM, Weinberg Z, Adesogan AT. Silage review: Foodborne pathogens in silage and their mitigation by silage additives. J. Dairy Sci. 2018; 101(5):4132-4142. DOI: https://doi.org/10.3168/jds.2017-13901.
https://doi.org/10.3168/jds.2017-13901... ), even though the control treatment (maniçoba with no additive) showed adequate parameters.

Regardless of the addition of cornmeal, maniçoba silage showed adequate chemical composition and a good fermentation profile for ruminant feeding and nutrition. Increasing levels of cornmeal improve the organic acid profile of maniçoba silage, and a cornmeal inclusion level of 30% stopped the production of butyric acid. Dry matter and total digestible nutrients were the chemical variables most influenced by cornmeal inclusion, whereas pH and butyric acid were the fermentative parameters most affected by cornmeal.

4. Conclusion

Including moderate levels of cornmeal in maniçoba silage is recommended to achieve the best fermentation profile and the highest concentration of digestible nutrients without mischaracterizing it as a roughage feed.

Acknowledgments

The present study was carried out with the support of the National Council for Scientific and Technological Development (CNPq).

References

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