Animal Science

Nutritional value of palm kernel meal, fruit of the royal palm tree (Roystonea regia), for feeding broilers

0000-0003-1585-2858Madeleidy Martínez-Pérez^{1  *}  , 0000-0002-6469-4289Yesenia Vives Hernández¹  , 0000-0003-0740-9346Bárbara Rodríguez¹  , 0000-0003-3656-7116O. G. Pérez Acosta¹  , 0000-0002-2641-1815Magalys Herrera Villafranca¹ 

¹Instituto de Ciencia Animal, Apartado Postal 24, San José de Las Lajas, Mayabeque, Cuba

Abstract

To determine the nutritional value of Roystonea regia fruit (palm kernel) meal for feeding broilers, an experiment was developed with 40 male animals, distributed in four treatments according to a completely randomized design: control (corn-soybean paste) and inclusion of 5, 10 and 15 % of palm kernel meal. The physical and chemical composition of the ingredient was calculated using descriptive statistics and Pearson correlation was applied to demonstrate the association degree among indicators. Apparent fecal retention of nutrients was studied by total excreta collection method. Crude protein was moderate, while ether extract and fiber fractionation contents were high. The analysis of physical properties showed low solubility and greater buffering capacity against acids with respect to bases (0.61 vs 0.24 meq). There was a high correlation between chemical and physical characteristics (greater than 85 %). Apparent fecal retention of neutral detergent fiber showed a reduction from 10 % inclusion of palm kernel meal in the ration, while control and 5 % did not differ among treatments. Regarding ether extract, the highest coefficient was reached with 5 %, and the lowest with 15 % (88.04 and 83.38 %, respectively) (P<0.05). It is concluded that palm kernel meal has adequate nutritional value for feeding broilers.

Key words: poultry; palm fruit meal; physical and chemical composition; apparent fecal nutrient retention

The royal palm (Roystonea regia (Kunth) O.F. Cook) is native of the Cuban archipelago. Studies carried out by ^{Caro et al. (2015)} and ^{Arias et al. (2016)} report that its nuts constitute a good source of fiber and energy for monogastric animals. Its use as an unconventional feed source for pigs has been well studied (^{Ly and Grageola 2016}). However, there are few reports about the productive performance when it is included in rations destined for broilers (^{Rodríguez et al. 2020}).

To include non-traditional foods in animal feed, it is necessary to study their nutritional value. The definition of this term is not simple and its calculation is not easily obtained, but it is necessary to emphasize the indicators that determine it (^{Savón 2005}). According to ^{Cáceres and González (2000)}, the calculation of nutritional value includes, as main indicators, chemical composition, intake, digestibility of its components and energy value of food, as well as the obtained animal production. Considering the above, it is necessary to develop studies that allow to estimate, on a scientific basis, the degree of use of feed, especially if it is a fibrous food, the introduction of which could affect the use efficiency of nutrients in poultry.

There are very few studies that address aspects related to the digestive use of palm kernels in poultry. Therefore, the objective of this study was to determine the nutritional value of Roystonea regia fruit meal for feeding broilers.

Materials and Methods

Animals and diets. Forty male broilers (HE₂₁), 21 d of age, with an average initial live weight of 750 g were used. They were individually housed, according to a completely randomized design, in 40 x 40 x 80 cm galvanized wire metabolic cages. Each cage had a feeder and two nipple-type drinkers. Water intake was ad libitum.

The experimental treatments consisted of four diets, formulated according to the requirements established by ^{NRC (1994)} for this category of poultry. The control consisted of a conventional corn-soybean paste diet. In the remaining three treatments, 5, 10 and 15 % of palm kernel meal were included, so that diets remained isoproteic and isoenergetic throughout the experimental period. Table 1 shows the percentages of inclusion of raw materials in the diets and its calculated composition. For preparing the palm kernel meal, the method proposed by ^{Vives et al. (2020)} was used, with the fruits of royal palm tree, obtained in the Mayabeque province, Cuba.

Table 1 Experimental diets corresponding to growth period (21-35 d) 

Ingredients	Control	Palm kernel 5 %	Palm kernel 10 %	Palm kernel 15 %
Corn meal	55.40	50.29	44.65	38.92
Soybean paste	35.21	35.00	35.25	35.55
Vegetable oil	5.50	5.80	6.15	6.55
Monocalcium phosphate	1.58	1.60	1.60	1.63
Calcium carbonate	1.40	1.40	1.40	1.38
Salt	0.30	0.30	0.30	0.30
Methionine	0.18	0.18	0.13	0.13
Choline chloride	0.13	0.13	0.22	0.24
Mineral and vitamin premix1	0.30	0.30	0.30	0.30
Palm kernel meal	0.00	5.00	10.00	15.00
Calculated analysis, %
CP	19.87	19.72	19.72	19.74
ME, kJ/kg	13.17	13.15	13.12	13.10
CF	2.84	4.25	5.67	7.10
Available P	0.45	0.45	0.45	0.45
Ca	0.91	0.92	0.92	0.93
Met. + Cys.	0.780	0.776	0.782	0.781
Lysine	1.07	1.06	1.05	1.05

¹Vitam. A, 10,000 IU; vitam. D3, 2,000 IU; vitam. E, 10mg; vitam. K, 2 mg; thiamine, 1 mg; riboflavin, 5 mg; pyridoxine, 2 mg; vitam. B₁₂, 15.4 µg; nicotinic acid, 125 mg; calcium pantothenate, 10 mg; folic acid, 0.25 mg; biotin, 0.02 mg. Mineral supplement: selenium, 0.1 mg; iron, 40 mg; copper, 12 mg; zinc, 120 mg; magnesium, 100 mg; iodine, 2.5 mg; cobalt, 0.75 mg

Experimental procedure. To determine the physical and chemical composition of palm kernel, six samples from six bags were analyzed in duplicate. For this, the content of each one was spread individually on a clean and flat surface and portions were taken from the four corners and from the center to form a mixture of approximately 1 kg. Samples were reduced to a particle size of 1 mm in a hammer mill and subsequently passed through a sieve of the same size to guarantee their uniformity.

For the study of apparent fecal retention of nutrients, the total excreta collection method was used (^{Ly and Lemus 2007}). This study was carried out in November at the facilities of the Institute of Animal Science, in Mayabeque, Cuba.

In the first seven days, the animals were adapted to cages and to diet intake. During this period, they had food and water at will. Subsequently, in the following five days, food was offered at a rate of 200 g per day, divided into two rations: morning and afternoon. Rejection was controlled for calculating the intake. Feces were collected, individually and quantitatively. Once the sampling of biological materials was finished, a mixture of the excreta was formed from the taking of an aliquot of 10 % of feces, which was kept frozen at -20 ºC until the moment of its analysis.

Determination of chemical composition. Percentage of dry matter (DM), nitrogen (N), crude protein (CP) and total ash was determined, according to the methodology described by ^{AOAC (2019)}. For the extraction of neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, cellulose and hemicellulose, the fractionation method of ^{van Soest et al. (1991)} was applied. Each analysis was performed by triplicate.

Determination of physical properties. Solubility was determined by the method of ^{Seoane et al. (1981)}. For water adsorption (WAC) and buffer capacities, the procedure described by ^{Savón et al. (1999)} was applied.

Apparent fecal retention of nutrients. It was determined by the following formula:

$Retention,\left(\%\right)=\left(\frac{intake-fecal excretion}{intake}\right)*100$

Experimental design and statistical analysis. Descriptive statistics was used for the analysis of physicochemical composition of palm kernel meal. For the study, position and dispersion statistics were used (mean, standard deviation and coefficient of variation). Pearson correlation was applied to know the association degree among indicators. Correlation values greater than 0.85 (85 %) were considered.

A completely randomized design was used, with four treatments and ten repetitions. For the analysis of apparent fecal nutrient retention, each animal constituted an experimental unit. In the necessary cases, mean values were compared using ^{Duncan test (1955)}. INFOSTAT statistical program (^{di Rienzo et al. 2012}) was used for all analyzes.

Results and Discussion

The physical and chemical composition of palm kernel meal is demonstrated in table 2. DM showed high content, which indicates low moisture content in the meal and confirms that the procedure for its preparation was adequate. According to ^{Sánchez et al. (2020)}, changes in nutritional quality depend on this. CP levels, similar to those reported by ^{Caro et al. (2015)}, were obtained in the western region of Cuba, to which Mayabeque province belongs, from which the source for this study comes. According to the cited authors, the fraction is considered relatively modest when compared to other oilseed sources, such as sesame (Sesamum indicum Linn., 24.02%) (^{Onainor et al. 2018}) and sunflower (Helianthus L., 23.90 %) (^{Zajac et al. 2020}).

Table 2 Physical and chemical composition of palm kernel meal 

Indicators, %		Mean (n=6)	SD	CV, %	Minimum	Maximum
DM		91.31	1.31	1.44	89.69	92.72
CP		8.77	0.14	1.57	8.58	8.90
EE		16.06	0.08	0.52	15.96	16.14
Ashes		5.90	0.32	5.35	5.37	6.24
NDF		72.55	1.40	1.94	70.81	74.11
ADF		55.84	0.66	1.19	55.16	57.01
Lignin		9.19	0.50	5.45	8.71	9.95
Cellulose		45.28	0.79	1.76	44.20	46.40
Hemicellulose		16.70	1.09	1.18	15.46	18.42
Solubility		12.77	0.69	5.40	12.16	13.86
Water adsorption capacity, g/g		7.81	0.38	4.86	7.13	13.86
Buffer capacity	meq acid	0.61	0.14	22.31	0.49	0.82
	meq basic	0.24	0.05	20.77	0.18	0.30

Regarding ether extract (EE), values obtained are within the interval reported by ^{Pérez-Acosta et al. (2020)} for the species (15.84-17.91 %). The high content in this fraction indicates good energy content in the seed. Studies carried out by ^{Vicente-Murillo et al. (2017)} found that fatty acids, between 8 and 18 carbon atoms, are present in R. regia oil. Palmitoleic, oleic and linoleic unsaturated acids, which are beneficial for health, stand out among them. The latter two are known to be hypocholesterolemic, and that their action is determined by the decrease of LDL cholesterol concentrations (bad) and the increase of HDL cholesterol (good) (^{Rincón and Martínez 2009}).

With respect to fibrous fractioning indicators, contents of NDF, ADF and cellulose were high, and coincide with the means previously reported by ^{Arias et al. (2016)}. In general, this high cell wall composition is inversely related to nutrient digestibility and they have low energy content in relation to other fractions (^{Lohaus et al. 2019}). However, lignin values were similar to those reported by ^{Caro et al. (2015)} and lower than those reported for rapeseed (Brassican apus) (12.89-13.15 %) (^{Stubbs and Kennedy 2017}). This component has an inhibitory effect on the optimal use of food, due to the strong covalent bonds that it establishes with the polysaccharides of the cell wall, such as cellulose and hemicellulose, which impose a barrier to its complete degradation (^{Oraby and Ramadan 2015}), so that the less it is present in the food, the better the digestion process will be.

Hemicellulose figures are in the range reported as an average by ^{Giger and Pochet (1987)} for different food sources (10-25 %). For monogastric animals, this fraction is more digestible than celluloses. The hemicellulose:cellulose ratio was 0.37. According to ^{Marrero (1998)}, the lower this ratio is within food, the less the fibrous component could be degraded.

The analysis of physical properties showed low solubility of the studied source, which can be related to high levels of cellulose and to lignin composition. According to ^{Hua et al. (2019)}, both components are part of the insoluble fraction of fiber and are also responsible for regulating the function of the gastrointestinal tract (GIT) of monogastric animals.

Water adsorption capacity is moderate, when compared with the values reported by ^{Arias et al. (2016)} (20.89 %). ^{Mudgil (2017)} stated that this characteristic is the capacity of fiber to swell and retain water in its fibrous matrix, which is related to fiber content, and depends on the relative proportions of the polysaccharides that compose it. Thus, hemicellulose has higher hygroscopic power than cellulose, and it is almost zero in lignin (^{González et al. 2007}). This explains the performance of this indicator in palm kernel.

Buffer capacity (acidic and basic) is one of the physical properties that is related to the regulation of fiber pH in the GIT. This indicator quantifies fiber resistance to vary its pH. As can be seen, palm kernel meal showed better buffering capacity against acids than against bases. This property within the ingredient shows that it can contribute to maintaining pH conditions in the GIT of monogastric species, which is very important, since there is a change in pH during the digestion process, from very acidic (1) to close to neutrality (6.8-7.2) (^{Denbow 2015}).

The analysis of physical properties showed high coefficients of variation, especially in the buffering capacity. These results could be related to the degree of precision of the analytical techniques used in the determination. This property is defined as the degree of agreement of a set of results with each other, which is the dispersion of these around their mean (^{Sharma et al. 2018}).

Table 3 shows the result of the correlation between chemical characteristics and physical properties. The solubility had the greatest dependence in relation to the contents of NDF (P = 0.02), ADF (P = 0.01) and cellulose (P = 0.02), and it was negative with respect to DM (P = 0.02). This result corroborates what was previously explained, which has to do with the insoluble nature of palm kernel fiber and its possible effect on the gastrointestinal tract of monogastric animals.

Table 3 Pearson correlation matrix for the physical and chemical composition of palm kernel meal 

	DM	EE	NDF	ADF	LIG	CEL	WA	Sol	ABC	BBC
DM	1.00
EE	-0.66	1.00
NDF	-0.79	0.86	1.00
ADF	-0.74	0.32	0.66	1.00
LIG	0.40	0.37	0.18	-0.39	1.00
CEL	-0.88	0.32	0.61	0.93	-0.62	1.00
WA	-0.77	0.32	0.66	0.63	-0.44	0.75	1.00
Sol	-0.87	0.62	0.88	0.93	-0.19	0.89	0.70	1.00
ABC	-0.53	0.38	0.72	0.64	0.12	0.54	0.56	0.76	1.00
BBC	0.58	-0.25	-0.15	-0.48	0.48	-0.60	-0.02	-0.46	-0.10	1.00

LIG-lignin, CEL- cellulose, WAC- water adsorption capacity, Sol-solubility, ABC-acid buffer capacity, BBC- basic buffer capacity

The high dependence between EE and NDF contents is interesting (P = 0.03). Studies of ^{Srikaeo et al. (2017)} with rice bran, sunflower and sesame oil observed that fibers exhibited the ability to retain oil, which could be related to surface properties of particles, the general charge density and the hydrophilic nature of fiber constituents. This explanation could be the cause of the present result, which should be demonstrated in subsequent studies.

Cellulose was negatively correlated with DM content (P = 0.02) and positively with that of ADF (P = 0.01). This is explained from the constitution of the latter according to the fractionation of the fibrous fraction proposed by ^{van Soest et al. (1991)}. This result is logical, considering that, from the ADF, during the fractionation of the cell wall by means of a digestion in acid solution, the cellulose values that compose the wall are obtained.

Apparent fecal retention of NDF showed a reduction from the 10 % inclusion of palm kernel meal in the ration, while in both, the control and the 5 %, there was no difference among treatments (table 4). ^{Leung et al. (2018)} reported similar values of this indicator for soybean (55.4 %) and oat (59.4 %), and higher for flax (61.20 %). The explanation for the differences is related to the fiber properties of each ingredient. In the latter, soluble fiber predominated, which can be digested by cecal fermentation, unlike the first two, which nature is more insoluble, as occurs with palm kernel.

Table 4 Apparent fecal retention of nutrients in broilers that consume palm kernel meal in the ration 

Retention, %	Treatments				SE±	P- value
	Control	Palm kernel 5 %	Palm kernel 10 %	Palm kernel 15 %
DM	70.42	72.36	69.98	66.11	1.96	0.1676
NDF	58.73^c	51.87^c	42.89^b	31.70^a	3.07	<0.0001
EE	86.28^ab	88.04^b	84.85^ab	83.38^a	1.17	0.0484

^a,b Values with different letters in the same row differ significantly at P < 0.05 (^{Duncan 1955})

Regarding apparent fecal retention of the lipid fraction, it was observed that the highest coefficient was reached with 5 %, and the lowest with 15 % (table 4). When evaluating other oilseeds, such as sesame (Camelina sativa L. Crantz), flax (Linum L.) and sunflower (Helianthus L.), fat digestibility decreased compared to control diet, which did not contain ground oilseeds, according to reports by ^{Zajac et al. (2020)}. The authors associated the effect with a high content of non-starch polysaccharides in soluble (~ 46 %) and insoluble (~ 54 %) form. Although the first fraction is found to be less than the second, its values are high, which increases the viscosity of digesta and, consequently, reduces the digestibility of all nutrients, specially lipids. The mechanism by which this occurs is related to the increase of thickness of the water layer, which must pass through solutes to reach the enterocyte membrane, and forms a barrier between enzyme and substrate with an anti-nutrient effect, as it decreases the absorption of glucose, lipids and amino acids.

Nevertheless, retention values for all treatments were high, so it can be stated that palm kernel contains high quality oils. Hence, greater use efficiency of these nutrients is observed in broilers. ^{Avazkhanloo et al. (2020)} reported similar performance with the inclusion of flax seeds in the ration of broilers. According to the cited authors, this occurs due to the increase of lipase activity, which results in improvements in emulsification and hydrolysis of dietary lipids, the formation of micelles and their transport to the epithelial surface. ^{Vives et al. (2020)} recorded an increase in this enzyme, when using this food resource in diets intended for broilers.

It is concluded that palm kernel meal has adequate nutritional value for feeding broilers.

Acknowledgements

Thanks to the work carried out by the Central Laboratory Unit of the Institute of Animal Science in the chemical-physical analyses, especially to the technician Yasmila Hernández Herrera.

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Received: June 14, 2021; Accepted: August 04, 2021

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Conflict of interest: The authors declare that there are no conflicts of interests among them

Author´s contribution: Madeleidy Martínez-Pérez: Original idea, experimental design, data analysis, writing the manuscript. Yesenia Vives Hernández: Conducting the experiment, data analysis, writing the manuscript. Bárbara Rodríguez: Experimental design, conducting the experiment, data analysis. O.G.Pérez: Conducting the experiment, data analysis. Magalys Herrera Villafranca: Statistical analysis