Digestibility and estimation of digestible energy of palm kernel (Elaeis guineensis) cake in guinea pigs (Cavia porcellus)

Luis Vela-Román, Mary Césare-Coral¹, Edgar Norabuena-Meza², María T Valderrama Rojas³, Elizabeth Paitan-Anticona⁴, F Airahuacho-Bautista⁵ and Sotelo-Méndez A

Facultad de Zootécnica, Universidad Nacional Agraria La Molina, Lima, Perú
fairahuacho@unjfsc.edu.pe
¹ Facultad de Ciencias, Universidad Nacional Agraria La Molina, Lima, Perú
² Facultad de Ingeniería Química y Textil, Universidad Nacional de Ingeniería, Lima, Perú
³ Facultad de Ingeniería Ambiental y Recursos Naturales, Universidad Nacional del Callao, Perú
⁴ Facultad de Ingenierías Alimentarias, Universidad Nacional del Centro del Perú, Huancayo, Perú
⁵ Departamento Departamento Académico de Zootecnia, Universidad Nacional José Faustino Sánchez Carrión, Huacho, Lima, Perú

Abstract

The objective of the research was to determine the digestibility of the nutritional fractions of palm kernel cake and to estimate the digestible energy required for the formulation of rations according to the animal species. Ten male guinea pigs (body weight: 725 ± 38 g) were distributed in individual metabolic cages. The control group (n: 5) was fed 100% wheat bran and the experimental group 40% palm kernel cake and 60% wheat bran. Both diets contained the minimum vitamin C requirement. The adaptation phase to the new feed lasted 10 days. For the next five days, 50 g of feed was fed and feces were collected daily. The nutrient digestibility coefficients determined by the indirect method were 69; 70; 81; 61; 66 and 53% for dry matter, crude protein, ether extract, crude fiber, nitrogen free extract and ash, respectively. The digestibility coefficients, multiplied by their caloric values, allowed estimating the digestible energy, which was 2720 kcal/ kg of palm kernel cake. The high carbohydrate content of palm kernel cake classifies it as an energetic ingredient. The good digestibility of its nutritional fractions at the digestive level provides amounts of digestible energy similar to that of conventional ingredients used in the integral feeding of guinea pigs.

Key words: apparent digestibility, crude fiber, gross energy, oil cake, wheat bran

Introduction

Oil palm (Elaeis guineensis) is one of the main sources of vegetable oil production in the world (Vijay et al 2016). After the oil is extracted from the fruit, a by-product called palm kernel cake is generated, rich in protein and fat, and used as one of the main components for ruminant feed formulation (Hashim 2012). However, its inclusion in poultry and swine feed is limited due to its high fiber content (Tafsin et al 2017).

The guinea pig (Cavia porcellus) is a strictly herbivorous animal, with a stomach fully lined with glandular epithelium and bulky caecum (Sakaguchi et al 1986; Shomer et al 2015). The passage of food through the guinea pig stomach is only 2 hours, while through the entire gastrointestinal tract is 20 hours (range 8-30) (Jilge 1980). However, with cecotrophy, a common behavior in guinea pigs (Hargaden and Singer 2012), the passage of food chyme through the gastrointestinal tract can be 60-70 h (Jilge 1980). These particularities make the guinea pig efficient in digesting crude fiber, even more efficiently than the rabbit (Sakaguchi et al 1987), in addition to efficiently digesting dry matter, organic matter and ash (Sakaguchi and Ohmura 1992).

The constant fluctuation and scarcity of traditional ingredients motivate to investigate alternative inputs that can be included in animal rations. According to Santos et al (2019), the use of palm kernel cake in animal feed is considerably limited due to the scarce knowledge of its nutritional qualities, the performance of animals fed with this residue and its economic value as a dietary ingredient. In order to include palm kernel cake in guinea pig diets, the present research determined the digestibility of dry matter, crude protein, ethereal extract, crude fiber, ash and nitrogen free extract by in vivo assays, and estimated the digestible energy.

Materials and methods

Facilities and equipment

The research was carried out in the Laboratory of Nutritional Evaluation of Foods of the Academic Department of Nutrition, Faculty of Animal Husbandry, Universidad Nacional Agraria La Molina.

Ten stainless steel metabolic cages with an area of 137 cm² (38 cm long, 36 cm wide and 30 cm high) were used. Each cage had a steel mesh floor and underneath, a funnel-shaped tray for separate collection of feces and urine. Metal feeders and clay drinkers were incorporated into the cage. An electronic scale (OHAUS GT 2100) with a sensitivity of 0.1 g was used for weighing the feces and feed.

Experimental animals and evaluated ingredient

Male guinea pigs, weighing 725 ± 38 g of the Cieneguilla UNALM genotype, were individually distributed in each metabolic cage, which represented the experimental unit. The control group consisted of five experimental units and were fed only wheat bran (basal diet). The experimental group received a diet composed of 40% palm kernel cake and 60% wheat bran (WB). Feed in the physical form of meal and water were supplied ad libitum. The feed contained 0.20 g vitamin C/kg; the minimum concentration recommended by the NRC (1995).

Digestibility experiment

During 15 days, the guinea pigs were acclimatized to the management, type of facility and feed supplied. For an adequate adaptation to the new feed, the guinea pigs of the experimental group received during the first four days, levels of palm kernel increased by 10%, until reaching the proportion of 40% palm kernel cake and 60% WB, a diet that they consumed for a period of 10 days. During the following five days of experimentation, 50 g of feed were fed daily to each experimental unit and the total feces were collected and individually refrigerated in polyethylene bags for subsequent analysis.

Proximal chemical analysis and estimation of digestibility coefficients

Samples of diets from both the control and experimental groups, as well as fecal samples collected from each experimental unit during the five days, were sent to the laboratory for proximate chemical analysis, according to AOAC (2005).

The apparent digestibility coefficients (DC) for the diets of the control and experimental groups were estimated by the direct method described by Crampton and Harris (1974), according to the following formula:

On the other hand, the apparent digestibility coefficients for palm kernel cake (DCp) were estimated by the indirect method, according to Crampton and Harris (1974):

Estimation of gross and digestible energy

The gross energy of the diet of the control and experimental groups, in addition to the palm kernel cake and feces, were estimated using the following formula (AEC 1978):

Where:

GE: Gross Energy, kcal/100 g.

CP: Crude Protein, %.

EE: Ethereal Extract, %.

CF: Crude Fiber, %.

NFE: Nitrogen Free Extract, %.

The digestible energy (DE) of the basal and experimental diet was estimated with the following formula:

Where:

DE: digestible energy of the basal or experimental diet, kcal/100g.

dc: digestibility coefficient, %.

The digestible energy of the palm kernel cake was estimated by the formula of Crampton and Harris (1974):

Where:

DEtp: digestible energy of palm kernel cake.

DEe: digestible energy of the experimental diet

DEb: digestible energy of the basal diet

% substitution: percentage by which WB is substituted

Results and discussion

The chemical composition of the diets fed and feces collected are shown in Table 1.

Table 2 shows the amounts of ingested chemical components and undigested remains in the collected feces. With this information, digestibility coefficients were estimated for each fraction determined by proximal chemical analysis.

The estimated digestibility coefficients for dry matter, crude protein, ethereal extract, crude fiber and ash did not differ by more than three percentage points between the basal and experimental diets. The digestibility coefficient for nitrogen free extract was lower by five percentage points for the experimental diet compared to the basal diet, due to the lower intake and higher elimination by feces of this fraction.

Table 3 shows the chemical composition and digestibility coefficients of the palm kernel cake. It also shows the estimated digestible energy of palm kernel cake using the digestibility coefficients of the chemical components shown in Table 2.

The chemical composition of the palm kernel cake determined in the present investigation was numerically similar to those reported by other investigations. Martínez et al (2021) report values of 16 % crude protein and 25 % crude fiber, while Ribeiro et al (2018) report values of 92% dry matter, 17% crude protein, 9.7% ether extract and 3.2% ash. da Silva et al (2020 report values of 90% dry matter, 16% crude protein, 7% ether extract and 2.8% ash.

There are no previous studies related to the nutritional value of palm kernel cake in guinea pigs. The rabbit (Oryctolagus cuniculus) is a species with a similar anatomy and digestive physiology to that of guinea pigs, so it is relevant to compare them in terms of the efficiency of nutrient utilization at the digestive level. Carrión et al (2011) when evaluating the nutritional value of palm kernel cake in growing rabbits determined the apparent digestibility of crude protein, neutral detergent fiber, ethereal extract and gross energy of 54; 43; 85 and 55%, respectively. These digestibility values, with the exception of ethereal extract, are lower than those found in the present study.

The protein digestibility coefficient of palm kernel cake protein in the present study was 70%, similar to that of rabbits according to FEDNA (2015). However, the published digestibility coefficient for crude energy is significantly lower. The DE for rabbits according to FEDNA (2015) is 1850 kcal and estimating the GE at 3868 kcal (using their published chemical values), gives an apparent digestibility of 48% for GE.

Palm kernel cake is shown as an alternative ingredient to WB, the main ingredient in whole-grain guinea pig diets. Hidalgo and Valerio (2020) reported values of 65% digestibility for WB with 9.3% crude fiber. In the present study, the digestibility coefficient for dry matter was 69% with a crude fiber content of 28.8%. That is, with a value three times higher in crude fiber, palm kernel cake showed a digestibility coefficient for dry matter higher by four percentage points, compared to WB.

The energy value of palm kernel cake estimated in the present study is numerically similar to that of other traditional ingredients used in guinea pig feeding, despite the high level of fiber. Hidalgo and Valerio (2020) estimated 2801 kcal DE/kg for WB, while Vergara (2008) reports a value of 2727 kcal DE/kg for alfalfa hay meal containing 17% crude protein and 30% crude fiber. Digestible energy content decreases as dietary fiber, the carbohydrate fraction resistant to digestion by mammalian enzymes in the small intestine, but partially or fully fermented in the hindgut, increases (Topping and Clifton 2001; Zhang et al 2013).

Conclusions

The high carbohydrate content of palm kernel cake shows it as an energetic ingredient for guinea pig feeding. The good digestibility of its nutritional fractions at the digestive tract level is related to an adequate contribution of digestible energy, similar to that of traditional ingredients such as WB and alfalfa hay.

Acknowledgments

The authors would like to thank the Laboratorio de Evaluación Nutricional de los Alimentos, where the experimental phase was carried out, and La Molina Calidad Total Laboratorios for providing the results of the chemical analyses performed.

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