An approach to the study of the nutritive value of mulberry leaf and palm oil in growing pigs

Una Aproximación al Estudio del Valor Nutritivo de Hojas de Morera y Aceite de Palma
en Cerdos en Crecimiento

 

Carlos González¹, Ricardo Tepper¹ and Julio Ly ²

 

¹Institute of Animal Production, Faculty of Agronomy, Central University of Venezuela. PO Box 4579, El Limón, Maracay, Venezuela.

²Swine Research Institute. PO Box 1, Punta Brava, Havana City, Cuba. E-mail: gonzalezc@agr.ucv.ve / jlyca@yahoo.com

 

Abstract

 

Forty eight crossbred castrated male pigs averaging 32 kg initial weight were employed according to a random block design arranged in a factorial 3×4 experiment to determine total tract digestibility coefficients of diets formulated to contain 0, 10 and 20% of mulberry (Morus alba) leaf meal and 0, 3, 6 and 9% of crude palm (Elaeis guineensis Jacq.) oil. Feed intake was fixed as 0.08 g DM/kg^0.75 per day given in two daily equal rations. The mulberry leaf meal contained crude protein (N×6.25) 14.50 and NDF 34.55% and 17.81 kjoule/g on dry matter basis respectively. There was no significant interaction (P > 0.05) between mulberry foliage meal and crude palm oil levels in any digestibility index. Overall, digestibility indices were high. Increasing levels of mulberry leaf meal in diet had a significant (P < 0.01) negative influence on DM, organic matter, NDF, N and energy respectively, This same trend, although not significant (P > 0.05) was observed for increasing levels of crude palm oil in the diet on digestibility indices of pigs. N and organic matter digestibility of mulberry as determined by difference were 43.65 and 64.65 % respectively, whereas digestible energy accounted for 9.41 kjoule/g DM. Digestible energy estimated for the crude palm oil was rather low 16.12 kjoule/g DM). It is suggested that mulberry leaf meal could be introduced up to 20% in diets for growing pigs with no deleterious influence on total tract digestibility indices. The use of palm oil up to 9% can contribute to increase the energy density of the diet. Due to the relatively low digestibility of crude palm oil, methods should be investigated in order to improve its nutritive value.

 

Key words: Pigs, mulberry leaves, crude palm oil, digestibility.

 

Resumen

 

Se emplearon 48 cerdos machos castrados con un peso promedio inicial de 32 kg, según un diseño de bloque al azar en arreglo factorial 3×4 para determinar coeficientes de digestibilidad aparente en todo el tracto digestivo, de dietas formuladas para contener 0; 10 y 20% de harina de hojas de morera (Morus alba), y 0; 3; 6 y 9% de aceite crudo de palma (Elaeis guineensis Jacq.). El consumo de alimento se fijó en 8% del peso metabólico (PV^0,75) por día en dos raciones iguales. La harina de hojas de morera contenía 14,50 y 34,55% de proteína bruta (N×6,25) y FDN así como 17,81 kjoule/g MS respectivamente. No hubo interacción significativa (P > 0,05) entre los niveles de harina de hojas de morera y aceite crudo de palma para ningún índice de digestibilidad. El incremento del nivel de harina de hojas de morera tuvo una influencia negativa (P < 0,01) en la digestibilidad de MS, materia orgánica, FDN, N y energía respectivamente. La digestibilidad del N y la materia orgánica de la morera determinada por diferencia fue 43,65 y 64,65% respectivamente, mientras que la energía digestible fue 9,41 kjoule/g MS. Se sugiere que la harina de hojas de morera pudiera ser introducida hasta un 20% en dietas para cerdos en crecimiento con baja influencia negativa de este nivel de inclusión sobre los índices digestivos de todo el tracto. El uso de aceite crudo de palma hasta 9% puede contribuir a incrementar la densidad energética de la dieta. Debido a la digestibilidad relativamente baja del aceite crudo de palma, debieran investigarse métodos para mejorar su valor nutritivo.

 

Palabras clave: Cerdos, crecimiento, hojas de morera, aceite crudo de palma, digestibilidad.

 

Recibido: 25 / 11 / 2004. Aceptado: 29 / 09 / 2005.

 

Introducción

 

The use of tree foliage for feeding animals has been examined in several moments [6], whereas in the specific case of mulberry (Morus alba) leaves or foliage, there are some indications suggesting that either its nutritive value [4, 9, 12] or its feeding value [13, 15, 21] for pigs, is not negligible. In parallel to these investigations, several studies has been conducted related to the possibility of use of palm (Elaeis guineensis Jacq) oil as a common ingredients in diets for pigs fed several types of foliage [2, 8, 17, 19] in order to compensate the decrease in energy density of such fibrous diets. In this aspect, it has been observed that total tract digestibility coefficients tend to decrease in the same manner that the proportion of palm oil increases in the diet [2, 17]. Moreover, Leduc [11] observed that pigs fed on crude palm oil showed a clear deterioration in DM and energy digestibility.

This communication reports further studies concerning the effect of the use of palm oil on mouth-to-rectum nutrient digestibility in pigs, and the nutritive value of mulberry leaf for pigs.

Materials and Methods

 

A total of 48 crossbred castrated male pigs averaging 32 kg initial weight were employed according to a random block design arranged in a factorial 3×4 experiment to determine total tract digestibility coefficients of diets formulated to contain 0, 10 and 20% of mulberry (Morus alba) leaf meal and 0, 3, 6 and 9% of crude palm (Elaeis guineensis Jacq.) oil according to swine nutritional requirements of National Research Council [14]. Mulberry leaves and petioles from an unknown cultivar grown at the Animal Production Institute (Universidad Central de Venezuela, Maracay), were separated from the stems, then sun-dried and milled to obtain a dry meal. Feed intake was fixed as 0.08 kg DM/kg^0.75 per day given in two daily equal rations. The mulberry foliage meal contained DM 89.34% and protein (N×6.25) 14.50, NDF 34.55, ether extract 3.81, ash 15.44% on dry matter basis respectively. The calorific value of mulberry leaf meal and crude palm oil were 17.81 and 40.00 kjoule/g DM respectively. Details related to the characteristics of the diets are presented in TABLE I.

The animals were housed in metabolism cages, in an open building at the Institute of Animal Production, Universidad Central de Venezuela, Maracay. Water was provided for ad libitum consumption from drinking nipples attached to the cages. Each experimental period consisted of five days of adaptation of the animals to the experimental diets, followed by another three days of collection of faeces. Feed refusals if any and faeces were collected two times per day, and conveniently frozen until analysis. Other details of the daily routine work are exposed elsewhere [19].

Duplicate samples of feed were analyzed for DM, ash, ether extract and N content as outlined by Association of Official Analytical Chemist (AOAC) [1]. Cell walls, identified as the insoluble material in neutral detergent solution (neutral detergent fibre, NDF), were determined as described by Van Soest et al. [22]. The organic matter content of samples was defined as the difference of 100 minus % ash. The gross energy content of the samples was determined in an adiabatic bomb calorimeter, using benzoic acid as calorimetric standard. The same analytical procedures were conducted in faeces, except for ether extract determinations. Estimations of nutrient digestibility of mulberry leaf meal and crude palm oil were made by difference [5].

TABLE I
characteristics of the diets (per cent in dry basis) / características de las dietas (% ms)

1 Premix of vitamins and minerals according to NRC [14] requirements.

Contrasts amongst means were made by the analysis of variance technique, and when significant differences (P < 0.05) were encountered, the Duncan´s multiple range and multiple F test was used for discrimination amongst means [20]. The SAS [18] computing package was used in all cases.

 

Results and discussion

 

There was not any symptom of animal discomfort during the conduction of the trial. Feed consumption was found to be complete, since no feed refusal was evident during the entire experimental work. There was no significant interaction (P > 0.05) between mulberry leaf meal and crude palm oil in any digestibility index.

A general significant trend (P < 0.01) of faecal DM concentration to decrease and excretion of fresh material to increase with increasing levels of mulberry leaves in the diet was observed (TABLE II). Accordingly, water and dry faecal output significantly (P < 0.01) increased with the introduction of mulberry leaf meal in the feed. In other experiments, Chiv et al. [4] observed an increased faecal material output when mulberry leaves were included in the diet up to 50%. This same trend was not significant when crude palm oil was introduced in the diet.

All digestibility criteria examined in the current experiment, except ash digestibility, decreased in value in the same manner that levels of either mulberry leaf meal or crude palm oil increased in the feed (TABLE III). In fact, either DM and organic matter digestibility or NDF, N and energy digestibility were significantly (P < 0.01) depressed when mulberry foliage was systematically increased in the diet.

Mouth-to-rectum digestibility values obtained by Ly et al [12] and Chiv et al [4] were rather high for pigs fed up to 50% of mulberry leaves. Nevertheless, it was not encountered in the above referred experiments, the same trend observed in the current study, of nutrient digestibility to vary inversely to the level of mulberry leaf meal included in the feed. The nature of the cultivar utilized in the Cambodian experiments, and the fact that petioles were not used in those studies could strongly explain these differences in results. In fact, mulberry leaf meal prepared at Chamcar Daung (Cambodia) had a high and low N and NDF content respectively, as compared to the chemical composition of the mulberry foliage employed in the current study. Nevertheless, this is not an abnormal condition, taken into account the studies of Pérez [16], who claimed that energy digestibility in diets for pigs, decreases in 1.03 units in response to the increase of one percent of NDF content in the feed. In this connection, it should be very important to establish the role of the large intestine in digestive processes of pigs fed mulberry leaves and foliage, the nature of the cultivar utilized, and the influence of leaves, petioles and stems on digestibility of the diet.

TABLE II
faecal characteristics in pigs fed mulberry leaf meal and crude palm oil / características fecales de cerdos alimentados con harina de follaje de hojas de morera y aceite crudo de palma

** P < 0.01. ^abMeans without letter in common in the same row differ significantly (P < 0.05).

TABLE III
faecal digestibility of nutrients in pigs fed mulberry leaf meal and crude palm oil / digestibilidad aparente en cerdos alimentados con harina de follaje de morera y aceite crudo de palma

* P < 0.05. ** P < 0.01. ^abcMeans without letters in common in the same row differ significantly (P < 0.05).

In the case of crude palm oil, Chhay and Ly [3] and Prak [17] observed that pigs fed increasing levels of this type of oil in the ration, showed a depression in total tract digestibility of ash and ether extract, thus suggesting the formation of insoluble salts from fatty acids in the intestinal lumen. This hypothesis could not be tested in the current investigation, but in fact ash digestibility tended to be low with increasing levels of crude palm oil in the diet.

There was a strong indication that either N digestibility was highly correlated (r = - 0.822; P < 0.001) to the NDF digestibility of the diet, thus suggesting that an important proportion of the N could be linked to the cell walls. In this connection, Trigueros and Villalta [21] reported that 56.6% of total N was linked to the cell wall in the mulberry foliage meal used in their trial at Izalco. In the current investigation, the relationship found was the following:

N digestibility, % = 52.91 – 0.47 NDF digestibility,
(S_yx = ± 3.32)

Estimates of nutrient digestibility indices of mulberry leaf meal are listed in TABLE IV.

There were no significant differences between digestibility indices for mulberry leaf meal in the case where the leaves were included in the diet. Therefore, all data were pooled (n = 32), and the resulting average values for DM, ash, organic matter, NDF, N and energy digestibility were 61.35, 85.13, 64.65, 19.98, 43.65 and 52.81% respectively. Estimated digestible energy value for mulberry leaf meal was 9.41 kjoule/g DM. As to be expected, N digestibility of mulberry leaf meal was low if compared to that reported previously [12], as a probable consequence of the differences in the chemical composition of the mulberry used in both experiments.

Contrary to what occurred with the foliage examined in the present study, when energy digestibility of crude palm oil was estimated by difference, the obtained values were extremely variable. Average values were 43.0, 33.2 and 44.7% if the oil was included at a rate of 3, 6 and 9% in the diet. The observed variability was from more than 100% to negative values for energy digestibility in the crude palm oil. A similar situation was encountered previously by Seijas et al. [19] when crude palm oil was included in diets for pigs fed trichanthera foliage. The high variability in energy digestibility for crude palm oil could be a consequence of the relatively low level of inclusion of the oil in the diet. Nevertheless, although not significantly (P > 0.05), energy digestibility of the diets decreased with either crude [19] or refined [3] palm oil included in the feed for pigs.

TABLE IV
nutrient digestibility of mulberry leaf meal estimated by difference / digestibilidad estimada por diferencia de nutrientes de harina de follaje
de morera

 

Nutrient digestibility of palm oil has not been extensively studied, and data related to its nutritive value are conflicting [7, 11]. On this matter, Seijas et al [19] found a value as low as 56.5% for ether extract digestibility of crude palm oil, and it was attributed to the influence of the high palmitic acid content of palm oil [10]. This fact merits further research.

 

Conclusions

 

It is suggested that if mulberry leaf meal is introduced up to 20% in diets for growing pigs, a decreasing effect on total tract digestibility indices should be encountered. The use of crude palm oil up to 9% can contribute to maintain the energy density of the diet. However, due to the relatively low digestibility of crude palm oil, methods should be investigated in order to improve its nutritive value.

 

Acknowledgments

 

The authors thank gratefully to the staff of the Pig Unit of the School of Agronomy of the Universidad Central de Venezuela. Similar gratitude is expressed to the librarians of the Swine Research Institute of Cuba for helping in the localization and organization of the bibliography herein mentioned.

 

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