Nutritive value for pigs of New Cocoyam (Xanthosoma sagittifolium); digestibility and nitrogen balance with different proportions of fresh leaves and soybean meal in a basal diet of sugar cane juice

Lylian Rodríguez, Irina Peniche*,T R Preston and K Peters **

UTA-TOSOLY, Socorro, Santander-Sur, Colombia
lylianr@utafoundation.org
* FUSM, Barranquilla- Colombia
** Humboldt University, Berlin

Abstract

The four treatments applied to 4 growing pigs in a 4*4 Latin square arrangement were levels of fresh leaves of New Cocoyam (Xanthosoma sagittifolium) (NC) equivalent to 0, 30, 60 and 100% substitution of the protein from soybean meal in a basal diet of fresh sugar cane juice. The pigs were crossbred castrated males (Yorkshire*Landrace*Pietran) with initial weight of 13.4±0.54 kg. They were maintained in metabolism cages made from wood and bamboo. Experimental periods were of 14 days with collection of faeces and urine during the last 5 days of each period.

There were significant effects of N intake on DM intake, urine N excretion, and N retention. Adjusting the data for these variables by covariance for differences in N intake changed markedly the treatment effects on DM intake and N retention. After adjustment, DM intake was highest for NC100 and lowest for NC0, while N retention was similar on all diets. N retention as a proportion of the N digested was higher on the diets containing Cocoyam leaves. Apparent OM digestibility declined from 920 to 808 and that of crude protein from 820 to 608 g/kg for the diets with increasing proportions of Cocoyam leaves.

It is concluded that the protein in fresh Cocoyam leaves has a high biological value and that the limiting nutritional factor is the lower digestibility of the protein compared with soybean meal.

Key words: Xanthosoma sagittifolium, feed intake, fibre, foliages, New Cocoyam, tropics

Valor nutritivo del Malangay (Xanthosoma sagittifolium) para cerdos; digestibilidad y balance de nitrógeno con diferentes proporciones de hojas frescas de Malangay y harina de soya en una dieta basal de jugo de caña de azúcar

Resumen

Los cuatro tratamientos asignados a 4 cerdos en crecimiento en un arreglo de cuadrado lation 4*4 fueron niveles de hojas frescas de Malangay (Xanthosoma sagittifolium) equivalentes a 0, 30, 60 y 100% de sustitución de la proteína de la harina de soya en una dieta basal de jugo fresco de caña de azúcar. Los cerdos empleados fueron machos castrados cruzados (Yorkshire*Landrace*Pietran) con un peso inicial de 13.4±0.54 kg. Se alojaron en jaulas metabólicas hechas de madera y bamboo. Los periodos experimentales fueron de 14 días con recolección de heces y orina durante los últimos 5 días de cada periodo.

Hubo diferencias significativas del consumo de N sobre el consumo de MS, la excreción de N en la orina, y la retención de N. Ajustando los datos de estas variables mediante covarianza por las diferencias de consumo de N se obtuvo un cambio marcado del efecto de los tratamientos sobre el consumo de MS y la retención de N. Después del ajuste, el mayor consumo de MS se obtuvo con el tratamiento NC100 mientras que la NC0 presentó el menor valor; la retención de N fue similar para todas las dietas. La retención de N expresada como proporción del N digerido fue mas alta en las dietas con hojas de Malangay. A medida que se incrementó la proporción de hojas de Malangay, la digestibilidad aparente de la MO disminuyó de 920 a 808, y también la de la proteína cruda (de 820 a 608 g/kg).

Se concluye que la proteína en las hojas frescas de Malangay posee un alto valor biológico y que el factor nutricional limitante es una menor digestibilidad de la proteína comparada con la harina de soya.

Palabras clave: Xanthosoma sagittifolium, consumo alimenticio, fibra, follajes, Malangay, trópicos

Introduction

This paper on the nutritive value for pigs of leaves of New Cocoyam is a contribution to a collaborative program (see http://mekarn.org/proprf/content.htm) aimed to develop locally available protein sources that promise to be viable alternatives to soybean and fish meals in diets for pigs. Foliages from sweet potato (Ipomoea batatas) (Le Van Anh 2004; Le Van An et al 2005; Sokha et al 2007), cassava (Manihot esculenta) (Bui Huy Nhu Phuc 2006; Nguyen Thi Hoa Ly 2006), mulberry  (Morus alba) (Chiv Phiny et al 2007a,b) and water spinach (Ipomoea aquatica) (Chhay Ty and Preston 2006a,b) have been researched in considerable detail. Attention is now being given to members of the Genus Colocasia (Rodríguez et al 2006; Pham Sy Tiep et al 2006; Ngo Huu Toan and Preston 2007), which are widely distributed in tropical latitudes, often as wild or uncultivated plants.

Taxonomy of the Genus Colocasia

The New Cocoyam (also referred to as "Giant Taro") is a member of the family of Araceae, of which there are one hundred genera and more than fifteen-hundred species. Their preferred habitats are in tropical or subtropical environments which are moist and shady. Some are terrestrial plants while others are vines, creepers, or climbers. Many species of the Araceae are also epiphytes. The major edible species are classified in two tribes and five genera: Lasioideae (Cyrtosperma and Amorphophallus); and Colocasiodeae (Alocasia, Colocasia, and Xanthosoma). Taro (Colocasia esculenta [L.] Schott) is considered as a single polymorphic species.

Taxonomic classification: Xanthosoma saggitifolium Schott:

Type: Fanerogamas
Sub-type: Angiospermae
Phylum or division: Mangnoliophyta
Class: Liliopsida (Monocotyledonous)
Order: Arum
Family: Araceae
Genus: Alocasia, Colocasia and Xanthosoma
Species: Xanthosoma saggitifolium

Origin and Geographic Distribution

Colocasia is widely distributed in the Indo-Malayan region (India and Bangladesh), Asia, Pacific islands, Egypt and the Mediterranea, Africa, Caribbean and America. Xanthosoma is native to South and Central America.

"New Cocoyam" (Xanthosoma sagittifolium) can be identified by the presence of a corm (see Figure1a and Photo 1a) which is absent in "Old Cocoyam" (Colocasia esculenta) (Figures 1b and Photo 1b).

Figure 1a. New Cocoyam or Giant Taro (Xanthosoma sagittifolium)		Figure 1b: Old cocoyam or Taro (Colocasia esculenta)
Photo 1a. New Cocoyam or Giant Taro (Xanthosoma sagittifolium)		Photo 1b: Old cocoyam or Taro  (Colocasia esculenta)

In a previous study (Rodríguez et al 2006), it was shown that fresh leaves of New Cocoyam (Xanthosoma saggitifolium) could replace 50% of the soybean meal with no differences in growth rates or feed conversion in growing pigs fed a basal diet of fresh sugar cane juice. The following experiment was designed to study the effects on apparent digestibility and nitrogen retention of feeding fresh Xanthosoma leaves as a complete replacement of the soybean meal in weaned pigs fed the same basal diet of fresh sugar cane juice.

Materials and Methods

Location

The study was carried out in the "Finca Ecológica", TOSOLY, Morario, Guapota, Department of Santander, Colombia (6° 18" N, 73° 32" W, 1500 msl) between February and May 2006. Air temperature ranges between 19 and 28°C in the day, falling to around 12°C during the night. Rainfall is between 2700 and 3000 mm/year.

Treatments and design

The four treatments (NC0, NC30, NC60 and NC100), applied to 4 growing pigs in a 4*4 Latin square arrangement,  were levels of fresh leaves of New Cocoyam equivalent to 0, 30, 60 and 100% substitution of the protein from soybean meal in a basal diet of fresh sugar cane juice. The pigs were crossbred castrated males (Yorkshire*Landrace*Pietran) with initial weight of 13.4±0.54 kg. They were maintained in metabolism cages made from wood and bamboo in which they were able to move freely (Photos 2a and 2b). Experimental periods were of 14 days with collection of faeces and urine during the last 5 days of each period.

Photo 2a: Metabolism cage made from wood and bamboo		Photo 2b: The pigs can move freely in the cage

Diets and feeding

The recently weaned piglets were bought from a commercial farm where they had been fed with commercial concentrates. As soon as they arrived at the TOSOLY farm they were offered fresh New Cocoyam leaves and sugar cane at increasing levels, replacing the commercial concentrate. The piglets accepted immediately the sugar cane juice but acceptance of the leaves was a more gradual process, requiring a period of two weeks before the planned levels of the leaves were consumed.  After this period of adaptation, the piglets were put in the metabolism cages.

Leaves plus petioles of New Cocoyam were harvested daily from plants of similar ages (30-35 days cutting interval) located in the farm. The leaves were separated from the petioles and passed first through a mechanical forage chopper. Sugar cane stalks grown on the farm were passed once through a 3-roll mill to separate the juice from the residual fibre (bagasse); the juice was then filtered through a coarse sieve (1 mm holes) and  weighed according to the intended offer level.  It soon became apparent that there were problems in ensuring accurate measurement of the intakes of the leaves as due to their physical form (as large pieces of 3-5 cm length), the piglets were throwing them out of the feed trough. Furthermore, they much preferred the sugar cane juice and left the leaves to be eaten later. At this stage we decided to mix the leaves with a portion of the sugar cane juice and homogenize the two feeds using a kitchen blender. In this form the piglets readily consumed the leaves and the problem of spillage were avoided.  

Soybean meal, or soybean and blended leaves, or blended leaves alone, were given as the first meal at 08.30h. After all the soybean and/or blended leaves/cane juice were consumed the remainder of the cane juice was given. The same procedure was repeated at 15.00h. The proportions of cane juice, soybean meal and leaves, and the amounts offered, were adjusted daily to maintain a crude protein content of 10% in the diet DM and no refusals. The soybean meal was purchased from a commercial supplier in the nearby town of Socorro. A mineral mixture (salt 33.3, rock phosphate 33.3 and magnesium limestone 33.3, parts by weight) was fed daily in quantities equivalent to 1% of the daily DM intake.

Measurements

The pigs were weighed in the morning, before being fed, at the beginning of the trial and after each period of 14 days. Faeces were collected from 530 am to 10 pm every day and were kept frozen in plastic bags until analysis. A representative sample (10% of total amount voided) was obtained from every animal. At the end of each period, the samples of faeces were thawed, mixed thoroughly by hand and then homogenized in a coffee grinder, prior to taking representative samples that were analyzed for DM, N, crude fibre and ash.. Urine was collected in a plastic bucket to which sulphuric acid was added to maintain the pH below 4.0 (10 ml daily of concentrated H₂SO₄), urine pH was measured once at mid day and every morning at weighing time.  The volume of urine was measured every day and 10% preserved in a freezer until the end of each period when the samples were mixed together and analyzed for N.

Chemical analyses

Ash, N and crude fibre in feeds and faeces, and N in urine, were determined by the methods of AOAC (1990). DM was determined by micro-wave radiation (Undersander et al 1993).

Statistical analysis

The data were analysed using the General Linear Model of the ANOVA option in he Minitab (2000) software. In the model the sources of variation were: treatments, periods, animals and error. When the “ F”  test was significant at the “ 5%”  level, the means were separated by the “Tukey”  test in the same Minitab software.

Results

There were slight differences between the planned levels of substitution of soybean protein by the protein from New cocoyam leaves (Table 1), with lower than intended levels for the intermediate treatments NC30 and NC60.

On the NC100 diet (zero soybean meal), New Cocoyam leaves provided almost 50% of the DM (Figure 2) and almost all the crude protein (Figure 3).

Figure 2: Proportions of diet DM derived from individual ingredients according to level of protein from fresh Cocoyam leaves replacing protein from soybean meal		Figure 3: Proportions of diet crude protein derived from individual ingredients according to level of protein from fresh Cocoyam leaves replacing protein from soybean meal

DM intake was relatively high on all the diets (range from 48 to 56 g/kg DM/kg), the lowest value being recorded on the diet with 100% replacement of soybean protein by Cocoyam leaves but with no differences among the other diets (Table 2). Intake of N was similar on diets NC0 and NC30 but then decreased significantly on diet NC60 with a further decrease on diet NC100. The crude protein concentration in the diet declined from 142 g/kg DM on the NC0 diet to 108 g/kg DM with the complete replacement of soybean by Cocoyam leaves (NC100).

Coefficients of apparent digestibility of DM, OM and crude protein were high on all diets (Table 2) with negative linear trends (Figures 4, 5 and 6) as the proportion of dietary N from Cocoyam was increased.  The rate of decline was more pronounced for apparent digestibility of crude protein compared with DM and OM.

Figure 4: Relationship between dietary N derived from New Cocoyam and apparent digestibility of DM in young pigs fed sugar cane juice and increasing proportions of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal		Figure 5: Relationship between dietary N derived from New Cocoyam and apparent digestibility of OM in young pigs fed sugar cane juice and increasing proportions of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal

Figure 6: Relationship between dietary N derived from New Cocoyam and apparent digestibility of crude protein in young pigs fed sugar cane juice and increasing proportions of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal

There were significant effects of N intake on DM intake (Figure 7), urine N excretion (Figure 8) and N retention (Figure 9). Adjusting the data for these variables by covariance for differences in N intake changed markedly the treatment effects on DM intake and N retention. After adjustment, DM intake was highest for NC100 and lowest for NC0, while N retention was similar on all diets (Table 2).

N retention as a proportion of N digested was significantly higher for the diets containing Cocoyam leaves compared with the NC0 diet in which all the protein was derived from soybean.  The pathway of excretion of dietary N differed markedly among diets (Figure 10). As the level of cocoyam protein in the diet increased, the proportion of dietary N excreted in faeces increased while the proportion excreted in the urine decreased.

Figure 7: Relationship between N intake and DM intake in young pigs fed sugar cane juice and increasing proportions (0 to 100%) of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal		Figure 8: Relationship between N intake and urine N excretion in young pigs fed sugar cane juice and increasing proportions (0 to 100%) of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal
Figure 9: Relationship between N intake and N retention in young pigs fed sugar cane juice and increasing proportions (0 to 100%) of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal		Figure 10: Proportions of dietary N excreted in faeces and urine and retained in young pigs fed sugar cane juice and increasing proportions of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal

Discussion

Attempts were made to control the intakes of sugar cane juice, soybean meal and Cocoyam leaves so as to achieve the desired proportions of these three ingredients in the diets. However, this was only partially successful with the result that proportions of protein from Cocoyam leaves were less than planned for treatments NC30 and NC60, while total N intakes were less than planned for diets NC60 and NC 100. The significant relationships between N intake and both DM intake and N retention imply that if the crude protein level in diet NC100 had been higher then the N retention response would also have been higher. This hypothesis will be tested in a subsequent experiment.

A related study to determine the nutritive value of New Cocoyam leaves (Xanthosoma sagittifolium) was reported by Leterme et al (2005). However, the nature of the basal diet used by these authors was quite different to the present work in that the energy component was based on maize grain (40% of the diet DM) and the New Cocoyam leaves supplied 35% of the diet DM. As a result the NDF content of their diet DM was 27% compared with 12.7% in the diet of the present experiment, this lower fibre level being possible through use of sugar cane juice as a fibre-free energy source. This difference in levels of NDF could the major reason why Leterme et al (2005) found that their pigs, although heavier (34 kg) and therefore older, would not eat more than 35% of the diet in the form of Cocoyam leaves. In the present study with younger and lighter pigs (20 kg on average) the leaves represented 50% of the diet DM in the NC100 treatment and overall DM intakes were high (>40 g DM/kg live weight).  There were also major differences in the apparent digestibility of the crude protein of the Cocoyam leaves which was calculated to be only 340 g/kg in the study of Leterme et al (2005) compared with a value of 600 g/kg in the present study. As a result Leterme et al (2005) estimated the digestible crude protein (DCP) of the leaves to be only 57 g/kg DM while in the present study the comparable value was 130 g DCP/kg DM. Leterme et al (2005) calculated the digestibility of the leaves by the “difference” method, in which the digestibility of the basal diet is determined separately and is assumed to be the same when combined with the leaves.  In the present experiment, all the protein in diet NC100 was derived from Cocoyam leaves thus the directly measured estimate of digestibility is likely to be a truer estimate of the nutritive value of the leaves.

The N retained as a proportion of the N digested was 26% greater on the diet with 100% Cocoyam protein compared with the 100% soybean diet  (unadjusted data). The  difference was even greater (34%) when the values were adjusted for differences in N intake (Table 2). This indicates that the biological value of the Cocoyam protein may well be higher than that of the soybean protein. Data on the ratios of methionine + cysteine as a proportion of the lysine (Table 3), and comparisons with the “ideal protein” and soybean meal, provide supporting evidence of the high biological value of the protein in New Cocoyam leaves.

The limiting factor in the New Cocoyam leaves is almost certainly the low digestibility of the protein, with N retention being closely related to the intake of apparently digestible crude protein (Figure 11).

Figure 11: Relationship between digestible crude protein (DCP) intake and N retention in young pigs fed sugar cane juice and increasing proportions (0 to 100%) of protein from fresh leaves of New Cocoyam  replacing protein from soybean meal

Chittavong Malavanh et al (2007a) fed Mong Cai gilts on diets in which the energy component was from ensiled cassava roots and broken rice with 70% of the protein provided either by a 50:50 mixture (DM basis) of ensiled Cocoyam leaves (Colocacia esculenta) and fresh water spinach (Ipomoeoa aquatica) or soybean meal. There were no differences in reproduction traits but weight loss during lactation was increased and piglet growth rate to weaning decreased on the diet with the cocoyam leaves and water spinach. These authors also concluded that the lower apparent digestibility of this diet (595 g/kg) compared with that on the soybean diet (816 g/kg) was probably the major reason for the poorer performance on the former diet (Chittavong  Malavanh et al (2007b).

Conclusions

·        The high DM intakes (>5% of LW) with fresh cocoyam leaves providing 47% of the total DM intake in  basal diet sugar cane juice are because:

Ø      The sugars are rapidly digested?

Ø      The fine particle size of the leaves (after blending of leaves with the sugar cane juice + minerals)?

Ø      The low fibre content of the leaves?

·        The protein in the fresh Cocoyam leaves appears to have a high biological value at least equal to that in soybean

·        The limiting nutritional factor in fresh cocoyam leaves is the lower digestibility of the protein (61%) versus soybean (81%).

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Received 21 October 2007; Accepted 14 December 2008; Published 1 January 2009

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