Digestibility and nitrogen balance in growing pigs fed a diet of sugar cane juice and fresh leaves of New Cocoyam (Xanthosomasagittifolium) as partial or complete replacement for soybean protein

LylianRodríguez, Irina Peniche* and T R Preston

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

Abstract

The four treatments applied to 4 growing pigs in a 4*4 Latin square arrangement were levels of fresh leaves of New Cocoyam (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*Piertran) 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.

Key words: N balance, New Cocoyam, pigs, sugar cane juice, Xanthosoma sagittifolium
 

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 cassava (Bui Huy Nhu Phuc 2006) and water spinach (Chha 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),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 (Cyrtospermaand Amorphophallus); and Colocasiodeae (Alocasia, Colocasia, and Xanthosoma). Taro (Colocasia esculenta [L.] Schott) is considered as a single polymorphic specie.

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 Figures 1a and 1c) which is absent in "Old Cocoyam" (Colocasia esculenta) (Figures 1b and 1d).

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

Materials and Methods

Location

The study was carried out in the "Finca Ecológica", TOSOLY, Morario, Guapota, Department of South 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 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*Piertran) 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.

Diets

Leaves plus petioles of New Cocoyam were harvested daily from plants of similar ages located in the farm. The leaves were separated from the petioles and passed first through a mechanical forage chopper, then liquidized with equal parts of fresh sugar cane juice in a kitchen blender. Soybean meal, or soybean and blended leaves, or blended leaves alone, were given as the first meal at 7.00am. After all the soybean and/or blended leaves/cane juice was 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. Stalks of sugar cane, grown on the farm, were passed once through a 3-roll mill to separate the juice from the residual fibre (bagasse). 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.

Results and discussion

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

Total intake of N was highest on the diet with 0 and 25% substitution of soybean protein by cocoyam leaves (Table 2) and was lowest with 100% protein substitution by cocoyam leaves. In part these differences reflected errors in calculation of the offer levels of diet ingredients since the assumed percentage of protein in the soybean (50% in DM, based on the value guaranteed by the vendor) was found to be less than the analysed percentage, determined on composite samples at the end of the experiment (53.2% in DM). Thus the diets with the highest percentage of soybean meal also had higher than intended levels of nitrogen.

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 (Table 2).

Implications

The high DM intakes (>5% of LW) with fresh cocoyam leaves providing 47% of the total DM intake are because:

• The sugars are rapidly digested?

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

• The low fibre content of the leaves?

The limiting nutritional factor in fresh cocoyam leaves is the relatively low digestibility of the protein (61 versus 81% for soybean)

The apparent advantage of the leaves is a higher biological value compared with soybean.