Studies on the nutritive value for pigs of New Cocoyam (Xanthosoma sagittifolium); digestibility and nitrogen balance with different levels of ensiled leaves in a basal diet of sugar cane juice

Lylian Rodríguez, T R Preston and K Peters *

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

Abstract

Four crossbred (Yorkshire*Landrace*Pietran) castrated male pigs with initial weight of 18.7±3.2 kg (mean ± SD) received varying proportions of ensiled New Cocoyam (Xanthosoma sagittifolium) leaves (ENCL) and fresh sugar cane juice in two consecutive periods to provide different levels of crude protein in the range of 80 to 160 g/kg of diet DM. In period 1, the planned levels were: 100, 120, 140 and 160 g/kg DM; in period 2 these were changed to 90, 110, 130 and 150 g/kg DM. The fresh sugar cane juice contained 20 to 21% total sugars. The Cocoyam leaves were macerated in a high-speed mechanical chopping machine and ensiled with addition of 10% (fresh basis) of sugar cane juice.

The leaf silage was of excellent quality as judged by smell and colour and the rapid fall in pH (< 4) within 3 days of ensiling the leaves. Recorded proportions of ENCL in diet DM were 0.49, 0.56, 0.67 and 0.76 in period 1 and 0.46, 0.48, 0.57 and 0.67 in period 2. DM intake was high on all diets (range from 32 to 53 g/kg LW) and showed a curvilinear response to increasing proportions of ENCL in the diet, with a maximum value at 0.55 of ENCL in diet DM. Apparent digestibility of DM decreased, and that of crude protein increased, as the proportion of ENCL in the diet DM increased. N retention increased with increasing proportion of ENCL in the diet, the relationship being curvilinear with the maximum value at 0.67 ENCL, equivalent to 130 g crude protein per kg of diet DM.

Key words: Curvilinear response, dry matter intake, N intake, production function design

Introduction

In a previous study in this series of experiments on the nutritive value of leaves of New Cocoyam (Xanthosoma sagittifolium) for pigs (Rodríguez et al 2009), it was postulated that the major constraint to their nutritive value as a replacement for soybean meal was the digestibility of the protein; by contrast the biological value of the protein appeared to be comparable to that in soybean.  Because of the lower digestibility of the protein, and the decision in that study to fix the dietary crude protein level to 10% of the dry matter, the intake of digestible crude protein (DCP) decreased curvilinearly as soybean was replaced by New Cocoyam leaves. In the diet with 100% replacement of soybean by New cocoyam leaves, the intake of DCP was only half that on the 100% soybean treatment. It was hypothesized that it was the low intake of digestible crude protein that was responsible for the lower N retention on the diet with 100% fresh Cocoyam leaves compared with the diet containing soybean meal.

In the previous study (Rodríguez et al 2009), the Cocoyam leaves were processed in a kitchen blender along with small quantities of sugar cane juice. This procedure is not suitable under practical conditions as “kitchen” blenders cannot deal with large quantities of material and industrial machines are expensive. It was therefore decided that for future studies it was more appropriate to use a high-speed cropping machine (TORMETAL SA; 3500 rpm), which it had been shown effectively macerates leaf material into very small pieces. Recent reports from Vietnam (Pham Tiep et al 2006; Du Thang Hang and Preston 2007) with leaves from Giant Taro (Alocacia macrorrhiza) showed the advantages from ensiling the leaves compared with feeding them fresh, as a means of reducing the concentration of calcium oxalate, which causes “itchiness” in the mouth and on the skin when the leaves are fed fresh. Ensiling is also a convenient management practice as harvesting can be programmed at appropriate intervals to take advantage of the normal life cycle of the leaves which lasts on average some 25 days.

The objective of the present study was therefore to determine the effect on nitrogen retention in young pigs of varying the level of ENCL in a basal diet of sugar cane juice to provide a range of crude protein in diet DM of between 100 and 150 g/kg.

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

Four crossbred (Yorkshire*Landrace*Pietran) castrated male pigs with initial weight of 18.7±3.2 kg (mean ± SD) received varying proportions of ensiled New Cocoyam (Xanthosoma sagittifolium) leaves in two consecutive periods to provide different levels of crude protein in the range of 80 to 160 g/kg of diet DM. In period 1, the planned levels were: 100, 120, 140 and 160 g/kg DM; in period 2 they were 90, 110, 130 and 150 g/kg DM. The energy component of the diet was fresh sugar cane juice. The pigs were maintained in metabolism cages designed for separate collection of urine and faeces (Rodríguez et al 2009). The experimental periods were of 14 days with collection of faeces and urine during the last 5 days of each period.

Diets and feeding

Leaves plus petioles of New Cocoyam were harvested from plants of similar ages located in the farm. The leaves were separated from the petioles and passed through a high-speed (3500 rpm) mechanical ensiling machine (Photo 1) which macerated the leaves into very small particles (Photo 2). The macerated leaves were then mixed with 10% of fresh sugar cane juice and ensiled in air-tight rigid plastic containers (Photos 3 y 4). 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). Half the daily allowance of ensiled leaves was mixed with equal parts (fresh basis) of fresh sugar cane juice and given as the first meal at 7.00am. After all the ensiled leaves/cane juice mixture was consumed the remainder of the allowance of cane juice (the allowance was 50%of the intended daily intake) was given. The same procedure was repeated at 15.00h. The proportions of cane juice and ensiled leaves were fixed to maintain the crude protein content of the diets at the programmed levels. The amounts offered were adjusted daily according to the appetite of the pigs so that there were no refusals. 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.

Photo 1. New Cocoyam leaves processed by a high-speed (3500 rpm) mechanical ensiling machine	Photo 2. New Cocoyam leaves mixed with 10% of fresh sugar cane juice and ensiled in air-tight rigid plastic containers
Photo 3. New Cocoyam leaves + Sugar Cane Juice ensiled in air-tight rigid plastic containers	Photo 4.  New Cocoyam leaves ensiled for one week

Measurements

The pigs were weighed in the morning, before being fed, at the beginning and end of each period. Representative samples of silage were taken at the beginning of the experiment for determination of DM, nitrogen and ash. The brix (% sugars) of the sugar cane juice was determined daily. During the 5-day collection period, faeces were collected at intervals during the day and night 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 (10 ml daily of concentrated H₂SO₄) was added to maintain the pH below 4.0. 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). The brix of the sugar cane juice was measured with a hand refractometer.

Statistical analysis

The data were subjected to regression analysis (Excel in Microsoft Office 2003 Software), in which the independent variables were proportion of diet DM from ensiled ENCL (or crude protein intake per kg live weight) and the dependent variables were the various measures of animal response (feed intake, apparent digestibility and N balance).

Results

Ensiling Cocoyam leaves

Despite the relatively low DM content (13.5%), the New Cocoyam leaves, the silage was of excellent quality as judged by smell and colour and the rapid fall in pH (< 4) within 3 days of ensiling the leaves (Figure 1). The Brix of the sugar cane juice was also relatively constant during the experiment (Figure 2).

Figure 1. pH of silage in period 1 of the experiment (Data in period 2 were similar)	Figure 2.  Brix of the sugar cane juice taken during collection days in periods 1 and 2

Feed intake

It was not feasible to offer the diets as complete mixtures of ensiled leaves and sugar cane juice as, when presented in this form in the feed trough, most of the juice separated from the silage, and the pigs were able to consume it first in preference to the silage. The result was variable amounts of refusals of widely different composition. For this reason the procedure was adopted of ensuring that all the allowance of silage (plus limited amounts of juice mixed with it) was consumed before giving the bulk of the cane juice. This method was effective in eliminating feed refusals but made it difficult to ensure that the “planned” proportions of silage and juice were maintained. The result was that the “recorded” ratios were slightly different from the “planned” ratios (Table 1). The recorded ratios were those used as independent variables in the regression analysis.

DM intake as a function of live weight (Table 1) was high on all diets (range from 32 to 53 g/kg LW) and showed a curvilinear response (Figure 3) to increasing proportions of ENCL in the diet. The maximum value was with 55% ENCL in diet DM. The crude fibre in the diet was totally derived from the ensiled Cocoyam leaves and accounted for 9% of the diet DM at the point of maximum DM intake (Figure 4). The ensiled Cocoyam leaf represented from 48 to 76% of the total DM intake, and 100% of the crude protein.

Figure 3. Relationship between proportion of ENCL in the diet DM and DM intake expressed as a function of live weight (periods 1 and 2)	Figure 4. Relationship between crude fibre content of diet and DM intake expressed as a function of live weight (periods 1 and 2)

The apparent digestibility of DM decreased (Table 2; Figure 5) and that of crude protein increased (Table 2; Figure 6), as the proportion of ENCL in the diet DM increased.

Figure 5. Relationship between proportion of ensiled New Cocoyam leaf (ENC) in the diet DM and apparent DM digestibility	Figure 6. Relationship between proportion of ensiled New Cocoyam leaf (ENC) in the diet DM and apparent crude protein digestibility

From the equation in Figure 5, the apparent DM digestibility of ensiled New Cocoyam leaf can be predicted as the value of “y” when “x”= 1 (ie: with 100% ENCL in the diet). The apparent DM digestibility of ENCL is thus 1028 - (402*1) = 626 g/kg. 

The other approach is to measure “apparent digestibility” by difference. In this case it is assumed the apparent DM digestibility of sugar cane juice is 100%. Taking the lowest (0.46) and highest values (0.76) for proportion of ENCL in the diet, the associated apparent DM digestibility coefficients of the diets are 839 and 749g/kg DM. The equation is:

 Y = ENCL * X + (1-ENCL)*D

Where “X” is apparent DM digestibility of ENCL, “Y” is the apparent digestibility of the diet mixture (expressed as fraction of 1) and “D” is the apparent digestibility  of sugar cane juice (=1 as 100% digestible);  ENCL is the proportion of ENCL in the diet

Rearranging the equation

X = (Y-(1-ENCL)*D)/ENCL

For D = 1 and ENCL  =  0.46;  X = 0.650 (or 650 g/kg)

For D = 1 and ENCL  =  0.76; X = 0.670 (or 670 g/kg)

These values are similar to that (626 g/kg) produced by prediction from the linear regression equation in Figure 5.

In a similar way the apparent digestibility of the crude protein in ensiled Cocoyam leaf can be calculated as: 271+ (539*1) = 810 g/kg.

N balance

N retention increased with increasing proportion of ENCL in the diet, the relationship being curvilinear (Figure 7). The maximum N retention was reached with 65% of ENCL in the diet DM, equivalent to about 5.5 g crude protein per kg of pig LW (Figure 8) and approximately 13% crude protein in the diet DM.

Figure 7.  Relationship between proportion of ensiled New Cocoyam leaf (ENCL) in the diet DM and N retention expressed as g N/kg LW	Figure 8. Relationship between intake of crude protein (as g/kg LW) and N retention expressed as g N/kg LW

Discussion

According to McDonald et al (2002), if the material to be ensiled has a relatively low DM content, it is advisable to use an additive with high dry matter content. In preliminary trials with fresh New Cocoyam leaves (containing about 15% DM) we followed this advice and used concentrated sugar cane juice (about 50% sugars) at 4% of the weight of fresh leaves. Subsequently we replaced the concentrated juice with fresh cane juice (about 20% sugars) at 10% of the fresh weight of the leaves with excellent results, the pH falling to below 4.0 in less than 3 days. Similar findings were reported by Chittavong Malaavanh et al (2007) and Du Thanh Hang and Preston (2007) who used 4% molasses to ensile leaves of Taro (Colocacia esculenta) and Giant Taro (Alocacia macrorrhiza), respectively, plants of the same family as New Cocoyam.

The diets supporting highest DM intakes (close to 50 g/kg live weight) had approximately 55% of the diet DM in the form of ensiled Cocoyam leaves. This indicates that high quantities of protein-rich leaves can be consumed even by young pigs when the energy component of the diet is devoid of fibre, as is the case with sugar cane juice.

The recorded apparent digestibility of the diet DM (820 g/kg DM) when the Cocoyam leaf silage provided 50% of the diet DM is similar to the value (832 g/kg DM)  reported in our previous experiment (Rodriguez et al 2007) in a similar diet containing equal quantities of DM from fresh Cocoyam leaves and sugar cane juice.. The predicted range in apparent digestibility of 626 to 670 g/ kg DM for the ensiled Cocoyam leaves as the only diet is slightly higher than was predicted for duckweed (Lemna minor) (610 g/kg DM) as the sole diet using a similar experimental design with sugar cane juice as the energy source (Rodriguez and Preston 1996).

The increase in the apparent digestibility of the crude protein of the ensiled Cocoyam leaves as their level in the diets increased presumably reflects the reduction in the proportion of total faecal N provided by endogenous N. At levels of 50% of ensiled Cocoyam leaves in the diet DM the apparent crude protein digestibility was slightly lower (530 g/kg) than that reported in the previous experiment (Rodriguez et al 2007) with a diet of the same composition.

The maximum level of N retention (0.35g/kg live weight) with 65% is similar to that reported by Rodríguez et al (2009) for a diet with 55% of the  DM as fresh leaves of New Cocoyam (0.38g N/kg live weight), in both cases with fresh sugar cane juice as the basal diet.

An optimum crude protein content of between 130 and 140 g/kg DM was found by Sokha et al (2007) for crossbred pigs of similar live weight (average 23 kg) fed low-protein basal diets of cassava root meal with rice bran (50:50), or broken rice, with the protein supplied by a mixture of fresh sweet potato vines and water spinach (50:50 DM basis). This result is similar to what was found in the present study with ensiled New Cocoyam leaves as the protein source  (130 g crude protein/kg DM).

Conclusions

• Fresh leaves of New Cocoyam were ensiled satisfactorily with 10% of sugar cane juice (fresh basis), the pH falling to less than 4.0 within 3 days
  
  
• Growing pigs (23 kg live weight) were able to consume diets containing up to 80% of the DM as ensiled New Cocoyam leaves at levels close to 40 g DM/kg live weight
  
  
• Maximum N retention was achieved with the ensiled New Cocoyam leaves providing 65% of the diet DM, providing a protein level of 130 g/kg diet DM and 5 g crude protein per kg live weight.
   

References

AOAC 1990:  Official Methods of Analysis, 15th edition. Association of Official Analytical Chemists, Arlington, VA

Du Thanh Hang and Preston T R 2007:  Taro leaves as a protein source for growing pigs in Central Viet Nam. MEKARN International conference on "Matching Livestock Systems with Available Resources". (Editors: T R Preston and B Ogle), 26-27 November 2007, Ha Long Bay, Vietnam http://mekarn.org/prohan/abstracts/hang_hue.htm

Minitab 2000 MINITAB^® Release 13.2 Statistical Software for Windows.

Pham Sy Tiep, Nguyen Van Luc, Trinh Quang Tuyen, Nguyen Manh Hung and Tran Van Tu 2006: Study on the use of Alocasia macrorrhiza (roots and leaves) in diets for crossbred growing pigs under mountainous village conditions in northern Vietnam. Workshop-seminar "Forages for Pigs and Rabbits" MEKARN-CelAgrid, Phnom Penh, Cambodia, 22-24 August,  2006. Article # 11. Retrieved, from http://www.mekarn.org/proprf/tiep.htm

Rodríguez Lylian and Preston T R 1996 Comparative parameters of digestion and N metabolism in Mong Cai and Mong Cai*Large White cross piglets having free access to sugar cane juice and duck weed. Livestock Research for Rural Development (8) 1. http://www.lrrd.org/lrrd8/1/lylian.htm

Rodríguez Lylian, Lopez D J, Preston T R and Peters K 2006: New Cocoyam (Xanthosoma sagittifolium) leaves as partial replacement for soya bean meal in sugar cane juice diets for growing pigs. Livestock Research for Rural Development. Volume 18, Article No. 91.  Retrieved October 21, 2007, from http://www.lrrd.org/lrrd18/7/rodr18091.htm

Rodríguez Lylian, Peniche Irina, Preston T R and Peters K 2009  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. Volume 21, Article # 16. Retrieved , from http://www.lrrd.org/lrrd21/1/rodr21016.htm

Thim Sokha, Preston T R  and  Khieu Borin 2007: Effect of different protein levels derived from mixtures of water spinach and fresh sweet potato vines in basal diets of broken rice or cassava root meal and rice bran for growing pigs MSc Thesis, MEKARN-SLU http://www.mekarn.org/MSC2005-07/thesis07/sokh1.htm

Undersander D, Mertens D R and Theix N 1993: Forage analysis procedures. National Forage Testing Association. Omaha pp 154.

Received 29 October 2007; Accepted 15 December 2008; Published 1 February 2009

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