Intake, digestibility and N retention by growing pigs fed ensiled or dried Taro (Colocasia esculenta) leaves as the protein supplement in basal diets of rice bran/broken rice or rice bran/cassava root meal

Chhay Ty, Khieu Borin, T R Preston* and Mea Sokveasna

Center for Livestock and Agriculture Development (CelAgrid), PO box 2423, Phnom Penh 3, Cambodia
chhayty@celagrid.org
* University of Tropical Agriculture (Colombia), AA #48, Socorro, Santander, Colombia

Abstract

The experiment was conducted in the Center for Livestock and Agriculture Development (CelAgrid) in Cambodia. Four crossbred castrated male pigs, weighing on average 20 kg, were allotted at random to 4 diets, in a 2*2 factorial within a 4*4 Latin square, to study the effect of ensiled and sun-dried Taro leaves on intake, digestibility and N retention. The basal diets were rice bran + broken rice or rice bran + cassava root meal (1:1 ratio). The basal diets were offered at 2% of live weight (DM basis) and the dried or ensiled leaves ad libitum.

Almost twice the quantity as DM was consumed as leaves when these were dried compared with the ensiled form. The taro leaves provided from 38 (ensiled) to 43% (sun-dried) of the dietary DM and from 75 (ensiled) to 82% (sun-dried) of the dietary protein. Apparent digestibility of DM and OM tended to be higher for the diets with dried versus ensiled Taro leaves. Coefficients for crude protein were lower, and for crude fiber, were higher for dried versus ensiled leaves. There were significant effects of N intake on urine N, faecal N and N retention. After adjusting these variables by covariance for N intake, there were significant effects of processing the Taro leaves on urine N (decreased in dried leaves) and faecal N (increased in dried leaves) but not on N retention. N retained as percentage of N intake was not affected by processing of the Taro leaves or by energy source . N retained as percentage of N digested was higher for dried versus ensiled Taro leaves and was not affected by differences in N intake.

The apparently higher nutritive value of sun-dried compared with ensiled Taro leaves may have been caused by inadequacies in the ensiling process, resulting in excessive breakdown of the protein and poor palatability. The relatively high values of N retention (equivalent to about 250 g/day of live weight gain) and of retained N as a proportion of digested N in the diet with sun-dried Taro leaves, are indicative of a high biological value of the Taro leaf protein, especially as it represented over 80% of the dietary crude protein in these diets.

Key words: Colocasia esculenta, digestibility, ensiling, leaves, N balance, pigs, sun-drying, taro

Introduction

Colocasia esculenta var. antiquorum known as Taro or Cocoyam is widely distributed in the humid tropics including India and South East Asia. Taro is recognized as a large coarse herb with crowns of large oblong-oval leaves and an abundance of large spherical underground tubers. Taro can be grown under flooded or upland conditions and it is one of the important crops for poor resource farmers in the tropics. In Cambodia, Taro is known in Khmer as 'Trao'. It is planted for home consumption of both tubers and petioles. However, when there is production in excess of household needs, Taro leaves and petioles are cooked and fed to pigs. Taro leaves are rich in protein, minerals and vitamins (AFRIS 2004).

Most Taro varieties contain an irritating or acrid agent and cannot be eaten fresh. Traditionally, the tubers are cooked before being fed to pigs. Uncooked Taro contains substances which irritate the digestive tract and may cause poisoning if fed in large quantities. It has been reported that the dried and ground Taro root has been used as a feed for poultry; with no toxic effects being observed, but at high levels of inclusion growth was poor (AFRIS 2004). Although cocoyam is widely cultivated in the rural areas of Cambodia and traditionally has been fed to pigs, there is a lack of information regarding its nutritive value as animal feed.

The aim of the present experiment was to study the effect of ensiling or drying Taro leaves on intake, digestibility and N retention of growing pigs given a basal diet of rice bran mixed with broken rice or rice bran mixed with cassava root meal.
 

Materials and methods

Location and duration

The experiment was carried out in the Center for Livestock and Agriculture Development (CelAgrid), located in Pras Teat village, Rolous Commune, Kandal steung district, Kandal province about 25km from Phnom Penh City, Cambodia from 26 November 2006 to 11 February 2007.

Treatments and design

Two factors were studied with 4 castrate male pigs (average initial weight 20 kg) in a 2*2 factorial arrangement within a 4*4 Latin square (Table 1).

The factors were:

Energy

Rice bran mixed with broken rice (1:1) (RBBR) or rice bran mixed with cassava root meal (1:1) (RBCRM)

Processing

Ensiled Taro leaves (ET) or dried Taro leaves (DT)

The pigs were housed in metabolism cages (80 x 80cm) designed to facilitate quantitative collection of faeces and urine. The construction and characteristics of the cages have been described previously (Chhay Ty et al 2003). Each experimental period consisted of 12 days with seven days for adaptation to the diet, followed by another five days for collection of faeces, urine and feed refusals.

Feeds and feeding

Taro leaves were harvested from lakes and ponds close to CelAgrid. One portion (about 50%) was hand-chopped with a knife into pieces of about 2 to 5cm and ensiled after mixing with rice bran and salt (10 kg rice bran, 0.5 kg salt and 89.5 kg Taro leaves). They were stored in air-proof plastic containers for 30 days before being fed to the pigs. The remaining portion of leaves was dried in sun light for 2 to 3 days and then ground in a hammer mill. The purpose of processing the Taro leaves was to reduce the content of calcium oxalate which causes irritation in the mouth and reduction in intake. Broken rice and rice bran were purchased from the rice mill near CelAgrid. Cassava root meal was purchased from a market in Phnom Penh.

The pigs were fed thrice daily with equal amounts at 8:00 am, 12:00 am and 16:00 pm. The energy components were mixed together and fed at a level equivalent to 2% of the live weight (DM basis). This portion of the diet was fed first and after it was consumed the ensiled or dried Taro leaves were offered to appetite, the quantities being adjusted to minimize residues. Water was supplied through nipple drinkers

Data collection

The pigs were weighed at the beginning of the trial and every 12 days. Samples of feeds offered and feed refusals and total amounts of faeces were collected every day and were kept frozen in plastic bags until analysis at the end of each period for DM, N, ash and crude fiber. Urine was collected in a plastic bucket to which sulphuric acid was added to maintain the pH below 4.0 (20ml of a solution of 10% concentrated sulphuric acid added daily). The volume of urine was measured everyday and 10% of the total volume stored until the end of each period, when it was analysed for N.

Chemical analyses

Chemical analyses of the feed ingredients and faeces were undertaken following the methods of AOAC (1990) for ash, N and crude fiber. The DM content was determined using the microwave method of Undersander et al (1993). The N content of urine was determined by the AOAC (1990) procedure.

Statistical analyses

The data were subjected to analysis of variance according to the general linear model of the Minitab software (Minitab release 13.31, 2000). The sources of variation in the model were: pigs, periods, processing, energy, interaction processing*energy and error.
 

Results

There were no health problems and the pigs were in positive body weight balance throughout the experiment.

Feed composition and intake

The crude protein and crude fiber fractions in the leaves (Table 2) were similar to those in a range of vegetative materials presently being studied as protein sources in pig diets (Preston 2006).

The energy component of the diet was consumed completely, but the there were major differences in the intake of the Taro leaves, which differed among the treatments (Table 3).

Almost twice the quantity as DM was consumed as leaves when these were dried compared with the ensiled form (Table 4; Figures 1 and 2). The interaction between processing and energy source was significant with the difference between dried and ensiled leaves much more pronounced on the RBCRM diet than on the RBBR diet (Table 4).

The proportion of the diet DM provided by the Taro leaves was much higher for the dried than the ensiled form. Highest intakes of leaves were recorded when they were dried and fed with the RBCRM diet; lowest intakes were with ensiled leaves in the same RBCRM diet. The taro leaves provided from 38 (ensiled) to 43% (sun-dried) of the dietary DM and from 75 (ensiled) to 82% (sun-dried) of the dietary protein.

Apparent digestibility coefficients

Apparent digestibility of DM and OM tended (P=0.09) to be higher for the diets with dried versus ensiled Taro leaves (Table 5).

Coefficients for crude protein were lower (Figure 3), and for crude fiber, were higher for dried versus ensiled leaves.

N balance

There were significant effects of N intake on urine N, faecal N and N retention (Table 6).

After adjusting these variables by covariance for N intake, there were significant effects of processing the Taro leaves on urine N (decreased in dried leaves; Figure 4) and faecal N (increased in dried leaves; Figure 5) but not on N retention (Figure 6).

N retained as percentage of N intake was not affected by processing of the Taro leaves or by energy source (Figure 7). N retained as percentage of N digested was higher for dried versus ensiled Taro leaves (Figure 8) and was not affected by differences in N intake.

Discussion

There is no obvious reason for the lower feed intake with the ensiled leaves other than perhaps the quality of the silage, as in a parallel experiment in CelAgrid, intakes of ensiled Taro leaves were high (Pheng Buntha et al 2007). The reason may be the use of rice bran as silage additive, which at 10% of the fresh Taro leaves is equivalent to 31% of the DM of the silage and with 20% crude fiber is effectively increasing the crude fiber in the silage by more than 30%. In the experiment of Pheng Buntha et al (2007) the leaves were ensiled with palm syrup (soluble sugars). Malavanh et al (2006) also reported good silage quality when 4% molasses was used to ensile Taro leaves.

Du Thanh Hang and Preston (2007) fed Mong Cai and crossbred Mong Cai x Large White pigs (mean live weight 25 kg) the same basal diet of rice bran and cassava root meal (1:1) supplemented with Taro leaves given in fresh, ensiled (with 4% molasses) or cooked form.. Intakes of leaves were highest when they were cooked (260 g DM/day), followed by ensiling (195 g/day) with lowest intakes when they were given fresh (124 g/day). N retention with the cooked leaves was 10.8 g/day and 10.2 g/day for the ensiled leaves, both being better than for fresh leaves (8.2 g/day). These results strongly suggest that ensiled Taro leaves are a good source of essential amino acids to supplement low-protein basal diets (rice bran plus cassava root meal).

The apparent DM digestibility (65.7 and 67.9% for diets with dried and ensiled leaves) was lower than reported by Rodrigúez et al (2006) and Pheng Buntha et al (2007) using, respectively, fresh leaves of New Cocoyam (Xanthosomasagittifolium) and ensiled Taro leaves (Colocasia esculenta) (83.4% and 87.7%). The lower values in the present study may be because of the fibre level in the diets as the former authors used sugar cane juice and sugar palm juice as energy source (zero fibre) whereas in our study half of the energy source was rice bran which contained 20.3% fibre.

The higher apparent digestibility of crude protein in the diet with ensiled leaves compared with sun-dried leaves may have resulted from partial fermentation of the protein in the ensiling process (Mcdonald et al 1995). The value for the diet with ensiled leaves (66.5%) was similar to that reported by Pheng Buntha et al (2007) (66.1%) for a similar diet with ensiled Taro leaves and higher than reported for a diet with fresh New Cocoyam leaves (61.4%) (Rodrigúez et al 2006).

The lower retention of digested N in the diet with sun-dried Taro leaves may have been the consequence of the same effects which increased the apparent N digestibility, namely the breakdown of protein to non-protein N due to ensiling, a process which is favoured when the ensiling process is extended due to lack of easily fermentable carbohydrate (Mcdonald et al 1995). The rice bran used as additive in the present study may have been limiting in this respect.

The taro leaves accounted for about 82% of the dietary protein when they were sun-dried and 75% when ensiled. The relatively high values of N retention (equivalent to about 250 g/day of live weight gain) and of retained N as a proportion of digested N in the diet with sun-dried Taro leaves, are indicative of a high biological value of the Taro leaf protein

Conclusions

• The apparently higher nutritive value of sun-dried compared with ensiled Taro leaves may have been caused by inadequacies in the ensiling process, resulting in excessive breakdown of the protein and poor palatability.
  
  
• The relatively high values of N retention (equivalent to about 250 g/day of live weight gain) and of retained N as a proportion of digested N in the diet with sun-dried Taro leaves, are indicative of a high biological value of the Taro leaf protein, especially it represented over 80% of the dietary crude protein these diets.

Acknowledgments

The authors would like to express their gratitude to the MEKARN project financed by the SIDA-SAREC Agency and to the Center for Livestock and Agriculture Development (CelAgrid), for providing resources for conducting this experiment.
 

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