Use of Cassava as Animal Feed

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Effects of cassava leaf meal on the rumen environment of local yellow cattle  fed urea-treated rice straw 

Duong Nguyen Khang and Hans Wiktorsson^* 

College of Agriculture and Forestry, National University of Ho Chi Minh City, VietNam.  
^*Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management,
PO Box 7024, 750 07, Uppsala, Sweden 

Abstract 

An experiment was conducted as a Latin square design with four rumen-fistulated local Yellow cattle with a mean live weight of 230 kg. The treatments were: (CLM0) urea-treated rice straw ad libitum plus 1 kg/d cassava root meal (basal diet), (CLM500) basal diet plus 500 g/d cassava leaf meal, (CLM1000) basal diet plus 1000 g/d cassava leaf meal, and (CLM1500) basal diet plus 1500 g/d cassava leaf meal. 

Total dry matter intake increased with increasing level of cassava leaf meal. The ruminal ammonia concentration and populations of protozoa  and bacteria tended to increase with increase in CLM supplementationon treatment. The in sacco degradability of cassava leaf meal was high (85 % of the DM had disappeared after 24 h of incubation) and of urea-treated rice straw was 64% after 72 h of incubation. There was a slight tendency for in sacco degradability of rice straw to increase with CLM supplementation. 

Key words: Cattle, cassava leaf meal, rice straw, intake, rumen environment, degradability

Introduction 

In Southeast Asia rice straw is the predominant dry season feed for ruminants, despite its low nutritive value (Wanapat 1984). It is deficient in readily fermentable energy, nitrogen, minerals and vitamins, and cannot provide for optimum microbial growth in the rumen or tissue development of the host. As a result, growth rates and milk production are generally low and often only about 10 % of the genetic potential of the animal (Leng 1995). 

Chemical and physical treatment of rice straw has been widely practiced as a method of improving intake and digestibility (Sundstol and Coxworth,1984). Ammoniation using urea has received major attention as an appropriate system for developing countries (Owen and Jayasuriya 1989). Further improvement in performance may be achieved by supplementing treated rice straw with fresh or dried forage. A good candidate for supplementation is cassava forage, which contains more than 20 % crude protein (Reed et al 1982), in a form which by-passes the rumen, since it is bound in a tannin-protein complex. 

Cassava forage has been shown to be an excellent source of protein, as a direct supplement or in concentrate mixtures (Wanapat 1995). In the Dominican Republic, fresh cassava leaves as the only source of forage in a diet of molasses-urea, supported good growth rates (>800 g/day) in fattening cattle (Ffoulkes et al 1978; Ffoulkes and Preston 1978; Ffoulkes and Preston 1979). The integral cassava plant has been used for dairy cow feeding as a supplement to pasture (Garcia et al 1994, Garcia and Herrera 1998). 

The hypothesis behind this study is that cassava leaf meal, fed together with urea treated rice straw, will  provide sufficient protein and energy for the growth of young cattle. 

The objectives of the study were: 

• to examine the effects of different levels of cassava leaf meal on ruminal ammonia concentration, ruminal pH and ruminal microflora population in heifers fed diets based on urea-treated rice straw and cassava root meal; 
• to study the rate and extent of rumen degradability of the feeds on the different rations.

Materials and methods 

Location 

The experiment was carried out at the experimental farm of the College of Agriculture and Forestry, Ho Chi Minh City, Vietnam. The mean air temperature was 28.2 °C and the mean relative humidity 76.5 %. 

Animals 

Four local Yellow cattle (20 - 24 months of age and 230 kg average live weight) were fitted with permanent rumen cannula 3 months before the commencement of the experiment. 

Housing 

The animals were placed in individual stalls in a barn with open sides. Clean, fresh water was available ad libitum during the whole experiment. 

Experimental design 

The treatments were arranged in a 4*4 Latin square. Each treatment period lasted for 30 days. The first two weeks of each period were for adaptation of the heifers and of the rumen microflora to the new diets. Data on daily feed intake were taken during 7 days of the third week. Feed samples for analysis were taken before feeding during the last 3 days of the same week, in sacco degradability was measured during the following 3 days of the fourth week, and rumen samples were taken during the last 2 days of each period. 

Diet and treatments 

The dietary treatments were:0, 500, 1000 and 1500 g DM/day of cassava leaf meal (CLM0, CLM500, CLM1000 and CLM1500). The cassava leaves were collected at the same time from one field after harvesting the roots. The leaves were air dried and ground. The animals had access to the feeds for the whole day. 

The basal diet consisted of urea-treated rice straw offered ad libitum and supplied once daily at about 07:30 h, together with a supplement (1 kg DM/animal/day) which consisted of cassava root meal and 20 g of a mixture of salt and minerals. The straw was treated with 50 g urea per 1000 g DM of straw, wrapped in an airtight plastic film and stored for 3 weeks before feeding. All the cassava root meal was bought on the market on one occasion.                                                                                                                                                           

Measurements 

All the feeds were weighed before feeding and supplied separately to the heifers. Refused feeds were weighed each morning during 7 days of the third week. The feeds were also sampled at these occasions and analyzed for calculation of daily dry matter and organic matter intake, according to the procedures of AOAC (1990). 

Feed samples were taken for analyses of nitrogen, ether extract, neutral detergent fiber, and acid detergent fiber (Table 1). The nitrogen and ether extract of the feed samples were determined according to the procedures of AOAC (1990). The neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations of feed samples were determined according to the procedure of Van Soest et al (1991). In sacco degradation of feed samples was determined during 72 h of each period. The bags were 60 x 120 mm and made from nylon filter cloth with a pore size of 28 microns (Saatifil PES 28/17), according to the procedure described by Orskov et al (1980). The sun-dried samples were milled in a grinder (1 mm) and weighed amounts (1.5 g) put in nylon bags. The bags were attached to plastic tubes and incubated in the rumen for 6, 12, 24, 48 and 72 hours. After incubation, the bags were washed by hand under running tap water until the water ran clear, and dried in a microwave oven to a constant weight. 

During 2 days (day 28 and day 29) of each 30 day period, ruminal fluid  samples were collected before feeding in the morning and then at intervals of 2 hours over an 8-hour period through a probe placed in a caudal position in the ventral part of the rumen. The protozoa population in the rumen fluid was estimated by diluting 8 ml of ruminal fluid with 16 ml of formaldehyde-saline solution (37 % formaldehyde with saline solution 1:9) and counting the protozoa under light-microscopy (100x magnification) using a 0.2 mm deep Dollfus counting chamber. Four fields in the counting chamber were filled and protozoa counted, according to the method described by Jouany and Senaud (1979) and Dehority (1993). 

A sample of rumen fluid was diluted 1:3 in formol saline solution and again diluted to 1:3 in formol saline solution (1 part of formol 37 % and 9 parts of saline 0.9 % solution). The fixed samples were stained with 2.5 mg of 4^’, 6 - diamidino - 2 phenylindole (DAPI; Sigma) per ml for 30 min. Each sample was filtered onto 0.2-mm-pore-size nucleopore filters. Cells were counted at a magnification of x1000 with a Nikon epifluorescence microscope equipped with a 100-W Hg lamp and an UV filter set (Navas et al 1993; Joux and LeBaron 1997). 

The rumen fluid pH was determined immediately after collection, by pH meter. The concentration of ammonia nitrogen in the rumen fluid (NH₃-N) was determined by diluting 15 ml of ruminal fluid with 5 drops of concentrated H₂SO₄ and distilling and titrating the released ammonia by the standard Kjeldahl procedure (AOAC 1990). 

Data were analyzed by ANOVA using the General Linear Model and Pairwise comparison in Minitab Statistical Software version 12.21.
 

Results and discussion

Chemical composition 

Feed intake 

The intake of straw and the total dry matter intake showed a continuous increase with increasing level of cassava leaf supplementation (Table 2). Cassava leaf meal accounted for 18, 17, 10 and 0% of the total dietary DM intake for treatments CLM1500  through CLM0. These results differ from those of Queiroz et al (1998a), who found no differences in dry matter intake of urea-treated corn stover, with or without supplementation of cassava hay, but are supported by the findings of Mom Seng et al (2001) who reported increased total DM intake by supplementing untreated rice straw with fresh cassava foliage. The differences in results between the studies are probably due to the differences in the chemical and nutritional quality and physical structure of the supplemented cassava feeds. The cassava leaf meal in the present study and the fresh cassava foliage used by Mom Seng et al (2001) contained  22 to 22 % crude protein, as compared to 14.1% crude protein in the cassava hay used by Queiroz et al (1998a). 

 Effects of cassava leaf meal levels on rumen pH and ruminal NH₃-N 

The ruminal pH and NH₃-N concentrations tended to increase with increasing amounts of cassava leaf meal (Table 3). Urea entering the rumen is hydrolyzed by microbial ureases to CO₂ and ammonia (Van Soest 1982). Later, ammonia is combined with hydrogen ions in the rumen fluid to form ammonia ions. This process depends on ruminal pH (Kajanapruthipong and Leng 1998). Ammonia moves readily across membranes as compared to ammonium ions, and appears to be more readily absorbed (Mooney and O’Donovan 1970). Chalmers et al (1971) found that when the pH in ruminal fluid is below 6.9, ammonia concentrations in both peritoneal liquor and jugular blood decrease, whereas the ammonia concentration in ruminal fluid remains constant. 

 

Effects of cassava leaf meal levels on microbial populations in the rumen 

Protozoal and bacterial populations in the rumen tended to increase with the increasing level of cassava leaf meal, especially the protozoa population. This result contrast with the finding of Mon Seng et al (2001) that cassava forage supplementation rice straw had no effect on the population of either large or small protozoa. 

Effects of cassava leaf meal levels on in sacco degradability of feeds in the rumen 

The degradation rate of cassava leaf meal was high, 75% of the organic matter having disappeared after 24 h of incubation. Degradability of the urea treated rice straw was slower with the maximum at about 65% of the organic matter after 72 h of incubation (Figures 1 and 2). Increasing levels of cassava leaf meal tended to increase the rate of degradability but the effects were rather small. These results are similar to those of Wanapat et al (1997),  who found that the degradability of cassava leaf meal after 72 h of incubation was 78.7 %. 

  

Acknowledgments 

The authors are grateful to the Swedish International Development Authority (SIDA/SAREC) and the International Foundation for Science (IFS) for equipment and funding for this study. 
 

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