Performance of young cattle fed rice straw sprayed with mixture of urea and molasses supplemented with different levels of cassava leaf meal

Ho Thanh Tham, Ngo Van Man^* and T R Preston^**

Department of Animal Husbandry, College of Agriculture and Applied Biology, Cantho University, Cantho City, Vietnam
httham@ctu.edu.vn
* Deparment of Animal Nutrition, Nong Lam University, Ho Chi Minh City, Vietnam
** UTA - TOSOLY - Finca Ecológica, Morario - Guapota - AA #48, Socorro, Santander, Santander del Sur, Colombia

Abstract

Fifteen young cross-bred Sindhi cattle (Red Sindhi x "Yellow" breed) were used to develop response curves relating growth rate and feed conversion with protein from cassava leaf meal (CLM), on a basal diet of rice straw sprayed with a mixture of urea/molasses (10% urea) (to provide 1 kg urea per 100 kg straw). A small quantity of local grasses was also supplied at 1% of body weight (in fresh matter). The levels of CLM were 0, 0.25, 0.5, 0.75 and 1% of live weight (in DM).

Observed intakes of the CLM on the supplementary treatments were 0.25, 0.48, 0.65 and 0.64% of live weight, equivalent to 92, 79, 62 and 56% of the amounts offered. DM intake, live weight gain and feed conversion were improved with significant linear trends according to the level of supplementation with CLM crude protein.

It is concluded that CLM can be used as a major source of by-pass protein in cattle rations based on urea-supplemented rice straw to improve growth performance and feed conversion.

Key words: bypass protein, linear trend, response curve

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 (Sundstøl and Coxworth 1984). However, a visible advantage of the method of spraying urea directly to rice straw is the simplicity, making it easy to apply in farmers' conditions. In addition, it appears to bring about similar responses of intake, DM digestibility, ruminal ammonia-N level and ability to stimulate activities of microbes as that provided by urea-treated rice straw (Hon et al 2000).

Ammonification 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), some of which is in a form that bypasses the rumen, since it is bound in a tannin-protein complex (Wanapat et al 1997).

Cassava forage has been shown to be excellent sources of protein, as a direct supplement or in concentrate mixtures (Wanapat 1995). Supplements are required to correct the deficiencies of essential nutrients; thereby increasing basal feed intake and hence animal production (Norton 1998). 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 and Preston 1978). The integral cassava plant has been used for dairy cow feeding as a supplement to pasture (Garcia et al 1994; Garcia and Herrera 1998).

Dry cassava leaf and stem meal have been used at the 35% level in dairy cow concentrates to advantage (FAO 2003). Khang (2004) found that cassava leaf meal at the level of 18% of dry matter in a diet of urea treated rice straw increased the intake, rumen ammonia nitrogen, rumen microflora population and degradability of the feed.

The objectives of the present study were to evaluate the effect of supplementing a basal diet of rice straw sprayed with mixture of urea and molasses with different cassava leaf meal levels on intake and growth rate of cross-bred Red Sindhi x "Yellow" cattle.

Materials and methods

Location and climate of the study area

The experiment was conducted in the livestock breeding farm of Soctrang province, Vietnam. The climate in this area is tropical monsoon with a rainy season between May and October and a dry season from November to April. The mean air temperature is 28.2°C. Average annual rainfall is 2000 mm/year. The duration of this study was 4 months, from May 2006 to September 2006.

Treatments and design

Five treatments were arranged in a Completely Randomized Design (CRD) with 3 replications. The treatments were levels of cassava leaf meal (CLM) equivalent to 0, 0.25, 0.5, 0.75 and 1% of body weight and designated: CLM0, CLM0.25, CLM0.5, CLM0.75 and CLM1. The experimental period lasted for 135 days. The first 15 days of the experiment was for adaptation of the cattle to the new diets, and the recording period of each treatment was 120 days.

Experimental animals, feeds and management

Fifteen young cross-bred Red Sindhi x "Yellow" cattle (7-8 months of age and 112±7.92 kg average live weight) were used in the experiment, which aimed to establish a response curve to cassava leaf meal in a basal diet of rice straw with added molasses-urea. The animals were vaccinated against Foot and Mouth disease (FMD) and placed in individual stalls in a barn with open sides.

The feeds used in the experiment were rice straw, CLM, local grasses, molasses, urea and a mineral block. The mixture of urea and molasses (1 kg urea and 9 kg molasses dissolved in 30 litres of water) was sprayed on to 100 kg rice straw using a watering can before it was offered to the animals. Cassava leaf meal was made from cassava leaves, which were bought in Tayninh province (the province belongs to South-East region of Vietnam, about 100 km from Ho Chi Minh City. The cassava leaves were harvested from farmers' fields after harvesting the roots and sun-dried for 2-4 days. Sun-drying consisted of spreading the leaves on the ground and turning them over while exposed to the sun, resulting in CLM for direct feeding or storage.

The fixed quantities of CLM were offered at 7:00 AM followed by the rice straw offered ad libitum at 8:30 AM, 11:00 AM, 4:00 PM and the remainder given at 7:00 PM. Local grasses were supplied at 1% of LW (in fresh matter) at 1:00 PM. The mineral block was available at all times by hanging in the stall. Clean and fresh water were offered ad libitum during the whole experiment.

Measurement and analysis

All the feeds were weighed before feeding and supplied separately to the cattle. Refused feeds were weighed each morning. The cattle were weighed at one-month intervals, in the morning before feeding. Live weight change was calculated as the slope of the regression of LW versus time.

Samples of rice straw, cassava leaf meal, local grasses, molasses and refusals were analyzed for dry matter (DM), crude protein (CP) and ash using procedures described by AOAC (1990). The neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations in feed samples were determined according to the procedure of Van Soest et al (1991).

Statistical analysis

Growth rates were determined as the linear regression of live weight against time. The data for feed intake, growth rate and feed conversion were analyzed as a completely randomized design using the General Linear Model (GLM) of the ANOVA program with the Tukey pair-wise comparison in Minitab software (Minitab release 13.1 2000). Sources of variation were: treatments and error. Linear or curvilinear regression equations were fitted to the performance data (dependent variables) with the independent variable being the level of cassava leaf meal.

Results

Chemical composition of diet ingredients

The chemical composition of the different feeds is given in Table 1.

Feed intake and live weight gain

Feed intake and live weight gain data of the cattle are summarized in Tables 2 and 3. 

Rice straw intake was highest in the treatment CLM0.5, significantly higher than in the other four treatments (P<0.001). CLM intake was highest in treatment CLM0.75 (771 g DM/day). The total daily DM intake per kg live weight (LW) increased with increase on the level of CLM in the diet. The DM intake per kg LW was significantly higher on the 1% CLM treatment compared to 0, 0.25, 0.5 and 0.75% CLM treatments (P<0.001). No refusals were seen of local grass, which was fed at constant amounts per 100 kg body weight on all treatments. Intake of urea and molasses was not significantly different among treatments.

At the CLM level of 0.25% of body weight, the cattle readily consumed all the CLM, while recorded intakes of CLM at 0.5, 0.75 and 1% of body weight were 79, 62 and 56% of planned intakes, respectively (see Table 3). Therefore, the actual CLM levels in CLM0, CLM0.25, CLM0.5, CLM0.75 and CLM1 treatments were 0, 0.25, 0.48, 0.65 and 0.64% of LW, respectively.

As the actual intakes of CLM were less then the planned levels, the response to the CLM supplementation was analysed by regressing the dependent variables (DM intake, live weight gain and feed conversion) against the observed CLM intakes (Figures 1 to 5). CLM intakes were expressed as g/kg live weight (Figure 1), g/kg DM intake (Figure 2) and g cassava protein/g of crude protein intake (Figure 3).

In all cases there were significant linear relationships between the response variable (live weight gain) and the independent variables. Similar relationships were observed for DM intake and DM feed conversion when regressed against cassava crude protein intake as proportion of total crude protein intake (Figures 4 and 5).

Discussion

Chemical composition of diet ingredients

The cassava leaf meal had a high CP content (20.36% of DM), which in within the range reported by several researchers (Ravindran et al 1986; Kiyothong 2003; Khang 1999; Chantaprasarn 2005). A separation of leaves and stems could further improve the nutritional properties of the cassava foliage. Numerous reports have shown that cassava leaf has high but variable protein content (170 to 400 g/kg on a DM basis) (Ravindran 1993).

Feed intake, live weight gain and feed conversion

In this study, cattle received approximately 1 to 1.5 kg green grass daily, which was mostly of agricultural weeds and from roadside grasses. The fresh grass was provided on all diets to ensure optimum rumen microbial activity. Hon et al (2000) reported that the rumen environments created by grass plus straw diets supported faster degradability of reference feeds than a diet of rice straw alone.

The total DM intake increased linearly with the level of crude protein provided by the CLM. This result could be attributable to the effect of supplementation of protein leaves to low quality roughage diets in the tropics as stated by Merkel et al (1999). These results differ from those of Queiroz et al (1998), who found no differences in DM intake of urea-treated corn stover, with or without supplementation of cassava hay, but are supported by the findings of Khang (1999) who reported increased total DM intake by supplementing urea-treated paddy straw with CLM. The CLM in the present study and the CLM used by Khang (1999) contained 20.4 to 22.5% crude protein, as compared to 14.1% crude protein in the cassava hay used by Queiroz et al (1998). The differences in results between the studies were probably due to the differences in the chemical and nutritional quality and physical structure of the supplemented cassava leaves as well as the specific characteristics of the feeds (Chenost and Sansoucy 1989). Other reasons could possibly be the difference in the basal diet, as in this research, urea-molasses sprayed rice straw was the basal diet, thus the effect of the CLM was to improve markedly the bypass protein status of the diet (Kiyothong 2003). A number of researchers around the world have also examined the benefits to ruminants fed forage, of supplementation with bypass protein meals (Leng 2005). Feeding poor quality forage with supplementing CLM possibly resulted in faster rumen outflow rates, thereby increasing DM intake. Voluntary intake was mentioned by Chenost and Sansoucy (1989). He believed that voluntary intake also depends on the appetite of the animals which varies according to the animal itself (age, physiology stage, former nutritional status) and to the environmental conditions (temperature, humidity) under which the animal is kept. In other words, the efficiency of utilization of low-quality roughages by ruminants for productive purposes is altered by numerous factors which are associated with the feed or the animal.

CLM accounted for 21, 22, 18, 10 and 0% of the total dietary DM intake for treatments CLM1 through CLM0. In the treatment CLM0.5, CLM was consumed about 18% of DM of the diet by cattle, which achieved highest LW gain. This is similar to the results of Khang (1999), who found that CLM at the rate of 18% of dry matter fed in the diet improved the intake, rumen ammonia nitrogen, rumen microflora population and degradability of feeds. At the CLM level of 0.25% of body weight, the cattle readily consumed all CLM as mentioned above, while recorded intakes of CLM at 0.5, 0.75 and 1% of body weight were 79, 62 and 56% of planned intakes, respectively. The reason for these refusals is not evident as previous authors have had no difficulty in feeding higher levels. Using cassava tops ensiled with molasses as a supplement to growing heifers, Man (2001) found that the proportion of cassava top silages could be as high as 38-42% of the dietary DM, which is higher compared to 22% of CLM in the diet in the present experiment.

Proportion of CLM crude protein to total crude protein corresponds with 0, 20, 34, 39 and 37% of the total crude protein supply. The CP content of the diet was 8.73, 9.86, 10.77, 11.22 and 11.01% for treatments CLM0, CLM0.25, CLM0.5, CLM0.75 and CLM1, respectively. These CP content are quite low compared with the requirement of young cattle. Although requirements for rumen degradable protein (RDP), rumen-undegradable protein (RUP), and total protein are dependent on animal factors, the concentration of available energy in the diet, and DM intake (NRC 2001), studies from the literature have indicated that concentrations of 11 to 13% CP in diets were adequate to obtain optimal microbial protein synthesis (Karsli and Russell 2002). Daily CP requirement given by NRC (2000) for beef cattle of 100 kg of LW and 300 g of daily LW gain was 12.4%. According to Preston and Leng (1987), molasses is an excellent carrier for urea and also provides trace elements. Molasses-urea mixtures can be easily distributed to small-scale farmers and used as a supplement. Moreover, between 10 and 30% of the diet, there are no particular problems with molasses for all types of livestock. Leng (1991) indicated that in most situations, adding urea to a low protein diet, such as that based on a cereal crop residue increases intake of the basal diet in addition to improving microbial growth and digestibility. Of the total protein supplied to animals through the diet, a part of it should be fermentable in the rumen to meet nitrogen requirements of microflora in the rumen. Inadequate fermentable nitrogen in the diet will affect microbial growth and reduce fiber digestion in the rumen (Manget 1997). This point of view is similar to that of Huq et al (1996), who reported that fermentable nitrogen had significant effect on weight gain when given along with bypass protein source, compared to when only bypass protein source was given.

Rate of live weight gain of cattle increased linearly with increasing proportion of CLM crude protein in the total diet crude protein, reaching a maximum at 34%, which achieved highest LW gain. This view is supported by Khuong and Khang (2005), who wrote that "increasing the level of cassava foliage to Sindhi x yellow cattle fed a urea-treated rice straw increased total DM intake and rate of LW gain". Ravindran (1993) reported that the true protein in cassava leaf was high (almost 0.85 of the crude protein fraction). Wanapat et al (1997) reported that the ruminal DM digestibility of cassava hay was relatively high while protein ruminal degradability was low indicating it would be a good source of bypass protein because of the formation of a tannin-protein complex. As reported by Barry and Manley (1984), the rumen tannin-protein complex is stable at the pH of the rumen but would dissociate at the lower pH in the abomasums. Makkar et al (1995) reported that tannins improved rumen efficiency by decreasing acetic acid and increasing propionic acid production, hence enhancing microbial protein synthesis.

In the present experiment, growth rates were increased three-fold (from 58 g/day to 214 g/day) for the cattle given CLM at 0.5% of body weight (CLM0.5) compared with the control treatment (CLM0). Additional weight gain observed from supplemental escape protein indicates that microbial protein synthesis may be insufficient to satisfy the metabolisable protein requirement, which probably limited gains by the cattle in control treatment (Karges et al 1992). In one experiment using urea-sprayed rice straw (2%) offered ad libitum plus fresh cassava leaves (3 kg/day) as a basal diet for local Yellow cattle, Nhan et al (2003) found a value of 183 g/day growth rate, which is slightly less than the 214 g/day growth rate in the treatment CLM0.5 in the present experiment. In a recent experiment in Cambodia, supplying fresh cassava foliage (3% of LW fresh basis) to a basal diet of untreated rice straw plus a rumen supplement, increased the growth rates of local Yellow cattle from 53 to 210 g/day (Seng Mom et al 2001). >From those results, it is clear the benefits of providing cassava leaf protein supplement to cattle consuming poor quality rice straw.

The improvements in feed conversion due to CLM supplementation mirrored the effects on growth rate, the two criteria being closely related (Figure 6).

Conclusions

• Growth rates and feed conversion of young crossbred cattle (Sindhi x Local "Yellow" breed) fed rice straw sprayed with urea and molasses, were improved with linear trends as the consumption of protein from cassava leaf meal increased from zero to 1.1 g/kg LW.

• The drying of cassava leaves and spraying urea on rice straw are very simple techniques to apply in farmer practice.

• Utilization of farm-produced cassava leaf meal as a supplement for fattening of cattle on rice straw can reduce dependence on concentrate feeds, with potential benefits from lower costs of feed and transport. This feeding system is recommended as an appropriate strategy for sustainable cattle production in the Mekong Delta of Vietnam.

Acknowledgements

The authors would like to express the most sincere thanks to all who assisted and supported in this study, particularly the MEKARN project financed by SIDA-SAREC. Appreciation is expressed to Mr. Tran Van Tam, Director of the livestock breeding farm of Soctrang province and the farm crew for assistance to use the animals. The authors would also like to thank Mr. Duong Minh Truong for assistance with animal care.

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