MATERIALS AND METHODS

Preparation of Yeast-Malate Fermented Cassava Chip (YMFCC): This technique is based on the method developed by Oboh (2006) and Boonnop et al. (2008), which enriching nutritive value of cassava chip with yeast (Saccharomyces cerevisiae) fermentation. The method for synthesis of YMFCC is as follows:

Animals, diets and experimental design: Ten, one-year old of male cattles weighing about 150±10 kg were randomly divided into 2 groups according to receive 2 groups of supplemental feeds by receiving concentrate at 14% CP (T1) and Yeast-Malate Fermented Cassava Chip (YMFCC). The composition of dietary treatments and Urea-Treated rice Straw (UTS) used are shown in Table 1 and 2.

Cows were housed in individual pens and individually fed concentrate at 1% BW. All cows were fed ad libitum of UTS with water and a mineral-salt block. Feed intake of concentrate and roughage were measured separately and refusals recorded. The experiment was run for 120 days, the first 15 days for treatment adaptation and for feed intake measurements whist the last 7 days were for sample collections of faeces, urine and rumen fluid. Body weights were measured each 30 days during the sampling period prior to feeding.

UTS was prepared by using 5% (W/W) urea mixed with 100 kg of water in 100 kg of Rice Straw (RS) batches (50:50, water to straw) and poured over a stack of straw and then covered with a plastic sheet for a minimum of 10 days before feeding to animals (Wanapat, 1990).

Data collection and sampling procedures: UTS, YMFCC and concentrate diets were sampled each 30 days and were composted by period prior to analyses. Feed, fecal and urine samples were collected by rectal sampling whist urine samples were collected by spot sampling during the last seven days of each period.

Table 1:	Ingredients of concentrate used in the experiment (DM% basis)

Table 2:	Chemical composition of concentrate, Yeast-Malate Fermented Cassava Chip (YMFCC) and Urea-Treated rice Straw (UTS)
1TDN = dig CP + Dig CF + dig EE x 2.25 +dig NFE

Composites samples were dried at 60^oC and ground (1 mm screen using Cyclotech Mill, Tecator, Sweden) and then analyzed for DM, ether extract, ash and CP content (AOAC, 1985), NDF, ADF and ADL (Goering and Van Soest, 1970) and AIA. AIA was used to estimate digestibility of nutrients (Van Keulen and Young, 1977).

Rumen fluid and blood samples were collected at 0, 2 and 4 h post-feeding on last period. Approximately 200 mL of rumen fluid was taken from the middle part of the rumen by a stomach tube connected with a vacuum pump at each time at the end of each period. Rumen fluid was immediately measured for pH and temperature using (HANNA instruments HI 8424 microcomputer) after withdrawal. Rumen fluid samples were then filtered through 4 layers of cheesecloth. Samples were divided into 2 portions. One portion was used for NH₃-N analyses where 5 mL of H₂SO₄ solution (1M) was added to 50 mL of rumen fluid. The mixture was centrifuged at 16,000 g for 15 min and the supernatant stored at -20^oC prior to NH₃-N analysis using the micro Kjeldahl methods (AOAC, 1985) and Volatile Fatty Acids (VFAs) analyses using a HPLC according to Zinn and Owens (1986). Another portion was fixed with 10% formalin solution in normal saline (Galyean, 1989).

The total count of bacteria, protozoa and fungal zoospores were made using the methods of Galyean (1989) based on the use of a haematocytometer (Boeco). A blood sample (about 10 mL) was drawn from the jugular vein at the same time as rumen fluid sampling, separated by centrifugation at 5,000 g for 10 min and stored at -20^oC until analysis of Blood Urea Nitrogen (BUN) according to the method of Crocker (1967).

Statistic analysis: The means of each parameter measured in the digestibility studies and internal parasitic egg counts were analyzed by the analysis of variance procedure of SAS (1998) and means were compared using t-test.

RESULTS AND DISCUSSION

Chemical composition of feeds: The chemical compositions of concentrate diets (T1), Yeast-Malate Fermented Cassava Chip (YMFCC) (T2) and urea-treated rice straw (UTS) fed in cattle are shown in Table 2. Crude proteins of concentrate, YMFCC and UTS were at 14.2, 29.1 and 7.9%, respectively. Diets containing high levels of cassava chip based diets had a slightly higher Non-Structural Carbohydrate (NSC) and lower NDF due to increased level of cassava chip in the diets. Furthermore, the chemical composition of UTS is presented in Table 2. Similar values for UTS have been similar to those reported by Wanapat (2000).

Effect on feed intake and digestibility of nutrients: The effects of supplementation of YMFCC as replacement concentrate on feed-intake and digestibility of nutrients in cattle are presented in Table 3. Feed intake were non-significantly different among treatments and was higher in cattles receiving T2 than T1 (2.6 and 2.5% BW). This result was in agreement with earlier work by Sommart et al. (2000) and Khampa et al. (2006) which reported that inclusion of cassava chip in diets resulted in satisfactory animal performance and had no negative effects on animal health in finishing beef cattle and lactating dairy cows.

Apparent digestibility of DM, OM, CP, NDF and ADF were non-significant different (p<0.05) for all diets, however digestible of nutrient intake tended to be higher in cattle fed YMFCC (T2) than T1. The slightly lower NDF digestibility of the cassava-based diets may have contributed to higher degradation in substantial decrease in fiber digestibility as reported by Hoover (1986). Furthermore, in the experiment by Erdman (1998) reported that the sources of starch influence the rate of NDF digestion differently at pH 6.8 than 5.5. In addition, when ruminal pH was reduced below 6.3 in dairy cows, ADF digestion could be decreased at 3.6% unit per 0.1 pH and may result in depressed feed-intake.

Characteristics of ruminal fermentation and blood metabolism: Rumen ecology parameters were measured for pH, NH₃-N and VFA (Table 4). In addition, BUN was determined to investigate their relationships with rumen NH₃-N and protein utilization. Rumen pH at 0, 2 and 4 h post-feeding was changed by dietary treatments, however the values were quite stable at 6.6-6.9, but all treatment means were within the normal range which has been reported as optimal for microbial digestion of fiber and also digestion of protein (6.0-7.0) (Hoover, 1986).

Table 3:	Effects of supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC) as a replacement concentrate on feed intake, digestibility of nutrients and average daily gain in cattle
T1 = Supplementation of concentrate at 14% CP. T2 = Supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC). NS = Non Significant (p>0.05), * = Significant (p<0.05)

Table 4:	Effects of supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC) as a replacement concentrate on rumen fermentation and blood metabolites in cattle
T1 = Supplementation of concentrate at 14% CP. T2 = Supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC). NS = Non significant (p>0.05), * = Significant (p<0.05)

Ruminal NH₃-N and BUN concentrations were altered by YMFCC (T2) supplement which containing high cassava-based diets. As NH₃-N is regarded as the most important nitrogen source for microbial protein synthesis in the rumen. In addition, the result obtained was closer to optimal ruminal NH₃-N (15-30% mg, Wanapat and Pimpa, 1999; Chanjula et al., 2003, 2004) for increasing microbial protein synthesis, feed digestibility and voluntary feed intake in ruminant fed on low-quality roughages.

The influence of supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC) as a replacement concentrate on production of total VFA, acetic acid proportion, propionic acid proportion, butyric acid proportion and acetic to propionic ratio are shown in

Table 5:	Effects of supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC) as a replacement concentrate on rumen microorganisms in cattle
T1 = Supplementation of concentrate at 14% CP. T2 = Supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC). NS = Non significant (p>0.05), * = Significant (p<0.05)

Table 4. Mean total VFAs and propionate concentrations in the rumen were significantly different by increased with receiving YMFCC (T2) than T1 (117.6 and 102.4 mM). However, it was found that total VFA concentration in all diets ranged from 70-130 mM, the range suggested by France and Siddons (1993). Especially, the acetate to propionate ratio was decreased by receiving YMFCC (T2) than T1 (2.7 and 4.1) but the supplementation of YMFCC (T2) increased the daily output of propionate without decreasing the production of acetate (23.9 and 17.8 mol/100 mol) and it was in agreement with the results reported by Callaway and Martin (1996) and Khampa et al. (2006).

Rumen microorganisms populations: Table 5 presents rumen microorganism populations. The populations of fungal zoospores, protozoa and total bacteria direct counts were significantly different and populations of bacteria had higher numbers in cattle receiving diets YMFCC (T2) than T1. In contrast, the present number of protozoa in the rumen was decreased by YMFCC supplementation in high cassava-based diets. In the experiment by Newbold et al. (1996) has shown that feeding 100 mg of malate per day in sheep caused an increase in the number of total bacteria and tended to increase the population of cellulolytic bacteria. In agreement with these observations, Lopez et al. (1999) reported that fumalate (another intermediate in the succinate to propionate pathway) increased the number of cellulolytic bacteria almost three-fold during fermentation in the RUSITEC system. In addition Guedes (2007) reported that yeast are usually related to stimulation of cellulolytic and lactate-utilizing bacteria in the rumen, increased fiber digestion and increased flow of microbial protein from the rumen which may be beneficial for feedlot cattle fed high-grain diets. As cassava chip can be readily degraded in the rumen and ruminal pH was decreased, malate could stimulate lactate utilization by S. ruminantium and could improve pH in the rumen. It is possible that supplementation of malate with yeast may play an important role in increasing bacterial populations. Moreover, Martin et al. (1999) reported that increasing dietary concentrations of malate might help to reduce problems associated with ruminal.

Conclusions and Recommendations: Based on this experiment, it could be concluded that supplementation of Yeast-Malate Fermented Cassava Chip (YMFCC) as a replacement concentrate at 14% CP could improved ruminal fermentation efficiency, digestibility of nutrients and increasing propionate production, but decreased acetate to propionate ratio. In addition, supplementation of YMFCC increase populations of bacteria, but decreased protozoal populations. However, further studies should be conducted, particularly on milk yield and compositions especially on Conjugated Linoleic Acid (CLA) in lactating cows fed straw based-diets.

ACKNOWLEDGEMENT

The authors wish to express sincere thanks to Rajabhat Mahasarakham University and Tropical Feed Resources Research and Development Center (TROFREC), Khon Kaen University and The National Research Council of Thailand for providing financial support of research and research facilities.