Effect of feeding untreated and urea treated rice straw on total  volatile fatty acids and bacteria production rates in cross  bred (Red Sindhi x Jersey) calves

S P Tiwari, Kiran Kumari and M K Gendley 

College of Veterinary Science and Animal Husbandry,Anjora, Durg (Chhattisgarh) 491001-India
drsptiwari@gmail.com

Abstract 

Experiment was conducted to study the effect of feeding ammoniated rice straw on ruminal total volatile fatty acid (TVFA) and bacterial production rates. Twelve, Red Sindhi x Jersey cross bred male rumen fistulated calves (1-1¹/₂ yrs) were divided into three equal groups. Animals were offered rice straw either untreated (I) or 4 per cent urea + 40 per cent moisture treated and ensiled for 30 days (II) or 5 per cent urea + 30 per cent moisture treated and ensiled for 30 days (III). Protein requirements were met through concentrate mixture.

Levels of NH₃-N and TCA-precipitable-N in strained rumen liquor (SRL) were significantly higher (20.34±0.022, 63.26±0.81 (II), 20.78±0.4l, 64.98±0.87 (III) (mg/100 ml SRL) in groups fed ammoniated straw as compared to control group (l3.58± 0.31, 45.94±1.91 mg/l00 ml SRL), respectively. The bacterial production rates in the rumen (g/day) were significantly higher in groups II and III (229.94±11.72 and 251.40±8.15) as compared to group I (158.61±13.71). TVFA concentrations (mmole/l00 ml SRL) and TVFA production rates (mmole /dl) were a1so significantly higher in groups II and III (14.00±1.19, 12.01±0.12 and 13.56±0.92, 11.92±0.38) as compared to group I (11.52± 0.43, 9.36±0.37).

The bacterial production rates were significantly co-related with TVFA, NH_3-N and TCA precipitable -N concentration in the rumen. Multiple regression equations relating bacterial production rates with (i) NH₃-N and TVFAconcentration in the rumen, (ii) NH₃-N and TVFA production rates. The data suggested that bacterial production rates were dependent on NH₃-N concentration and a significant co-relation was observed.

Key words: ammonia nitrogen, protein requirement, strained rumen liquor

Introduction

Cereal straws and stovers are essentially energy feeds high in cell wall constituents which may be as high as 80 per cent of the total DM (Jayasuriya 1987), two third of this may be cellulose and hemicelluloses. Lignin is another important cell wall material which acts as a physical barrier between potentially digestible materials (cellulose and hemicelluloses) and digestible enzymes and the efficient utilization of such cellulosic feed materials (Varga and Kolver 1997).

Many physical (chopping, grinding, irradiation, pressure cooking etc.) and chemical (NaOH, Ca (OH)₂, NH₄OH and NH₃) treatments have been developed (Gao Tengyun 2000). Ammonia (by urea hydrolysis) treatment of coarse roughages crop residues has shown promise by way of breaking lignin carbohydrate bonds and thereby improving their nutritive values (Gao Tengyun 2000). In the present study, chopped rice straw was treated with ammonia (urea) to see the effect on bacterial and VFA production rates and their inter-relationship in cross-bred calves.

Materials and methods 

In earlier preliminary studies chopped rice straw (500 g each) was treated with four levels of urea (0, 3, 4 and 5 per cent on DM basis) and two moisture levels (30 and 40 per cent by weight) in polythene bags for 30 days in the laboratory. On the basis of in vitro digestibility data, nylon bag DM disappearance and chemical composition of untreated and. treated straw, two levels of urea and moisture (4 per cent urea + 40 per cent moisture and 5 per cent urea + 30 per cent moisture) were selected for the large scale urea treatment of rice straw for detailed in vivo studies. For this, chopped rice straw appropriately mixed with urea and water was filled in the cemented silos and covered with double layers of polythene sheets at the top and ensiled for 30 days. Twelve, Red Sindhi x Jersey cross bred  male fistulated calves (1-1¹/₂ yrs) were divided randomly into three equal groups and fed rice straw ad libitum either untreated (I), or 4 per cent urea + 40 per cent moisture treated, ensiled for 30 days (II) or 5 per cent urea + 30 per cent moisture treated ensiled for 30 days (III). The concentrate mixture (groundnut cake 40 parts, crushed barley 40 parts, wheat bran 17 parts, mineral mixture 2 parts and salt 1 part) was fed to all the animals to meet their protein and energy requirements (NRC 2001). The ammoniated straw was not considered as supplementation rather as enrichment. Vitablend was given to all the animals as a source of vitamin A, in drinking water. After a preliminary feeding period of 21 days, the rations were divided into 12 equal parts and offered to animals at 2 hour intervals to ensure a near steady state of ruminal fermentation.

The in vivo total volatile fatty acids (TVFA) production rates were determined by the use of 1, 2 ¹⁴C-Sodium acetate (Leng 1970) (200 to 250 µci dose per animal) adopting single isotope dilution technique using aqueous scintillation fluids (Bray 1960). The radioactivity in the processed samples was counted in Packard Tricarb Liquid Spectrometer Model BPLO. TVFA concentration in the rumen was estimated by Markham's distillation apparatus. Ammonia N in SRL was estimated (Conway 1967) and bacterial production rates were determined in vivo using ¹⁵S sodium sulphate (Singh et al 1977). The data were analyzed statistically (Snedecor and Cochran 1967) and linear as well as multiple regression equations were developed.

Results and discussion 

The dry matter intake varied from 1.8 kg to 2.4 kg per 100 kg body weight in the different groups being lowest in group I (2.85 kg/day) followed by group III (4.9) and the highest (5.18 kg/day) in group II. The concentrate was fed at the rate of 1kg/day to all the animals in different groups. However roughage intake varied as 1.85, 4.18 and 3.9 kg per day in group I, II and III respectively.

Chemical composition of various feeds offered to animals is given in Table l.

CP contents of rice straw increased due to ammonia (urea) treatment. The ruminal bacterial production rates expressed as g /day or g/mole TVFA produced were significantly higher in the groups where animals were fed ammoniated rice straw as compared to untreated straw fed animals (Table 2).

This higher production of microbial protein in ammoniated rice straw fed groups was associated with the enhanced digestibility of fibrous constituents of straw (Jain et al 2005) due to ammoniation. TCA-precipitable-N was also significantly higher in groups II and III as compared to group I. Obviously, this could be attributed to the increased microbial protein synthesis in the rumen of the animals fed ammoniated rice straw. Other worker also observed the same trend (Leng 1972). The values of ammonia-N were also significantly (P<0.05) higher in the groups where animals were fed ammoniated rice straw as compared to the group I, where untreated rice straw was fed. These higher values may be due to more soluble N in the rations containing urea treated straw as compared to control ration, which in turn provides a readily available source of soluble N for rumen microbial growth. Similar results were also observed by earlier workers Hadjipanayiotou (1982).

The data suggested that bacterial production rates were dependent on NH₃-N concentration and a significant co-relation was observed. Thus, the independent linear regression equations were developed .

(i) Y_BP      = 15.3815+ 10.8557x (AN),   (n= 12,   r = 0.821; significant at 1% level)

(ii) Y_BP    = 33.2755 + 4.247x (TCA-N), (n=12, r = 0.852; significant at 1% level)

(iii) Y_BP   = -96.3599+ 27.9072 x (VFA prod. rates) {n=12, r' = 0.6448; significant at 1% level)

Where,

Y_BP = bacterial production rates (g/day),
AN = NH₃N concentration in the rumen (mg/100 ml SRL),
TCA-N = TCA-precipitable-N in the rumen (mg/100 ml SRL) and
VFA prod. Rates = VFA production rates (moles/day).

Thus, the optimal bacterial production rates in the rumen is as much dependent on VFA production rates as it is on the availability of NH₃N. In accordance with equation (i) and (iii), it can be indicated that for the bacterial production rate of 200 g/day, the optimum level of NH₃N in rumen liquor and VFA production rate must be 17 mg/100 ml SRL and 10.62 mole/day, respectively. Considering that there is a close and significant co-relation between bacterial production rates and NH₃-N concentration on one hand and VFA concentration on other hand combined multiple regression equations were developed as under:

(iv) Y_BP = 24.5292+11.2583 x (AN)-1.2657 x TVFA conc. (n =12; R² =0.676; significant at 1% level)

(v) Y_BP = -68.1495+4.4665 x (AN) +18.0259 x (TVFA PR) (n =12, R² =0.7383; significant at 1% level)

The above multiple regression equations signify that if any of the above constituents viz. NH₃-N and TVFA was limiting, the bacterial production rate would be adversely affected. In other words, to achieve optimal bacterial production rate, the adequate amounts of NH₃-N and VFA must be simultaneously available. Studies (Leng and Nolan 1984) also suggest that the optimum values of NH₃-N in rumen fluid may be as high as 15 to 20 mg/100 ml depending upon the diet. In the present study the concentration of NH₃ - N in rumen fluid was 13.58 to 20.78 mg/100 ml, which is well within the optimum range of maximum microbial protein synthesis.

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Received 17 August 2008; Accepted 29 September 2008; Published 5 December 2008

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