FEEDING TRIALS ON RABBITS USING A SACCHAROMYCES CERE VISIAE STRAIN

r A fast growing (growth rate k = 0 63h-I) strain YI8 from grapes containing 52% protein was used in the feeding trials on rabbits. The total serum protein and albumin levels were the same and were not signl-ficantly different in all the four groups. The body weight measurements indicated that the mean effects due to control, yeast and ca~ein diets levels are the same. But the mean effect due to low protein diet is lower than the control, yeast and casein diets levels. Histopathological studies of liver and kidney revealed no abnormal findings. It appears that this yeast protein has no deleterious effects.


Introduction
Rotein malnutrition among children is the most common public health problem in developing countries. This is mainly due to the non-availability of good quality protein foods. This prompted us to look for cheap high quality microbial protein sources. Yeast was selected as the microorganism for: this study. Yeasts contain lower level of nucleic acids and are rich in vitamins and minerak3 The cultivation of microorganisms depends on the economic feasiblity of producing a protein product which can compete with the conventiobal preparations of foods and feeds in the market. Baker's 'S. Seevaratnam e t . al.

Preparation of Yeast Powder
The Saccharomyces cerevisiae strain was grown in 1 9 1 of the minimal medi-um4 containing 50gl-' sucrose as the carbon source. The containers were aerated using a suction pump. The cells were harvested in the late exponential'phase, usually after 18h, by centrifuging a t 2460g for 15 min in a MSE refrigerated centrifuge at 4 ' . Th& packed yeast cells were washed with normal saline and centrifuged again under same conditions. The cells were autoclaved at 103k Pa for 1 5 min and oven dried at 8 0 '~ for 16h. This was powdered using a micro mill.

Feeding of Rabbits
Young white 3 months old New Zealand rabbits were fed with a low protein diet containing 50% rice bran and 50% rice flour (7% protein) and adequate amounts of vitamins and minerals ( Table 1). The vitamins and minerals were incorporated into the diet by mixing log of "Premix" which is commercially manufactured and sold as animal food. The rabbits were fed at the rate of -8Og/diet/animal/ day and water ad libitum for 4 weeks. They were then divided into four groups and each group had 4 rabbits. Low protein group animals were continued on low protein (7%) diet while the control group received a mixed high protein diet (16% protein).  7 ~i c e ' b r a n Note . 1) 80g diet was given/animal/day with lOOg of cabbage.
2) The animals were supplied with adequate vitamins and minerals and water ad libitum. The minerals & vitamins were incorporated by mixing l o g of "Premix" which is commercially manufactured and sold as animal food.
Yeast group was fed on a rice diet (5% protein) supplemented with 11% yeast protein, while casein group received rice diet (6% protein) supplemented with casein (10%). Except the low protein group that received a 7% protein diet the rest of the groups had 16% protein in their diets (Table 1). All rabbits were supplied with adequate amounts of vitamins, minerals and water ad libitum. All rabbits in the different groups were maintained in their respective diets for a period of 8 weeks.

2.3' Body Weight and Serum Protein Levels
Body weights of these rabbits were recorded at .ten day intervals. Blood samples from an ear vein were taken at 10 day intervals and analysed for total protein by Lowry's method5 and albumin by bromocresol green (BCG) dye binding m e t h~d .~ Globulin levels were determined by the difference between the total protein and albumin.

Postmortem and Histopathological Studies
Rabbits from all four groups were anaesthetized, the body cavity opened and, the internal organs examined. The liver and kidney were excised and prepared for histological examinations. Specimens from the liver and kidney were fixed in 10% formal saline for embedding in paraffin. Sections (4pm in thickness) were cut using a microtome (Shanton) and stained with haematoxylin and eosin (H & E ) stain.  Table 2 shows the weight gain of the rabbits. The results were statistically analysed by Analysis of Variance ( Table 3). The observed F (Fratic) value was greater than the table (F) value. Hence the H, null hypothesis was rejected arid HI hypothesis (mean effects due to all the diets levels u s not the same) was accepted. To find out the main effects of the diet further statistical analysis (Student 't' distribution) was done. From this analysis ( Table 3) it was concluded that the mean effect due t o low protein diet was lower than the mean effects due to control (p2 ), yeast (p3 ) and casein (p4) diets. But the mean effects due to cdntrol (p2), yeast ( p 3 ) and casein (p4) were the same. Similar results were obtained by the feeding studies of Candida lipolytica and Candida tropicalis grown on hydrocarbon with broiler chick^.^ Feeding Trials on Rabbits using Saccharomyces Cerevisiae . 7 7.

Serum Protein Levels
. Table 4 gives the blood serum protein levels. Total serum protein and albumin levels in all the four groups were similar and there were no significant differences between the groups. This could be due to all the groups getting k more than the minimum amount of protein per. day in their diets. Note : N o significant changes in the serum protein levels ; serum protein levels were analysed at 10 days interval.

Postmortem and Histopathological Studies
All the animals appeared healthy a n d there were no observable changes in the internal organs. Sections from the liver of the rabbits fed with yeast proteins (Figure 1) showed normal architecture. There were no evidence for parenchymal cell necrosis.  This shows that there ai-e no deleterious substances in the yeast protein produced by strain Y1 at 11% concentration. Further studies have to be carried out with increased supplementation of yeast protein to detect'any toxic compounds that may be present in lower amounts.
Gastro-intestinal disturbances. usually arise by the consumption of living microbial cells which can survive gastric acidity and which on entering ' , the intestine can multiply and ferment carbohydrates liberating C 0 2 and toxic amines. They may also utilize B group vitamins at the expense of the host. All these effects are prevented by autoclaving at 1 2 0 '~ for 15 rnih before incorporating into feed.

S. Seevaratnam et. al.
Feeding trials on rabbits using S. cerevisiae strain Yl shows, that the strain has no deleterious substances and it appears that this yeast diet is compasable t o the good quality casein.