PROTEIN EVALUATION OF RABBIT MEAT by ANNE MARGARET SCHLUTZ, B.A.
A THESIS IN FOOD AND NUTRITION
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN HOME ECONOMICS
Approved
Accept/ed
Dean of the Gradu^/^ Schokl
December, 1974 (Lops2
ACKNOWLEDGEMENTS
I would like to express sincere appreciation to Mrs. Clara McPherson for her counsel and able assistance and also to Dr. S. P. Yang. I also thank Drs. John Pelley and Willis Starnes, and Harvey Olney of the Texas Tech University School of Medicine for their assistance and encouragement, and also my parents.
11 TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
LIST OF TABLES iv Chapter
I. INTRODUCTION 1
Statement of the Problem 1
Purposes 2
Hypothesis 2
II. REVIEW OF LITERATURE 3
The Potential Value of Rabbit Meat 3
History of Rabbit Meat 6
Description of Rabbit Meat 8
Nutritive Value of Rabbit Meat 9
III. METHODS AND PROCEDURES 19
Selection of Meat Samples 19
Chemical Analyses 19
The Bioassay 21
Statistical Analysis of Data 25
IV. RESULTS AND DISCUSSION 26
Chemical Analyses 26
Amino Acid Analyses . . . . ^ 26
Rat Growth Experiment 28
V. SUMMARY AND CONCLUSION 37
Summary 37
Conclusions 37 LIST OF REFERENCES 39
11• 1• LIST OF TABLES
Table Page 1. Comparison of Farm-Raised Rabbits and Wild Rabbits 10 2. Composition of Raw Domesticated Rabbit Flesh 11 3. Composition of Rabbit Meat 13 4. Nutritional Value of Rabbit and Other Meats 15 5. Composition of Experimental Diets 23 6. Protein, Fat and Moisture Content of Cooked Tissues 24 7. Essential Amino Acid Content of Rabbit, Chicken, Beef, Pork, Cod, and Casein and the FAO Amino Acid Pattern (gm/lOO gm Protein) 27 8. Effect of Feeding Young Rats an Other wise Adequate Diet Containing 9% Protein from Different Sources 29 9. Analysis of Variance of Mean Weight Gain of Young Rats 30 10. Differences in Weight Gains (g) Among Rats Fed an Otherwise Adequate but Protein-Free Diet for 28 Days or the Same Diet Supplemented with 9% Pro tein from Chicken, Rabbit, Beef, Pork, Cod or Casein 30 11. Analysis of Variance of Mean Food Consumption of Young Rats 31 12. Differences Among Food Intakes (g) of Rats Fed an Otherwise Adequate but Protein-Free Diet for 28 Days or the Same Diet Supplemented with 9% Pro tein from Chicken, Rabbit, Beef, Pork, Cod, and Casein 32
IV Table Page 13. Analysis of Variance of Mean PER of Young Rats 33 14. Differences Among Protein Efficiency Ratios for Various Protein Sources .... 33 15. Analysis of Variance of Feed Efficiency of Young Rats 34 16. Differences in Feed Efficiency (g) Among Rats Fed an Otherwise Adequate but Protein-Free Diet for 28 Days or the Same Diet Supplemented with 9% Pro tein from Chicken, Rabbit, Beef, Pork, Cod or Casein 35 CHAPTER I INTRODUCTION
Animal products are the most efficient source of dietary protein (1,2). The classical solution to protein deficiencies has been to add meat, milk, and/or eggs to the diet. Unfortunately, the distribution of meat cannot be im proved since the consumption of animal protein is determined largely by income, cultural patterns, and religions (3). The need for low cost quality proteins has prompted research for new sources. Recently the breeding of rabbits for human consumption has greatly increased (4). It seems feasible that in the future, rabbit meat, as a source of inexpensive high quality protein, may be more abundantly used in the American diet as well as the diets of people in other countries.
Statement of the Problem Humans inherently possess dignity and pride and do not willingly eat foods which they consider to be inferior. Rabbit meat was consumed to a large extent during wartimes by civilians since it was not considered a meat and thus was not rationed. Another negative implication dates back to ancient times when man believed he developed the charac teristics of the animal he ate. If he ate a lion, he would be fierce and strong; if he ate a rabbit, he would be meek and mild (5). Therefore, rabbit dishes may have adverse connotations dating back not only to prewar days, but to times of primitive man. One may think of rabbit meat as the strong, gcimy-flavored hare usually hunted in the wilds.
However, the commercially bred rabbits which consist of all white meat are different from the wild hare, and are quite acceptable for human consumption. Since there is contra dicting information in the literature concerning the protein quality of domesticated rabbit, an accurate evaluation of the protein content is needed to prove its value as an ac ceptable protein source for man.
Purposes
This study was undertaken to evaluate the quality of domesticated rabbit by determination of: 1) total protein, fat and moisture content, 2) amino acid content, and 3) the protein efficiency ratio (PER) by a bioassay procedure.
Hypothesis
In determining the protein quality of rabbit the following hypotheses were tested:
1) There is no difference in protein quality of
rabbit and that of chicken.
2) There is no difference in the protein quality
of rabbit and that of beef.
3) There is no difference between the protein
quality of rabbit and that of pork. 4) There is no difference in the protein quality of rabbit and that of cod. CHAPTER II REVIEW OF LITERATURE
The Potential Value of Rabbit Meat
Seventy per cent of the world's population is under nourished and children in certain areas of the world are still victims of kwashiorkor, which is due to an inadequate supply of high quality protein (6). Although protein is not a limiting factor in the United States, there is evidence that protein quality may be a problem under certain ethnic or low income dietary situations, or due to a lack of educa tion (5,6) .
Morrison and Campbell proved that high quality ani mal protein was a more efficient protein source than vege table protein by feeding one group of rats casein, and another group a vegetable diet. (The vegetable diet con sisted of 85% soybean and 10% wheat since soybean lacks methionine and wheat lacks lysine). On the higher quality protein diet (casein), less food was needed to meet nutri tional quality. When the lower quality protein (vegetable diet) was used, quantity had to make up for quality (7). Bender (8) concluded that an adult diet requires no more than 6% of calories in the form of protein and a mixed vegetable diet can be of equal value to animal pro tein. However, diets of lower protein percentage are ade quate only when sufficient food is eaten to meet calorie requirements (9). The F.A.O. suggested that by the year A.D. 2000, a threefold increase in total protein supplies would be needed and a fivefold increase in animal protein supplies would be needed in the developing countries. The protein food programs often include encouragement for animal pro duction and these activities are frequently supported by international organizations(10).
The efficiency with which farm animals convert feed- stuffs into food for man has received much attention. Food conversion ratio is the number of pounds of feed required to produce one pound of live animal tissue (11). Swine, dairy cattle (milk) and poultry (eggs and broilers) are the most efficient converters of feed energy and protein into food for humans. Poultry is intermediate and beef and cattle are the least efficient. The values for energy are of little importance because animal production is needed primarily for protein sources and not as contributors of energy in the human diet (12). Rabbits are good food converters. The commercial ized all white meat rabbit gives a well fleshed carcass (13). The feed conversion of an entire rabbit herd which includes young replacement stock is 3.4 to 4 lbs. of feed to produce 1 lb. of body tissue. The feed cost to produce a lb. of edible meat is about 28C. Both feed conversion and feed cost include the total amount of feed for offspring, doe and buck (14). The number of young per year that a doe can produce varies from 24-45 depending on the strain (12). Most commercial meat producers raise 4-6 of 8 fryers each year per individually raised doe (15). In any comparison of food conversion in animals, it should be remembered that the nonruminants consume a smaller proportion of the whole crop. Rabbit is especially effi cient in crop consumption as it consumes its mother's milk for 50% of its life. Ninety-eight percent of commercialized rabbits are 8-10 weeks of age when they go to market, and weigh from 2 to 3 lbs. The food efficiency of animals varies with the pro portion of body fat they store. Therefore, future needs should be aimed toward producing animals low in fat and high in protein content since much of the fat in meat products is discarded rather than served as food energy (12). In this case, rabbit would be more efficient since it has a lower fat and higher protein content than chicken, beef, pork and lamb (16). Holmes (10) mentions food production per unit acre as an important factor in nutritional efficiency. Crop pro duction is superior to any form of animal production when comparing the amount of food produced per unit acre. Never theless, there are continuous problems of palatability and acceptability of vegetable protein and the nutritive value still requires critical evaluation. Broilers seem the most productive when compared to pork and beef (10). The production of broilers in 10 weeks, weighing 3 lbs. has become the most efficient means of pro ducing flesh. For rabbit, the conversion of grain to flesh is now at the rate of 2 1/2 lbs. of grain to 1 lb. of flesh. This is to be compared with the conversion of 4 lbs. of grain per lb. of pork and 10 lbs. of grain per pound of beef.
History of Rabbit Meat
For centuries domestic rabbit was an essential item in the diet of Europeans. Although the history of the farm- raised domestic rabbit is quite recent, his wild ancestor was an important food item wherever he lived throughout the world. When the Romans invaded England, in the era of Caesar, they brought with them the forerunner of the domes tic rabbit, and the English have been rabbit producers and consumers ever since. Poachers of "Merrie England" hunted rabbits in fabled Sherwood Forest and on the estates of their Lords. The symbols and coats of arms of most French restaurants incorporate the rabbit into their seals. Most paintings of European kitchens show one or more rabbits hanging near the stove. Englishmen are well aware of the importance of the rabbit as a basic food. In 1954, the British Rabbit Council reported that nearly a million English households were rais ing rabbits and that there was a total of seven and a half million breeding rabbits within the limited confines of the British Isles (15).
To the American pioneers, wild rabbit was in many instances an important food source. During the long treks through savage territory and the long months of establish ing new settlements, it was often "rabbit or nothing." Among the pioneers who took their livestock with them, many included a pair of domesticated rabbits as an important livestock necessity and upon establishing their new home, began raising rabbits without delay. As America became an agricultural society, rabbit continued to be an important meat product. Almost every farmer had his cow shed, his chicken coop and his rabbit hutch, and rabbit meat took its place on the dinner table as a regular meat course. In the meantime, wild rabbit hunting ceased to be a necessity and evolved into a sport and few men are lacking in memories of the hunt, followed by the rabbit fry. The rabbit is of importance in exploration. During World War II survival training included the catching and preparing of rabbits for survival in whatever parts of the wilderness the service men might be stranded. When the U.S. Navy Operation Deep Freeze packs supplies for its Antartic Expedition, several hundred pounds of domestic rabbit meat are always included. Although pioneer hunters ate rabbit simply because it was available. Armed Forces survival 8 training specifies rabbit because of its high protein con tent (15) .
Description of Rabbit Meat
According to codes of Federal Regulations the com mercial rabbit is a young domestic rabbit, weighing from 1 1/2 to 3 1/2 lbs. The flesh is tender, fine grained and bright pearly pink in color (17) . Deboned, cooked, commer cial rabbit is similar to chicken in appearance and taste. Two main breeds for meat production in the United States are the New Zealand White and the Californian (15). The New Zealand breed has two varieties. Red and White, and was developed from the Belgian Hare and the Golden Fawn as strictly an American strain. Its normal weight will range from 9 to 12 lbs. at maturity. The Californian was evolved in 1928 as a blend of the finer features of the Himalayan, Standard Chinchilla, and the White New Zealand. The Cali fornian is comparable in weight to the White New Zealand. Both breeds have excellent white fur and are true albinos (15). The wild rabbit (Lepus leporidae), which the Amer ican pioneers eagerly sought and contemporary hunters chase, is not the same breed of animal as the rabbit now being raised (Royctolagus cuniculus). Rabbits when cooked have tender, whitish meat that is delicate in flavor, whereas the meat of the hare is dark, sinewy in texture, and has a gamy odor. The toughness of the meat is due to extensive exercise and the gamy taste results from the wild hare's varied diet. The flavor differs depending upon the section of the country in which he is found. In the western prairie the wild rabbit is preseasoned with sage, which he eats in abundance. in other areas wild herbs of many sorts and even tree bark give the hare a strong flavor (15).
Extreme care is taken in the raising of domestic, farm-bred rabbits to prevent toughness and a tainted flavor. Domestic rabbits are restricted to specially constructed wire pens built off the ground. The 8 to 10 square foot hutches permit sufficient exercise to keep the breeding stock healthy, yet still keep the meat tender and fine- textured. The rabbits are fed a commercially manufactured balanced diet, in pellet form (17). No strongly flavored greens such as kale or cabbage or garden greens such as lettuce are fed these animals in order to avoid flavoring the meat unduly. The total en vironment is carefully controlled with proper temperature, humidity, sanitation and even piped in music for its sooth ing effect. A comparison of the tissue of farm-raised rabbits and wild rabbits is given in Table 1 (15).
Nutritive Value of Rabbit Meat Commercialized rabbit is relatively low in fat, high in moisture and protein (4). Table 2 (18) indicates the 10 amount of fat, protein, calories, essential amino acids, vitcimins, minerals, general constituents, and energy values,
TABLE 1 COMPARISON OF FARM-RAISED RABBITS AND WILD RABBITS
Constituent Rabbit
Domestic Farm-Raised Wild Texture Tender, fine-grained Tough and juicy sinewy Color of Meat All white meat Dark, reddish Flavor Mild, delicate, Gamy, slightly nutty strong Availability All seasons Strictly seasonal Quality Wholesome, healthful Pro hibited for sale in most states
McMillin (4) studied the composition of rabbits of varying age and sex. The edible portion was separated quan titatively (excluding the heart, liver and kidneys) from the bones and waste, and analyzed for moisture, protein, ether extraction, fuel value and ash. McMillin's results are listed in Table 3. 11
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u ou s Q) rd Q) CO h O C EM J3 •H 0 CO * 0) CN CO -P A tn CM O CO ftg in •H to CO CO +J 0 1 rC CO o Cl4 1 o iH CO o CO * o ^ o rH 0) D4 U 0) CO 0) a 3 CO iH cn rd g > O u Tl •H CO • u U t7> o CN •H g CN Q> o . rd o U rd in 13 TABLE 3 COMPOSITION OF RABBIT MEAT Constituent Range Average Moisture 63.08-70.40% 66.74% Protein 19.70-21.03% 20.36% Ether Extract 8.46-15.71% 12.08% Fuel Value 716-1011 cal./lb 863.5 cal./lb, Ash 1.02-1.07% 1.04% Protein The nutritive value of a protein depends upon the kind and amount of its amino acids (19). Rabbit, therefore/ should be a good source of protein, according to Grace (20) who evaluated the composition of rabbit meat and concluded that it contained all the essential amino acids necessary for man. The data from Table 2 does not provide information on tryptophan. Altman and Dittmer (18) did not indicate the methods used for amino acid analysis. The HCl hydroly sis used in the classical analysis of amino acids usually destroys tryptophan. Therefore this amino acid must be determined individually by a different method (21). B-Complex Vitamins Table 2 also indicates that rabbit is deficient in ?wP 14 niacin• • . Tryptophan is a precurser of niacin (22) and the rabbit has a dietary need for this vitamin (23). Wooley and Sebrell (23) first showed this by demonstrating an in creased growth rate in rabbits with the addition to the feed of 10 mg of niacin per kg of body weight. Balance studies proved considerable synthesis of niacin (11.2 meg niacin intake and 178.9 meg niacin output). Addition of free tryptophan to the purified diet also proved that the rabbit is capable of using tryptophan as a niacin precursor. Results indicated that tryptophan was more effective as a free amino acid than if given as part of casein. Thus, according to this study, rabbit could be increased in niacin content if the diet were supplemented with free tryptophan. Fat and Moisture Wilson (24) compared carcass composition of young and adult bucks and does and noted that the flesh of females contained 4.65% more fat than that of the males. Sotillo (25) studied male and female rabbits for fat and moisture content and also concluded that fat and water content were greater for females than males and that generally the per centage of water content decreased with age. Meat from the wild rabbit was lower in water content, drier and less appetizing. SS««^' 15 Nutritive Value of Rabbit As Compared to Other Ma-jor Meat Sources Rabbit meat is high in protein, lower in fat, and higher in moisture than most other meats (4,15,26,27) as evidenced in Table 4 (28). TABLE 4 NUTRITIONAL VALUE OF RABBIT AND OTHER MEATS C Edible portion, uncooked Protein Fat Moisture Calor- % % % ies Rabbit (tender, young) (with giblets) 20.8 10.2 67.9 795 Chicken (fryer) (with giblets) 20.0 11.0 67.6 810 Veal (medium fat) 19.1 12.0 67.6 840 Turkey (medium fat) (with giblets) 20.1 20.2 58.3 1,190 Lamb (medium fat) 15.7 27.7 55.8 1,420 Beef (medium fat) (good grade) 16.3 28.0 55.0 1,440 Pork (medium fat) 11.9 45.0 42.0 2,050 Kizevetter and Dikaskajar found that rabbit flesh is as good a source of protein as beef, veal, mutton, pork or chicken, but contains less fat than beef, mutton or pork. It has a high content of extractives and collagen substances which makes it most suitable as a base for meat jellies (27) 16 Delgrado and Pujol (29) fed isocaloric diets to rats for 10 days with the following types of meat as the sole protein source: beef in jelly, boiled ham, rabbit in sauce and seasoned minced veal. The coefficients of digestibility of protein for ham, rabbit, veal and beef respectively were 86.5; 83.6; 81.7 and 75.5. Beef gave the highest biological value, 61.06. The coefficients of net protein utilization ranged from 48.6 for veal to 46.02 for rabbit. The coefficient of digestibility is the difference of protein found in the food and that in the feces. This difference represents the availability of protein to the body tissues. Thus if the feces from a given diet contain 5% as much protein as was contained in the food, this pro portion is assumed to have been lost and the coefficient of digestibility of dietary protein would be 95% (30) . In the above study, pork had the highest coefficient of digesti bility, 86.5%; followed by rabbit, 83.6%. Biological Value (B.V.) is the percentage of absorbed nitrogen that is retained in the body and not excreted in the urine. The body requires a certain quantity of amino acids in the proper proportions. If any amino acid is sup plied in an insufficient amount, it will limit the supply of tissue protein synthesized. The other amino acids re gardless of the amount present are used only in the amount required for tissue protein. The remainder will be used for energy after deamination. Therefore, proteins deficient in f3»- 17 essential amino acids will have a low biological value (31). According to Delgrado and Pujol, beef had the highest bio logical value, indicating that it had optimum proportions and amounts of essential amino acids. Net protein utilization measures the percentage of absorbed nitrogen retained for growth and for the replenish ment of endogenous losses through urine and feces. Biologi cal value and digestibility measure only the retention of nitrogen in the body. A protein source that is fully uti lized without waste has an NPU of 100. Egg, which is con sidered the perfect protein has an NPU of 90 (32) . Veal and rabbit have an NPU of 48.6 and 46.02 respectively. A study was conducted which compared live, dressed and cooked New Zealand Red Rabbit to chicken broilers. Ap proximately half of the live weight was lost when the rabbit was dressed; for chicken it was somewhat less. The rabbit was cooked in 1 hour and 15 minutes, and the chicken in 2 hours and 30 minutes; yet, the rabbit was more tender (33). The Belgian hare and the New Zealand Red Rabbits were compared to chicken broilers, beef and veal hind and forequarters, and pork shoulders to determine water, pro tein, fat and fuel value per pound. Rabbit meat was the highest in protein and second lowest in fat and calories according to McMillin (4). There is conflicting data on the amounts of fat, protein, amino acid and moisture in rabbit. However, the 18 majority of the studies indicate that rabbit is high in protein and moisture and low in fat and calories compared to other prime sources of meat consumed by man. CHAPTER III METHODS AND PROCEDURES Selection of Meat Samples Samples of the following five meats were chosen for evaluation of protein quality: chicken, rabbit, beef, pork and cod. All edible portions of rabbit, chicken (excluding the organ meats), cod and 9-12 rib section of the longis- simus dorsi of beef and pork were selected for study. Longissimus dorsi is the best index for protein quality measurement (26,34,35). The samples were weighed, cooked by dry heat, reweighed, and deboned. Edible portions were ground in a Waring blender, freeze-dried, reground in a Sorval Omnimixer and refrigerated for later use in the bioassay and chemical analyses. Chemical Analyses Determination of Protein Content Crude protein content was determined by the macro- Kjeldahl method (36). Since no dependable protein-specific detection method is available, the Kjeldahl procedure is the most reliable and frequently used (37). Most proteins contain approximately 16 percent nitrogen (40). Orr and Watt (39) determined factors for converting the nitrogen 19 20 content of foods to protein (41). The crude protein con tent of products such as animal tissue can be obtained by multiplying nitrogen by 6.25. West (38) stated that the nitrogen content of a food protein rarely varies suffi ciently from 16 percent to necessitate the use of a factor other than 6.25 (40). The macro-Kjeldahl procedure used for nitrogen analysis was a modification of the method described by the Association of the Official Agricultural Chemists (25). Duplicate representative samples of each variety were analyzed for crude protein content. Determination of Total Fat Content Fat content was analyzed quantitatively by the soxhlet ether extraction. It was heated at 120^ C until the ether reached the boiling point and then turned down to 60^ C. The extraction was run for 18 hours. The pro cedure utilized was that described by Lees (42). Ground samples of each variety of meat were dried overnight at 100° C in a drying oven and then weighed. Two samples of each type of meat were used for the fat analysis. Determination of Moisture Content A 2 gm sample of each type of meat was weighed and dried in a drying oven at 120° C for 24 hours. Weight loss was assumed to be moisture content and was calculated as follows: 21 Dry matter % = wt. of sample (dry) x 100 wt. of sample (wet) Moisture % = 100- dry matter % (21) Determination of Amino Acid Composition The amino acid composition of the five types of meat was established by a column chromatographic method utilizing a Beckman 121 Auto Amino Acid Analyzer (41) . Samples con taining 10+ 0.1 mg protein were hydrolyzed under vacuum in 5 ml of 6 N HCl acid for 22 hours at 110° C. The hydroly- sate was filtered and evaporated to dryness. A pH 2.2 Na citrate buffer solution was added to the hydrolysate to a final volume of five ml. An aliquot of 0.2 ml was introduced into each of the two columns for analysis. The Bioassay Fifty-six male albino rats of the Sprague-Dawley strain, 24 days old, were placed in three large screen- bottomed cages. The animals were given laboratory chow pellets and distilled water ad_ libitum for 48 hours. After the 48 hour adjustment period, the rats were weighed and randomly assigned to seven groups of 8 rats each. Weights of the animals ranged from 53 to 64 grams with an average weight of 59 grams. The animals were dis tributed so that each group weighed about the same. They were individually housed in raised screen bottomed cages. ,JK« 22 Distilled water and food were supplied ad libitum. At the end of the 28 days, the experimental diets were removed. The food consumption was established by the difference in weight of that supplied and that left at the end of the experiment. Composition of the Diets The composition of the seven experimental diets is given in Table 5. The diets were isocaloric and each con tained 1% vitamin mixture, 8% lipid, 5% salt mixture, and 1% nonnutritive fiber. Diets 1-6 contained 9% protein. Cornstarch was used in each diet to make the final weight 100% (21). Diet 7 was a negative control containing no protein. Diet 6 was used as a positive control (containing casein as the source of protein). Diets 1-5 contained chicken, rab bit, beef, pork and cod, respectively, as the sole source of protein. The amount of freeze-dried tissue added to each diet was determined by the protein content of the dried material. The protein content of each diet was con stant, being 9%. Total lipid content of each Seunple was determined by petroleum ether extraction. The protein, fat, and moisture values for each of the five varieties of cooked tissues are given in Table 6. Corn oil was used in each of the seven diets to raise the final lipid content to 8%. 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The higher the ratio of weight gain to protein intake, the better is the protein. This is the simplest method for evaluating protein since it requires only an accurate mea sure of dietary intake and weight gain (42). Most food manufacturers use PER for its simplicity; however, all con ditions must be carefully controlled. Calories must be isocaloric, the protein fed should be adecjuate but not ex cessive since at high levels of protein intake, weight gain does not increase proportionately with protein intake. This is the standard method used by laboratories for evaluating protein quality (21). Statistical Analysis of Data One way analysis of variance was used to test the five diets for differences in protein quality when fed to experimental animals. Duncan's new multiple range test was used to deteinmine significant differences among the groups of animals in relation to food intake, weight gain and PER (43). CHAPTER IV RESULTS AND DISCUSSION Chemical Analyses The crude protein, fat, and moisture content of the samples are shown in Table 6. Calculated by N x 6.25, the crude protein values ranged from 20.32% to 29.91% for cooked meat. The protein and fat content of pork, beef and rabbit were higher than the comparative values of cooked chicken meat. Cooked cod and chicken had the lowest fat and pro tein content and the highest moisture content. Amino Acid Analyses The essential amino acid content of rabbit, chicken, beef, pork, cod and casein are compared to the FAO amino acid pattern in Table 7 (44). Casein, the reference pro tein (39), is higher than the other protein sources in isoleucine, phenylalanine, and valine. Chicken has the highest leucine and lysine contents. Rabbit has the high est methionine content and beef is highest in tryptophan. The Food and Agriculture Organization of the United Nations developed a pattern of desirable ratios for the eight essential amino acids (45). The tryptophan require ment has been given the value of 1 and the amounts of other amino acids are expressed as multiples of this. The pro visional pattern currently in use is: tryptophan, 1; 26 27 n 00 Id •H 0) o o • a VO 00 in CO Id o u VO <^ iH a\ in CO CO r- o • • • • • • • • u ^ cy» o •^ CO in VO o CO VO in 00 VO VO t CO €0 •cn -TN en o IH 00 00 Q) M 00 ro O VO U t •H O o in CO in VO o rH -p iH 00 00 •H ^ VO CM r- 00 • • • • • • • • g -^ Rat Growth Experiment The growth data of the rats fed an otherwise ade quate but protein-free diet or the same diet supplemented with 9% protein (N x 6.25) from chicken, rabbit, beef, pork, cod or casein, are summarized in Table 8. Analysis of vari ance was used to test the hypothesis that the experimental treatments equally affected weight gain, food consumption, protein efficiency ratio and food efficiency ratio. The number of rats in the experimental groups dif fered as one of the rats was lost due to improper closing of the cage and one was discarded due to illness. There fore, treatment means were used as individual entries (43). 29 For each hypothesis, data are shown in table forms and results are summarized. TABLE 8 EFFECT OF FEEDING YOUNG RATS AN OTHERWISE ADEQUATE DIET CONTAINING 9% PROTEIN FROM DIFFERENT SOURCES Treatment No. Initial Weight Food PER^ NPR^ of Weight Gain Intake Rats (g) (g) (g) (g) (g) Chicken 8 58.75 54.06 243.74 2.52 1.55 Rabbit 7 57.78 123.50 336.27 4.02 3.34 Beef 8 58.78 112.68 320.37 3.97 3.24 Pork 8 58.37 98.62 316.83 3.45 2.74 Cod 7 59.00 95.85 309.48 3.55 2.72 Casein 8 57.81 62.68 216.56 3.25 2.13 Protein- 8 58.44 -20.66 88.87 free Weight Gain (g) ^Protein Efficiency Rativ« I • o = protein Intake (g) Gain in Weight of Test Group- Loss of Weight of Non-Protein Group (g) ^Net Protein Ratio - Protein Intake (g) Results of the analysis of variance (Table 9) were used to test the hypothesis that the experimental treat ments 1-5 equally affected weight gain. This hypothesis was rejected at the 0.05 level of significance. Table 10 shows the results of Duncan's New multiple Range Test on mean weight gain of young rats. According to this test. 30 TABLE 9 ANALYSIS OF VARIANCE OF MEAN WEIGHT GAIN OF YOUNG RATS Source of Degree of Sum of Mean F Variation Freedom Squares Value Treatments 5 29099.92 5819.98 35.46 Error 40 6565.39 164.13 *«Significan . t at the 0.05 level of significance TABLE 10 DIFFERENCES IN WEIGHT GAINS (g) AMONG RATS FED AN OTHERWISE ADEQUATE BUT PROTEIN-FREE DIET FOR 28 DAYS OR THE SAME DIET SUPPLEMENTED WITH 9% PROTEIN FROM CHICKEN, RABBIT, BEEF, PORK, COD OR CASEIN Treatment Mean- Rabbit 123.50* a,b Beef 112.68 .b,c Pork 98.62 c,d Cod 95.86 Chicken 62.68^ Casein 54.06 ^Means with the same superscript are not significantly different (P > 0.05). 31 animals on Diet 11,.containing rabbit, gained significantly more weight than those on all the other diets except beef. There was a significant difference (P > .05) weight gain of rats on all diets except when comparing the beef to rabbit, and pork to cod diets. Table 11 shows the results of the analysis of vari ance which was used to test the hypothesis that there was no difference in the food consumed by the rats on all the diets. This hypothesis was rejected at the 0.05 level of significance. Table 12 shows that rats on the rabbit- containing diet consumed a significantly greater amount of food than rats on all other diets. Rats on the beef- containing diet consumed the second most significant amount of food when compared to the other diets. TABLE 11 ANALYSIS OF VARIANCE OF MEAN FOOD CONSUMPTION OF YOUNG RATS Source of Degree o f Sum of Mean F Variation Freedom Squares Value Treatments 5 91020.49 18204.10 6.29* Error 40 115743.85 Significant at the 0.05 level of significance 32 TABLE 12 DIFFERENCES AMONG FOOD INTAKES (g) OF RATS FED AN OTHERWISE ADEQUATE BUT PROTEIN-FREE DIET FOR 28 DAYS OR THE SAME DIET SUPPLEMENTED WITH 9% PROTEIN FROM CHICKEN, RABBIT, BEEF, PORK, COD, AND CASEIN Treatment Mean Rabbit 336.27^ Beef 320.37^'^ Pork 316.84^'^'^ Cod 309.49^'^ Chicken 243.74^ Casein 216.56 ^Means with the same superscript are not significantly different (P > 0.05). The hypothesis that the protein efficiency ratio was equal in the rats fed diets 1 through 6 was rejected at the 0.05 level of significance as tested by analysis of variance (Table 13) . The rabbit diet had a significantly higher PER (P > .05) than all the other treatments except beef (Table 14). Chicken had a significantly lower (P > .05) PER than all other treatments. Beef had a significantly higher PER than all the other treatments except the rabbit and cod treatments. The cod, pork and casein diets had a signifi cantly lower PER than the rabbit-containing diet and a 33 TABLE 13 ANALYSIS OF VARIANCE OF MEAN PER OF YOUNG RATS Source of Degree of Sum of Mean F Variation Freedom Squares Value Treatments 5 11.86 2.37 9.85 Error 40 9.64 0.24 Significant at 0.05 level of significance TABLE 14 DIFFERENCES AMONG PROTEIN EFFICIENCY RATIOS FOR VARIOUS PROTEIN SOURCES Treatment Mean' Rabbit 4.03' a,b Beef 3.98 b,c Cod 3.55 c,d Pork 3.44 c,d,e Casein 3.25 Chicken 2.52 ^Means with the same superscript are not significantly different (P > 0.05). 34 higher PER than the chicken-containing diet. The hypothesis that there was no difference in the feed efficiency for the rats fed Diets 1-5 was rejected at the 0.05 level of significance (Table 15). Duncan's mul tiple range test (Table 16) showed that animals on the diet with rabbit meat as the sole protein source used less feed per gram of weight gain than did animals on the other diets; however, the variation was not significantly different from the beef-containing diet. Rats on the beef-containing treat ment had the second most significantly (p > .05) low feed efficiency. Rats on the chicken-containing diet consumed the greatest amount of feed per gram of weight gain when compared to all other diets. This difference was signifi cant (P > .05) . TABLE 15 ANALYSIS OF VARIANCE OF FEED EFFICIENCY OF YOUNG RATS Source of Degree of Sum of Mean F Variation Freedom Squares Value Treatment 5 16.12 3.22 14.69* Error 40 8.22 0.22 'significant at the 0.05 level of significance 35 TABLE 16 DIFFERENCES IN FEED EFFICIENCY (g) AMONG RATS FED AN OTHERWISE ADEQUATE BUT PROTEIN-FREE DIET FOR 28 DAYS OR THE SAME DIET SUPPLEMENTED WITH 9% PROTEIN FROM CHICKEN, RABBIT, BEEF, PORK, COD OR CASEIN Treatment Mean^ Chicken 4, .52^ Casein 3. .47^ Pork 3. .22^'^ 2ob,CTd - Cod 3, Beef 2. .82® Rabbit 2. .76®'^ -^Means with the same superscript are not significantly different (P > 0.05). The crude protein content of rabbit (Table 6) is higher than that of chicken, cod, and beef. Pork had the highest crude protein content. The lower protein figures for chicken and cod are probably due to the higher moisture content of these tissues. Even though rabbit has a lower crude protein content than pork, it is higher in all the essential amino acids. Rabbit is also lower in fat than beef or pork. Rats on the rabbit diet gained more weight, had a higher food intake, a higher protein efficiency ratio 36 and ate less feed per gram of weight gain than animals con suming the other diets. However, the comparison was not significantly different from these four variables of ani mals consuming the rabbit diet when compared to the beef- containing diet at the 0.05 level of significance. The amino acid content of rabbit was higher than beef except for tryptophan, therefore, the results of this bioassay indicated that the animals on the rabbit contain ing diet had biologically the most efficient feed conver sion, -the best—protein effi<:iency ratio and the -greatest weight gain and food intake of all the other diets. CHAPTER V SUMMARY AND CONCLUSION Summary Chicken, rabbit, beef, pork and cod were compared for protein evaluation. They consisted of 24.60, 27.75, 27.35, 29.91 and 20.32 percent crude protein for chicken, rabbit, beef, pork and cod respectively. Amino acid analy sis showed rabbit to be higher than pork in all the essen tial amino acids. All the meats compared-favorably to the reference protein (casein), in their amino acid content. Experimental diets containing each of the five meats and casein as the total protein source were fed to young rats. Statistically, the analysis of the data showed that the rats fed diets containing rabbit had the best PER ratio, a more efficient feed conversion and a greater weight gain and food intake than the other diets except the beef- containing diet. However, biologically, th^ rabbit-con taining diet had comparatively better results of these four factors than all the other diets including the beef-contain ing diet. Therefore, from the above data one can conclude that rabbit is a most acceptable source of protein. Conclusions The study has shown that a diet containing rabbit as the sole source of protein promoted the growth of young 37 38 rats, had a higher PER, weight gain, food consumption and lower feed efficiency at a 0.05 level of significance than the diets of pork, chicken or cod. Biologically it was also superior in these four factors when compared to the beef-containing diet, but differences were not statisti cally significant. The essential amino acids of all these meats compared favorably to the FAO amino acid pattern and the reference protein (casein). Only pork had a higher protein content than rabbit, but rabbit contained a better ratio of amino acids than pork. Although chicken had a better ratio of amino acids when compared to pork, it had a lower crude protein con tent. The biological value of a protein depends mainly on its amino acid content, though the amino acid composition of protein is similar for all meats (47). 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