GRAHAM (1934) reported that the

Transcription

1 Minimum Protein Requirement of Laying Pullets at Different Energy Levels* E. C. MlLLER,t M. L. SUNDE AND C. A. ELVEHJEM Departments of Poultry Husbandry and Biochemistry, University of Wisconsin, Madison 6, Wisconsin GRAHAM (1934) reported that the average level of protein intake was 12.9 when laying hens were fed an 18 protein laying mash plus corn and oats. Some birds laid well on a diet containing 12 to 13 protein while others required 14 to IS protein. Nonlaying birds appeared to thrive and prepare to lay on an 11 protein diet. Heiman et al. (1936) studied the protein requirement of Single Comb White Leghorn pullets. These workers found that a 13 all-plant-protein diet would not maintain body weight. When fish meal was added to the diet, the marginal protein level for weight maintenance and egg production appeared to be 14. Heuser (1936) reported that 16 dietary protein was optimal for laying hens. MacDonald (1938) reported that hens fed a diet containing protein laid as well as hens receiving IS protein. Carpenter et al. (1954) studied the effect of dietary protein level on egg production with all-vegetable, or vegetable and animal protein diets. With fish meal as the protein supplement to the basal cereal diet, an all- Published with the approval of the Director of the Agricultural Experiment Station, College of Agriculture, Madison, Wisconsin. * Supported in part by the Research Committee of the Graduate School from funds supplied by the Wisconsin Alumni Research Foundation, Madison, Wisconsin. These data were presented at the 45th Poultry Science meeting, August 7-, t Present address: Animal and Poultry Husbandry Research Branch, Beltsville, Maryland. (Received for publication December, 1956) 681 mash ration containing 11 total crude protein was equal to mashes containing higher protein levels in supporting egg production of birds kept in laying houses. The amino acid requirements known for the laying hen were established on diets containing IS to 17 protein. These proteins were selected for their low content of one of the essential amino acids. The amino acid requirements were established by supplementing the diets with the limiting amino acid until optimum production was obtained. Grau (1948) reported that the amino acid requirement of chicks is dependent upon the level of protein used in the diet. If a lower level of protein could be used in the laying diets, the amino acid requirement might also be reduced. In formulating laying diets containing amino acids instead of protein, it would be advantageous due to the expense of crystalline amino acids to know the minimum amount of protein needed for optimum egg production and body weight maintenance. Since purified diets were low in fiber and contained a high level of carbohydrate, it was necessary to determine the effect of varying the dietary energy levels on egg production at different levels of protein. Heuser and co-workers (1945) showed that rations low in fiber content supported a higher rate of egg production than similar diets containing high fiber feed-stuffs. Hill et al. (1956) studied the effect of dietary energy levels on the rate of egg production. In those investigations, the protein level was kept constant and the energy levels

2 682 E. C. MILLER, M. L. SUNDE AND C. A. ELVEHJEM varied. Only during the cold months was any effect of dietary energy level on egg production noted. In the studies to be reported here, the first series of experiments was undertaken to determine the minimum amount of dietary protein required for weight maintenance and egg production using a constant level of dietary energy. The second series of experiments was performed to determine what effect an increase in dietary energy had on egg production and weight maintenance with various levels of protein. EXPERIMENTAL PROCEDURE AND RESULTS Single Comb White Leghorn pullets selected on the basis of egg production and body weight were used for all of the experiments. The pullets were kept in laying batteries having raised wire floors. Feed, water and oystershell were fed ad libitum. They were artificially inseminated each week using pooled semen from New Hampshire male, and all eggs were pedigree marked and weighed at the time of setting. The eggs were set at weekly intervals and they were candled on the seventh and eighteenth day of incubation. The diet B x of Robblee et al. (1948) was used as the control diet in all hen experiments. A thermometer designed in such a way as to give both high and low temperatures for each 24-hour period was used. The extreme temperatures during the experimental period were 45 and 8S F. The levels of productive energy in the diets were calculated from Table 18 of "Energy values of feedstuffs for poultry" by Titus (1955). A value of 2,900 Calories of productive energy per pound was used for the white grease. It was assumed that the oat hulls or oat mill feed did not contribute any dietary energy. The protein content of all experimental diets was determined by the Kjeldahl method. Periodically the resulting checks were raised to four weeks of age to determine if the protein level or the energy level of the maternal diet affected the growth of the offspring. Experiment 1. Four hens were placed on each experimental diet on March 4, The basal diet (R200) used in this experiment is given in Table 1. The ingredients and the proportions used in this diet were selected to supply levels of amino acids which should be adequate for the hen. The protein level of the diet was increased by replacing corn with fish meal. Table 2 gives the levels of dietary protein and energy fed to each group and the results obtained during the 15-week experimental period. Excellent egg production was obtained in all groups, indicating that 12 protein (N X 6.25) was adequate for egg production for the 15-week period. A weight loss occurred on the 12 protein diet TABLE 1. Composition of basal diets Feedstuffs Ground yellow corn Wheat bran Wheat middlings Ground oats Dried whey Alfalfa leaf meal, 20 protein Iodized salt Calcium phosphate, dibasic Feeding oil (1500A-300D/gm.) Vitamin mix* Manganese sulfate mono hydrate Choline chloride Penicillin G, procaine Crude soybean oil Dextrinized cornstarch L arginine HC1 DL phenylalanine Protein (Kjeldahl) Productive energy Calories/ pound R S R * Vitamin mix supplies the following vitamins in milli per kilogram of diet: riboflavin 6; thiamine HC1 4; calcium pantothenate 15; niacin 0; pyridoxine HC1 4; menadione 0.5; biotin 0.2; vitamin B I ; folic acid 4.

3 PROTEIN REQUIREMENT AND ENERGY LEVELS FOR PRODUCTION 683 TABLE 2. Effect of dietary protein level on egg production and body weight maintenance over a fifteen week laying period Group Percent protein Productive energy Calories/pound Average egg production Pounds of feed/ dozen eggs Average change in body weight, gms. Increase in final egg weight over initial weight, gms. Experiment 1 R R R Control diet even though this group consumed about three-fourths of a pound of feed more per dozen of eggs produced than the other groups. These pullets had about reached their mature weights when this experiment was started. The egg weights of the group received 12 protein did not increase as much during the experimental period as did the other groups. Experiment 2. Ten pullets were placed on each experimental diet November 29, The basal diet (R198) is similar to diet R200 except that dextrin (autoclaved corn starch) was used to replace corn to reduce the protein level of the diet to. Again fish meal was used to raise the protein level of the diet. When fish meal Group Percent protein Productive energy Calories/pound Average egg productuon Pounds of feed/dozen eggs Average change in body weight, gms. Increase in final egg weight over initial weight, gms. 6.2 was added, corn was removed from the diet. Table 3 gives the levels of dietary protein and energy fed to each group and the results obtained during the 16-week experimental period. The egg production that resulted from feeding levels of, 11 and 12 protein was not as good as the egg production of the groups receiving more than 12 dietary protein. More feed was required to produce a dozen eggs when the protein level of the diet was reduced to or below 12. The group receiving 12.9 protein was more efficient, however, then the group of hens receiving 14 protein. The pullets fed the 12.9 ration laid as many eggs as those receiving either 14 or 16 protein in their mash. In contrast to the results of the first experiment, the pullets receiving diet R200 (R198 plus 24 corn instead of dextrinized corn starch) in the second experiment gained body weight (Table 3). Average egg weight increased the most in the group receiving the ration containing 12.3 protein and the control diet. In this experiment, 12.3 protein improved egg weights more than two out of the three higher protein levels. Experiment 3. In this experiment, each experimental group contained six pullets. TABLE 3. Effect of dietary protein level on egg production and body weight maintenance for a sixteen week laying period R S R Experiment R R R Control diet

4 684 E. C. MILLER, M. L. SUNDE AND C. A. ELVEHJEM TABLE 4. Composition of basal diets R 300 R 400 Protein premix* Iodized salt Calcium phosphate, dibasic Feeding oil (1500A-300D) Vitamin mix** Manganese sulfate mono hydrate Dextrinized cornstarch Oat mill feed 28.9 Qround oat hulls 21.1 Protein, (Kjeldahl) Productive energy Calories/ pound * Protein premix. Ground yellow corn Wheat bran Wheat middlings Oat groats Dried whey Dehydrated alfalfa meal, 17 protein Fish meal, 60 protein R R ** Vitamin mix supplies the following vitamins in per kilogram of diet: riboflavin 6; thiamine HCl 4; calcium pantothenate 15; niacin 0; pyridoxine HCl 4; menadione 0.5; biotin 0.2; folic acid 4; vitamin Bi Table 4 shows the basal diet (R300) and the protein premix used for this experiment. To increase the level of protein or energy in the diet the protein premix and/or choice white grease 1 were added at the expense of oat mill feed and dextrinized corn starch. The protein premix was used to insure that each experimental diet contined the same ratios of protein feedstuffs. This kept the amino acid ratios constant. The amounts of fat added were 0, 5 and. This made it possible to reach the desired energy levels. The choice white grease 1 Choice white grease is made from inedible pork and possibly some beef waste. The grease used here contained approximately 2.4 free fatty acids, had a titer value of thirty-nine and had a F.A.C. color rating of nine to eleven. was stabilized with Tenox II. 2 This experiment was started in December, The basal diet (group 1) was calculated to contain protein. The protein from the oat hulls or the oat mill feed was not included in this calculated value. The protein values given in Table 5 were Kjeldahl analyses and included these materials. Table 5 gives the level of dietary energy and protein fed to each group and the results obtained during the 12-week experimental period. Although the dietary protein levels ranged from to 20.9, birds on the protein diet with the lowest energy level maintained the highest egg production. The hens in all groups laid at a rapid rate during the experimental period except for groups 3 and 16. One pullet in group 3 stopped laying two days before she was placed on the experimental diet, and stayed out of egg production during the remainder of the experimental period. The other five pullets laid at an average rate of production of 64. Varying the energy content had no consistent effect on production. The Calorie-protein ratios of these diets varied from 31 to 74 Calories of productive energy per pound of feed for each of protein. A statistical analysis 3 showed that there were no significant differences in egg production between the various group. Apparently the Calorie-protein ratio of laying diets is not as important as it is for growing diets. As the energy level of the diet was increased, less feed was required to produce a dozen eggs in most instances, although only 2 Eastman Chemical Products Inc., Kingsport, Tenn. Added to supply level of.02 butylated hydroxyanisol,.01 citric acid and.005 propyl gallate to the white grease. 'Analysis of variance gave a calculated F. of (needed for significance at the 5 level 2.12).

5 PROTEIN REQUIREMENT AND ENERGY LEVELS FOR PRODUCTION 685 a &a?s < 0-2 to ; H Hi «<! H m w ON lo 00 >o C-J * O) *# O ^ *0 - S i -.-!-* co>0 foio O ^Oco IO t- ^W \0 * C0"0 OTfH to >o io I T * VO o >o t- *" * <o 1 Si '2.s.g ff ili! ' 5>iS >*a II JWS four groups were more efficient than group 1. Group 1 was fed the diet with the lowest protein and energy content. Generally as the energy content of the diet was increased the gain in body weight also increased. A large part of that weight increase was abdominal fat. The hens fed the low level of protein (Table 5) and the lowest level of energy were more efficient than the hens fed the higher levels of protein. Only 4.43 pounds of feed were required per dozen eggs when Calories were fed. When the caloric content was raised to or, the pounds of feed per dozen eggs increased to 4.92 and 5.13 respectively. With the other protein levels, as the energy content increased, the efficiency also increased. This indicates that perhaps the Calorie-protein ratio may exert some effect at this level of protein. At the end of the 12-week experimental period, all groups were fed the control diet for one week and then used for Experiment 4. Experiment 4. The same groups of pullets used in Experiment 3 were used in Experiment 4. The same group of hens was kept as the control group (Diet 16). The diets fed the other groups were reversed. By this procedure, the group formerly receiving the low protein, low energy diet was switched to the highest protein, highest energy diet and vice versa. The energy content of the basal diet was raised from to 745 Calories of productive energy per pound. This was done by removing some of the lower energy feedstuffs from the protein premix. Oat hulls were taken directly from the huller, fanned and then ground to get a very pure product. Table 4 shows the basal diet (R400) and the protein premix. The methods used for increasing the energy and protein levels in this experiment were the same as those used in Experiment 3 except that ground oat hulls were used in place of oat mill feed. Table 6 shows the levels of

6 686 E. C. MILLER, M. L. SUNDE AND C. A. ELVEHJEM a s 14 If I I t n o as o MS OJ - a W v 1/7 r-.ro Ov IO U">u"i 00 -H -H 00»0 vo <0 fo-^ *-t O d o CS lo «*"«* OO SwS Jifl a 8-3 SfS-SJ SB S S3 S u > dietary protein and energy fed to each group and the results obtained during the 18-week experimental period. The results of this experiment confirm the results obtained in Experiment 3. Varying the dietary energy levels from to 1,075 Calories did not affect egg production in this experiment. A statistical analysis again showed no significant variations in egg production. Excellent feed conversion into eggs was obtained in group 3 fed the protein diet containing 1,075 Calories of productive energy per pound. In fact only two lots had better conversion of feed to eggs than the basal lot with the high energy level. Both the lots that had better feed efficiencies than Lot 3 were also getting the high energy diet, indicating again that increasing the energy content increased the feed efficiency of the ration. Effect of dietary protein level of the maternal diet on growth rate of chicks. Chicks were hatched from all the groups of hens in all four experiments. Hatchability of the fertile eggs was not affected by the protein content of the diet. Varying the energy level did not have an effect either. Fertility was not affected. Throughout each experiment, at regular intervals, groups of chicks were raised to four weeks of age on a complete chick starting mash containing 21 protein. No effect of the maternal dietary protein level on the rate of chick growth was observed. The average 4-week weights of the chicks from the various experimental groups in one experiment varied from 333 to 350. The chicks from hens fed the control diet averaged 344. The results from the other experiments were very similar. Effect of dietary fat content and storage on yolk mottling. In the fourth experiment, eggs were broken out and examined for mottled yolks. Mottling of yolks is a defect that has been reported by Schaible et al.

7 PROTEIN REQUIREMENT AND ENERGY LEVELS FOR PRODUCTION 687 (1935) but recently this condition has had more attention focused upon it. Since fat has been added to commercial laying diets during the period when the incidence of mottling increased, eggs were broken out and examined to determine if the level of added dietary fat affected yolk mottling. The eggs were held at room temperature (65 to 70 F.) until examined. To determine if the length of storage at room temperature increased the incidence of mottled yolks, the eggs were examined after one to seven days of storage. The effect on mottling of the length of time stored is shown in Figure 1. Severe mottling was observed in eggs stored for five or more days at room temperature. Since the effect of storage reached the maximum incidence by the fifth day at room temperature, eggs were broken out on the fifth day after being laid % EFFECT OF AGE OF EGG ON YOLK MOTTLING \ \ - \ \ \ * \ ^NONE / \ Ay \. /SLIGHT J J V \MODERATE 7 ; ' / v--' / *- ' SEVERE iiiii.nl inn Trrrttl' DAYS NUMBER OF EGGS EXAMINED FIG. 1 TABLE 1 White grease added l0 %> 5% 0%. Effe;t of dietary fat on yolk mottling None % Mottling Slight Examined on the fifth day. M?f" Severe Number of eggs and examined to determine the effect of the level of the dietary fat fed the hens. The results shown in Table 7 indicate that an increase in the level of dietary fat did not increase the number of severity of the mottled yolk. Egg size. The changes in egg weight with the difference protein levels are also interesting. In the first experiment, the hens receiving the 12 protein diet did not increase the size of their eggs as fast as the hens receiving more protein. In the second experiment (Table 3) all groups increased in egg size at about the same rate. At least no definite trends are evident. The same thing is true in the third and fourth experiments. Table 8 shows these changes. In Experiment 3, the smallest gain in egg weight was 1.3, and the largest gain was 7.7. With more mature birds which were used in the fourth experiment, the biggest increase was 2.6, and the biggest decrease was 3.7. The birds in the first experiment on the lowest protein level did not receive any animal protein. The diets used by Thornton et al. (1956) did not contain any animal protein and in this instance also the hens receiving the 11 ratio without supplements of lysine laid smaller eggs. The data here are not adequate to prove one way or the other that animal protein in the diet affects egg size. This should be studied further. DISCUSSION In three out of four experiments, excellent egg production (70.6, 77, and 64 per-

8 688 E. C. MlLLEE, M. L. SUNDE AND C. A. ELVEHJEM TABLE 8. Effect of dietary protein and energy levels on change in egg weig Group No IS 16 Protein Experiment 3 Productive energy - Calories/ pound 871 Initial Avei rage egg weight Final Gain cent) was obtained with the lowest protein level fed. In the second experiment when the protein content was dropped to, egg production was reduced (49.6 ). Increasing the protein content in this experiment to 11.1 protein did not improve egg production appreciably (Table 3). When the protein content of the diet was increased to 12.3, the average egg production was This was not as good as the production on higher protein levels in this experiment (72-75 ). Thornton et al. (19S6) reported that 11 protein was adequate for egg production for birds held in cages. In the experiments reported here, excellent egg production was obtained with protein levels between 12 and 13. Diets of a similar nature should be tested under floor conditions with large numbers of birds to clarify further this protein requirement situation. Others, Heuser (1936), Clark et al. (1942) and Reid et al. (1951) have reported that more protein is needed. Certainly protein quality and vitamin additions may be a factor. Also amino acid combinations must be considered. It is possible to design rations with practical ingredients which will be low in certain amino acids. In formulating rations which do not provide liberal excesses of protein, care must be taken to balance the amino acids in the Protein Productive energy Calories/ pound Experiment 4 Initial Average egg weight Final Change ingredients as accurately as possible by selecting specific feedstuffs. Perhaps under more ideal conditions even lower levels of protein would be satisfactory. Shaw et al. (1955) and Thornton et al. (1956) were able to obtain excellent egg production with lower levels of protein. In our experiments, the protein content of the diets are reported on the basis of Kjeldahl analysis and include the protein from the oat hulls in the third and fourth experiments. Probably the laying hen cannot use much of this protein. When 29 oat hulls were used they contributed about one total protein to the low protein diets. Oat hulls lend themselves rather well to experiments where on wants to vary the energy content and still keep the protein content nearly constant. Without this material in the ration perhaps even less than 12 protein would be adequate for egg production. The age of the pullets must also be considered. In some of the experiments reported here, the pullets had only been in production about two months. In others they had been in production for as long as six or seven months when the experiment was started. Growing pullets that are laying may need more protein than fully grown birds. This is reasonable since these growing and laying pullets must lay down more

9 PROTEIN REQUIREMENT AND ENERGY LEVELS FOR PRODUCTION 689 protein materials than a hen that is only laying eggs. Increasing the productive energy levels of the diet from to 75 did not affect egg production at any of the protein levels fed, but the amount of feed required to produce a dozen eggs was decreased as the dietary energy level was increased. These pullets were maintained in a room which varied from 45 to 85 F. Perhaps an effect of energy would have been obtained if the birds were maintained under lower temperature conditions (Hill et al., 1957). It is possible that at a lower room temperature, an effect of energy upon the protein requirement would also be observed. Apparently the effects of these diets on the pounds of feed required to produce a dozen eggs are rather complex. For instance, in Experiment 1, the hens receiving 12 protein containing 943 Calories of productive energy per pound required 5.77 pounds of feed per dozen eggs. Those receiving 13.4 protein required 4.92 pounds of feed. The data here suggest that the birds were overconsuming the ration to get more protein. The best efficiency in the second experiment was obtained with 12.9 protein. In the third experiment with the low energy diet (C) the group receiving the lowest level of protein ( ) was the most efficient. With the medium level of energy (C) the group getting 18.3 protein was the most efficient. With the high level of energy (C) the group receiving 20.9 protein was the most efficient. In the fourth experiment of the groups receiving Calories per pound, the group getting protein was the most efficient. The most efficient of the groups getting Calories was the 14.1 protein group. The most efficient of the groups getting 1,075 Calories was the group receiving 19.2 protein. If the data in any one series are inspected closely, it is apparent that there are little or no differences in efficiency between different protein levels within one energy level. Considerable differences are apparent, however, between the different energy levels. The protein level of the maternal diet did not affect the rate of growth of the chick. This substantiates the observation of McFarlane et al. (1), Ingram et al. (1950) and Miller et al. (1954) that if a hen lays an egg, the amino acid content of that egg will be essentially normal. SUMMARY Good egg production was obtained when the experimental diets contained to 13 dietary protein. Egg production was not affected by the level of energy at the levels of protein used in these experiments. In Experiments 3 and 4 good egg production was obtained even when the Calories of productive energy of the diets ranged from 31 to 86 for each protein. It appears that a wide Calorieprotein ratio of the diet can be tolerated by the laying pullet without affecting egg production. Decreasing the level of protein in the diet to did not affect egg weight at any of the energy levels used when animal proteins were included in the rations. The addition of white grease to the experimental diets resulted in a decrease in the amount of feed required to produce a dozen of eggs. The level of dietary energy or protein in the maternal diet did not affect the growth rate of the chicks. The level of white grease added to the basal diets did not increase the incidence of yolk mottling. Mottling became more severe with all rations after five days of storage at room temperature. REFERENCES Carpenter, K. J., J. Duckworth and G. M. Ellinger, Economies in the use of animal byproducts in poultry ration. II Vitamin and

10 690 E. C. MILLER, M. L. SUNDE AND C. A. ELVEHJEM amino acid provision for laying hens. J. Agricultural Sci. 44: Clark, T. B., T. D. Runnels, J. H. Rietz and C. E. Weakley, Jr., Egg production and mortality of White Leghorns fed high and low protein rations. Poultry Sci. 21: 468. Graham, J. C, Individuality of pullets in balancing the ration. Poultry Sci. 13: Grau, C. R., Effect of protein level on the lysine requirement of the chick. J. Nutrition, 36: Heiman, V., J. S. Carver and J. L. St. John, The protein requirement of laying hens. Washington Agr. Exp. Station Bull Heuser, G. F., The protein requirements of laying hens. Proc. VI World's Poultry Congress. 1: Heuser, G. F., L. C. Norris, H. T. Peeler and M. L. Scott, 194S. Further studies on the apparent effect of digestibility upon growth, weight maintenance and egg production. Poultry Sci. 24: Hill, F. W., D. L. Anderson and L. M. Dansky, Studies of the energy requirements of chickens. Poultry Sci. 35: Ingram, G. R., W. W. Cravens, C. A. Elvehjem and J. G. Halpin, Relation of tryptophan and lysine to egg production, hatchability and composition of the protein of hen's eggs. Poultry Sci. 29: MacDonald, A. J., The protein requirement of laying birds. Agric. Progress, 15: 1-1. Hartman, R. C, and D. F. King, Keeping Chickens in Cages, 4th edition. R. C. Hartman, Publisher, Redland, California, 304 pp. $5.00. The authors, in their Preface, said they wrote this book to provide a practical working manual and guide for keeping layers in individual cages. It is proper to spell the word PRACTICAL in capital letters because the material presented in the book is based principally on information obtained from visits to hundreds of cage poultrymen and the practical experience and pioneer research of Dr. King, the junior author who joined the senior author in the preparation of this fourth edition. This is an excellent combination of authors which in itself recommends the book to operators of the cage system, to students and makes it a must to anyone newly engaged in the operation of an individual cage system egg laying farm. Because this book is based so largely BOOK REVIEWS (Continued McFarlane, W. D., H. L. Fulmer and T. H. Jukes, 1. Studies in embryonic mortality in the chick. 1. The effect of diet upon the nitrogen, amino-nitrogen, tyrosine, tryptophan, cystine and iron content of the proteins and on total copper of the hen's eggs. J. Biol. Chem. 24: Miller, E. C, M. L. Sunde, H. R. Bird and C. A. Elvehjem, The isoleucine requirement of the laying hen. Poultry Sci. 33: Reid, B. L., J. H. Quisenberry and J. R. Couch, Aureomycin, vitamin Bi 2, methionine and the level of protein in mature fowl nutrition. Poultry Sci. 30:935. Roblee, A. R., C. A. Nichol, W. W. Cravens, C. A. Elvehjem and J. G. Halpin, The effect of the hen diet and chick diet on the needs of the chick for an unidentified growth factor. Poultry Sci. 27: Schaible, P. J., J. A. Davidson and J. M. Moore, The yolk surface in fresh eggs. Poultry Sci. 15: Shaw, R. B., and E. W. Nightall, The influence of protein levels on poultry production. J. Sci. Food Agric. 6: Thornton, P. A., R. E. Moreng, L. G. Blaylock and T. E. Hartung, The effects of dietary protein levels on egg production, egg size, egg quality and feed efficiency. Poultry Sci. 35: Titus, H. W., Reprint from The Scientific Feeding of Chickens. Second Edition, Interstate Printers and Publishers. Danville, Illinois. on practical experience there are no reference lists at the end of chapters or the end of the book. To those who so often measure a book by the number of reference citations this will be a disappointment. However, once read the realization should come that this whole book is page after page a reference a practical, useful easy to read and easy to understand book which needs no reference list. In 1950 when the first edition of this book was published by Roland Hartman, even he did not realize how rapidly this system would spread around the world not only in warm climate but also would be adapted to cold climate. The first chapter "The Individual Cage System" starts the reader off with a feeling of interest since it briefly covers the history of the single deck individual cage system, the thirteen advantages and four disadvantages of the system, answers the queson page 70S)