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Dietary Energy Levels for Laying Hens as Related to Age and Environmental Temperatures
TAPAZOLE AND IODINE UPTAKE
is to increase the apparent release rate of thyroidal I131, it is suggested that 0.025% tapazole in the ration may be sufficient for most fowls. REFERENCES Sell, J. L., and S. L. Balloun, 1960. The effects of methimazole on weight gains, carcass composi-
1483
tion, thyroid gland weight and blood components of cockerels. Poultry Sci. 39: 930-937. Stahl, P. R., 1960. Factors affecting thyroxine secretion rate in the domestic fowl. Ph.D. Thesis, University of Missouri. Pipes, G. W., B. N. Premachandra and C. W. Turner, 1958. Measurement of the thyroid hormone secretion rate of individual fowls. Poultry Sci. 37:36-41.
Dietary Energy Levels for Laying Hens as Related to Age and Environmental Temperatures
A. A. KURNICK, H. B. HINDS, M. W. PASVOGEL1 AND B. L. REID Department of Poultry Science, University of Arizona, Tucson (Received for publication December 23, 1960)
L
AYING rations of high energy content •'were reported to support higher rates of egg production as early as 1945 by Heuser et al., and an inverse relationship between dietary fiber level and egg production efficiency was observed by Bird and Whitson (1946). Lillie el al. (1952) noted that the feeding of a laying diet supplemented with lard produced a marked improvement in feed conversion of layers. McDaniel et al. (1957) reported a 12.2% improvement in feed conversion through an increase in productive energy level from 962-1,050 Calories per pound in a 17% protein diet. During the cold weather months only, Hill, Anderson and Dansky (1956) noted an improvement in the rate of egg production at the higher energy levels studied. No difference in rate of production was obtained during the other portions of the year. Feed requirement per dozen eggs was lowered 12% by a 100 Calorie increase in the productive energy content of the diet. Body weight tended to in1 Present address, Peter Chicago, Illinois.
Hand
Foundation,
crease during the laying period as the energy content of the diet was increased. In a subsequent paper, Hill (1956) employed the Byerly (1941) partition equation as a means of evaluating the rations employed by Hill, Anderson and Dansky (1956). Calculations of relative efficiencies based on comparison of observed feed consumption with that predicted by the Byerly equation showed a linear relationship between the productive energy level of the diet and relative efficiency. Higher productive energy resulted in greater relative efficiency. Anderson et al. (1957) were unable to substantiate the previous report by Thayer (1953) that levels of B-vitamins, above those recommended as the requirements, were needed for maximum egg production when high energy rations were fed. Combs and Helbacka (1960) in studies with rations of 14.6-19.1% protein and 909-1,096 Calories of productive energy per pound, concluded that a C:P ratio as wide as 66.6:1 was adequate to support 60% egg production. Layers permitted free-choice selection of feeds, chose rations
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1. EFFECT ON EGG PRODUCTION, BODY WEIGHT AND FEED CONVERSION
1484
A. A. KURNICK, H. B. HINDS, M. W. PASVOGEL AND B. L. REID
The high ambient temperatures associated with a large portion of the year in Arizona have made necessary and possible the study of age, dietary energy and temperature relationships with laying hens. EXPERIMENTAL PROCEDURES
Single Comb White Leghorn pullets from the University poultry flock were selected and placed on three experimental laying rations at the ages shown in Table 2, with the exception of the first study in which the birds were all fed a 965 Calorie diet for the 18-22nd week prior to the initiation of the experiment. All birds were selected on the basis of body weight and degree of sexual maturity and were divided into six pens of 40 birds each. Two such selected groups were fed each of the dietary treatments. The diets employed in these studies (Table 1) contained 965, 865
and 765 Calories productive energy per pound (Titus, 1955). The diets all contained the same protein level of 17% (calculated), the energy being adjusted by the addition of either glucose monohydrate or wood pulp (Solka-floc) or a combination of these. Five separate experiments have been conducted with these diets, employing birds attaining sexual maturity as shown in Table 2. Throughout each of the experiments body weights, egg production and feed consumption rates were determined and summarized at 28-day intervals. Ambient temperatures were determined on a maximum and minimum basis at bird height level daily. The birds were maintained on dirt floors covered with cane litter and no culling was practiced during the studies. Feed was mixed biweekly for each pen; a basal mix consisting of all constant ingredients was used to prepare the individual diets with the addition of glucose monohydrate or wood pulp (Solka-floc) to obtain the required energy levels. Feed and water were supplied ad libitum throughout the experiments. RESULTS
Birds hatched during the month of January reached sexual maturity (5% production) earlier than those hatched during the other months of the year (Table 2). The number of days required to reach sexual maturity reflected the season of the year, that is, environmental temperature and length of day during which growth and development occurred. Birds hatched in May or June and grown during the hot part of the year required 182 and 194 days, respectively, to reach sexual maturity whereas birds hatched during either April or March required 168 and 159 days, respectively, to attain a similar level of maturation (Table 2). It will also be noted that birds reaching sexual maturity earli-
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of an average C:P ration of 59.6:1. Cunningham, Cotterill and Funk (1960) have studied the effect of season and age of bird on egg yield, egg size and quality. It was concluded that egg weight tended to be greater in the spring and smaller during periods of high temperature, while Haugh units declined with age of bird, regardless of season. Decreased rates of egg production have been reported to occur during high summer temperatures (Wilham, 1931; Hutt, 1938; Hinds, 1949). In addition, temperatures above 65°F. caused reductions in egg size according to Bruckner (1936) and Warren et al. (1950). Wilson (1949) demonstrated a decreased rate of feed consumption and lowered body weights in hens subjected to weekly rises in ambient temperatures. Campos, Wilcox and Shaffner (1960) reported a sudden severe drop in egg production in some strains of layers upon exposure to 100°F. for a 24-hour period. Egg weight, shell thickness and feed consumption were likewise adversely affected by exposure to the high ambient temperature.
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ENERGY LEVELS FOR LAYERS TABLE 1.—Composition of experimental diets 965 Cal.*/lb.
865 Cal.*/lb.
%
765 Cal.*/lb.
%
%
20.00 29.78 19.15 3.00 2.00 2.00 0.30 4.25 2.00 0.02 2.50
20.00 29.78 19.15 3.00 2.00 2.00 0.30 4.25 2.00 0.02 2.50
20.00 29.78 19.15 3.00 2.00 2.00 0.30 4.25 2.00 0.02 2.50
Glucose monohydrate Wood cellulose (Solka-floc)
15.00
—
7.50 7.50
15.00
100.00
100.00
100.00
Total Calculated analysis: Protein% Fat, Fiber,% Calcium, % Phosphorus, % Arginine, % Methionine, % Cystine, % Lysine, % Tryptophan, % Cal.—Protein ratio
•
17.00 2.34 2.46 2.48 0.83 0.950 0.329 0.286 0.864 0.194
17.00 2.34 9.96 2.48 0.83 0.950 0.329 0.286 0.864 0.194
17.00 2.34 17.46 2.48 0.83 0.950 0.329 0.286 0.864 0.194
56.800
50.900
45.000
* Calories of productive energy (Titus, 1955). ** Supplied the following per pound of diet: 4,500 I.U. vitamin A, 700 I.C.U. vitamin D3, 2.0 mg. riboflavin, 12.5 mg. niacin, 5.0 mg. D-calcium pantothenate, 200 mg. choline chloride, 6 meg. vitamin Bi 2 , 2.5 I.U. d-alpha tocopheryl acetate, 1.0 mg. menadione sodium bisulfite, 2.0 gm. procaine penicillin, 10.0 mg. aureomycin and 56.75 mg. butylated hydroxytoluene.
est did so when the average body weight was lower than that of birds requiring a longer period to reach the same degree of production with the exception of the March hatched pullets which were the lowest in body weight at maturity of all the hatches tested (Table 2). The combined effects of light and higher ambient temperatures during the growing season resulted in delayed sexual maturity in the May and June hatched pullets, and slightly retarded the maturity of birds hatched in April and March (Table 2) as compared to those hatched in January. The highest rates of total egg production in relation to time of hatch were obtained with pullets hatched during March,
April, May or June, regardless of diet fed. The January hatched pullets exhibited the lowest production rates on all three diets. Calculated average production figures for the three experimental diets also indicated that the poorest production performance was obtained with the January TABLE 2.—Effect of dale of hatch on age and body weight at sexual maturity
Phase No.
Date hatched
April IS, June 27, Jan. 13, Mar. 17, M a y 12, 1
1958 1958 1959 1959 1959
Age at sexual r(days) lJcf 168 194 128 159 182
Approximately 5% production.
Age at Average initiation body weight of exptl. at initiation diet feeding of study (days) (gm.) 178 200 130 165 196
1,813 1,805 1,731 1,640 1,825
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Ground yellow corn Ground milo Solv. soybean oil meal (44% protein) Fish meal (62% protein) Meat and bone scraps (50% protein) Dried whole whey Salt Ground limestone Dicalcium phosphate MnSCv5H 2 0 (70%) Vitamin pre-mix**
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A. A. K U R N I C K , H. B. H I N D S , M. W. PASVOGEL AND B. L.
TABLE 3.—Effect
Exp. No.
Date hatched
1
April, '58
2
3
4
5
June, '58
Jan., '59
March, '59
May, '59
Average of all hatches
hatched pullets, lowering the productive energy level of the diet by 100 Calories resulted in a decrease of 12.8% in feed conversion; while lowering 200 Calories, from 965 Calories per pound, caused a 26.8% decrease in feed conversion (Table 3). These changes in productive energy amounted to 18.1 and 4 5 % respectively, for 100 and 200 Calorie decreases in the diets fed the June hatched pullets, and 15.5 and 39.6% with the birds hatched in J a n uary. The feeding of 865 and 765 Calorie diets to March hatched pullets lowered feed conversion by 2.8 and 30.0% respectively, as compared to the 965 Calorie diet, while M a y hatched pullets consumed 2.8 and 16.0% more feed per dozen eggs when fed 865 and 765 Calories of produc-
of season of hatch and diet on performance of laying hens Dietary energy (Cal./lb.)
Feed % production conversion (hen-day basis) (lbs. feed/doz. eggs)
Therms/ dozen eggs
Change in body weight (grams) + 123 0 -125
965 865 765
61.1 61.0 59.9
4.78 5.39 6.06
4.60 4.65 4.63
Average
60.8
5.41
4.63
965 865 765
61.4 62.4 52.2
4.83 5.70 7.01
4.66 4.93 5.36
Average
58.9
5.85
4.98
965 865 765
55.7 55.0 48.3
5.33 6.16 7.45
5.14 5.33 5.70
Average
53.0
6.31
5.39
965 865 765
59.0 62.3 50.4
4.88 5.02 6.34
5.71 4.34 3.83
Average
57.4
5.41
4.63
965 865 765
58.0 60.9 58.0
4.99 5.12 5.78
4.82 4.43 4.42
Average
59.0
5.30
4.56
965 865 765
58.1 59.1 53.0
4.97 5.46 6.46
4.80 4.72 4.94
+ 128 + 26 -206
+348 +254 + 142
+ 50 + 22 - 98
+221 + 78 + 52
+ 174 + 76 -128
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hatched pullets (Table 3). The average production for all diets fed to J a n u a r y pullets was 53.0%, compared to 57.4-60.8% for the other four experiments. The feeding of a low energy diet containing 765 Calories per pound did not appreciably lower the rate of production among birds hatched in April or May, but resulted in a 9 % lower production rate with the June and March hatched birds and 7 % lower production in birds hatched in January. Pounds of feed required per dozen eggs on the respective experimental diets appeared to be lowest in birds fed the highest energy level (Table 3). As would be expected, the feeding of the lower energy diets increased the amount of feed required per dozen eggs produced. With the April
REID
E N E R G Y L E V E L S FOR
LAYERS
1487
tive energy per pound than those fed the 965 Calorie diet (Table 3). In general, the therms of productive energy required per dozen eggs produced were comparable, regardless of diet, a t approximately equivalent egg production levels (experiments 1 and 5, Table 3). In experiment 2, with June hatched pullets, the 9 - 1 0 % reduction in egg production on the 765 Calorie diet as compared to the 965 and 865 Calorie levels increased the therms of productive energy from 4.66 and 4.93, respectively, to 5.36 (Table 3). The same trend was noted with J a n u a r y and March hatched pullets. The highest average energy requirements per dozen eggs were obtained with J a n u a r y hatched birds; these pullets began laying in M a y
and had dropped to a rather low rate of lay by the onset of the colder portions of the laying year—the time of highest energy requirement (Figure 1). If all data with respect to the three diets are summarized (Table 3) a 5 - 6 % lower rate of production is noted for the 765 Calorie diet. No differences were noted between the two higher energy levels. It should be pointed out t h a t wood cellulose (Solka-floc) was used to adjust the energy level so as not to alter the amino acid ratio of any of the diets employed. These data indicate that 4.72-4.94 therms of productive energy are required per dozen eggs. T h e fiber content of 17.46% in the 765 Calorie diet apparently did not allow the birds to consume sufficient quantities of
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FIG. 1. Effect of ambient temperature and caloric density on percent production of pullets hatched at different times of the year. 1. Calories per pound of diet and total percent production. (Shaded areas denote cooler portions of the year.)
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A. A.
K U R N I C K , H.
B.
TABLE 4.—Effect
H I N D S , M.
W.
PASVOGEL AND B. L.
REID
of energy and fiber level on calorie intake * Ave. Calories consumed/hen/day
Exp. No. 1
2
Hatched
865
765
Oct. 15-Mar. 31 Apr. 1-Aug. 18
246.1 208.6
242.3 208.1
225.0 209.0
Jan. 8-Mar. 31 Oct. 15-Dec. 8 Apr. 1-Oct. 14
230.5
228.4
203.9
216.0
218.9
195.7
Jan., 1959 Cool Hot
Oct. 14-Mar. 28 May 26-Oct. 13
247.4 193.2
252.8 185.8
195.2 168.5
March, 1959 Cool Hot
Oct. 14-Apr. 25 Apr. 26-Jul. 19
244.2 208.7
242.0 196.0
201.5 193.6
May, 1959 Cool Hot
Nov. 10-Apr. 25 Apr. 26-Oct. 10
266.3 198.8
250.0 199.8
230.6 192.8
April, 1958 Cool Hot June, 1958 Cool
4
5
energy during the colder months of the year; this is reflected in the egg production rates (Figure 1). Approximately 10% more feed was required per dozen eggs when the 865 Calorie diet was fed, while 30% more feed was consumed on the 765 Calorie diet as compared to the highest energy level (965 Cal./lb.). A comparison of average energy intake figures per hen per day (Table 4) during the cool and hot periods of these experiments (cool = October 15-April 28; hot = April 29-October 14) indicates that the birds were able to consume approximately equal amounts of energy on the two high energy diets, while the 765 Calorie diet could be consumed at a rate to supply only 79-92% of the energy intake of birds fed the higher energy diets during the colder months (Table 4). Energy intake figures for the hot portions of the experiments show comparable figures for all three diets with the exception of birds hatched in January. The lower energy intake of the 765 Calorie lots (January hatch) may be partially explained by the differences in body weight
and production rate during the hot periods (Figure 1 and Table 3). The differences in energy intake levels (Table 4) noted for the 765 Calorie diet during the colder portions of the year are also indicated by the rates of egg production (Figure 1). In each experiment, except experiment 2 with June hatched birds, the low energy diet supported a lower rate of egg production during the colder portions of the year, while the summer production rates for the 765 Calorie lots were equivalent to those obtained with the two higher energy diets in each case regardless of age of the birds and stage of production (Figure 1). In two experiments (April and March hatches) the lowest energy level supported a higher rate of production (3-5%) during the summer months (Figure 1) than was obtained with the feeding of either 965 or 865 Calories of productive energy per pound. In these two cases the low energy diet apparently prevented the severe production decline observed with the two higher energy diets during the hot periods of the laying year.
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965
Hot 3
Periods & dates
1489
ENERGY LEVELS FOE LAYERS
March pullets reached the peak of production (70%) in 8-12 weeks after sexual maturity in September and also exhibited a winter slump of around 15% during the months of January and February followed by a recovery to 70% production in March and April (Figure 1). May pullets showed a pattern of egg production similar to that obtained with the April birds. The production peak was attained after 16-20 weeks followed by a decline, somewhat more severe than was noted with the April hatch, to around 30% production at the termination of the experiment in November. The low energy diet (765 Cal./lb.) failed to support body weight at the level ob-
tained with the feeding of either the 965 or 865 Calorie diet (Table 3). In each case the medium energy diet produced pullets which exhibited average body weights intermediate between the high and low energy diets. Mortality was not affected by the dietary treatments employed in these studies. DISCUSSION
Under the climatic conditions existing in southern Arizona, it would appear that birds hatched during the months of March-June attain the highest rates of total egg production. These birds require longer to reach sexual maturity and the peak of production, but appeared to be better able to withstand the summer heat with an adequate production level. The higher production rates of these birds resulted in greater feed conversion figures as compared to the January hatched pullets. One advantage to January hatched pullets is that the peak in production was attained during the summer months, indicating that age may be employed to overcome some of the adverse effects due to summer heat. The use of high fiber-low energy diets for laying strain pullets is to be avoided during the colder seasons of the year due to the inability of the hens to consume amounts sufficient to satisfy both body maintenance and egg production requirements. Some advantage may be realized with the use of such diets during the warmer months to avoid the diminished intake of protein, vitamins and minerals on high energy diets when the energy requirements are reduced due to summer temperatures. A 15-25% reduction in feed intake (energy) was noted between the winter and summer portions of these studies. The winter protein intake of around 18-19 grams per bird per day on the high energy diet was thus reduced to
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Monthly egg production rates obtained on the respective diets (Figure 1) indicate rather marked differences between birds hatched at different times during the year. The time required to reach the "peak" of production, as well as the production level at that time, appear to be indicative of the age, season (temperature and light) and perhaps body weight of the birds at the onset of production. April hatched pullets, beginning production in October, required 16-20 weeks to reach a production peak of around 70% (Figure 1), while birds hatched in June reached sexual maturity (5% production) in January and required only 8-12 weeks to reach a 75-80% production peak. The April hatched pullets (experiment 1) were able to sustain a fairly high rate of production for a longer period of time than did the June hatched birds. January hatched pullets attained 5% production with the onset of warm weather (April), peaked in production at 70% after 12 weeks (during July), exhibited a definite winter slump to 35-40% production during January and February followed by a rise in production rate to 60-65% at the end of the experiment in March.
1490
A. A. KURNICK, H. B. HINDS, M. W. PASVOGEL AND B. L. REID
SUMMARY
A total of five experiments have been conducted, employing diets of 17% protein and productive energy levels of 965, 865, and 765 Calories per pound. The birds in each experiment were hatched at different times during the year (April, June, January, March and May). Birds were housed on cane litter in individual colony houses. January hatched pullets attained sexual maturity at 128 days of age followed by the March (159 days), April (168 days), May (182 days) and June (194 days) hatches. January hatched birds showed a lower rate of production over the entire experiment than other birds employed in these studies. Feed conversion (lb. of feed/ dozen eggs) was greatest for the April hatched birds fed the 965 Calorie diet (4.78 lbs. of feed/dozen eggs). The feeding of 765 Calories of productive energy per pound resulted in lower rates of production in three of the five experiments (June, January, and March
birds). The average of all five experiments indicated a 5-6% lower production rate due to the feeding of the low energy diet. The lower production rate on this diet appeared to be due to the inability of the birds to consume sufficient amounts of feed during the colder months of the year due to the high dietary fiber level (17.46%). Wood cellulose (Solka-floc) was used to decrease the energy level of the 965 Calorie diet by replacing 15% glucose monohydrate. Energy intake decreased 15-26% during the summer months as compared to the winter periods in these studies. The low energy diet was beneficial in maintaining higher intakes of protein (above 18 gm./bird/day), vitamins and minerals during the summer months, but proved to stimulate higher summer production ( 3 5%) only in two experiments. Body weight was essentially maintained at the two higher dietary energy levels, while 765 Calories of productive energy per pound failed to support body weight to the same extent. The use of low energy-high fiber diets for laying strain pullets, especially during the colder months of the year is not recommended on the basis of results obtained in these studies. ACKNOWLEDGMENTS
The authors are indebted to the following companies for the vitamins and antibiotics employed in these studies: Distillation Products Industries, Rochester, New York; Merck and Company, Rah way, New Jersey; Heterochemicals, Inc., Valley Stream, New York; American Cyanamid Company, Inc., Pearl River, New York; and Chas. Pfizer and Company, Inc., Terre Haute, Indiana. REFERENCES Anderson, G. J., C. F. Peterson, A. C. Wiese and C. E. Lampman, 1957. The effect of high level
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16-17 grams during the summer, compared to an intake of 17-21 grams per hen per day on the 765 Calorie diet during the summer. The actual required daily protein intake is not known and would of course depend on protein quality, rate of production and body weight. The relationship between egg production and body weight appears to be rather obscure. The 765 Calorie lots did not in any experiment attain the body weight of birds fed the two higher energy diets at the same time during the studies although comparable production levels were observed during the hotter periods. An inverse relationship apparently exists in that at high production rates body weight is lost; followed by a recovery in body weight during low production periods provided the dietary energy level is adequate.
1491
ENERGY LEVELS FOE LAYERS
Hill, F. W., D. L. Anderson and L. M. Dansky, 1956. Studies of the energy requirements of chickens. 3. The effect of dietary energy level on the rate and gross efficiency of production. Poultry Sci. 35: 54-59. Hinds, H. B., 1949. Environmental factors and their effect on the natural egg cycle. Arizona Agr. Expt. Sta. Bull. 222. Hutt, F. B., 1938. Genetics of the fowl. VII Breed differences in susceptability to extreme heat. Poultry Sci. 17:454-462. Lillie, R. J., J. R. Sizemore, I. L. Milligan and H. R. Bird, 1952. Thyroprotein and fat in laying diets. Poultry Sci. 31: 1037-1042. McDaniel, A. H., J. D. Price, J. H. Quisenberry, B. L. Reid and J. R. Couch, 1957. Effect of energy and protein level on cage layers. Poultry Sci. 36: 850-854. Thayer, R. H., 1953. Vitamin levels in high energy layer-breeder rations. Poultry Sci. 32: 927. Titus, H. W., 1955. The Scientific Feeding of Chickens. The Interstate Printers and Publishers, Inc., Danville, Illinois. Warren, D. C , R. Conrad, A. E. Schumacher and T. B. Avery, 1950. Effects of fluctuating environment on laying hens. Kansas Agr. Expt. Sta. Bull. 68. Wilham, O. S., 1931. The relation of temperature egg production. Panhandle Agr. Expt. Sta. Bull, 28: 1-15. Wilson, W. O., 1949. High environmental temperature as affecting the reaction of laying hens to iodized casein. Poultry Sci. 28: 581-592.
NEWS AND NOTES EDITORIAL NOTE The Editor was hospitalized from September 25th to November 4th as a result of coronary thrombosis. He is now at home but it will be some weeks before he can resume his normal duties. He wishes to take this opportunity to thank the many persons who sent letters, cards and messages. They were greatly appreciated. The proof-reading, paging, etc., of this November issue has been done by staff members of the Department of Poultry Science and the Department of Nutrition at the College, under the direction of Dr. I. Motzok of the Department of Nutrition. He has also taken care of the many other duties associated with the editorial office. The Editor expresses his thanks.
and equip an $8,500 structure at the North Dakota State University, Fargo, as a gift to the experiment station to inaugurate a "random sample" turkey meat production test. The building will be 40 feet wide and 96 feet long, insulated, and equipped with an electric ventilation system and completely automatic feeding system. General research in turkey feeding and nutrition will be combined with the random sample tests which will be conducted jointly by the University, the U.S. Department of Agriculture, and the North Dakota Poultry Improvement Board. MAINE NOTES
Dr. Francis H. Bird of Battle Creek, Michigan, has been appointed Head of the Department of Poultry Science at the University of Maine, Orono. NORTH DAKOTA NOTES • He succeeds Professor J. Robert Smyth, who retired The North Dakota Turkey Federation will build on June 30th. (Continued on page 1536)
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vitamin supplementation of high and low energy rations on egg production and egg shell quality. Poultry Sci. 36:1369-1376. Bird, H. R., and D. Whitson, 1946. Effect of diet on efficiency of egg production. Poultry Sci. 25: 210-214. Bruckner, J. H., 1936. The effect of environmental conditions on winter egg production. Poultry Sci. 15: 417-418. Byerly, T. C , 1941. Feed and other costs of producing market eggs. Maryland Agr. Expt. Sta. Bull. Al. Campos, A. C , F. H. Wilcox and C. S. Shaffner, 1960. The influence of fast and slow rises in ambient temperature on production traits and mortality of laying pullets. Poultry Sci. 39: 119129. Combs, G. F., and N. V. Helbacka, 1960. Studies with laying hens. I. Effect of dietary fat, protein levels and other variables in practical rations. Poultry Sci. 39: 271-279. Cunningham, F. E., O. J. Cotterill and E. M. Funk, 1960. The effect of season and age of bird. 1. On egg size, quality and yield. Poultry Sci. 39: 289-299. Heuser, G. F., L. C. Norris, H. T. Peeler and M. L. Scott, 1945. Further studies on the apparent effect on digestibility upon growth, weight maintenance and egg production. Poultry Sci. 24: 142-145. Hill, F. W., 1956. Studies of the energy requirements of chickens. 4. Evidence for a linear relationship between dietary productive energy level and the efficiency of egg production. Poultry Sci. 35:59-63.
is to increase the apparent release rate of thyroidal I131, it is suggested that 0.025% tapazole in the ration may be sufficient for most fowls. REFERENCES Sell, J. L., and S. L. Balloun, 1960. The effects of methimazole on weight gains, carcass composi-
1483
tion, thyroid gland weight and blood components of cockerels. Poultry Sci. 39: 930-937. Stahl, P. R., 1960. Factors affecting thyroxine secretion rate in the domestic fowl. Ph.D. Thesis, University of Missouri. Pipes, G. W., B. N. Premachandra and C. W. Turner, 1958. Measurement of the thyroid hormone secretion rate of individual fowls. Poultry Sci. 37:36-41.
Dietary Energy Levels for Laying Hens as Related to Age and Environmental Temperatures
A. A. KURNICK, H. B. HINDS, M. W. PASVOGEL1 AND B. L. REID Department of Poultry Science, University of Arizona, Tucson (Received for publication December 23, 1960)
L
AYING rations of high energy content •'were reported to support higher rates of egg production as early as 1945 by Heuser et al., and an inverse relationship between dietary fiber level and egg production efficiency was observed by Bird and Whitson (1946). Lillie el al. (1952) noted that the feeding of a laying diet supplemented with lard produced a marked improvement in feed conversion of layers. McDaniel et al. (1957) reported a 12.2% improvement in feed conversion through an increase in productive energy level from 962-1,050 Calories per pound in a 17% protein diet. During the cold weather months only, Hill, Anderson and Dansky (1956) noted an improvement in the rate of egg production at the higher energy levels studied. No difference in rate of production was obtained during the other portions of the year. Feed requirement per dozen eggs was lowered 12% by a 100 Calorie increase in the productive energy content of the diet. Body weight tended to in1 Present address, Peter Chicago, Illinois.
Hand
Foundation,
crease during the laying period as the energy content of the diet was increased. In a subsequent paper, Hill (1956) employed the Byerly (1941) partition equation as a means of evaluating the rations employed by Hill, Anderson and Dansky (1956). Calculations of relative efficiencies based on comparison of observed feed consumption with that predicted by the Byerly equation showed a linear relationship between the productive energy level of the diet and relative efficiency. Higher productive energy resulted in greater relative efficiency. Anderson et al. (1957) were unable to substantiate the previous report by Thayer (1953) that levels of B-vitamins, above those recommended as the requirements, were needed for maximum egg production when high energy rations were fed. Combs and Helbacka (1960) in studies with rations of 14.6-19.1% protein and 909-1,096 Calories of productive energy per pound, concluded that a C:P ratio as wide as 66.6:1 was adequate to support 60% egg production. Layers permitted free-choice selection of feeds, chose rations
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1. EFFECT ON EGG PRODUCTION, BODY WEIGHT AND FEED CONVERSION
1484
A. A. KURNICK, H. B. HINDS, M. W. PASVOGEL AND B. L. REID
The high ambient temperatures associated with a large portion of the year in Arizona have made necessary and possible the study of age, dietary energy and temperature relationships with laying hens. EXPERIMENTAL PROCEDURES
Single Comb White Leghorn pullets from the University poultry flock were selected and placed on three experimental laying rations at the ages shown in Table 2, with the exception of the first study in which the birds were all fed a 965 Calorie diet for the 18-22nd week prior to the initiation of the experiment. All birds were selected on the basis of body weight and degree of sexual maturity and were divided into six pens of 40 birds each. Two such selected groups were fed each of the dietary treatments. The diets employed in these studies (Table 1) contained 965, 865
and 765 Calories productive energy per pound (Titus, 1955). The diets all contained the same protein level of 17% (calculated), the energy being adjusted by the addition of either glucose monohydrate or wood pulp (Solka-floc) or a combination of these. Five separate experiments have been conducted with these diets, employing birds attaining sexual maturity as shown in Table 2. Throughout each of the experiments body weights, egg production and feed consumption rates were determined and summarized at 28-day intervals. Ambient temperatures were determined on a maximum and minimum basis at bird height level daily. The birds were maintained on dirt floors covered with cane litter and no culling was practiced during the studies. Feed was mixed biweekly for each pen; a basal mix consisting of all constant ingredients was used to prepare the individual diets with the addition of glucose monohydrate or wood pulp (Solka-floc) to obtain the required energy levels. Feed and water were supplied ad libitum throughout the experiments. RESULTS
Birds hatched during the month of January reached sexual maturity (5% production) earlier than those hatched during the other months of the year (Table 2). The number of days required to reach sexual maturity reflected the season of the year, that is, environmental temperature and length of day during which growth and development occurred. Birds hatched in May or June and grown during the hot part of the year required 182 and 194 days, respectively, to reach sexual maturity whereas birds hatched during either April or March required 168 and 159 days, respectively, to attain a similar level of maturation (Table 2). It will also be noted that birds reaching sexual maturity earli-
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of an average C:P ration of 59.6:1. Cunningham, Cotterill and Funk (1960) have studied the effect of season and age of bird on egg yield, egg size and quality. It was concluded that egg weight tended to be greater in the spring and smaller during periods of high temperature, while Haugh units declined with age of bird, regardless of season. Decreased rates of egg production have been reported to occur during high summer temperatures (Wilham, 1931; Hutt, 1938; Hinds, 1949). In addition, temperatures above 65°F. caused reductions in egg size according to Bruckner (1936) and Warren et al. (1950). Wilson (1949) demonstrated a decreased rate of feed consumption and lowered body weights in hens subjected to weekly rises in ambient temperatures. Campos, Wilcox and Shaffner (1960) reported a sudden severe drop in egg production in some strains of layers upon exposure to 100°F. for a 24-hour period. Egg weight, shell thickness and feed consumption were likewise adversely affected by exposure to the high ambient temperature.
1485
ENERGY LEVELS FOR LAYERS TABLE 1.—Composition of experimental diets 965 Cal.*/lb.
865 Cal.*/lb.
%
765 Cal.*/lb.
%
%
20.00 29.78 19.15 3.00 2.00 2.00 0.30 4.25 2.00 0.02 2.50
20.00 29.78 19.15 3.00 2.00 2.00 0.30 4.25 2.00 0.02 2.50
20.00 29.78 19.15 3.00 2.00 2.00 0.30 4.25 2.00 0.02 2.50
Glucose monohydrate Wood cellulose (Solka-floc)
15.00
—
7.50 7.50
15.00
100.00
100.00
100.00
Total Calculated analysis: Protein% Fat, Fiber,% Calcium, % Phosphorus, % Arginine, % Methionine, % Cystine, % Lysine, % Tryptophan, % Cal.—Protein ratio
•
17.00 2.34 2.46 2.48 0.83 0.950 0.329 0.286 0.864 0.194
17.00 2.34 9.96 2.48 0.83 0.950 0.329 0.286 0.864 0.194
17.00 2.34 17.46 2.48 0.83 0.950 0.329 0.286 0.864 0.194
56.800
50.900
45.000
* Calories of productive energy (Titus, 1955). ** Supplied the following per pound of diet: 4,500 I.U. vitamin A, 700 I.C.U. vitamin D3, 2.0 mg. riboflavin, 12.5 mg. niacin, 5.0 mg. D-calcium pantothenate, 200 mg. choline chloride, 6 meg. vitamin Bi 2 , 2.5 I.U. d-alpha tocopheryl acetate, 1.0 mg. menadione sodium bisulfite, 2.0 gm. procaine penicillin, 10.0 mg. aureomycin and 56.75 mg. butylated hydroxytoluene.
est did so when the average body weight was lower than that of birds requiring a longer period to reach the same degree of production with the exception of the March hatched pullets which were the lowest in body weight at maturity of all the hatches tested (Table 2). The combined effects of light and higher ambient temperatures during the growing season resulted in delayed sexual maturity in the May and June hatched pullets, and slightly retarded the maturity of birds hatched in April and March (Table 2) as compared to those hatched in January. The highest rates of total egg production in relation to time of hatch were obtained with pullets hatched during March,
April, May or June, regardless of diet fed. The January hatched pullets exhibited the lowest production rates on all three diets. Calculated average production figures for the three experimental diets also indicated that the poorest production performance was obtained with the January TABLE 2.—Effect of dale of hatch on age and body weight at sexual maturity
Phase No.
Date hatched
April IS, June 27, Jan. 13, Mar. 17, M a y 12, 1
1958 1958 1959 1959 1959
Age at sexual r(days) lJcf 168 194 128 159 182
Approximately 5% production.
Age at Average initiation body weight of exptl. at initiation diet feeding of study (days) (gm.) 178 200 130 165 196
1,813 1,805 1,731 1,640 1,825
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Ground yellow corn Ground milo Solv. soybean oil meal (44% protein) Fish meal (62% protein) Meat and bone scraps (50% protein) Dried whole whey Salt Ground limestone Dicalcium phosphate MnSCv5H 2 0 (70%) Vitamin pre-mix**
1486
A. A. K U R N I C K , H. B. H I N D S , M. W. PASVOGEL AND B. L.
TABLE 3.—Effect
Exp. No.
Date hatched
1
April, '58
2
3
4
5
June, '58
Jan., '59
March, '59
May, '59
Average of all hatches
hatched pullets, lowering the productive energy level of the diet by 100 Calories resulted in a decrease of 12.8% in feed conversion; while lowering 200 Calories, from 965 Calories per pound, caused a 26.8% decrease in feed conversion (Table 3). These changes in productive energy amounted to 18.1 and 4 5 % respectively, for 100 and 200 Calorie decreases in the diets fed the June hatched pullets, and 15.5 and 39.6% with the birds hatched in J a n uary. The feeding of 865 and 765 Calorie diets to March hatched pullets lowered feed conversion by 2.8 and 30.0% respectively, as compared to the 965 Calorie diet, while M a y hatched pullets consumed 2.8 and 16.0% more feed per dozen eggs when fed 865 and 765 Calories of produc-
of season of hatch and diet on performance of laying hens Dietary energy (Cal./lb.)
Feed % production conversion (hen-day basis) (lbs. feed/doz. eggs)
Therms/ dozen eggs
Change in body weight (grams) + 123 0 -125
965 865 765
61.1 61.0 59.9
4.78 5.39 6.06
4.60 4.65 4.63
Average
60.8
5.41
4.63
965 865 765
61.4 62.4 52.2
4.83 5.70 7.01
4.66 4.93 5.36
Average
58.9
5.85
4.98
965 865 765
55.7 55.0 48.3
5.33 6.16 7.45
5.14 5.33 5.70
Average
53.0
6.31
5.39
965 865 765
59.0 62.3 50.4
4.88 5.02 6.34
5.71 4.34 3.83
Average
57.4
5.41
4.63
965 865 765
58.0 60.9 58.0
4.99 5.12 5.78
4.82 4.43 4.42
Average
59.0
5.30
4.56
965 865 765
58.1 59.1 53.0
4.97 5.46 6.46
4.80 4.72 4.94
+ 128 + 26 -206
+348 +254 + 142
+ 50 + 22 - 98
+221 + 78 + 52
+ 174 + 76 -128
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hatched pullets (Table 3). The average production for all diets fed to J a n u a r y pullets was 53.0%, compared to 57.4-60.8% for the other four experiments. The feeding of a low energy diet containing 765 Calories per pound did not appreciably lower the rate of production among birds hatched in April or May, but resulted in a 9 % lower production rate with the June and March hatched birds and 7 % lower production in birds hatched in January. Pounds of feed required per dozen eggs on the respective experimental diets appeared to be lowest in birds fed the highest energy level (Table 3). As would be expected, the feeding of the lower energy diets increased the amount of feed required per dozen eggs produced. With the April
REID
E N E R G Y L E V E L S FOR
LAYERS
1487
tive energy per pound than those fed the 965 Calorie diet (Table 3). In general, the therms of productive energy required per dozen eggs produced were comparable, regardless of diet, a t approximately equivalent egg production levels (experiments 1 and 5, Table 3). In experiment 2, with June hatched pullets, the 9 - 1 0 % reduction in egg production on the 765 Calorie diet as compared to the 965 and 865 Calorie levels increased the therms of productive energy from 4.66 and 4.93, respectively, to 5.36 (Table 3). The same trend was noted with J a n u a r y and March hatched pullets. The highest average energy requirements per dozen eggs were obtained with J a n u a r y hatched birds; these pullets began laying in M a y
and had dropped to a rather low rate of lay by the onset of the colder portions of the laying year—the time of highest energy requirement (Figure 1). If all data with respect to the three diets are summarized (Table 3) a 5 - 6 % lower rate of production is noted for the 765 Calorie diet. No differences were noted between the two higher energy levels. It should be pointed out t h a t wood cellulose (Solka-floc) was used to adjust the energy level so as not to alter the amino acid ratio of any of the diets employed. These data indicate that 4.72-4.94 therms of productive energy are required per dozen eggs. T h e fiber content of 17.46% in the 765 Calorie diet apparently did not allow the birds to consume sufficient quantities of
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FIG. 1. Effect of ambient temperature and caloric density on percent production of pullets hatched at different times of the year. 1. Calories per pound of diet and total percent production. (Shaded areas denote cooler portions of the year.)
1488
A. A.
K U R N I C K , H.
B.
TABLE 4.—Effect
H I N D S , M.
W.
PASVOGEL AND B. L.
REID
of energy and fiber level on calorie intake * Ave. Calories consumed/hen/day
Exp. No. 1
2
Hatched
865
765
Oct. 15-Mar. 31 Apr. 1-Aug. 18
246.1 208.6
242.3 208.1
225.0 209.0
Jan. 8-Mar. 31 Oct. 15-Dec. 8 Apr. 1-Oct. 14
230.5
228.4
203.9
216.0
218.9
195.7
Jan., 1959 Cool Hot
Oct. 14-Mar. 28 May 26-Oct. 13
247.4 193.2
252.8 185.8
195.2 168.5
March, 1959 Cool Hot
Oct. 14-Apr. 25 Apr. 26-Jul. 19
244.2 208.7
242.0 196.0
201.5 193.6
May, 1959 Cool Hot
Nov. 10-Apr. 25 Apr. 26-Oct. 10
266.3 198.8
250.0 199.8
230.6 192.8
April, 1958 Cool Hot June, 1958 Cool
4
5
energy during the colder months of the year; this is reflected in the egg production rates (Figure 1). Approximately 10% more feed was required per dozen eggs when the 865 Calorie diet was fed, while 30% more feed was consumed on the 765 Calorie diet as compared to the highest energy level (965 Cal./lb.). A comparison of average energy intake figures per hen per day (Table 4) during the cool and hot periods of these experiments (cool = October 15-April 28; hot = April 29-October 14) indicates that the birds were able to consume approximately equal amounts of energy on the two high energy diets, while the 765 Calorie diet could be consumed at a rate to supply only 79-92% of the energy intake of birds fed the higher energy diets during the colder months (Table 4). Energy intake figures for the hot portions of the experiments show comparable figures for all three diets with the exception of birds hatched in January. The lower energy intake of the 765 Calorie lots (January hatch) may be partially explained by the differences in body weight
and production rate during the hot periods (Figure 1 and Table 3). The differences in energy intake levels (Table 4) noted for the 765 Calorie diet during the colder portions of the year are also indicated by the rates of egg production (Figure 1). In each experiment, except experiment 2 with June hatched birds, the low energy diet supported a lower rate of egg production during the colder portions of the year, while the summer production rates for the 765 Calorie lots were equivalent to those obtained with the two higher energy diets in each case regardless of age of the birds and stage of production (Figure 1). In two experiments (April and March hatches) the lowest energy level supported a higher rate of production (3-5%) during the summer months (Figure 1) than was obtained with the feeding of either 965 or 865 Calories of productive energy per pound. In these two cases the low energy diet apparently prevented the severe production decline observed with the two higher energy diets during the hot periods of the laying year.
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965
Hot 3
Periods & dates
1489
ENERGY LEVELS FOE LAYERS
March pullets reached the peak of production (70%) in 8-12 weeks after sexual maturity in September and also exhibited a winter slump of around 15% during the months of January and February followed by a recovery to 70% production in March and April (Figure 1). May pullets showed a pattern of egg production similar to that obtained with the April birds. The production peak was attained after 16-20 weeks followed by a decline, somewhat more severe than was noted with the April hatch, to around 30% production at the termination of the experiment in November. The low energy diet (765 Cal./lb.) failed to support body weight at the level ob-
tained with the feeding of either the 965 or 865 Calorie diet (Table 3). In each case the medium energy diet produced pullets which exhibited average body weights intermediate between the high and low energy diets. Mortality was not affected by the dietary treatments employed in these studies. DISCUSSION
Under the climatic conditions existing in southern Arizona, it would appear that birds hatched during the months of March-June attain the highest rates of total egg production. These birds require longer to reach sexual maturity and the peak of production, but appeared to be better able to withstand the summer heat with an adequate production level. The higher production rates of these birds resulted in greater feed conversion figures as compared to the January hatched pullets. One advantage to January hatched pullets is that the peak in production was attained during the summer months, indicating that age may be employed to overcome some of the adverse effects due to summer heat. The use of high fiber-low energy diets for laying strain pullets is to be avoided during the colder seasons of the year due to the inability of the hens to consume amounts sufficient to satisfy both body maintenance and egg production requirements. Some advantage may be realized with the use of such diets during the warmer months to avoid the diminished intake of protein, vitamins and minerals on high energy diets when the energy requirements are reduced due to summer temperatures. A 15-25% reduction in feed intake (energy) was noted between the winter and summer portions of these studies. The winter protein intake of around 18-19 grams per bird per day on the high energy diet was thus reduced to
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Monthly egg production rates obtained on the respective diets (Figure 1) indicate rather marked differences between birds hatched at different times during the year. The time required to reach the "peak" of production, as well as the production level at that time, appear to be indicative of the age, season (temperature and light) and perhaps body weight of the birds at the onset of production. April hatched pullets, beginning production in October, required 16-20 weeks to reach a production peak of around 70% (Figure 1), while birds hatched in June reached sexual maturity (5% production) in January and required only 8-12 weeks to reach a 75-80% production peak. The April hatched pullets (experiment 1) were able to sustain a fairly high rate of production for a longer period of time than did the June hatched birds. January hatched pullets attained 5% production with the onset of warm weather (April), peaked in production at 70% after 12 weeks (during July), exhibited a definite winter slump to 35-40% production during January and February followed by a rise in production rate to 60-65% at the end of the experiment in March.
1490
A. A. KURNICK, H. B. HINDS, M. W. PASVOGEL AND B. L. REID
SUMMARY
A total of five experiments have been conducted, employing diets of 17% protein and productive energy levels of 965, 865, and 765 Calories per pound. The birds in each experiment were hatched at different times during the year (April, June, January, March and May). Birds were housed on cane litter in individual colony houses. January hatched pullets attained sexual maturity at 128 days of age followed by the March (159 days), April (168 days), May (182 days) and June (194 days) hatches. January hatched birds showed a lower rate of production over the entire experiment than other birds employed in these studies. Feed conversion (lb. of feed/ dozen eggs) was greatest for the April hatched birds fed the 965 Calorie diet (4.78 lbs. of feed/dozen eggs). The feeding of 765 Calories of productive energy per pound resulted in lower rates of production in three of the five experiments (June, January, and March
birds). The average of all five experiments indicated a 5-6% lower production rate due to the feeding of the low energy diet. The lower production rate on this diet appeared to be due to the inability of the birds to consume sufficient amounts of feed during the colder months of the year due to the high dietary fiber level (17.46%). Wood cellulose (Solka-floc) was used to decrease the energy level of the 965 Calorie diet by replacing 15% glucose monohydrate. Energy intake decreased 15-26% during the summer months as compared to the winter periods in these studies. The low energy diet was beneficial in maintaining higher intakes of protein (above 18 gm./bird/day), vitamins and minerals during the summer months, but proved to stimulate higher summer production ( 3 5%) only in two experiments. Body weight was essentially maintained at the two higher dietary energy levels, while 765 Calories of productive energy per pound failed to support body weight to the same extent. The use of low energy-high fiber diets for laying strain pullets, especially during the colder months of the year is not recommended on the basis of results obtained in these studies. ACKNOWLEDGMENTS
The authors are indebted to the following companies for the vitamins and antibiotics employed in these studies: Distillation Products Industries, Rochester, New York; Merck and Company, Rah way, New Jersey; Heterochemicals, Inc., Valley Stream, New York; American Cyanamid Company, Inc., Pearl River, New York; and Chas. Pfizer and Company, Inc., Terre Haute, Indiana. REFERENCES Anderson, G. J., C. F. Peterson, A. C. Wiese and C. E. Lampman, 1957. The effect of high level
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16-17 grams during the summer, compared to an intake of 17-21 grams per hen per day on the 765 Calorie diet during the summer. The actual required daily protein intake is not known and would of course depend on protein quality, rate of production and body weight. The relationship between egg production and body weight appears to be rather obscure. The 765 Calorie lots did not in any experiment attain the body weight of birds fed the two higher energy diets at the same time during the studies although comparable production levels were observed during the hotter periods. An inverse relationship apparently exists in that at high production rates body weight is lost; followed by a recovery in body weight during low production periods provided the dietary energy level is adequate.
1491
ENERGY LEVELS FOE LAYERS
Hill, F. W., D. L. Anderson and L. M. Dansky, 1956. Studies of the energy requirements of chickens. 3. The effect of dietary energy level on the rate and gross efficiency of production. Poultry Sci. 35: 54-59. Hinds, H. B., 1949. Environmental factors and their effect on the natural egg cycle. Arizona Agr. Expt. Sta. Bull. 222. Hutt, F. B., 1938. Genetics of the fowl. VII Breed differences in susceptability to extreme heat. Poultry Sci. 17:454-462. Lillie, R. J., J. R. Sizemore, I. L. Milligan and H. R. Bird, 1952. Thyroprotein and fat in laying diets. Poultry Sci. 31: 1037-1042. McDaniel, A. H., J. D. Price, J. H. Quisenberry, B. L. Reid and J. R. Couch, 1957. Effect of energy and protein level on cage layers. Poultry Sci. 36: 850-854. Thayer, R. H., 1953. Vitamin levels in high energy layer-breeder rations. Poultry Sci. 32: 927. Titus, H. W., 1955. The Scientific Feeding of Chickens. The Interstate Printers and Publishers, Inc., Danville, Illinois. Warren, D. C , R. Conrad, A. E. Schumacher and T. B. Avery, 1950. Effects of fluctuating environment on laying hens. Kansas Agr. Expt. Sta. Bull. 68. Wilham, O. S., 1931. The relation of temperature egg production. Panhandle Agr. Expt. Sta. Bull, 28: 1-15. Wilson, W. O., 1949. High environmental temperature as affecting the reaction of laying hens to iodized casein. Poultry Sci. 28: 581-592.
NEWS AND NOTES EDITORIAL NOTE The Editor was hospitalized from September 25th to November 4th as a result of coronary thrombosis. He is now at home but it will be some weeks before he can resume his normal duties. He wishes to take this opportunity to thank the many persons who sent letters, cards and messages. They were greatly appreciated. The proof-reading, paging, etc., of this November issue has been done by staff members of the Department of Poultry Science and the Department of Nutrition at the College, under the direction of Dr. I. Motzok of the Department of Nutrition. He has also taken care of the many other duties associated with the editorial office. The Editor expresses his thanks.
and equip an $8,500 structure at the North Dakota State University, Fargo, as a gift to the experiment station to inaugurate a "random sample" turkey meat production test. The building will be 40 feet wide and 96 feet long, insulated, and equipped with an electric ventilation system and completely automatic feeding system. General research in turkey feeding and nutrition will be combined with the random sample tests which will be conducted jointly by the University, the U.S. Department of Agriculture, and the North Dakota Poultry Improvement Board. MAINE NOTES
Dr. Francis H. Bird of Battle Creek, Michigan, has been appointed Head of the Department of Poultry Science at the University of Maine, Orono. NORTH DAKOTA NOTES • He succeeds Professor J. Robert Smyth, who retired The North Dakota Turkey Federation will build on June 30th. (Continued on page 1536)
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vitamin supplementation of high and low energy rations on egg production and egg shell quality. Poultry Sci. 36:1369-1376. Bird, H. R., and D. Whitson, 1946. Effect of diet on efficiency of egg production. Poultry Sci. 25: 210-214. Bruckner, J. H., 1936. The effect of environmental conditions on winter egg production. Poultry Sci. 15: 417-418. Byerly, T. C , 1941. Feed and other costs of producing market eggs. Maryland Agr. Expt. Sta. Bull. Al. Campos, A. C , F. H. Wilcox and C. S. Shaffner, 1960. The influence of fast and slow rises in ambient temperature on production traits and mortality of laying pullets. Poultry Sci. 39: 119129. Combs, G. F., and N. V. Helbacka, 1960. Studies with laying hens. I. Effect of dietary fat, protein levels and other variables in practical rations. Poultry Sci. 39: 271-279. Cunningham, F. E., O. J. Cotterill and E. M. Funk, 1960. The effect of season and age of bird. 1. On egg size, quality and yield. Poultry Sci. 39: 289-299. Heuser, G. F., L. C. Norris, H. T. Peeler and M. L. Scott, 1945. Further studies on the apparent effect on digestibility upon growth, weight maintenance and egg production. Poultry Sci. 24: 142-145. Hill, F. W., 1956. Studies of the energy requirements of chickens. 4. Evidence for a linear relationship between dietary productive energy level and the efficiency of egg production. Poultry Sci. 35:59-63.