Seasonal Commercial Egg Production Curve Differences1

Seasonal Commercial Egg Production Curve Differences1 ALLAN P. RAHN

Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication October 6, 1975)

ABSTRACT The statistical and economic significance of seasonal differences in commercial egg production curves were assessed. The time profile of both the number and weight of eggs laid by White Leghorn pullets was found to differ significantly statistically between housing seasons. Imputed differences in the value of gross egg receipts suggest that seasonal production differences as well as seasonal egg price patterns should be considered in formulating commercial layer flock replacement plans. POULTRY SCIENCE 55: 1302-1307, 1976

I

N appraising commercial layer flock replacement plans, differences in egg production which are related to the time of year pullets are housed should possibly be considered. In their search for optimal layer flock replacement policies Low (1965) and Parlour and Halter (1970) assumed that layer performance was unaffected by date of housing. However, Noles et al. (1969) recognized seasonal differences in the number and size of eggs laid by flocks started at different times of the year. The objective of this study was to measure these possible differences and evaluate their statistical and economic significance. MATERIALS AND METHODS Observations by 4-week time intervals on the number and size and grade of eggs laid per hen housed during the lay period of 59 White Leghorn commercial egg flocks were obtained. This information was collected from the records of one firm over a 1962 to 1967 observation sampling period. Similar husbandry practices were followed in both the pullet grow-out and egg production phases of these flocks. Pullets were reared in open

1. Presented at the 64th Annual Meeting of the Poultry Science Association, Inc., at Washington State University.

sided houses with a conventional constant light day program utilized when appropriate. Layers were also housed in curtain sided houses in either cages or on the floor. The egg production records of each flock were divided into the seasonal classifications of spring, summer, fall or winter placed flocks based on their 20 weeks of age housing date. Spring was defined to include observations from flocks housed within the March 26 to June 17 calendar period. The calendar periods of June 18 to September 9, September 10 to December 2 and December 3 to March 26 were correspondingly defined as summer, fall or winter housed flocks, respectively. Of the 59 flocks, 12 were housed in the spring, 17 in the summer, 14 in the fall, and 16 in the winter period. The size and quality of eggs laid as well as the number are important determinates in economic evaluations. Therefore, estimates of the weight of eggs laid per hen housed during each 4-week period of lay were also made. The per dozen expected weights assigned to each size and quality grade category are presented in Table 1. Average weights for U.S. Consumer Grade A or better eggs are based on the official weight classes for shell eggs. The B-Grade and Bloods weights were derived as weighted averages of the official weight classes using the observed typical Grade A size distribution as weights. Average weights for Check and Loss eggs

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INTRODUCTION

COMMERCIAL EGG PRODUCTION CURVES

TABLE 1.—Expected weights for classes of shell eggs U.S. consumer grade

Weight per dozen

Grade A or better Jumbo Extra large Large Medium Small P-wee Grade B Check Loss Bloods

(8.)

(oz.)

893 808 723 638 553 468 686 743 743 686

31.5 28.5 25.5 22.5 19.5 16.5 24.2 26.2 26.2 24.2

form. However, alternative functional form specifications indicated that a fourth-degree polynomial of the regressor covariate lay period gave superior estimation performance. Thus, three different equation specifications involving the regressand variables number and weight of eggs laid per hen housed, the regressor classification variable denoting housing season, and the fourth-degree polynomial of period-of-lay regressor variables were postulated. In the Equation 1 specification, all observations of both regressand variables were independently regressed on their associated period-of-lay regressor variables. In the second equation specification (Equation 2), the observations on both regressand variables were independently regressed on their associated point-of-lay regressor variables plus dummy regressor variables permitting the level of the function to vary between housing seasons. The third equation specification (Equation 3), permitted the coefficients of the period-of-lay regressor variables (i.e., the slopes) as well as the level of the function to vary between housing seasons with both independently analyzed regressand variables. Although estimation was accomplished through four distinct equations, this proce-

TABLE 2. -Arithmetic means of primary data on the number and weight of eggs laid per bird housed by

season 4-Week lay period

Number

Weight

1 2 3 4 5 6 7 8 9 10 11 12 13 14 Sum

Doz. 0.33 1.44 1.82 1.79 1.70 1.62 1.52 1.47 1.35 1.31 1.26 1.26 1.21 1.19 19.27

Kg. 0.18 0.86 1.15 1.17 1.15 1.13 1.08 1.07 0.99 0.97 0.94 0.94 0.90 0.88 13.40

Spr ing

Summer Number Weight Doz. 0.33 1.30 1.68 1.78 1.64 1.58 1.50 1.47 1.41 1.39 1.38 1.30 1.24 1.15 19.18

Kg. 0.18 0.77 1.06 1.18 1.12 1.11 1.07 1.07 1.02 1.01 1.00 0.95 0.90 0.84 13.29

Winter

Fall Number

Weight

Number

Weight

Doz. 0.38 1.54 1.85 1.75 1.73 1.67 1.65 1.54 1.48 1.44 1.32 1.21 1.11 1.05 19.74

Kg. 0.22 0.96 1.21 1.18 1.19 1.16 1.15 1.08 1.04 1.02 0.95 0.88 0.81 0.77 13.64

Doz. 0.40 1.53 1.91 1.81 1.73 1.67 1.58 1.52 1.40 1.33 1.20 1.15 1.05 0.97 19.32

Kg. 0.23 0.94 1.23 1.19 1.16 1.13 1.09 1.07 1.00 0.96 0.88 0.84 0.78 0.72 13.21

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were assumed to be slightly greater than this weighted average because of an expected greater incidence of shell damage in the larger weight classes. The arithmetic means of the primary data utilized in this study are shown in Table 2. To ascertain the statistical significance of differences in the level and time pattern of both the number and weight of eggs laid per hen housed in various seasons of the year, a multiple regression covariance procedure was utilized. Based on standard production curves a third-degree polynomial of the regressor covariate lay period would be hypothesized as the appropriate functional

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A. P. RAHN

TABLE 3.—-Covariance analysis of equation

specifications

F test statistics obtained for equation 2 versus 1' 3 versus 22 Equation 1.75 6.21*. Egg numbers 2.02 6.89* Egg weights 1 Test to determine differences in intercepts between seasons (slopes assumed constant). 2 Test to determine differences in slopes between seasons. * Significant at the 1 percent level of significance.

dure is tantamount to estimation through a single equation with appropriate dummy variable constructs permitting both intercepts and slopes to vary by housing season. The null hypothesis of no statistically significant differences in the level, time pattern or level and time pattern of the regressand functions between housing seasons was tested by utilizing F ratio test statistics as presented by Johnston (1960).

1200

o,

600

housed

Equation F : 189

400

-

300

-

200

•

Statistics R:

0.79

€

—r—

5 6 4-Week

7 8 9 1 0 11 Lay Pe r i od s

12

13

14

FIG. 1. Predicted egg weights, by 4-week lay periods, for White Leghorn pullets housed in different seasons of the year.

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Season

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COMMERCIAL EGG PRODUCTION CURVES

•

Period

Index

RESULTS The results of the covariance analysis for the three alternative equation specifications are presented in Table 3. The null hypothesis of no significant differences in the level of the function (slopes assumed to be uniform) between seasons cannot be rejected at customary significance levels for either regressand variable. However, the null hypothesis of no significant differences in the slope of the function between seasons can be rejected at highly significant levels. Thus, statistically significant differences between housing seasons in the time profile of both the number and weight of eggs laid by White Leghorn pullets were found; but no statistically signif-

icant differences between housing seasons in the overall level are indicated. DISCUSSION

To appraise the economic ramifications of the differences found in the time profile of eggs laid by pullets housed in different seasons of the year, the discounted value of gross egg receipts was calculated. 2 The number of grams of large egg equivalents which could be marketed in each four-

2. The discounted value of gross eggs receipts is defined as Z/i, [Ri/(1 + r)']. Where the gross egg receipts for the ith 4-week period of lay and the discount rate are denoted as Rj and r, respectively.

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FIG. 2. Seasonal price pattern of at-farm average prices paid for Grade A White Large eggs, Georgia 1967-1972 (January through December).

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A. P. RAHN

TABLE 4.—Discounted value of gross egg receipts' Price level Housing season Spring Summer Fall Winter

Uniform

Seasonal

$/thou. birds 10,043 9,944 10,210 9,887

$/thou. birds 10,066 10,009 10,219 9,734

1 Based on an eight percent discount rate, a 56 week period-of-lay and an average egg price level of 55.4 cents per dozen.

TABLE 5.—Differences in the discounted value of gross egg receipts' Housing seasons

Price level Uniform Seasonal $/thou. birds $/thou. birds

Spring minus winter 156 332 Summer minus winter 57 275 Fall minus winter 323 485 'Based on an eight percent discount rate, a 56 week period-of-lay and an average egg price level of 55.4 cents per dozen.

ACKNOWLEDGMENTS Appreciation is hereby expressed to Dr. Richard K. Noles and Georgia Fresh Eggs for providing the data used in this study. The technical assistance of Faye Brill is also gratefully acknowledged.

REFERENCES Johnston, J., 1960. Econometric Methods. 2nd Ed., McGraw-Hill Book Company, Inc., New York, N.Y., pages 192-207. Low, E. M., 1965. Choosing a policy of stock replacement in commercial egg production. Univ. of Reading, Dept. of Agr. Econ. Misc. Study 38. Noles, R. K., L. H. Long and J. C. Fortson, 1969. Determining the optimum replacement policy for commercial layers. Poultry Sci. 48: 636-645. Parlour, J. W., and A. N. Halter, 1970. A study of the economics of force molting in commercial egg production. Technical Bulletin No. 112, Oregon State University Agricultural Experiment Station, Corvallis, Oregon. Rahn, A. P., 1975. Seasonal price and volume patterns

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week period during a 56-week lay cycle of a flock housed in each season was obtained through a prediction equation using the parameter estimates for the weight equation specification shown above to be superior. The equation performance statistics and the associated predicted egg weights are illustrated in Figure 1. These weight estimates were then converted into dozens of large egg equivalents through division by 815 grams (24 oz.). Egg market prices were assumed to be either a uniform 55.4 cents per dozen throughout the year or to vary seasonally in a "typical" price pattern as reported by Rahn (1975). The season pattern utilized is presented in Figure 2 which depicts the price level assumed in each 4-week calendar period as a percentage of the uniform price level. A discount rate of 8% was assumed to adequately account for differences in the value of gross egg receipts due to the time period in the lay cycle they are received.

The discounted value of gross egg receipts by housing season and the associated differences relative to the winter season, are presented in Table 4 and Table 5. The differences in the value of gross egg receipts under the uniform price level assumption reflect both the impact of time value of money considerations and total egg production differences. Thus, although seasonal differences in the level of the egg weight function was not statistically significant, the discounted value of these differences are apparent. When the impact of seasonally varying price levels is also considered, the discounted value of gross egg receipts from fall, summer, or spring housed flocks were estimated to exceed those of winter housed flocks by 485, 275, and 332 dollars per thousand birds. Therefore, seasonal egg production and egg price level differences should appropriately be considered in formulating commercial layer flock replacement plans.

COMMERCIAL EGG PRODUCTION CURVES

for commodities of economic importance to the commercial egg industry in Georgia. Research

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Report No. 209. University of Georgia College of Agriculture Experiment Stations, Athens, Georgia.

Objective Color Values of Non-Frozen and Frozen Broiler Breasts and Thighs C. E. LYON, W. E. TOWNSEND AND R. L. WILSON, JR.

United States Department of Agriculture, Agricultural Research Service, Richard B. Russell Agricultural Research Center, Athens, Georgia 30604 (Received for publication October 6, 1975)

POULTRY SCIENCE 55: 1307-1312, 1976

INTRODUCTION

S

EVERAL reports have been published concerning bone darkening of poultry which has been frozen. Koonz and Ramsbottom (1947) reported that when bones containing red marrow were frozen and defrosted, hemoglobin was oxidized to methemoglobin and color of the bones changed from red to shades of brown, gray and black. They also found that hemoglobin content of bones was greater in young than in mature animals, and that in defrosted, immature chickens, some of the pigment escaped through the porous, spongy, incompletely calcified walls of the bones and accumulated on adjacent tissues, which appeared darkened when cooked. Brant and Stewart (1950) reported that extent of bleeding, degree of carcass separation and chilling method did not affect bone color. They also reported that rate of

freezing and storage conditions did not influence bone darkening to a practical degree. Roasting the chicken 30 min. or more prior to freezing reduced bone discoloration significantly. Woodroof and Shelor (1948) reported that heating chicken pieces at 190° F. (87.8° C.) for 10 min. and then freezing reduced bone darkening, but adversely affected the flavor of the meat. Ellis and Woodroof (1959) reported that heating chicken legs and thighs to an internal temperature of 180° F. (82.2° C.) before freezing effectively controlled meat darkening, due to heat coagulation of the bone marrow prior to freezing. Spencer et al. (1961) found darkening in all broilers subjected to freezing but not in non-frozen controls. Length of frozen storage had no effect on degree of bone darkening. Streeter and Spencer (1973) used air blast, " F r e o n , " "Nitreon" and liquid nitrogen spray to freeze

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ABSTRACT Four experiments were conducted to measure objectively color differences in non-frozen and frozen (air blast and Freon immersion) broiler breasts and thighs. Frozen pieces were stored for 6 days at -23° C. and non-frozen for 6 days at 2° C. In the first experiment internal color was compared of non-frozen and frozen uncooked breast and thigh pieces. In the second experiment non-frozen and frozen breast and thigh pieces were water cooked (end-point temperature of 88° C.) prior to color evaluation. The third and fourth experiments compared objective color readings of non-frozen and frozen thigh pieces with the femur removed from half the samples. Uncooked thighs were objectively evaluated in the third experiment, and water cooked samples in the fourth. Uncooked frozen samples from Experiments 1 and 3 were thawed overnight at 2° C. prior to color evaluation. Frozen breast pieces were significantly darker than non-frozen when cooked. Frozen uncooked thighs were significantly darker and redder than non-frozen; frozen cooked thighs were significantly darker but not redder than non-frozen cooked thighs. Thighs with the femur removed prior to freezing and cooking were significantly lighter than thigh pieces frozen and cooked with femur intact. Total color difference values were calculated from the L, a L and b L values to demonstrate color differences between non-frozen and frozen, bone-in and bone-out pieces.