Effect of Storage and Layer Age on Quality of Eggs From Two Lines of Hens 1

Effect of Storage and Layer Age on Quality of Eggs From Two Lines of Hens 1 F. G. Silversides*,2 and T. A. Scott *Crops and Livestock Research Centre, Charlottetown, Prince Edward Island, Canada C1A 7M8 and Nova Scotia Agricultural College, Truro, Nova Scotia, Canada B2N 5E3; and Pacific Agri-Food Research Centre, Agassiz, British Columbia, Canada V0M 1A0 ABSTRACT Eggs from and hens was greater than that of eggs from hens, and between 28 and 59 wk of age were stored for up to 10 d to produce a sample of 5,763 eggs differing in the three it decreased as the hen age increased and with increasing time in storage. The ph of the albumen was not different major determinants of albumen quality. Eggs from ISA- between strains, and the effect of hen age was small, but Brown hens were larger and had less yolk, more albumen, it increased with time in storage. Regression coefficients of the height of the inner thick albumen on the weight and a greater percentage of shell than those from ISAof the egg were between 0.058 and 0.102, showing that White hens. Egg size increased with increasing age of the the fixed regression of 0.05-mm albumen height per gram hen, although more for the hens than the ISAof egg implied by the Haugh unit is wrong. The statistical Brown hens, and the yolk increased more in size than did association between albumen ph and egg weight was the shell and albumen. During storage, albumen weight very low. If albumen quality is being used as a measure decreased and yolk weight increased slightly. The height of the inner thick albumen of eggs from hens of freshness, then the albumen height is biased by the strain and age of hen, whereas the albumen ph is not. (Key words: egg quality, layer strain, storage, egg component) 2001 Poultry Science 80:1240 1245 INTRODUCTION Albumen quality is a standard measure of egg quality that is most often measured as the height of the inner thick albumen or a function of this, such as the Haugh unit. The unit proposed by Haugh (1937) uses a log scale and applies an adjustment for egg weight corresponding to a regression of 0.05 mm/g (Eisen et al., 1962). The Haugh unit has been used extensively (Williams, 1992), although many authors (Eisen et al., 1962; Nestor and Jaap, 1963; Kidwell et al., 1964; Silversides and Villeneuve, 1994) have criticized it and have shown that the adjustment for egg weight implied by the Haugh unit is incorrect, except possibly in the sample of eggs measured by Haugh (1937). Silversides and Villeneuve (1994) proposed simply measuring the height of the inner thick albumen without a correction for egg weight. Albumen quality can also be measured by the albumen ph, but according to Hunton (1987) this procedure can be time consuming. Williams (1992) reviewed factors that affect albumen height. A few nutritional factors have been implicated, but, overall, nutrition is relatively unimportant. The major influences on albumen height are the strain and age of the hen laying the egg and storage time and conditions. Poggenpoel (1986) found that the heritability of albumen height is 0.48 in a line of White Leghorns selected for egg production, and albumen height differs between strains (Toussant et al., 1995; Scott and Silversides, 2000). As the age of the hen increases, the albumen height decreases even as the egg weight and total amount of albumen increase (Hill and Hall, 1980; Silversides, 1994). The albumen height of all eggs is at maximum when the egg is laid and decreases with increased storage time. Freshly laid and stored eggs from two lines of hens were studied over a full laying cycle in order to investigate the importance of age and strain of the hen and the period of storage on egg quality as measured by the height and the ph of the albumen. MATERIALS AND METHODS 2001 Poultry Science Association, Inc. Received for publication November 14, 2000. Accepted for publication April 9, 2001. 1 Agriculture and Agri-Food Canada Contribution Number 648. 2 To whom correspondence should be addressed: fsilversides@ nsac.ns.ca. Eggs were obtained from and hens. Eggs were collected over 4-d periods when the hens were 25, 31, 45, and 59 wk old. For each storage time and age, an attempt was made to measure 150 eggs from each strain; however, these measurements were not always 1240

EFFECTS OF STRAIN AND STORAGE ON EGG QUALITY 1241 possible, and between 89 and 193 eggs were measured for each strain at each storage time and age. Eggs that were laid overnight were not used for the experiment. Fresh eggs were collected and measured within 2 h of being laid. Samples of eggs were stored for periods of 1, 3, 5, and 10 d at room temperature. At sampling, eggs were weighed and broken onto a flat surface where the height of the albumen was measured half way between the yolk and the edge of the inner thick albumen by using an electronic albumen height gauge. 3 The yolk was separated from the albumen and weighed. The ph of the albumen was measured immediately using a ph meter (model 360i). 4 The shells were dried at room temperature for 3 d, then at 60 C for 3 d, and weighed; the weight of the albumen was calculated as the difference between the weight of the egg and the weight of the yolk and shell. Statistical Analysis All data were analyzed using the SAS statistical package (Littell et al., 1991). An ANOVA with the general linear models procedure included the main effects of age, storage time, and strain of hen, and the two- and three way interactions between these factors. The effect of strain was significant for all measures except albumen ph. The data were also analyzed separately for each strain with the ANOVA including the effects of age and storage time and the interaction between these effects. When the main effects were significant, the means were separated using Duncan s test. Correlation coefficients (r) were calculated using the PROC CORR procedure of SAS software to determine the relative importance of the three egg components in determining egg weight. The PROC REG procedure of SAS software was used to investigate the effect of egg weight on albumen height and ph among all of the eggs of each strain and among the eggs of each strain separated into the four ages and the five storage times. The PROC REG procedure was also used to investigate the effect of storage time and age on albumen quality. Probabilities of less than 0.05 were considered significant for all analyses. RESULTS The eggs from hens were larger than those from hens, with more shell and albumen but less yolk. Table 1 shows these differences as percentages of the eggs to eliminate the effect of egg weight on the amount of the principal components. For and hens, as the hen ages increased, egg size increased, with the greatest increase in the weight of the yolk. The weight of the albumen also increased with age of the hen, and there was an increase in the amount 3 Queensboro Instruments, Ottawa, ON, Canada K2A 2J3. 4 Corning Incorporated, Corning, NY 14831. of shell until Week 45. However, when considered as a percentage of the egg, the shell and albumen decreased with increasing age of the hen. With several exceptions, egg weight decreased with storage, albumen weight decreased, yolk weight increased, and the change in shell weight was unclear. Measurement of the components as proportions of the whole egg removed any inconsistencies, and longer periods of storage resulted in a greater percentage of shell and yolk and a lesser percentage of albumen. Interactions between strain and age were significant. The ANOVA are not shown, but the changes for each strain can be observed in Table 2. At 25 wk, eggs from hens were heavier than those from hens, but as the age of the hens increased, the increase in the size of eggs from hens was less than that of eggs from hens. The shell, as a percentage of egg weight, decreased more for eggs with increasing age of the hen than it did for eggs. With increasing age, the increase in the percentage yolk and decrease in percentage albumen of eggs were greater than those of eggs. The strain by storage interaction was significant only for the percentage shell, which increased slightly with increasing storage times for eggs but was variable for ISA- White eggs. The importance of the weight of egg components in determining egg size was investigated using correlation analysis for each age of hen and for each storage time (Table 2). All three major components were significantly associated with egg weight, with the correlation coefficients between egg and albumen weights being highest. The association of yolk weight with egg weight was less important in eggs from young hens than for older hens. Other changes in the correlation coefficients with age of the hen or period of storage were small. At all ages and storage times, the yolk was more closely associated with egg size for eggs from hens than for those from hens. hens laid eggs with greater albumen height than did hens, but the albumen ph was not affected by the strain (Table 3). Albumen height decreased with increasing age of the hen for both strains. The effect of hen age on albumen ph was not large, and although it was significant, it was not in a consistent direction overall or separately for each strain. As expected, time in storage decreased the albumen height and increased the albumen ph of eggs from both strains. Several interactions between strain and layer age were significant for albumen height and can be observed (without the AN- OVA) in Table 3. Albumen height of eggs from hens was uniformly less than that of eggs from hens, except at 59 wk when the difference between strains was larger. Among fresh eggs, the difference between and eggs was greater than among eggs stored for 10 d (1.35 vs. 0.69 mm, respectively). The effect of egg weight on albumen quality (Table 4) was dependant on the group of eggs being studied. Egg

1242 SILVERSIDES AND SCOTT TABLE 1. The effect of layer age and storage time on weight and proportions of eggs from two lines of layers Egg weight Shell Yolk Albumen Egg weight Shell Yolk Albumen (g) (%) (g) (%) 25 wk 52.49 d 10.75 a 23.61 d 65.64 a 56.44 c 10.61 a 22.39 d 67.01 a 31 wk 55.97 c 10.36 b 25.65 c 63.99 b 58.50 b 10.49 b 24.17 c 65.34 b 49 wk 60.49 b 9.92 c 27.30 b 62.78 c 63.39 a 10.24 c 24.95 b 64.81 c 59 wk 61.71 a 9.52 d 28.16 a 62.32 d 63.65 a 10.03 d 25.66 a 64.32 d SEM 0.14 0.02 0.06 0.06 0.17 0.03 0.07 0.08 Fresh 57.45 b 10.12 b 24.98 c 64.90 a 61.01 a 10.18 d 23.61 c 66.22 a 1 d 58.92 a 9.99 c 26.15 b 63.85 b 60.84 a 10.22 d 23.76 c 66.03 a 3 d 57.41 b 10.22 a 26.14 b 63.64 c 60.72 a 10.34 c 24.35 b 65.32 b 5 d 57.06 b 10.19 ab 26.32 b 63.49 c 59.67 b 10.45 b 24.54 b 65.00 c 10 d 57.03 b 10.26 a 27.05 a 62.69 d 59.40 b 10.60 a 25.04 a 64.36 d SEM 0.16 0.02 0.06 0.07 0.19 0.03 0.08 0.08 (P) Source of variation Age <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Age storage <0.01 <0.05 NS NS <0.01 0.05 <0.05 NS a d Means of storage times with different superscripts are different at P < 0.05. 1 The total number of observations is given in parentheses and varied from 89 to 193 at each level of age storage. weight had a significant negative effect on albumen height among eggs from hens, but the association was not significant among eggs from hens. At each individual age of hen, larger eggs were associated with higher albumen for both strains, with regression coefficients between 0.059 and 0.102 mm per gram of egg. At each individual storage time, all of the associations between egg weight and albumen height for both strains were significant and negative. The R 2 values between 0 and 0.09 indicated that the egg weight was relatively unimportant in determining albumen height. The relationship between egg weight and albumen ph overall was low for both strains, and negative, and the two measures were independent at most of the four ages. The regression of albumen ph on egg weight was significant for several periods of storage for each strain. The R 2 TABLE 2. Correlation coefficients (r) between egg components and egg weight (g) at five storage times for eggs from two lines of hens at four different ages 1 values indicated that egg weight was not an important factor in determining the albumen ph. The importance of age of the hen and storage of the egg on measures of egg composition and egg quality in the two lines was investigated using regression analysis (Table 5). The R 2 values of the simple regressions showed that age was more important in determining egg weight and egg components for the line (R 2 = 0.28 to 0.47) than for the line (R 2 = 0.08 to 0.26). The regressions of egg weight and egg components on length of storage were significant and similar in both lines, but R 2 values were low. The regression of albumen height on age of the hen was significant among eggs from both lines, whereas that of albumen ph on hen age was not. The period of storage explained a large amount of the variation in both albumen height and ph in both lines. n Shell Yolk Albumen n Shell Yolk Albumen All 2,931 to 2,993 0.64 0.82 0.93 2,714 to 2,785 0.67 0.72 0.94 25 wk 768 to 779 0.67 0.49 0.95 702 to 718 0.66 0.38 0.95 31 wk 737 to 754 0.67 0.67 0.95 723 to 743 0.65 0.62 0.96 49 wk 783 to 802 0.69 0.68 0.95 673 to 689 0.64 0.60 0.95 59 wk 743 to 758 0.64 0.63 0.94 616 to 635 0.59 0.56 0.94 Fresh 629 to 639 0.64 0.86 0.95 510 to 523 0.65 0.78 0.95 1 d 542 to 548 0.64 0.82 0.94 637 to 645 0.65 0.65 0.92 3 d 527 to 537 0.65 0.84 0.94 574 to 590 0.70 0.75 0.94 5 d 673 to 689 0.64 0.82 0.93 441 to 451 0.68 0.73 0.93 10 d 560 to 580 0.64 0.82 0.92 552 to 576 0.74 0.77 0.94 1 All correlation coefficients are significant at P < 0.01.

EFFECTS OF STRAIN AND STORAGE ON EGG QUALITY 1243 TABLE 3. The effect of layer age and storage time on albumen height and ph of eggs from two lines of layers Height ph Height ph (mm) (mm) 25 wk 7.79 a 8.60 c 6.81 a 8.69 b 31 wk 7.22 b 8.72 a 6.25 b 8.74 a 45 wk 6.52 c 8.71 a 5.58 c 8.57 c 59 wk 6.40 d 8.66 b 5.21 d 8.70 b SEM 0.03 0.01 0.04 0.01 Fresh 9.68 a 7.43 e 8.33 a 7.43 e 1 d 7.95 b 8.42 d 6.93 b 8.44 d 3 d 6.78 c 8.99 c 5.68 c 8.99 c 5 d 5.83 d 9.23 b 4.81 d 9.21 b 10 d 4.75 e 9.32 a 4.06 e 9.32 a SEM 0.04 0.01 0.04 0.01 (P) Source of variation Age <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 Age storage <0.01 <0.01 <0.01 <0.01 a e Means of layer age and storage times with different superscripts are different at P < 0.05. 1 The total number of observations is given in parentheses and varied from 89 to 193 at each level of age storage. DISCUSSION These data confirm the differences between and hens that were described by Scott and Silversides (2000) and extend the observations over the full production cycle. Eggs from hens were initially larger than those from hens, but egg size increased at a slower rate, so egg size was more consistent throughout the production cycle for ISA- Brown than for hens. The percentage of shell followed a similar pattern. Of the three egg components, yolk size increased the most with the age of the hen and the percentage shell and albumen declined. The effects TABLE 4. The regression coefficients (b) of albumen height and ph on egg weight at different ages and periods of storage of age of the hen have been described previously (Hill and Hall, 1980; Silversides, 1994). The effects of storage were also expected (Heath, 1977; Ahn et al., 1999) as material from the albumen passed through the yolk membrane and was lost through the shell. In both strains, the amount of albumen was closely associated with the egg weight, suggesting that it is the major determinant of egg size. The association of the yolk weight with the egg weight was higher in eggs from than those from hens, likely because the yolks of ISA- White eggs were larger and because they changed more with age of the hen. Two measurements were used to determine albumen quality. The eggs from hens had lower albumen height than those from hens, and albumen height decreased with the age of the hen and with storage time. Albumen ph was not different between strains and increased with storage time but not with age of the hen. These data confirm that there is no inherent relationship between egg weight and albumen height. Albumen height has often been converted into Haugh units. The Haugh unit formula implies a positive regression of 0.05 mm of albumen height per gram of egg weight (Eisen et al., 1962). However, among all eggs from each strain, and among eggs separated according to age, the regressions of albumen height on egg weight were negative rather than positive. The regressions of albumen height on egg weight were positive only when eggs were separated by the age of the hen; these were all well in excess of the regression of 0.05 mm/g egg. If the principal differences between egg weight and the height of the inner thick albumen are due to age of the hen, the regression implied by the Haugh unit is not only wrong, but in the wrong direction as well. If the principal differences are due to storage, the regression of the Haugh unit is not large enough. It is clear from these data that no fixed regression of albumen height on egg weight, such as that implied by the Haugh unit, will be correct. Albumen height ph Albumen height ph Dependent variable n b R 2 b R 2 n b R 2 b R 2 All 2,985 0.027** 0.01 0.006* 0 2,778 0.008 0 0.013** 0.01 25 wk 774 0.081** 0.02 0.011 0 713 0.091** 0.03 0.005 0 31 wk 754 0.075** 0.02 0.010 0 743 0.059** 0.02 0.007 0 45 wk 801 0.102** 0.06 0.030** 0.04 688 0.081** 0.06 0.025** 0.03 59 wk 656 0.060** 0.02 0.011 0 634 0.069** 0.04 0.013* 0.01 Fresh 639 0.054** 0.07 0 0 520 0.053** 0.05 0.002 0 1 d 546 0.058** 0.07 0.004* 0.01 644 0.050** 0.04 0.004* 0.01 3 d 535 0.026** 0.02 0.008** 0.08 590 0.023** 0.01 0.007** 0.07 5 d 688 0.047** 0.06 0.001 0 451 0.033** 0.03 0.002* 0.01 10 d 577 0.048** 0.09 0.011** 0.16 573 0.027** 0.03 0.006** 0.07 *P < 0.05. **P < 0.01.

1244 SILVERSIDES AND SCOTT TABLE 5. Regression coefficients (b) of egg measures on age of hen (wk) and storage period (d) 1 Age Storage Age Storage Dependent variable b R 2 b R 2 b R 2 b R 2 Egg weight 0.27** 0.41 0.11** 0.01 0.22** 0.26 0.17** 0.01 Shell % 0.04** 0.35 0.02** 0.01 0.02** 0.08 0.04** 0.04 Yolk % 0.13** 0.47 0.17** 0.06 0.09** 0.25 0.15** 0.05 Albumen % 0.09** 0.28 0.19** 0.08 0.07** 0.14 0.19** 0.08 Albumen ph 0 0 0.16** 0.61 0 0 0.15** 0.58 Albumen height 0.04** 0.07 0.46** 0.63 0.05** 0.10 0.39** 0.53 1 Regression coefficients and coefficients of determination are based on 2,931 observations for the line and 2,712 observations for the line. *P < 0.05. **P < 0.01. At this point, we may ask why we measure albumen height in determining egg quality, the presumption being that quality relates to the functionality of the albumen. Li-Chan and Nakai (1989) and Robinson (1987) have provided comprehensive reviews of the chemistry of albumen quality. Ovalbumin, ovotransferrin, ovomucoid, ovomucin, lysozyme, and globulins make up approximately 90% of the albumen protein, with the ovomucin being most important in determining the height of the inner thick albumen (Toussant and Latshaw, 1999). Isolated ovomucin is extremely viscous, and it has excellent foaming properties when combined with other proteins (Johnson and Zabik, 1981). However, only 1.5 to 3.5% of the total protein in albumen is ovomucin, and other proteins such as globulin and ovotransferrin have foaming properties that are almost as good as those of ovomucin yet make up much larger proportions of the albumen (Li-Chan and Nakai, 1989). It is not clear from the scientific literature that moderate differences in albumen height are associated with altered functional characteristics of the egg. Whereas the functional importance of albumen height is unclear, it can give a measure of the freshness of the egg because the height of the inner thick albumen decreases in a logarithmic fashion with storage time. When Heiman and Carver (1936) proposed the albumen index and Haugh (1937) proposed the Haugh unit, storage and transportation were poorly developed and freshness of an egg was of primary interest. Measures of albumen quality based on the height of the albumen were simple and the equipment needed to measure it was portable. These data show that quality measurements based on albumen height of fresh eggs are biased by the strain and age of the hen. The albumen ph was not affected by the age or strain of hen and can be used to measure freshness of an egg without this bias. The concern of Hunton (1987) that measurement of ph is time consuming has been minimized by modern ph meters. 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