Effects of Early Maturation of Brown Egg-Type Pullets, Flock Uniformity, Layer Protein Level, and Cage Design on Egg Production, Egg Size, and Egg Quality

ENVIRONMENT AND HEALTH Effects of Early Maturation of Brown Egg-Type Pullets, Flock Uniformity, Layer Protein Level, and Cage Design on Egg Production, Egg Size, and Egg Quality L. J. KLING, R. O. HAWES, R. W. GERRY, and W. A. HALTEMAN1 Department of Animal and Veterinary Sciences and Department of Mathematics, University of Maine at Orono, Orono, Maine 04469 (Received for publication July 15, 1984)

1985 Poultry Science 64:1050-1059 INTRODUCTION

Traditional rearing programs for egg-type females involve reducing growth rate and delaying sexual maturity so that pullets are at an "optimal" chronological age and weight at time of first egg (North, 1978a). It would appear detrimental economically to delay pullet maturity. Strong (1978) estimated an additional cost of $.0125 per Single Comb White Leghorn (SCWL) pullet for each day's delay after 19 weeks of age. Because brown egg-type pullets are heavier and consume more feed, the additional cost would be even greater. Early housing of brown egg-type pullets could be of benefit to the brown egg industry through reduced replacement pullet cost and increased production efficiency. A reduction in days to sexual maturity of SCWL pullets was achieved by Harrison et al.

1

Department of Mathematics.

(1969) with increased photoperiod. Pullets exposed to 14 hr of light and 10 hr of dark (14L/10D) at 14 weeks of age averaged 163 days to first egg compared with 178 days when exposed at 20 weeks of age. Although the early-housed birds matured at an earlier age, they took considerably longer to respond to the increased photoperiod, 65 vs. 38 days. The lag in response time to the increased photoperiod suggested that factors in addition to increased photoperiod were necessary to induce sexual maturity. Reduced egg size is the single greatest economic drawback to the early induction of sexual maturity. Harrison et al. (1969) reported a consistent positive association between age at stimulation and early egg weight. Early-stimulated pullets persisted in smaller egg size throughout the entire egg production cycle. A similar effect of early sexual maturity on egg weight was observed by Bell et al. (1982). Average egg weight from 20 to 68 weeks of age was 57.7, 58.8, and 59.4 g for pullets stimu-

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ABSTRACT Eight-week-old Harco Sex-Link pullets were assigned to four growing regimens. Feed was restricted to Group 1. The birds reached an average weight of 1.52 kg at 20 weeks of age and were then light stimulated. Group 2 received the same ration ad lib and reached an average weight of 1.64 kg at 16 weeks. At this age they were light stimulated. Birds in Groups 3 and 4 were separated into two weight classes at 8 weeks of age. Those below the median weight received an 18% protein grower ration and those above the median weight a 16% ration. Group 3 birds were grown similarly to Group 1; Group 4 birds were grown similarly to Group 2. At housing, each group was equally divided and given either a 17 or 19% protein layer ration. Two cage designs (standard and reverse) were used and each treatment combination was equally represented. Ad lib-fed, early-housed pullets reached 1.64 kg at 16 weeks of age, but they did not come into production until 19.4 weeks of age. Hen-day percent production (HDP) was significantly less than for the late-housed pullets. Feed per dozen eggs was not affected by the early housing, but earlyhoused pullets laid significantly smaller eggs and feed per gram egg was significantly increased. Hens in reverse cages on a 19% protein layer ration laid the largest eggs in weight and size. Although early housing had a detrimental effect on average egg weight, it appeared possible to manipulate egg weight and size distribution through a combination of cage design and layer protein. Birds grouped by body weight at 8 weeks had higher uniformity, but this trait was not correlated with egg numbers or size. Moreover, housing body weights were not significantly correlated with egg size, suggesting factors other than body weight were responsible for the smaller eggs from early-housed pullets. (Key words: early maturation, uniformity, layer protein, cage type)

EARLY MATURATION BROWN EGG TYPE PULLETS

2 Harco Sex—Link, Feeding and Management. Arbor Acres Farm, Inc. Technical Service Department, Glastonbury, CT 06033.

weight in brown-egg females that the breeders recommend as optimal. The present study was undertaken to evaluate egg production performance in brown egg-type pullets housed prior to 20 weeks of age but at a breeder's recommended 20-week-old body weight. Pullets were grouped during the growing period based on 8-week body weights to examine the relationship between flock uniformity and subsequent egg production.

MATERIALS AND METHODS

Marek's vaccinated, 1-day-old Harco SexLink chicks (n = 1512) were randomly distributed into two floor pens and fed a 22% protein starter ration (Table 1). The birds received 24 hr of light to 3 days of age and subsequently maintained on 8 hr of light until housed. At 8 weeks of age, the birds were transferred to rearing cages in accordance with the experimental treatment outlined. Seven birds were placed in each cage (265.4 cm 2 /bird) with eight cages constituting a replicate. Pullets were vaccinated for avian encephalitis (AE) at 11 weeks and for Newcastle disease (ND)/infectious bursal disease (IB) at 15 days of age and at 6 weeks; an additional IB vaccine was given at 15 weeks. On day of housing they were vaccinated subcutaneously with attenuated ND virus. At 8 weeks, 784 birds were individually weighed, randomly distributed to their respective experimental groups, and fed a 16% protein grower ration (Table 1). Half (392) were given the ration ad lib and housed when their average weight was 1.64 kg, the breeder's recommended housing weight. 2 Feed was restricted for the remaining 392 birds so they would reach an average weight of 1.64 kg at the end of 20 weeks of age. In an attempt to improve flock uniformity, the remaining 784 birds were separated into groups of 56 birds. All birds within a group (56) were weighed individually. Those birds falling below the median weight were grouped together and given an 18% protein grower ration, and those falling above the median weight were grouped together and given a 16% protein grower ration (Table 1). Half received their respective rations ad lib and were housed when their average weight was 1.64 kg. The other half followed a controlled feeding program so that birds would reach an average weight of 1.64 kg at 20 weeks of age. At the

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lated at 18, 20, and 22 weeks of age, respectively. Leeson and Summers (1980) reported a similar trend of increased egg weight with delayed stimulation but found this effect statistically significant only at 26 weeks of age. However, there was a significant difference in the percentages of large and small eggs in favor of the late-housed group. They concluded from these results that average egg weight per se was not a good indicator of egg size distribution. This is an especially important economic consideration because of the large differential in price per dozen between eggs less than medium grade and those greater than medium grade. Leeson and Summers (1980) further reported substantial differences in body weight at time of housing with pullets housed at 15, 18, and 21 weeks of age weighing 1181, 1307, and 1576 g, respectively. Bell et al. (1981) investigated the relative performance of SCWL pullets segregated into two weight classes. Although there were no differences in egg production, light weight pullets produced significantly smaller eggs. Thus, total egg mass significantly favored the pullets that were heavier at stimulation. The data of Summers and Leeson (1983) also suggest that differences in pullet body weight have a substantial effect on egg weight. When pullets were classified at 18 weeks of age into one of four weight groups ranging from a mean low weight of 1108 to 1383 g, their performance records during the first 6 weeks in the laying house (19 to 25 weeks of age) showed the heavier weight pullets producing not only a greater number of eggs but eggs of larger size. Earlier studies dealing with decreased age at sexual maturity (Bray et al, 1965; Harrison et al, 1969; Leeson and Summers, 1980; Bell, 1982 involved housing of underweight pullets. The reduced egg size in early maturing pullets may be associated with the smaller body size of the pullet at stimulation. Attempts have been made to attain a "mature" body weight in SCWL pullets at an age earlier than 20 weeks without much success (Cunningham and Morrison, 1976; Leeson and Summers, 1981). It is less difficult to obtain the "mature" body

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KLING ET AL. TABLE 1. Composition of the starter, grower, and layer rations

Ingredients

Starter

16% Grower

18% Grower

17% Layer

19% Layer

tn> 1 Wf )

64.26 12.70 1.25 15.86

58.95 12.70 1.25 20.63

66.58

58.58

1.25 18.40 2.50

1.25 24.00 2.50

1.90 1.40 1.40

2.50 1.30 1.45

.90 .40

2.75

7.95

8.70

.05

.05

.05

.05

.50 .32 .02 .35

.50 .32

1.00

1.00

.50 .10 .35 .02

.40 .05 .35 .02

(3.4 g) 2,858 17.0 3.24

(3.4 g) 2,860 19.0 3.54

.52 .30

.55 .32

(2'. 5 g) 2,977 16.1 .90 .65 .27

.35

(3.0g) 2,959 18.0 .90 .65 .29

.35

1

Supplies the following in milligrams per kilogram of ration: 4.99 Cu (copper oxide); 49.74 Zn (zinc oxide); 24.97 Fe (ferrous sulfate monohydrate); 74.80 Mn (manganous oxide); 1.25 I (calcium iodate). 'Supplies .1 ppm Se (sodium selenite). 3

Supplies the following per gram of premix: 2209 ICU vitamin D 3 ; 441 IU vitamin A.

"Supplies the following per kilogram of premix: 660 mg riboflavin; 109.8 mg calcium pantothenate; 4.4 g niacin; .416 g menadione sodium bisulfite; 2.64 mg vitamin B 1 2 .

time of housing, the 56 birds in each replicate were rerandomized within their respective groups and divided into two experimental units in the cage house. Each experimental unit in the cage house was factorially assigned to one of two rations; a conventional 17% protein layer mash or a 19% protein layer mash (Table 1). All birds were given 14 hr of light per day at the time of housing, regardless of the age at housing. Because an inadequate number of cages of similar design were available, two cage type designs were employed. A standard cage was 30.5 cm wide and 40.6 cm deep, whereas a reverse cage was 40.6 X 30.5 cm. Each cage held three hens. An experimental unit consisted of eight standard cages (24 hens) or six reverse cages (18 hens). Treatments were balanced between the two cage designs so treatments were equally represented within each cage type. The data were to be pooled if no cage type x

treatment interactions existed. However, an interaction was found; therefore, cage type became a fourth variable. Eggs from each experimental unit were collected daily up to 34 weeks of age, group weighed, and separated according to size. Eggs less than 49 g were categorized as small, 50 to 56 g as medium, and those exceeding 56 g as large and above. From 35 to 72 weeks of age, egg production was recorded daily, but egg sizing was done on only 3 consecutive days every 28 days. Mortality was recorded daily; feed consumption was recorded weekly. Body weights of all birds were recorded at time of housing. Every 28 days of the production period, the weight was recorded on 6 birds per experimental unit. The data were analyzed a s a 2 x 2 x 2 x 2 factorial design: a. age at housing (16 vs. 20 weeks)

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Ground yellow corn 55.51 Wheat middlings 6.50 Alfalfa meal (17%) 1.25 Soybean meal (dehulled) 26.34 Meat and bone meal (47%) 2.50 Fish meal (65%) 2.50 Animal fat 2.59 Dicalcium phosphate .63 .83 Limestone Trace mineral mix 1' Trace mineral mix 21'2 .05 .50 Vitamin premix l 3 .40 Vitamin premix 2" .10 Choline chloride (25%) Iodized salt .35 Methionine Vitamin A concentrate (30,000 IU/g) (2.3 g) 2,996 Kcal/kg 22.0 Crude protein, % .90 Calcium, % .70 Phosphorus, % .37 Methionine, %

EARLY MATURATION BROWN EGG TYPE PULLETS

b. grouping procedure (grouped vs. randomly placed) c. layer protein level (17 vs. 19%) d. cage design (standard vs. reverse)

transformed value = 2 x arc sine \/%7T00 before analysis of variance was performed (Winer, 1971). For ease of interpretation, however, the percentage values are shown in all tables and figures. To test the effect of degree of uniformity at housing on subsequent egg production and egg size, degree of uniformity was correlated with eggs per hen housed and egg size. Uniformity was defined as the percentage of hens in the experimental unit that weighed within 10% of the average body weight for that group (North, 1978a). Average body weights at each 28-day period were correlated with egg production and egg size for that group to determine if there was any relationship between these variables. RESULTS AND DISCUSSION

Body Weight at Housing. The ad lib-fed/ early-housed pullets reached the breeder's recommended housing body weight at 16 weeks of age. The early-housed/randomly-placed pullets weighed 1.64 kg at housing and the early housed/grouped-pullets weighed 1.65 kg (Table 5). The restricted-fed pullets, both grouped and randomly placed, were housed at 20 weeks of age (late housed) and weighed 1.52 kg. This was 7.0% less at housing than the breeder's recommended housing weight due in part to an error in feed allocation during the growing period. Age at First Egg. Although the breeder's recommended weight of 1.64 kg was achieved in the ad lib-fed pullets at 112 days of age, these early-housed pullets averaged 135.5 days of age at first egg. Average age at first egg for the late housed pullets was 152.2 days. Thus, the early-housed birds required 23.5 days of photostimulation to initiate production, whereas the late-housed birds required only 12.2 days. Age at first egg was not affected by the grouping treatment, layer protein level, or cage type.

This lag in response to the photostimulation of the early-housed pullets is congruent with that observed by Harrison et al. (1969), suggesting that factors in addition to "optimal" weight and increased photoperiod are involved in the attainment of sexual maturation. Egg Production and Mortality. For the first 4-week period (17 to 20 weeks), the earlyhoused pullets averaged only 1.6% hen-day production (HDP). Egg production increased rapidly thereafter but did not peak as high as with the late-housed pullets (Fig. 1). The early-housed pullets laid at a higher rate than the late-housed pullets during the second 4week period (21 to 24 weeks), as the latehoused pullets were just coming into production. There was no significant difference in egg production during Period 3 (25 to 28 weeks) between early- and late-housed pullets, but the late-housed pullets had significantly higher egg production in every period thereafter except the last period (69 to 72 weeks). Overall, from housing to 72 weeks, the late-housed pullets had significantly higher percent HDP than the early-housed pullets (Table 2). However, the early-housed pullets were significantly delayed in their response to the increased photoperiod and because hendays began to accumulate at time of housing (16 or 20 weeks), percent HDP, is biased against the early-housed birds. Hen-day production is not an adequate measure of egg production when comparing two groups with different numbers of accumulated hen-days. Moreover, the overall rate of production is not as important as the total number of eggs produced.

16

20

24

28

32

36

40

44

48

S2

56

60

64

68

72

WEEKS OF ACE

FIG. 1. Percent hen-day production of earlyhoused ( ) and late-housed ( ) pullets.

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An analysis of variance was performed on 28-day period data (with Period 1 being 17 to 20 weeks) and on cumulative data (housing to 72 weeks). Because percentage values are not always normally distributed, all percentage values were transformed according to the equation:

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KLING ET AL. TABLE 2. The effect of grouping, layer protein level, and cage design in early-housed and late-housed pullets on eggs per hen housed, mortality, and hen-day percent production

Grouped

Protein level

Cage type 1

Early-housed HHP

Mortality

Late-housed HDP

HHP

Mortality

_/rt/ \. .

<"')

(no.)

HDP

(vo)—

17 17 19 19

Std Rev Std Rev

224.5 232.5 231.0 228.1

21.9 14.8 18.8 16.7

63.3 64.3 64.4 63.1

231.6 230.7 236.3 235.4

10.4 18.5 14.6 9.2

66.6 69.9 70.4 69.7

No No No No

17 17 19 19

Std Rev Std Rev

228.3 241.6 243.0 211.1

11.4 14.8 7.3 18.5

62.8 66.4 64.7 61.9

228.4 245.4 236.5 261.6

11.1 5.6 18.0 7.4

68.4 70.6 70.4 72.9

HHP

Mortality

HDP

ANOVA2 Age at housing Grouping Cage type Protein level Housing X group X cage Housing X protein '.X cage

.048 .162 .411 .538 .042 .054

.075 .054 .280 .896 .030 .058

<.001 .352 .252 .444 NS NS

1

Std = Standard; Rev = reverse; HHP = hen-housed production; HDP = hen-day production. The probability of the F ratio is shown for all single sources of variation but only for significant treatment interactions. ANOVA = Analysis of variance. 2

Cumulative eggs per hen housed (HHP), percentage mortality, and HDP are depicted in Table 2. The effects of the delayed response of the early-housed pullets to increase photoperiod on HDP is clearly evident as is the effect of mortality on HHP. The high mortality in particular groups dramatically affected egg production. The single greatest cause of death was fatty liver hemorrhagic syndrome, which accounted for 21% of all mortality; early-housed birds experienced greater mortality than late-housed birds. The second major cause was prolapse of the uterus, accounting for approximately 15% of all mortality; there was no difference in frequency between early-housed and latehoused birds. Approximately 5% died from Marek's disease or lymphoid leucosis and 9% from peritonitis. The remaining birds died of miscellaneous causes. The additional eggs produced by the earlyhoused pullets in the first two periods were not enough to counteract the lower rate of production in the latter part of the production cycle (29 to 68 weeks of age). This is contrary to what was observed by Leeson and Summers (1980) who reported a significantly greater

number of eggs from housing to 23 weeks of age in early-housed pullets and no significant effect on egg production after 24 weeks of age. Moreover, Bell et al. (1982), evaluating the effects of varying the age of sexual stimulation on the laying performance of two strains of White Leghorn pullets, found overall HHP to be significantly greater in 18-week-old housed pullets than in 20-week-old housed pullets. In the present experiment, the lower egg production of the early-housed birds from 29 to 68 weeks of age was not anticipated. Presumably, the increased photoperiod at a time when the pullets were not physiologically receptive may have had detrimental effects on the subsequent production. Moreover, feeding a layer mash with 3.5% calcium 4 weeks prior to sexual maturation may also have had deleterious effects. It is noteworthy that although the early-housed birds produced at a significantly lower rate from 25 to 68 weeks of age, the rate of decline in production throughout the production cycle was not greatly different from the later-housed birds (Figure 1). Peak production, however, was greatly reduced. Overall, layer protein level, cage design, and the grouping of the pullets during the growing period had no

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Yes Yes Yes Yes

EARLY MATURATION BROWN EGG TYPE PULLETS

There was a significant layer protein level x cage type interaction effect on feed per dozen in the cumulative data. Generally, hens housed in reverse cages and given 17% protein layer rations and those housed in standard cages given 19% protein layer rations were more efficient than their counterparts given 19 and 17% protein layer rations, respectively. Different results are obtained when expressing feed efficiency as feed consumed (8 to 72 weeks) per gram of egg produced. Feed per gram was significantly less in the late-housed pullets than in the early-housed pullets. Although the early-housed pullets produced egg numbers as efficiently as late-housed pullets, they were less efficient for production of egg mass. This is a direct result of the effect of age at housing on average egg weight. Egg Size. Late-housed pullets produced larger eggs (62.7 g) than the early-housed pullets (61.6 g) (Table 3). Although the difference of 1.1 g is statistically significant, both values fall within the commercial grade "large". There was no significant effect of grouping during the growing period or layer protein level on average egg weight. Although there was a trend toward increased weight of eggs from

TABLE 3. The effect of grouping, layer protein level, and cage design in early-housed and late-housed pullets on feed efficiency and average egg weight Late-housed

Early-housed

Grouped

Protein level

Cage type 1

Yes Yes Yes Yes

17 17 19 19

Std Rev Std Rev

2.63 2.46 2.51 2.49

(g/g) 3.58 3.33 3.43 3.32

(g) 61.2 61.5 60.9 62.4

2.56 2.51 2.44 2.49

(g/g) 3.40 3.32 3.26 3.28

62.7 62.8 62.3 63.1

No No No No

17 17 19 19

Ste Rev Std Rev

2.58 2.50 2.47 2.63

3.48 3.41 3.35 3.50

61.9 61.0 61.3 62.7

2.58 2.40 2.45 2.40

3.43 3.20 3.25 3.19

62.5 62.5 62.9 62.7

ANOVA2

Feed/doz

Feed/g

Egg weight

Age at housing Grouping Protein level Cage type Protein X cage

.099 .804 .224 .208 .026

Feed (kg/doz)

1 2

.006 .732 .131 .084 .097

Egg weight

Feed (kg/doz)

Egg weight (g)

.001 .727 .192 .057 .017

Std = Standard; Rev = reverse.

The probability of the F ratio is shown for all single sources of variation but only for significant treatment interactions. ANOVA = Analysis of variance.

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significant effect on HDP. The significant interaction of housing, cage type, protein level, and the grouping procedure on percent mortality caused a corresponding effect on HHP (Table 2). Average housing weight (16 weeks) in the early-housed pullets was negatively correlated with cumulative HHP, i.e., the groups with the largest body weight laid significantly fewer total eggs. This correlation was not observed in the late-housed (20-week-old) pullets. The early-housed hens remained larger than the late-housed hens throughout the production cycle. Average housing weight was not significantly correlated with cumulative percent mortality. Feed Efficiency. Efficiency of production, as expressed by feed consumed per dozen eggs produced (feed/dozen), is presented in Table 3. Because the birds were housed at different ages, the feed consumed from 8 weeks of age to housing is included in the cumulative feed/ dozen eggs. There was no significant effect of age at housing on the overall feed per dozen eggs, indicating that the early-housed birds are as efficient in production as late-housed pullets when efficiency is expressed as feed per dozen.

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KLING ET AL.

and above. The egg grade categories are obviously not independent of one another, i.e., a decrease in the percentage of small eggs must result in a larger percentage of medium and large eggs. The corresponding increase, however, is not always statistically significant. Age at housing had a significant effect on all of the egg size categories; early-housed birds had larger percentages of small and medium eggs and a lower percentage of large eggs. As with average egg weight, the effect of housing on egg size distribution was most evident in the first third of the production cycle. The early-housed pullets produced a significantly smaller percentage of small eggs in Period 2. However, because the early-housed pullets were at a much higher rate of production than those late housed, they laid a greater number of small eggs. The two groups laid a similar number of small eggs in Period 3. After Period 3, there was a dramatic decline in the percentage of small eggs and after Period 4 the percentage of small eggs was of minor concern. The effect of protein on percentage of small eggs by treatment is shown in Table 4. Overall, the feeding of the 19% layer ration resulted in a significantly lower percentage of small eggs

TABLE 4. The effect of grouping, layer protein level, and cage design in early-housed and late-housed pullets on egg size distribution Early-housed

Grouped

Protein level

Cage type 1

Small

Yes Yes Yes Yes

17 17 19 19

Std Rev Std Rev

No No No No

17 17 19 19

2

Late-housed

Medium

Large

6.9 7.0 7.3 4.7

18.5 19.9 20.2 15.3

Std Rev Std Rev

6.1 6.6 5.7 5.3

18.3 21.6 17.6 15.9

Small

Medium

Large

Small

Medium

Large

74.6 73.1 72.5 80.0

2.9 3.4 3.6 3.0

11.9 14.7 16.6 14.5

85.1 81.9 79.8 82.5

75.6 71.9 76.7 78.8

3.9 4.0 2.8 3.1

15.7 16.4 12.7 14.1

80.4 79.6 84.5 82.7

("V

ANOVA3 Age at housing Grouping Protein level Cage type Protein X cage

<.001 .733 .050 .423 NS

<.001 .952 .213 .945 .050

<.001 .939 .131 .876 .052

1

Std = Standard; Rev = reverse.

2

Eggs less than 49 g, small; 50 to 56 g, medium;greater than 57 g, large.

3

The probability of the F ratio is shown for all single sources of variation but only for significant treatment interactions. ANOVA = Analysis of variance.

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hens housed in reverse cages, (P = .057), there was also a significant protein level X cage interaction (Table 3). Hens housed in reverse cages and given the 19% protein layer mash produced eggs of higher average weight than birds on the 17% diet, whereas hens housed in standard cages showed little or no effect of the added protein on average egg weight. This effect was most evident in the early-housed pullets. Although early-housing had a detrimental effect on average egg weight, it appears possible to manipulate egg weight through cage type and protein level of the laying ration. Early-housed pullets (grouped and random) in reverse cages given a 19% protein layer ration laid eggs of similar average weight to those of the late-housed pullets (Table 3). Average egg weight can be a deceiving measure of egg size, especially in the early stages of production when the production of double- and triple-yolked eggs skew the average weight upward. Distribution of eggs according to grade weight categories is a better estimate of egg size for the producer because of the large differential in price per dozen between eggs of medium grade or less and those that grade large

EARLY MATURATION BROWN EGG TYPE PULLETS

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TABLE 5. The effect of grouping, layer protein, and cage type design in early-boused and late-housed pullets on interior egg quality and shell thickness Late-housed

Early-•housed Grouped

Protein level

Cage type 1

Haugh units

Yes Yes Yes Yes

17 17 19 19

Std Rev Std Rev

83.2 81.7 83.6 85.1

.355 .361 .357 .355

84.8 84.5 85.0 85.3

.359 .361 .362 .360

No No No No

17 17 19 19

Std Rev Std Rev

83.5 82.9 82.8 84.4

.357 .357 .353 .359

84.2 82.8 84.4 84.2

.358 .362 .362 .361

ANOVA 2

Haugh units

Shell thickness

Age at housing Grouping Protein level Cage type Protein X cage

.012 .204 .023 .860 .023

Shell thickness

Haugh units

(mm)

1 2

Shell thickness (mm)

.003 .983 .848 .194 NS

Std = Standard; Rev = reverse.

The probability of the F ratio is shown for all single sources of variation but only for significant treatment interactions. ANOVA = Analysis of variance.

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single most important factor controlling egg weight for young pullets. In the present investigation, there was a negative correlation of body weight at housing with cumulative average egg weight. This was due primarily to the fact that the early-housed pullets weighed 7% more at housing than the late-housed pullets. When the data were analyzed separately for the earlyand late-housed pullets, there was no significant correlation of average group body weight at housing and subsequent percentage of large eggs or of average egg weight. There was, however, a significant correlation between the Period 2 average group body weight and Period 2 average group egg weight in the early-housed pullets that was not observed for the late-housed pullets. This correlation was not observed in either early- or late-housed pullets in any period thereafter. It appears that body weight within a group of birds treated similarly can be an important criteria of egg size, but merely increasing the body weight of early housed pullets did not ensure larger egg size. A "uniform" flock, defined as one in which 70% of the pullets are within 10% of the average weight of the flock, is considered a highly desirable goal (Bell, 1978; North, 1978a;

(4.4%) compared with the feeding of the 17% layer ration (5.0%). This effect was most evident in the first four periods. Very few small eggs were laid during the remainder of the production cycle so the statistics are not reliable. The decreasing effect of feeding the 19% layer ration on the percent of small eggs resulted in a corresponding increase in the percent of large eggs, but this effect was not statistically significant. A protein level X cage type interaction persisted throughout the production cycle relative to the percentage medium and large eggs. Hens housed in reverse cages and given the 19% protein ration and those in standard type cage given the 17% protein ration laid smaller percentages of medium eggs and larger percentages of large eggs than their counterparts given 17 and 19% protein rations, respectively. The effect was most pronounced in the earlyhoused pullets (Table 4). Initial egg size appears to be related to the chronological age of the hen and not to the prior number of eggs laid. The cause of small egg size in early-housed pullets is a topic that warrants further investigation. Summers and Leeson (1983) suggest that body weight is the

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KLING ET AL.

TABLE 6. Effects of grouping at 8 weeks in earlyhoused and late-housed pullets on the percentage uniformity and weight at time of housing Early-housed

Late-housed

Uniformity

Weight Uniformity

(%)

(kg)

(%)

(kg)

1.65 1.64

82.7 78.7

1.52 1.52

Grouped 86.0 Random 77.8

Weight

Cunningham, 1980). According to North (1978b, 1980), highly uniform flocks will reach peak egg production earlier and will peak higher than a nonuniform flock. Grouping the pullets according to their 8-week-old body weight improved uniformity of both the earlyand late-housed pullets (Table 5). Uniformity, however, was not found to be significantly correlated with HHP, average egg weight, or percentage large eggs. There is no indication from this experiment that improvement of uniformity improves production performance. Pettite et al (1981, 1982) also concluded that a deliberate increase in flock uniformity of broiler breeders did not result in improved egg numbers. Interior Egg Quality and Eggshell Thickness. Interior egg quality and shell quality were determined every 4 weeks. Early-housed birds had significantly decreased Haugh units (Table 6). However, the decline did not result in a lowering of the grade of these eggs. The AA grade quality eggs requires a Haugh unit measurement greater than 72 (North 1978a) and at no time did Haugh unit measurements fall below this value. There was, as expected, a substantial decline in interior egg quality with increased age of the hen. At 30 weeks the overall average of Haugh units was 90.3. By 72 weeks, the overall average fell to 77.8, but at no time did the average Haugh units of the earlyhoused pullets differ from the late-housed pullets by more than 3%. Haugh units were significantly affected by percentage protein in the layer ration, and there was a significant protein level X cage type interaction. Increased protein significantly improved the interior quality of eggs from hens housed in reverse cages. This effect was not observed from hens housed in standard cages.

ACKNOWLEDGMENTS

This research was supported by State and Hatch funds allocated to the Maine Agricultural Experiment Station of the University of Maine at Orono and in part by grants from Agway Inc., Syracuse, NY, and Arbor Acres Farm, Inc., Glastonbury, CT. Vaccines for this research were kindly donated by the Maine Biological Laboratories, Waterville, ME. The authors are indebted to H. Michael Opitz for outlining the health program for this study; to Lorraine Whitmore King for assistance in data analysis; to Ruth LeClair and Rebecca

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1 Uniformity was calculated as the percentage of birds falling within 10% of the mean body weight.

Eggshell quality was also adversely affected by early housing. The investigators observed a marked difference in the number of uncollectible eggs in the early phase of the experiment for the early-housed pullets. The effect of housing on shell thickness was most noticeable in the early part of the production cycle. At 42 weeks there was no significant effect; however, egg quality of the early-housed pullets declined more rapidly than that of the late-housed pullets, and at 62 weeks there was again a significant depression. The reason for the decreased shell quality early in lay may be related to the increased photoperiod when the pullets were not physiologically capable of responding. Present day pullets are maturing at a younger age and it behooves the producer to keep pace with these genetic advancements. There are consistent economic pressures to house pullets as quickly as possible but without any detrimental effects. As observed in the past (Harrison et al, 1969), egg size appears to be the single greatest drawback to early housing. In this investigation, it was shown that although body weight is positively associated with early egg size in early-housed pullets, the manipulation of body weight does not quarantee larger egg size. A combination of cage design and additional protein had the greatest effect on increasing egg size in early-housed pullets. The additional cost associated with increased percent protein and with the reverse cage systems, however, needs to be weighed against reduced pullet replacement cost and increased egg numbers, assuming that early housing can result in increased egg production as observed by previous investigators (Leeson and Summers, 1980; Belief al. (1982).

EARLY MATURATION BROWN EGG TYPE PULLETS

Carr for assistance in data collection; and to Nona Treworgy for her secretarial assistance. REFERENCES

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