Evidence Concerning Genetic Improvement in Commercial Stocks of Layers1

Evidence Concerning Genetic Improvement in Commercial Stocks of Layers ! G. E. DlCKERSON U.S. Meat Animal Research Center, Agricultural Research Service, U.S. Department of Agriculture, 225 Baker Hall, Lincoln, Nebraska 68583, AND MATHER

(Received for publication March 9, 1976)

ABSTRACT Genetic interpretation of time trends in Random Sample Test results was studied by comparing laying performance of six major commercial stocks (A) with that of the Cornell Randombred Leghorn controls (B) under low floor (F) and high cage (C3 and C5) densities of housing: 1860 vs. 1390 cm.2 during floor rearing to 20 weeks and 2230 on floor vs. 622 and 372 cm2 in cages to 72 weeks of age. Each commercial stock and each of two replicates of controls had 180 pullets per brooding density and six floor laying pens of 20 birds each plus five blocks of 9 and five of 15 birds each in 41 x 46 cm. cages. Other management was identical for all birds. Ratio of cage to floor means (C/F x 100) for A vs. B stocks was 98 vs. 91 for egg mass/hen housed, 88 vs. 90 for feed/hen-day, 108 vs. 100 for egg/feed weight, 95 vs. 88 for eggs/live hen-day, 97 vs. 89 for eggs/hen housed, 101 vs. 102 for weight/egg laid, 104 at 20 weeks and 103 vs. 107 at 71 weeks for body weight and 97.5 for albumen height; sexual maturity and adult mortality were unaffected but 0_to_20 week % mortality was 5.1/2.0 vs. 6.6/3.7. Ratio of commercial to control stocks (A/B x 100) under F, C3 and C5 environments was 116, 125 and 124 for egg mass/hen; 102, 102 and 97 for feed intake; 118, 128 and 129 for egg/feed weight, comparison with RST trends suggests genetic changes from 1958 to 1970 in commercial stocks under F and C environments of about 8 and 14% in both egg number and egg mass/hen housed, none in feed intake, 9 and 16% gain in both eggs/live hen-day and feed conversion, 3 and 8% lighter final body weight, 8% earlier 1st egg, 4% greater albumen height but little change in mortality, egg size or shell strength. POULTRY SCIENCE 55: 2327-2342,

INTRODUCTION

D

U R I N G the last two d e c a d e s , selective breeding for more efficient egg p r o d u c tion in chickens has been accompanied by large changes in flock m a n a g e m e n t from low-density floor litter to single-bird-wire cages and then to increasingly c r o w d e d h o u s ing in multiple-bird-wire floored cages (Dicke r s o n , 1965). According t o analysis of the Combined Summaries of R a n d o m Sample Egg Production Tests ( R . S . T . 1958-1973), the unselected Cornell R a n d o m b r e d Control strain (King et al., 1959) declined about 12% in egg mass per hen housed and 8% in egg mass per unit of feed c o n s u m p t i o n b e t w e e n

1. Published as Paper Number 5068, Journal Series, Nebraska Agricultural Experiment Station.

1976

1959 and 1966, w h e r e a s the Commercial strain-cross stocks of layers at least maintained their absolute levels of p e r f o r m a n c e (Dickerson, 1968). T h e d o w n w a r d trend in control strain performance w a s interpreted by D i c k e r s o n (1968) to m e a n that average test conditions had w o r s e n e d as R . S . T . managements shifted from low-density floor housing toward highdensity cage housing in efforts to simulate commercial e n v i r o n m e n t s . By maintaining performance during an adverse environmental trend, the Commercial stocks actually must have b e e n improving, except t o t h e extent that the unselected pure strain control may have been more sensitive t h a n the commercial crosses to the worsening test envir o n m e n t s . Clayton (1968), on the other h a n d , has interpreted the same trends in R . S . T .

2327

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F. B.

Department of Poultry and Wildlife Sciences, University of Nebraska, Lincoln, Nebraska 68583

2328

G. E. DICKERSON AND F. B. MATHER

Experimental duplication of average environmental changes in R.S.T. conditions between 1958 and 1968 is difficult, but review of management reports from the tests indicated that a shift from floor-litter pens to wire-floored cages and a marked increase in bird numbers per unit area were the major identifiable changes in management. The experiment reported here was undertaken to compare representative major commercial strain cross stocks of layers (A) with Cornell Randombred Controls (B) in both low-density, floor-litter housing (F) and high-density wire cage housing (C). Information from such an experiment was expected to help determine what proportion of the increasing R.S.T. superiority of Commercial stocks over the

Cornell control was caused by (1) genetic improvement in commercial stocks expressed under an uncrowded floor-litter environment (A-B under F vs. that in 1958 R.S.T.) and by (2) less adverse effects of cage crowding on Commercial than on Control stocks (C-F for A vs. C-F for B), which could be either preexisting or the result of selection in A.

MATERIALS AND METHODS The stocks used were Babcock B-300, Cornell Randombred, DeKalb 161, Heisdorf and Nelson "Nick-chick," Hy-Line 934-E, Kimber K-137 and Shaver Starcross 288. Age of hatchery breeding flocks supplying eggs was 41 weeks for the Controls and ranged from 32 to 44 weeks for the other stocks. The chicks were hatched on January 7, 1970 from 1,080 eggs of each Commercial stock and from 1,800 eggs of the Controls. Egg weight averaged 54.5 grams for Controls and ranged from 55.8 to 59.9 grams for the Commercial stocks. Percent hatch of fertile eggs was 87.9 for the Controls and ranged from 85.8 to 97.5 for the Commercial stocks. Number of pullet chicks wingbanded was

TABLE 1.—Rearing and laying environment (E) for each of six Commercial laying stocks (A) and of two samples of Cornell Randombred Control strain (B)

Rearing to 20 weeks Density

E

Density

F, Floor pens 2.0 ft. ) (2.4 ft.2, >/bird 2230 cm. 2 / 2 1860 c m . ) bird) C3, 3 /cage, bot1.5 ft.2 J tom rows > /bird (.67 ft.2, 1390 cm. 2 j 622 cm. 2 /bird) C5, 5/cage, top 2 1.5 ft. ) rows (.4 > /bird ft.2, 372 2 1390 cm. J cm. 2 /bird) 2

Laying (20 to 72 weeks) Pens or Number of birds per cages/ stockStockblock block Stock Blocks Total 20 120 960 1

15

45

360

75

600

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performance to mean that the unselected Cornell Randombred stock may have gradually deteriorated genetically (e.g., from natural selection, epistatic recombination loss or inbreeding depression) and that the commercial stocks have shown little or no genetic improvement. Clayton's interpretation questions the usefulness of the Randombred Control stock as an indicator of environmental change over time.

2329

GENETIC IMPROVEMENT IN LAYERS

was the only condition that differed between the two groups. Examination of R.S.T. ration composition indicated no changes between 1958 and 1968 expected to influence layer performance appreciably. Therefore, the same chick starter ration was fed from hatching to 8 weeks of age, the same grower ration was fed from 8 to 20 weeks of age and the same laying ration was fed from 20 to 72 weeks of age (Table 2). Birds received light continuously until 4

TABLE 2.—Composition (%) of chick starter, grower and laying rations used for all stocks and housing treatment Ingredients Ground yellow corn Ground milo Wheat standard middlings Soybean meal (50% C.P.) Meat and bone scraps (50% C.P.) Fish meal (60% C.P.) Dehydrated alfalfa meal (17% C.P.) Dried whey Ground limestone Dicalcium phosphate Salt (Na CI) Trace mineral mix Animal fat Hygromix Vitamin premix DL Methionine, MHA or Hydan Coccidiostat (Amprol+) • Calculated Composition: Crude protein Metabolizable energy, kcal. /kg. Methionine Methionine + cystine Calcium Phosphorus, total Phosphorus, available

Starter 0 to 8 weeks 58.3

— — 24.2 2.5 2.5 5.0 2.5 0.5 1.0 0.4 0.05 a 2.0 0.25 1.0

—

Grower 8 to 20 weeks 48.1

Laying 20 to 72 weeks 67.8

—

— —

35.0 3.5 4.0

— 5.0 2.5 0.2 0.5 0.4 0.05"

— 0.25 0.8C

—

0.05

0.05

21.4 2972 0.52 0.83 1.11 0.75 0.51

15.2 2892 0.37 0.61 0.82 0.75 0.45

15.5 5.0

— 2.5

— 5.0 1.25 0.40 0.05" 2.0

—

0.50 d 0.05

— 16.6 2973 0.34 0.57 2.95 0.77 0.56

a gm. each of manganese and of iron, 9 gm. of copper, 31 gm. l kg. of mineral mix provides of iodine and 111 gm. of zinc. b 1 kg. of mineral mix provides 66 gm. of manganese and 88 gm. of zinc. c 1 kg. of vitamin premix provided 330,690 U.S.P. units stabilized vitamin A, I ,183 I.C. units vitamin D 3 , 1,102 I.U. vitamin E, 8,818 mg. niacin, 661 mg. calcium pantothenate, 331 mg. riboflavin, .88 mg. vitamin B, 2 , 33,069 mg. choline chloride, 1.1 gm. antibiotic and 100 gm. DL Methionine, Hydan or M.H.A. d l kg. of vitamin premix provided 1,102,000 U.S.P. units stabilized vitamin A, 198,413 I.C. units vitamin D 3 and 882 mg. riboflavin.

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360 per Commercial stock and 720 for the Control stock. A random one-half of the chicks from each stock were intermingled and brooded on wood shaving litter in each of two floor pens in a windowless house from hatch until 20 weeks of age. To simulate the change in conditions between the 1958 (F) and 1968 (C) Random Sample Tests, the F and C groups were brooded at 1860 cm. 2 and 1390 cm2 (2.0 ft.2 and 1.5 ft.2) per bird, respectively (Table 1). Floor space per bird

2330

G. E. DICKERSON AND F. B. MATHER

TABLE 3.—Form of analysis for data recorded in thirteen 28-day periods Source D/F Error" Genetic stocks Commercial vs. control (S,) 1 S, x R Control, repl. 1 -repl. 2(S 2 ) 1 S2 x R Among 6 commercial stocks (S3) 5 S3 x R Environments Floor vs. cage (E,) C3 vs. C5 (E 2 ) Periods (P) S, x E, S, x E 2 S2 x E, S 3 x E, S, x P S2 x P SjXP E, x P E2 x P S, x E, x P S, x E2 x P S 2 x E, x P P O 7 " 1 S3xE,x P S3 x E2 x P a

1 1 12 1 1 1 1 5 5 12 12 60 12 12 12 12 12 12 60 60

E, x R E2 x R P x S, S, x E, x R S, x E 2 x R S2 x E, x R S2 x E2 x R S, x E, x R S3 x E2 x R S, x P x R S2 x P x R S3 x P x R E, x P x R E 2 x P x Sj S, x E, x P S, x E 2 x P S 2 x E, x P S2 x E2 x P S3 x E, x P S3 x E2 x P

D/F

13 13 65

X X X X X X

R R R R R R

9 4 156 9 4 9 4 45 20 156 156 780 108 108 108 48 108 48 540 240

R refers to replicate blocks within housing

(120 in F) plus five sets of three 3-bird cages and five of three 5-bird cages (45 in C3 and 75 in C5); the Control stock had double these numbers. The six Commercial and two Control samples were distributed randomly within each of the six blocks of floor (F) pens and the five blocks of C3 and C5 cages (Table 1). The birds were in the laying facilities from 20 to 72 weeks of age. During this time, daily egg production and mortality were recorded. Egg weight was determined each 28-day period by individually weighing all eggs laid on 2 consecutive days. Egg specific gravity and albumen height were determined at 28, 40, 52 and 64 weeks of age for all eggs laid on 2 consecutive days. Feed consumption was measured for each 28-day period by floor pens and by sets of three cages. All pullets were weighed at 20 and 71 weeks of age. A balanced factorial analysis of variance was used to estimate effects and to obtain tests of statistical significance (Table 3). The three treatments (E), seven genetic stocks (S) and 13 periods (P) were considered as fixed variables; the six blocks of F and five blocks of C3 and of C5 treatments were random replicates (R). Periods were omitted for traits measured only once per bird; only four periods were involved for the two egg quality traits. RESULTS AND DISCUSSION Housing Density. Growing mortality (Table 4) was about twice as great (P < .001) at the high as at the low housing density (5.9 vs. 2.9%) for both A and B stocks, especially during early brooding (0 to 8 weeks). Neither age at 50% production nor laying house viability were significantly affected by the housing environments. (Table 5). Number of eggs per hen housed in 3-bird and 5-bird cages averaged 11% below that in floor pens for Control (P < .01) but only 5% lower in 5-bird cages for Commercial layers (P < .05). Weight

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days of age, 20 hours per day until 7 days of age, 14 hours until 20 weeks of age and 15 hours until the end of the study. The birds were moved from the brooder house to the laying house at 20 weeks of age on May 27. To continue 1958 Random Sample Test environment during the laying period, 20 birds were placed in each of 48 floor-litter (F) pens on wood shavings at a density of 2,230 cm. 2 (2.4 sq. ft.) per bird. Simulation of 1968 conditions was continued by housing either three or five birds per cage (C3 or C5) at densities of 622 or 372 cm. 2 (.67 and .40 ft.2) per bird, respectively. The six Commercial stocks each had six floor pens of 20 birds

2331

GENETIC IMPROVEMENT IN LAYERS

TABLE 4.—Growing mortality of Commercial (A) and Control (B) stocks in two rearing densities % Mortality by period--weeks 8-20 1-20 ic

Stocks

No. 2 brooded

Low (F) (1860 cm.2) (2.0 ft.2)

A B

1080 352

1.1 0.6

0.5 0.9

0.4 2.3

0.8 3.1

2.0 3.7

High (C) (1390 cm. 2 ) (1.5 ft.2)

A B

1080 353

3.2 2.6

1.2 1.4

0.7 2.6

1.9 4.1

5.1 6.6

2 1** 2.0*

0.7 0.5

0.3 0.3

1.1* 1.0*

3 ]#** 2 9***

Density

A B

0-20

*P < .05. **P < .01. ***P< .001. per egg laid was 1.7% (P < .01) smaller in 5-bird than in 3-bird cages but was almost identical in floor pens and 5-bird cages. Total egg weight per hen housed increased in 3-bird and declined only 6% in 5-bird cages for Commercial birds but averaged 9% lower in cages and 6% lower in 5-bird than in 3-bird cages for Control birds (P < .01). Albumen height was reduced about 2.5% (P < .05) in both 3-bird and 5-bird cages below levels for floor birds. Specific gravity was consistently (P < .01) but very slightly (0.3%) lower in 5-bird than in 3-bird cages. Means for performance traits that influence efficiency of feed conversion in egg production during the thirteen 28-day periods from 20 to 72 weeks of age are shown in Table 6, with corresponding relative performance levels and statistical significance for contrasts in housing density (E, and E 2 ) and genetic stocks (S,) and their interactions. Body weight at 20 weeks was 4% heavier (P < .001) for pullets of both stocks when reared with less floor space per bird and placed in 3-bird or 5-bird cages. Birds in cages were heavier (P < .01) at 71 weeks of age than those in floor pens by 3% for A but by 7% for B stocks and body weights were lighter for 5-bird than for 3-bird cages, especially in A birds (P < .001). Relative egg numbers/hen-day was depressed much more in

Control than in commercial pullets (P < .01) by cage housing (-12 vs. -5%) but only the Commercial birds were lower (-5%) in 5-bird than in 3-bird cages (P < .01). Weight/egg increased more in cages compared with floor pens for control than for commercial birds (P < .05) but was smaller in 5-bird than in 3-bird cages (P < .01). Total egg mass per hen-day again was depressed (P < .001) more in Control (-10%) than in Commercial (-4%) birds (P < .05) by cage housing and only in 5-bird cages for Commercial birds. Depression of feed consumption per hen-day in cages below that in floor pens was similar for Control and Commercial birds (9.5 and 11.5%) but was lower in 5-bird than in 3-bird cages only for Commercial birds (P < .05). The larger increase in egg/feed conversion of caged over floor birds for the Commercial than for the Control birds (+8.3 vs. - 0 . 3 % , P < .001) is the direct consequence of the larger average effect of cage crowding on egg mass per hen-day for Control than for Commercial birds ( - 1 0 vs. —4%) and the slight difference in feed consumed (—9.5 vs. -11.5%). The housing treatments definitely influenced pattern of laying performance. Caged birds began laying earlier but laid at a lower rate beginning in the 3rd period (Fig. 1, P < .001). However, feed conversion

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(C-F)

0-1

Significant (P < * P < .05. **P < .01. * * * P < .001.

a

F C3 C5

%(C - F ) / F = E, %(C5 -- C3) / C 3 = E2

C5

C3

F

Environment (E)

= s,

%(A - B ) / B

Stock (5) A B A B A B A B A B (-9.0)*** (-7.3)*** (-9.2)***

Age 50% production (days) 160 176 159 171 159 175 (-0.8) (-1.7) (0.2) (2.3) (-2.6) (-4.8) (-0.5)

(-1.7) (-1.5) (-2.3) (-6.4)

Hen 89 92 89 93 87 87

(-2.9) (-4.1) (-0.4)

(1.5) (0.9) (0.0) (-3.7)

Hen-day 92 94 93 97 93 93

% Viability Eggs/hen housed 239 218 238 199 226 192 (-2.9) a (-10.6)** (-5.0)* (-3.7)* (9.6)*a (19.8)*** (18.2)*** (-2 (5 (4 (5

(-

(0 (2

5 5 6 5 5

lai

Wt

TABLE 5.—Mean and relative (%) laying performance of Commercial (A) and Control (B) stocks in flo weeks of age

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x x x x x

P P P E, x P E2 x P

= s,

(-0.5) (-0.1) (-0.4) (-0.6) (-1.0)

(3.8)*** (4.3)***

A B

A B %(A - B) / B

20 weeks 1497 1502 1557 1567 1549 1565 (3.0)** (7.4)*** (_5 9)*** (-2.6)** (—5.4)*** (—7 7)*** (-10.9)***

71 weeks 1977 2090 2098 2274 1974 2216

Body weight (g.)

Stock (S) A B A B A B

#*# *** — — —

(-4.6)** (0.0) (12.9)**= (24.5)*** (18.7)***

(-5.1)**= t—\ \ 9)***

Eggs/henday (%) a 72.1 63.9 70.1 56.3 66.8 56.3

"Equal weighting of each 4-week period. "Adjusted to 150--500 day of age record to compare with R.S.T. trends in Fig. 8. = Significant (P < .05) S, x E , or E 2 interactions. * P < .05. * * P < .01. * * * P < .001.

S, E, E2 S, S,

c3 c5

% ( C - F)/F = E, %(C5 - C3) /C3 = E2 F

C5

C3

F

Environment (E)

*** ** — —

(1.4)= (2.9)** (-1.2)** (—2.4)*** (6.4)***= (4.2)*** (5.4)***

Wt./egg (g.) a 59.4 55.8 60.6 58.2 59.9 56.8

(1 (3 (2

((-

(-4 (-1

wt da

TABLE 6.—Mean and relative (%) laying efficiency of Commercial (A) and Control (B) stocks in flo 28-day periods (P)

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2334

G. E. DICKERSON AND F. B. MATHER

«

2

3

4

5

6

7

8

9

10

II

12

13

4-WEEK PERIODS, 20 TO 72 WEEKS OF AGE

3 4 5 6 7 8 9 10 II 4-WEEK PERIODS. 20 TO 72 WEEKS OF AGE

12

13

FIG. 2. Feed conversion in floor pens (A) and 3-bird {%) and 5-bird (O) cages, by 28-day periods.

FIG. 1. Hen-day rate of egg production and egg weight in floor pens (A) and in 3-bird (0) and 5-bird cages (O) by 28-day periods. (eggs/feed, Fig. 2) was better (P < .001) in cages during the first 6 periods and equal to that for floor pens thereafter because of the much lower feed consumption in cages, expecially in 5-bird cages. Albumen height was higher at 28 and 40 weeks but lower at 52 and 64 weeks for floor pens than for cages (Fig. 3, P < .001). Specific gravity was highest for 3-bird and lowest for 5-bird cages and intermediate for floor pens at 40 and 52 weeks of age, but not at 28 or 64 weeks (P < .001).

FIG. 3. Effects of housing density on albumen height (solid lines) and specific gravity (broken lines) at four ages.

Commercial vs. Control Performance. The small apparent mean advantage of the six Commercial (A) stocks over Control (B) in growing mortality (Table 4) and disadvantage in laying house mortality (Table 5) were too inconsistent for significance (P > .05).

However, the Commercial stocks began laying 2 weeks earlier (Table 5, Fig. 4), produced many more eggs per hen housed in floor pens (+10%) and especiall y in cages (+19%), larger eggs (+6 and +4.6%), and greater egg mass

40 AGE, WEEKS

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2

FEED I7HEN-DAY

2335

GENETIC IMPROVEMENT IN LAYERS

10

AGE AT 5 0 % PRODUCTION

m7?.

15

20

25

30

FLOOR, 2 2 3 0 cm? ( 2 . 4 F T , 2 ) 3/CAGE, 6 2 2 cm. 2 (.67 F T 2 ) 5/CAGE, 3 7 2 c m 2 ( . 4 F T . 2 )

VIABILITY/ HEN-HOUSED

15

20

25

30

FLOOR, 2 2 3 0 c m ? ( 2 . 4 F T 2 ) ,

BODY WT 20WKS.

3/CAGE, 622 6 2 2 cm c m 22(.67FT. ( . 6 7 F T .22 ) 3/CAGE,

V777,

BODY WT 71 WKS.

L B M J

5/CAGE, 3 7 2 c m 2 ( . 4 F T 2 )

VIABILITY/ HEN-DAY X EGGS/ HEN-OAY

EGGS/HENHOUSED

m.

S////////SYA

11 1

Ll'.'.'li . ".!

m

E6GWT./ EGG MASS/ HEN-HOUSED

//S////////////////1

HEN-DAY

mm m

JJJl?ts/ssf/f^

J

FEED/ HEN-DAY

ALBUMEN HEIGHT

WT EGGS/WT FEED/ HEN-DAY

SPECIFIC GRAVITY -10

-5

0

5

10

15

20

25

% DEVIATION, COMMERCIAL FROM CONTROL

30 (A-Bl/B

FIG. 4. Relative laying performance of Commercial (A) to Control (B) stocks under three housing environments. per hen housed ( + 16 and +25%); albumen height was 6% greater but specific gravity was not superior for Commercial birds. Mean body size at housing was nearly the same for Commercial and Control pullets (Table 5, Fig. 5), but Commercial birds weighed 5% less on floor and 8 to 11% less in cages at 71 weeks of age, produced more eggs per hen day (+13 and +22%), larger eggs (+6 and +5%), and greater egg weight per hen day (+20 and +27%) on a daily feed intake only 2% higher in floor pens and 3-bird cages and 3% lower in 5-bird cages. Consequently, the egg/feed conversion of Commercials exceeded that of Control pullets by 18% in floor pens but by 28%+ in the cages ( P < .001). Superiority of Commercial over Control birds increased after the first 4 or 5 months of lay in rate of egg production and hence in egg mass and in feed conversion (P < .001, Fig. 6), partly because the egg size advantage did not change and body size advantage increased during the laying year.

-10

-5

))j»))))))))y)))))))j* 0

5

10

15

20

25

% DEVIATION, COMMERCIAL FROM CONTROL

30 (A-8)/8

FIG. 5. Relative efficiency of Commercial (A) to Control (B) stocks under three housing environments. Estimates of Genetic Improvement from Random Sample Tests. An analysis of time trends in Random Sample Test results (Dickerson, 1968) indicated a substantial increase from 1958 to 1966 in the contemporary relative superiority of Commercial strain-crosses produced by six major breeders over the Cornell Randombred Control birds. Part of this apparent genetic improvement in the Commercial layers could have arisen from a greater adverse effect of known increasing housing density in R.S.T. on performance of the unselected Controls than on that of the Commercial stocks. Results from the present experiment can be used to help interpret these R.S.T. time trends. In Fig. 7, the R.S.T. time trends (Dickerson, 1968) in egg mass per hen housed are shown for the means of six major Commercial stocks of layers (A) and for the contemporary samples of the Controls (B). Superimposed on this graph are the results from the present experiment (Table 5) for the 1970 samples of Commercial strain-cross layers from the

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^^?\

WT./EGG LAID

2336

2 3 4 5 6 7 8 9 0 II 12 4-WEEK PERIODS, 2 0 TO 72 WEEKS OF AGE

13

FIG. 6. Feed conversion and egg weight per hen day for six Commercial (A) and Cornell Randombred Control (B) stocks by 28-day periods.

1970 FLOOR (5-61-7 RST SUMMARY IA"-B) 1958 RST SUMMARY[A-B)<: 1970 FLOOR (B) OR RST SUMMARY IB] V '4 0

a_EiAji 1970 CAGE ( A } j

1970 FLOOR I A K

13.5 6 COMMERCIAL STOCKS ( A ) ^ RST SUMMARY

150 ? 5 1970 FLOOR I B ] '

CORNELL COMTROLIBI^ RST SUMMARY 1970 CAGE I BlTi 60

61 61-62 YEARS

62-63

63-64

64-65

^110 65-66

FIG. 7. Comparison of R.S.T. time trends with 1970 experimental performance of Commercial (A) and Cornell Randombred Control (B) stocks under spacious floor pen (F) and crowded cage (C) housing, for egg mass per hen housed.

same six breeders and of the same Cornell Randombred Control stock under F and C environments. Note that the 1970 floor-litter performance for Controls (B) fits very closely that for the 1958 to 1959 R.S.T. data. Also, the loss in R.S.T. performance of Controls from 1958 to 1966 was little more than the large effect of cage crowding vs. floor housing on the 1970 sample of Control birds, AE(B). However, reduction in egg mass per hen housed from cage crowding was slight for the Commercial stocks (AE(A) = - . 3 kg.) and the superiority of Commercial over Control stocks (A — B) in floor pens was twice as great in 1970 as in 1958 (2 vs. 1 kg.). These results suggest strongly that the decline in R.S.T. egg mass per Control hen housed from 1958 to 1966 was environmental rather than genetic and that the Commercial stocks have improved about 1 kg., or 80grams (0.6%) per year, in egg mass per hen housed under spacious floor-litter conditions over the 12 years from 1958 to 1970. Because of the much greater tolerance or adaptability of the Commercial crosses to crowded cage management in the 1970 experiment ( A E ( A ) « A E ( B ) ) , the total change in their superiority over the Control birds, from floor-litter housing in 1958 to crowded cages in 1970, would approximate 1,750 g. per hen housed or 146 g. (about 1.0%) per year. How much of the 1970 difference in tolerance to cage crowding was characteristic of the Commercial and Control stocks in 1958 and how much was achieved by breeder selection between 1958 and 1970 cannot be judged from these results. However, the similarity of 1958 R.S.T. to 1970 F, and that of the R.S.T. decline from 1958to 1966 to AE(B) in 1970, for the Control stock (Fig. 7) do not suggest genetic deterioration in the unselected Control stock. Similar comparison of R.S.T. and present experimental results for feed/egg mass (Fig. 8, Table 6) indicates that 1970 cage crowding hardly changed the feed conversion of Controls (AE - B) but did sharply improve

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I

G . E . DlCKERSON AND F . B . M A T H E R

GENETIC IMPROVEMENT IN LAYERS g/«9 -100

I970FL00R (B) or RST SUMMARY (BK 1958 RST SUMMARY [A-BX

-200 I95~8 FLOORlS-SPr . -300 ~~\. AG{A)FL00R< RST SUMMARY (A-§!>^ -400 -500

-100 -200 -300 -400 -500

1970 FLOOR (A-•B)V

AGIAICAGEC

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2337

Commercial over Control stocks (A - B) in 1958 R.S.T. "floor" pens (R.S.T.; Dickerson, 1968) and of subsequent genetic changes in (A - B) to 1970 for Commercial stocks from the same six major breeders under uncrowded floor litter (F) and crowded cage (C) environments are as follows for components of layer performance: (A - B) Genetic in 1958 change in (A - B) R.S.T. 1958 R.S.T. to 1970

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'61 '61-62 62-63 63-64 '64-65 '65-66 YEARS

FIG. 8. Comparison of R.S.T. time trends with 1970 experimental performance of Commercial (A) and Cornell Randombred Control (B) stocks under spacious floor pen (F) and crowded cage (C) housing, for feed weight/egg weight per hen-day. feed/eggs for the Commercial birds (AE — A from 2.71 to 2.50, P < .001). This large gain in feed/eggs from cage housing of Commercial birds consisted of a larger reduction in feed intake than in egg output (-11.5 vs. -4.1%), but cage housing affected feed and egg output about equally for Controls ( - 9 . 5 vs. -10.1%). The superiority of Commercials over Controls in g. feed/kg. eggs in floor-litter pens (A - B in F) more than doubled from 1958 R.S.T. to the 1970 experiment (from -190 to -468), a gain of -278 g. in 12 years, or about 0.8% per year. Including the better adaptability of the Commercial birds to crowded cages, total change in superiority over Controls from 1958 in R.S.T. to 1970 in cages (A — B in C) would be about -690 + 190 = -500 g. in 12 years, or about 1.4%per year. The superiority of Commercial over Control birds in lower total costs/kg. of eggs would be even greater because of rearing and fixed nonfeed costs per bird. Estimates of genetic superiority of six

"Floor" Mortality, 1-72 wks. +3 +4 (%) Body wt., 71 wks. -163 -46 -67 (g.) Age @ 50% produc-13 -15 tion (days) Eggs/hen housed 14 29 7 (no.) 0.8 2.6 0.0 Wt./egg laid (g.) Egg mass/hen 992 1788 978 housed (g.) 2.1 6.1 10.1 Eggs/hen-day (%) Feed /period hen0 -2 2 day (g.) -278 -500 Feed (g.) /eggs (kg.) --190 4.1% 4.6% 1.6% Albumen height -.4% -.4% .4% Specific gravity The estimate of (A - B) for 1958 R.S.T. (and for later years also) is based on "regressed" means for B and A stocks and thus will differ slightly from the observed mean difference. However, the bias in 1958 was so negligible that adjustment for it was ignored (e.g., 0.6 eggs/hen housed, +0.1 days of age at 50% production). Genetic change in superiority of Commercial over Control birds from 1958 R.S.T. to 1970 was about 2 weeks earlier age at 50% production under F or C, 14 eggs under F and 29 eggs under C per pullet, .8 g. per egg under F and none under C. Eggs/hen-day (%) increased by 6% under F and 10% under C, but total mortality worsened 3 or 4%. Body weight at 71 weeks declined 67 g. (3%) under F and 163 g. (8%) under C but feed consumption did not change. Albumen height increased 4 to 5% under both F and C, but specific gravity remained unchanged.

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2338

G. E. DICKERSON AND F. B. MATHER

under simulated 1958 low density (F) housing. Important additional gains were expressed under the crowded cage environment (C). The latter may represent either response to selection for adaptation to cage crowding or a general attribute of strain crosses which could have been expressed in 1958 as well. Only the former could be considered as genetic improvement beyond that expressed under uncrowded floor litter (F) management.

Genetic deterioration in Control performance from inbreeding, loss of epistatic superiority or natural selection is not expected to be important because of the large effective population size (N e = 246, Gowe et al., 1959; inbreeding only about 0.2 x 15 = 3% from 1955 to 1970), the 3 years of inter se mating before use in R.S.T. and the precautions followed to avoid natural selection (King et al., 1959 and 1963). King et al. (1963), Kinney et al. (1968) and Garwood et al. (1974) have provided evidence that performance of the Cornell Randombred Control has remained ramarkably constant when maintained under an environment intended to be static. Of course, control of poultry environment can seldom approach completeness; hence, the need for "genetically constant" control populations as indicators of environmental changes. Important genetic gains have occurred in Commercial stocks when measured

There were large and real (P < .001) differences among the six Commercial stocks in each of the traits which influenced efficiency of converting feed into eggs (Tables 7 and 8), but there were only minor and entirely nonsignificant stock differences or interactions between stocks and housing densities for net feed conversion per live hen-day. Stocks ranking higher in egg weight/hen-day also required enough more feed per day to keep eggs/feed nearly the same among the six stocks.

Differences Among Commercial Stocks. In the preceding part of this report, only the combined mean of the six Commercial stocks (A) was compared with the unselected Control (B) stock. However, the question of continuing genetic improvement in efficiency of egg production also involves differences among the widely distributed Commercial stocks developed by breeders. Differences in body and egg size, rates of lay and sexual maturity are known to exist, but how do these relate to net efficiency of converting feed into eggs?

Age at 50% production, (F + C3 + C5) / 3 in tables, ranged from 148 to 169 days, again with some real stock differences in adaptation to more crowded rearing and adult cage housing (P < .001 for S 3 x E , ) . Mean eggs/hen-day ranged from 67 to 73% (P < .001), but all stocks were similarly reduced under cage housing (P > .05 for S 3 x E , ) . Stocks ranged from 212 to 254 eggs per bird

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The effects of cage crowding on the Randombred Control in this 1970 experiment (Tables 5 and 6) provide a reasonable explanation for the decline of Controls from 1958 to 1966 in R.S.T. for egg mass produced per live hen-day and per hen housed but not for the corresponding increase in feed /eggs (kg.) per live hen-day. Evidently, 1970 cage crowding reduced feed intake of Controls much more than in R.S.T. time trends. The small 1970 cage effects on feed/egg conversion, mortality and sexual maturity of Controls (AE • B) do not explain the larger R.S.T. declines in these traits (Dickerson, 1968; Clayton, 1968). The mild upward R.S.T. time trend in 71-week body weight of Controls agrees but the stability in R.S.T. egg weight trends disagrees somewhat with expected effects of more cage crowding on Control birds (Table 6). These discrepancies between the actual R.S.T. time trends and the 1970 cage effects for Control birds (AE • B) suggest that R.S.T. environmental changes in health, lighting programs or other factors also were involved.

2339

GENETIC IMPROVEMENT IN LAYERS

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2341

GENETIC IMPROVEMENT IN LAYERS

six Commercial stocks had achieved very similar levels of efficiency in live hen-day conversion of feed into eggs in spite of large differences in body size, feed intake, rate of lay, egg size and sexual maturity. This situation may have arisen largely from differences between breeders in relative emphasis on component traits, but it also may be the result of alternative biological pathways towards increased efficiency in metabolic processes. The shape of a water-filled bag can be changed readily at the same volume! ACKNOWLEDGMENTS This experiment was funded by the Department of Poultry and Wildlife Sciences, Nebraska Agricultural Experiment Station. Computing assistance by Dr. R. F. Mumm, Statistical Laboratory, and data preparation by Ms. Minnie Royal are gratefully acknowledged. The authors also thank Dr. T. B. Kinney, formerly Leader, North Central Poultry Breeding Project; Kimber Farms, Inc.; Hyline International; DeKalb Agricultural Research Inc.; H and N, Inc.; Babcock Industries, Inc.; and Shaver Poultry Breeding Farms, Ltd. for providing hatching eggs of the Cornell Randombred and of the six Commercial stocks of layers. REFERENCES Clayton, G. A., 1968. Some implications of selection results in poultry. World's Poultry Sci. J. 24: 37-57. Dickerson, G. E., 1965. Random sample performance testing of poultry in U.S.A. World's Poultry Sci. J. 21: 345-357. Dickerson, G. E., 1968. Lessons to be learned from poultry breeding. Proc. Symposium Animal Breeding in the Age of AI, Univ. Wisconsin and American Breeders Service, Madison, Wisconsin, p. 69-99. Garwood, V. A., R. N. Shoffner, P. C. Lowe and R. S. Grant, 1974. A comparison of three control populations. Poultry Sci. 53: 2009-2015. Gowe, R. S., A. Robertson and B. D. H. Latter, 1959. Environment and poultry breeding problems. Poultry Sci. 38:462-471. King, S. C., J. R. Carson and D. P. Doolittle, 1959.

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housed (P < .001), with some real differences in adaptability to cage crowding (P < .05). Mean egg size varied from 57 to 62 grams (P < .001), but egg size increased similarly under cage housing for all stocks. Total egg mass ranged from 12.0 to 15.2 kg. per hen housed and from 39 to 44 g. per live hen-day among the six stocks (P < .001), but effects of housing density did not differ significantly among stocks. Stock means varied (P < .001) in body weight from 1465 to 1582 g. at housing and from 1935 to 2140 g. at 71 weeks and differed in daily feed consumed from 105 to 114 g. There were no significant stock differences in the effect of housing environment on either body weight or feed consumption. There were highly significant differences in sexual maturity and persistency among the six Commercial stocks (P < .001 for S 3 x P for eggs/hen-day, egg weight, egg weight/hen-day and eggs/feed per hen-day in Table 8 and Fig. 6). Stock x period interaction was also real (P < .001 for S x P) but slight in feed consumed. These stock x period interactions even differed between 3-bird and 5-bird cages for eggs/feed and eggs/hen-day (P < .05) and for egg weight (P < .001), and between floor pens and cages for rate of lay (P < .001) and egg weight/henday (P < .05). When the large real stock differences in all of the facets of performance are considered, it was surprising to find no real stock differences in egg mass/feed per hen-day. The large stock differences in adult mortality (7 to 21%, P < .001) and in effects of cage crowding on mortality (P < .05) do add importantly to stock differences in rearing costs per kilogram of eggs per hen. Inclusion of fixed costs per bird would increase net efficiency advantage for stocks producing greater egg income per bird. Price differentials for egg size, shell traits and albumen score also influence income per bird from different Commercial stocks. However, the

2342

G. E. DICKERSON AND F. B. MATHER

The Connecticut and Cornel] randombred populations of chickens. World's Poultry Sci. J. 15: 139159. King, S. C , L. D. Van Vleck and D. P. Doolittle, 1963. Genetic stability of Cornell randombred control population of White Leghorns. Genetic Res. 4: 290-304. Kinney, T. B., Jr., P. C. Lowe, B. B. Bohren and

S. P. Wilson, 1968. Genetic and phenotypic variation in Randombred White Leghorn controls over several generations. Poultry Sci. 47: 113-123. R.S.T. Reports of Random Sample Egg Production Tests. United States and Canada. 1958 to 1973. ARS 44-79 (0 to 12) and ARS-NE-21 (0 to 12). Animal Improvement Programs Lab., Agricultural Research Service, U.S. Department of Agriculture.

PARK W. WALDROUP, K E N N Y R. H A Z E N , WILLIAM D . BUSSELL AND ZELPHA B . JOHNSON

Department of Animal Sciences, University of Arkansas, Fayetteville, Arkansas 72701 (Received for publication March 12, 1976)

ABSTRACT Feeding trials were conducted with broiler breeder hens to determine optimum daily intake of protein for maximum performance. Pullets were grown to 24 weeks of age on limited feed intake to maintain the body weights within the limits suggested by the breeder. A controlled-feeding system was used during the laying period with step-wise increase in calorie intakes. In the first study corn-soybean type diets were used to supply 14 to 22 grams of protein/day in 2 gram increments. In the second study daily protein intakes of 14.5 to 24 grams were compared. In addition, diets supplying 14.5 and 16 grams of protein daily were also fed with an additional 200 mg/day of lysine and methionine. The results of these studies suggest that the protein requirement of broiler breeder hens fed corn-soybean meal diets without supplemental amino acids is 20-22 grams per day. POULTRY SCIENCE 55: 2342-2347, 1976

N

UTRITIONAL studies with broiler breeder hens have usually been concerned with ways to retard sexual maturity or limit weight gains by restricting intake of calories or of one or more of the essential amino acids. Little information is available on the needs for specific nutrients during the laying period. Waldroup and Hazen (1976) have reported on trials in which the daily energy allotment of the broiler breeder hen was determined. In regard to the needs for protein and for specific amino acids, a paucity of reports exists. Waldroup et al. (1966) could show no difference in performance of broiler breeder hens that were ad libitum-fed diets

1. Published with the approval of the Director of the Arkansas Agricultural Experiment Station.

containing 13 and 17% protein except for a reduction in weight gains of the group fed 13% protein. Summers etal. (1967) fed broiler breeder hens diets containing 12 to 18% protein, apparently on an ad libitum basis. Although rate of egg production and efficiency of feed utilization were slightly lower for the hens fed 12% protein as compared to the higher levels, none of the differences were statistically significant. Most broiler breeder companies give recommended levels of nutrients to use in formulating feeds for their birds. For the most part, these are based primarily upon modifications of diets that have been shown to be adequate for Leghorn-type hens. Since the meat-type broiler breeder consumes about 1.5-2 times the amount of feed than does the egg-type hen, there is no reason to conclude that the same nutrient limits should

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Studies on the Daily Protein and Amino Acid Needs of Broiler Breeder Hens 1