Increase of egg weight with age in normal and dwarf, purebred and crossbred laying hens

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Increase of egg weight with age in normal and dwarf,

purebred and crossbred laying hens

F Minvielle, P Mérat, Jl Monvoisin, G Coquerelle, A Bordas

To cite this version:

Original

article

Increase of

_egg

_weight

with

_age

in normal and

_{dwarf, purebred}

and

crossbred

_laying

hens

F

_Minvielle,

P

Mérat JL Monvoisin G

_Coquerelle,

A Bordas

Institut National de la Recherche

_{Agronornique,}

Laboratoire de

_Génétique

Factorielle

78!352

Jouy-en-Josas cedex,

France

(Received

2 November 1993;

accepted

2 June

₁₉₉₄₎

Summary - An

exponential

curve, W = P -

Q

_exp

(-Rt)

was fitted _{to egg}

weights

(W)

of individual hens from 8

_genetic

_groups tested for egg

production

from 18-51 weeks of age

(t).

The groups were constituted of the combination of genotype at the sex-linked dwarfism locus

_(normal

or

_dwarf)

and line

_(White

_Leghorn,

Brown

_Egg

and both

reciprocal

crosses).

The

_{least-squares}

mean of the residual standard deviation about the curve was between

1.27 and 1.74 g in the 8 groups and estimated values of the initial

P-Q

and mature egg P

weights

were between 26.9 and 33.9 g and 56.9 and _{65.8 g,}

_{respectively.}

Effects of _genotype and line as well as heterosis were estimated for both _egg

_weights

and for rate of

_growth

relative to the

_{remaining expected growth}

_(R).

R was smaller for dwarf hens which thus

reached mature egg

weight

later than normal females.

Significant

heterosis was found for

both egg

weights

of dwarf hens

(12.6

and

9.5%)

and for the initial egg

weight

of normal

ones

_(12.8%).

_Negative

heterosis for R obtained for dwarf hens

_(-17.4%)

_corresponded

to

a flatter _egg

weight

curve of these crossbreds.

egg weight

/

age of hen

/

heterosis

_/

dwarfism

_/

exponential curve

Résumé - _{Évolution comparée} du poids de l’oeuf avec _l’âge de la poule chez des femelles normales ou naines et pures ou croisées. On a

_ajusté

individuellement une

courbe de la

_forme

W = P -

Q

_exp

(-Rt)

au

_poids

de

_l’ceuf

(W)

mesuré entre 18 et 51 sem

d’âge

(t)

chez des

_poules

de

_{8 groupes génétiques définis}

_par la corn.binaison du

génotype

au locus de nanisme lié au sexe

_(normal

ou

nain)

et de la

lignée

(souche

Leghorn

blanche,

souche à

_ceuf

brun et leurs croisements

_{réciproques).}

L’écart type résiduel

_après

ajustement

de la courbe

_{exponentielle}

aux valeurs de

_poids,

évalué _pour

_chaque

_{groupe par}

la méthode des moindres

_carrés,

a

_pris

des valeurs

_comprises

entre

_1,27

et

_1,74

g. De la

même

manière,

les estimations des

poids

du

premier

œuf (P - Q)

étaient situées entre 26,9 9

et

_3.i,9

g, et celles de

l’ceuf

à maturité entre 56,9 et 65,8 g d’autre part. On a évalué les

effets

du

_génotype

et de la

_lignée

et l’hétérosis pour les

poids

de

_l’ceuf

et l’accroissement de

poids journalier

relativement au

poids

restant à gagner

(R).

La valeur de R était

inférieure

que les

femelles

normales. Un hétérosis

_significatif

a été obtenu pour les 2

poids d’ceuf

chez

les

poules

naines

_(12,6

et

_9,5%)

et pour le

_poids

du premier

ceuf

chez les

_femelles

normales

(12,8%).

L’hétérosis

_négatif

trouvé pour R chez les

poules

naines

_(-17,4%)

_correspond

au

fait

que la courbe du

poids

de

_l’ceuf

étaient

_{plus aplatie}

chez les croisés de ce

_génotype.

poids de l’aeuf

_/

_âge de la _poule

_/

hétérosis _/ nanisme

_/

courbe _{exponentielle}

INTRODUCTION

Egg

weight

increases

_{curvilinearly}

_{with age of hen}

_(Cowen

et

_al,

_1964).

_Although

it

_might

be

_advantageous

to have

_egg-laying

hens

_{producing quickly}

and

_regularly

eggs within a limited

_weight

_range

_(Poggenpoel

and

Duckitt,

1988),

few works have

analyzed

the

_relationship

between _egg

_weight

and _age, or evaluated its

_variability.

A non-linear

_equation

with 3

_parameters

_(mature

_egg

_weight,

_egg

_weight

_range and

rate _{of increase of egg}

_weight)

was

_proposed

_{by Weatherup}

and Foster

(1980).

_They

compared

parameters

of the curves fitted for _pure and crossbred hens but

_they

did

not evaluate the effect of heterosis on the

_shape

of the curve. The same

_type

of curve was used

_by

Foster et al

₍₁₉₈₇₎

to

_{help produce}

a

_weekly

forecast of the number

of class A

_{(British grading)}

_{eggs in} several commercial flocks.

_Recently,

Shalev and Pasternak

₍₁₉₉₃₎

applied

the method of

Weatherup

and Foster to _egg

_weight

and

grading

for several avian

_species.

An

_analogous

but

_exponential

curve was

developed

by

Yoo et al

₍₁₉₈₃₎

who estimated the

_heritability

of the 3

_parameters

of the curves

obtained for hens from 2 selected lines.

The sex-linked dwarfism gene dw is associated with several unfavourable effects

on _egg

_traits,

and

_particularly

on _egg

_weight

(Merat, 1990).

In a recent

_work,

the influence of heterosis on the reduction of

production

associated with dw was

explored

and some

_advantage

was found for crossbred dwarf hens

_(Merat

et

_al,

1994).

However,

the _egg

_weight

at the _age of 43--45 weeks was still about _{4 g}

lighter

in dwarf than in normal crossbred hens. In the

_present

_study,

the egg

weight

increase of normal and dwarf hens of 2

_parental

_pure lines

_(White

_Leghorn

and Brown

_Egg)

with age and their

reciprocal

crosses were

compared

and the effects

of dw and heterosis on the

_shape

of the

_exponential

curve of _egg

_weight

with time

were estimated in order to

_explore

the

_dynamics

_{of egg}

_weight

in relation to dw and

crossbreeding.

MATERIALS AND METHODS

Birds

Genetic

_types

and

_genotypes

have been described

_{previously by}

M6rat et al

_(1994).

Briefly,

pure and

crossbred,

normal and dwarf

progenies

were obtained in a

single

hatch from a White

Leghorn

line and a Brown

Egg

line

(11

DW dw males _per

line mated to 3 or 4 females

each)

maintained in our

laboratory.

Hens were

protein,

2 600

_kcal/kg

_{metabolizable energy,}

3.4%

_calcium)

was

_provided

ad libitum.

Performances

reported

elsewhere

_(Merat

et

_al,

₁₉₉₄₎

can be summarized as follows.

Both normal and dwarf Brown

_{Egg purebred}

females were heavier at 17 weeks

(by

513 and 366 g,

respectively)

and at 52 weeks

_(by

743 and 495 _g,

_{respectively)}

than their White

_Leghorn

_{counterparts.}

_They

also started

_laying

earlier

_(14.8

and 17.7 d

earlier,

respectively),

and laid more _eggs

(22.6

and 23.9 more _up to 51 weeks of _age,

respectively),

which were heavier

(by

3.8 and 5.1 _g,

respectively).

Finally,

crossbreds

had intermediate

_{body weights}

but

_performed

at the same level as the _pure Brown

Egg

line for _egg

_production

traits. Data and statistical

_analysis

A total of 430 birds were tested for _egg

_production

from 18 to 51 weeks of age.

Weekly,

and then _every other

_week,

3 consecutive _eggs were collected from each

bird.

_Double-yolk,

soft-shelled or broken _eggs were

discarded,

the total

weight

of

2 normal eggs was recorded and the

_{corresponding}

mean

_weight

was calculated. A

maximum number of 29

_weights

could be obtained for each hen.

_Fifty-three

hens

were excluded because

_they

died or

_{stopped laying early.}

An

_exponential

curve, W = P -

Q

exp

(-Rt),

was fitted to the series _{of egg}

weights

of each

_{remaining hen, using}

the Nlin

_procedure

_(SAS

Institute,

1988).

Under this model described

_{by Brody}

₍₁₉₆₄₎

and

_applied

to _egg

_{weight by}

Yoo et al

_(1983),

egg

weight

(W)

increases with age

(t)

and R is the rate of

_growth

relative to the

_growth

_yet

to be made: R =

(dW/dt)/(P - W).

The

_parameter

Q

is the range of

weights

from initial egg

weight

to mature _egg

_weight

and P -

_Q

is the _egg

_weight

for t =

_0,

ie at the _age of 18 weeks in this

_experiment.

Residual standard deviation about the curve was also calculated as a measure of the

goodness

of fit of the curves to the data. The _{iterative process} failed to _converge for 22 hens

(11

normal and 11

_dwarf).

_{Correspondingly,}

reasonable estimations of

_{P, Q}

and R could not be obtained for them.

Inspection

of the actual egg

weight

curves of

these hens revealed that

_they

did not reach the

_{self-inhibiting phase}

of

_decreasing

slope during

the whole _span of the

_experiment.

For _every variable

_describing

the

shape

of the egg

weight

curve

(namely

P, P - Q, R

and the residual standard

deviation)

of the

_remaining

356

_hens,

a

_2-way

_analysis

of variance with interaction

was

_performed.

The main effects were

_genotype

at the sex-linked dwarfism locus

(normal

or

dwarf)

and

_genetic

_type

_(Leghorn,

Brown

_{Egg, Leghorn}

x Brown

_Egg,

Brown

_Egg

x

_Leghorn).

Variables with

_{significantly positively}

skewed distributions

(P,

Q,

and

_R)

were transformed with the

_log

transformation

(Gill, 1978)

and then

analyzed,

without

_changing

the

_significance

of the effects or the heterosis. Therefore

results are

_given

on untransformed data. Means of lines within each

phenotype,

normal and

dwarf,

were

_compared

also

_by

the Student-Newman-Keuls

procedure.

Correlations with

_parameters

of the

_exponential

_egg

_weight

curve and with _egg

production

traits

_(egg

_number,

_age at first egg, egg

weight

at end of test and

_body

weights

at 17 and 52 weeks of

_age)

were calculated both within and across

_genotypes.

From linear combinations of

_{least-squares}

means, heterosis was estimated for both

normal and dwarf

_hens,

crossbred

_advantage

was calculated for each

reciprocal

cross

and

_reciprocal

crossbred

_performances

were

_compared.

All

_analyses

were

_performed

RESULTS

Least-squares

means for the variables that describe the

_shape

of the _egg

_weight

curve, with the

significance

levels of main effects and

interactions,

are listed in table 1. Dwarf birds had smaller egg

weights

(P

<

_0.05),

both

_initially

and at

maturity,

a lower rate of

_change

of egg

weight

increment and a smaller residual

standard deviation about the curve

(P

<

_0.001).

Initial egg

weight

line differences

(P

<

_0.05),

with

_larger

_eggs from crossbreds than from White

_Leghorn

_hens,

persisted only

marginally

(P

<

_0.10)

in mature egg

weight,

but more

clearly

_among

dwarf hens.

_{Only marginal}

line differences

_(P

<

_0.10)

were found for the rate of

change

in egg

weight

increment but the residual standard deviation about the curve was

significantly

lower

(P

<

_0.001)

in the White

_Leghorn

line.

Correlations with

_parameters

of the

_exponential

_egg

_weight

curve and several

production

traits recorded

_during

the

_experiment

are

_presented

in table II.

’

Correlations between the rate R and the other

_parameters

of the

_exponential

curve were

_significant

_(P

<

_0.001)

and

_negative

for both normal and dwarf hens. Mature egg

weight,

P,

was associated

positively

(P

<

_0.001)

with

_Q

and P -

_Q

to

the same extent in normal and dwarf females. Initial _egg

_weight,

_{P &mdash; Q,}

had

_positive

correlations with

_Q

in dwarf hens

_(P

<

_0.05)

and with the residual standard deviation in normal females

_(P

<

_0.05).

For both

_types

of

_females,

mature _egg

_weight,

_P,

was

_positively

correlated with

actual

_{body weight}

at the

_beginning

_(P

<

_0.05)

and the end

_(P

<

_0.01)

of the test

_period

and with mean _egg

weight

(2-week

_egg collection at 43 weeks of

_age)

(P

<

_0.001).

_However,

it was not associated with _age at first _egg and it was

correlated

_negatively

_(P

<

_0.05)

with egg number of normal hens. Total egg

weight

gain,

Q,

was

_hardly

associated with

_body

_weights

and was not correlated with _age at first _egg.

_However,

it increased with mean _egg

weight

(P

<

_0.01)

and decreased with

_higher

egg number

(P

<

_0.001)

in normal _{females. Initial egg}

_weight,

P -

_Q,

was correlated with all 5

_traits,

_similarly

in dwarf and normal hens. Association

was

_negative

_only

with _age at first egg

(P

<

_0.01).

The rate R was

_{significantly}

correlated with egg number of dwarf females

only

(P

<

_0.05).

_Larger

residual standard deviation was associated with

higher body weights

(P

<

_0.01)

and egg

weight

(P

<

_0.05)

of normal

_hens,

and with

_higher

17-week

_body

_{weight (P}

<

_0.05)

of dwarf females.

Correlations between

_production

traits are

_given

here for the sake of

complete-ness.

They

were

_quite

similar for both

_types

of hens. Correlations of _egg number

with egg

weight

were the

_{only non-significant}

values

(P

>

_0.05).

Table III contains

_percentage

_superiority

for each

_reciprocal

cross and

_heterosis,

separately

for dwarf and normal

hens,

with

_{corresponding}

_comparisons

of crossbred

superiority.

Heterosis of initial egg

weight,

P -

Q,

was

significant

(P

< 0.01 or

P <

_0.001)

for all crossbred

_types

but it was not different between normal and dwarf hens. At

_maturity,

heterosis for _egg

_weight,

_P,

was

_significant

_(P

< 0.05

or P <

_0.01)

for dwarf hens

_{only. Negative}

heterosis

_(P

< 0.10 or P <

_0.05)

was

obtained for the rate of

_change

R of the _egg

_weight

curve of dwarf females. Crossbred

advantage

was not different in the 2

_reciprocal

crosses,

except

for R in normal hens

(P

<

_0.05).

There was some heterosis

(P

<

_0.10)

of the same

_magnitude

in normal

DISCUSSION

Residual standard deviation about the non-linear curve fitted to _egg

_weights

is a measure of the

goodness

of fit of the curve to the data. Values between 1.27 and 1.74 g obtained in this

_experiment

_{(table I)}

_compare

_favourably

with those around 2 _g

_{reported by Weatherup}

and Foster

₍₁₉₈₀₎

and Yoo et at

_(1983).

While the former authors did not find _any effect of the breed on the residual standard

deviation,

a

consistently

smaller value

_{(table I)}

was found for the White

_Leghorn

line used

in this

_study,

and more

generally

for dwarf hens.

However,

this observation _may

be scale related as both White

Leghorn

and dwarf hens laid smaller _eggs.

Indeed,

correlation of residual standard deviation with mean _egg

_weight

was 0.20 for normal

hens and was -0.01

(not significant)

for dwarf females while the correlation with

initial egg

weight, P-Q,

was 0.15 for normal hens

(table II).

On the other

hand,

no

association was found between residual standard deviation and mature _egg

_weight,

P,

in either

_type

of hens.

Moreover,

as dwarf hens

produce

fewer defective _eggs

(Merat,

1990),

their _egg

_weight

increase with age

might

also be more

_regular.

The observed egg

weight

was

_larger

in the Brown

_Egg

line than in the White

Leghorn

line

_(Merat

et

_at,

_1994),

as was the case for the initial egg

weight

(P -

Q)

estimated for normal and for dwarf hens

_(31.9

versus 29.1 _g and 30.0 versus 26.9

_g).

This could be

_expected

as the Brown

_Egg

line was a heavier line

(Merat

et

at,

1994).

However,

the

_{corresponding}

values of heterosis

_{(table III)}

were

_surprisingly

_large,

and

_yet

_agreed

well with actual values above

10%

_(data

not

_shown)

measured from _{all 68 eggs} obtained at 20 weeks of _age. Heterosis for initial egg

weight

was

the same in the 2

_genotypes,

a reflection of the fact that P -

Q

was associated with all main

_production

traits to the same extent in normal and dwarf females

(table

II).

As

_{anticipated, adjusted}

mature _egg

_weight

was

larger

than the observed mean _egg

_weight

at 43-45 weeks of _age

_{reported by}

M6rat et at

₍₁₉₉₄₎

but the

ranking

of the

_purebreds

and crossbreds within

_genotype

was

_quite

similar to that in their

_report,

with little differences between lines

_{(table I).}

At

_maturity,

while normal

_Leghorns

had

_caught

up with the 3 other normal

types

for egg

weight,

dwarf

_Leghorns

still had smaller _egg

_weight

_{(table I),}

which induced the

_significant

positive

heterosis

reported

for dwarfs

_(table

_III).

_Negative

correlation of P

with

egg number

_{(table II)}

in normal hens buffered mature _egg

_weight

differences between crossbreds and

_purebreds

that could have been

_anticipated

from initial egg

weights,

thereby reducing

heterosis. On the

_contrary,

the absence of a similar correlation in

dwarf hens allowed maintenance of heterosis at

_maturity

for this

_genotype.

Good correlations between

_Q

and P were to be

_expected

as the _range of _egg

weight,

Q,

is extended more

by

_raising

its upper

limit, P,

than

by decreasing

its

lower

_end,

P -

_Q.

As a matter of

_fact,

no

_significant

_negative

correlation was

found between

_Q

and P -

_Q.

_Furthermore,

the

_positive

correlations found between initial and mature _egg

_weights

reflect the obvious

_biological

association between the 2 traits. On the other

hand,

the

positive

correlation between

_Q

and P -

_Q

in dwarf hens does not have a

straightforward explanation.

As initial _egg

weight

was

The smaller rate of

_change

_{in egg}

_weight

increment

_(table

_I)

for dwarf hens

(egg

weight

curve was

flatter)

delayed

attainment of mature egg

weight.

Moreover,

negative

heterosis for dwarf crossbreds

_{(table III)}

indicates that within the range of _ages and

_weights

observed in this

_experiment

the curve was flatter for those

2

_genetic

_types.

This is confirmed

_by

the

_only

_significant

_(and

_negative)

correlation

involving

R,

with egg number in dwarfs

(table

II),

which indicates

that,

among

dwarfs,

mature _egg

_weight

would be reached later

_by

hens

_laying

more _eggs. On

the

contrary,

positive

heterosis obtained

_only

for normal

_Leghorn

x Brown

_Egg

crossbreds,

showed that

_{curvilinearity}

was enhanced

by

this cross

_{and, therefore,}

that mature egg

weight

could be reached earlier.

As the

_exponential

curve was flatter

(for

smaller R

values),

mature _egg

_weight,

P,

was reached

later,

thereby allowing

for

larger

_{extreme egg}

weights

and egg

weight

range, and for the

negative

correlations found between those traits and R.

An ideal egg

weight

curve would be one

_starting

at a

_high

initial

_weight

and

quickly

increasing

towards a

_high

mature _egg

_weight.

In this

work,

favourable combinations for the 3

_parameters

of the curve were obtained for all normal size

genetic

types except

the _pure

_Leghorn,

and

_particularly

for the

_Leghorn

x Brown

Egg

cross with its fast rate of increase.

_Among

dwarf groups, pure

Leghorns

were even more at a

disadvantage

as their initial and mature _egg

_weights

were both

smaller.

_Reciprocal

crossbreds had

_higher

initial _egg

_weight

than

_purebreds

but took

_longer

to reach their mature

_weight,

which was also

larger,

while _pure Brown

Egg

had a better rate of

change.

The interest of the dwarf gene in crossbred hens

reported by

M6rat et al

₍₁₉₉₄₎

for egg

production

traits was somewhat confirmed

here for the evolution _{of egg}

_weight,

but

_increasing

R in crossbred dwarfs would make them even more

_acceptable

_{for egg}

_production.

More

_generally,

the

_present

_study

confirmed the value of the

_exponential

curve

to describe the increase of egg

weight

with age for several

genetic

types.

It has also shown that the

_shape

of the curve was affected

_by

_genetic

differences between lines

through

its 3

_parameters.

The

_expected

crossbred

_advantage

for _egg

_weight

was also

obtained

_by

_comparing

values of the

_{corresponding}

parameters

for

_purebreds

and crossbreds.

_Heterosis,

however,

was

generally higher

than

usually reported

from

actual

measurements,

maybe

because

_they

were made before

_maturity

(constant

egg

size)

was reached.

ACKNOWLEDGMENTS

The technical assistance of the staff at the

Poultry Experimental

Unit in La Mini6re is

greatly appreciated.

Grateful

acknowledgment

is made to M Chalot for

_preparing

data

and M Boitard for data transfer.

Special

thanks to an _anonymous and tenacious reviewer

for constructive and

stimulating

comments.

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