Livestock
Research for Rural Development 20 (9) 2008

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Evaluation of litter traits in a crossing project of V-line and Baladi Red
rabbits in Egypt

Y M K Youssef, M Baselga*, M H Khalil**, S Gad-Alla and M L Garcia***

Animal Production Research Institute, Ministry of Agriculture, Dokki, Cairo,
Egypt;
*Departamento de Ciencia Animal, Universidad Politecnica de Valencia,
Camino de Vera 14, Apdo 22012, 46071, Spain
**College of Agriculture &
Veterinary Medicine, Al-Qassim University, Buriedah 51452 P.O. Box 6622,
Al-Qassim, Saudi Arabia
***Departamento de Tecnología Agroalimentaria,
Universidad Miguel Hernández, Ctra Beniel Km. 3.2 Orihuela 03312, Alicante
Spain
[email-masked]

Abstract

Four-years crossing scheme involving Spanish V-line (V) and
Egyptian
Baladi Red (B) rabbits was practiced to produce five genetic groups of V,
B, ½B½V, (½B½V)2, and ((½B½V)2)2. A new line
with a genetic structure of ((½B½V)2)2 was synthesized and
named APRI. A total of 2834 litters produced from 848 does pedigreed by 477 dams
and 272 sires were used to evaluate litter size at birth (LSB) and weaning
(LSW), litter weight at birth (LWB) and weaning (LWW), and pre-weaning litter
gain (PLG). A generalized least square procedure (GLS) was used to estimate
direct additive, direct heterosis, maternal heterosis, and direct recombination
effect.

Heritabilities
for litter traits were mostly low and ranging from 0.01 to 0.18, while
the permanent environmental effects were mostly moderate and ranged from 0.09 to
0.33. Direct additive effects were mostly in favour of V-line does; indicating
significant effects only for LSB and LWB by 23.0% and 24.2%, respectively,
relative to the average of the means of V and B. All estimates for direct
heterosis were significant and ranging from 20.0 to 27.7 %. The magnitudes of
the estimates of maternal heterosis were mostly opposite to the magnitude of
direct heterosis since the estimates were negatively unfavourable; ranging from
-10.0 to 12.3 % comparing to the founder breeds.

Key words: additive effects, crossbreeding,
heterosis, litter traits, rabbits, synthetic line

Introduction

In
2003, a co-operative crossbreeding rabbit project was established between Egypt
and Spain to develop new line of meat rabbits suitable for hot climate. The
V-line rabbits used in this project were crossed with an Egyptian Baladi Red
(B). Traits related with
productivity of the does, such as litter sizes and weights and milk production
are considered the most important traits for an efficient production and some of
these traits are objectives of selection to develop maternal lines of rabbits
(Estany et al 1989: Gómez et al 1996; Rochambeau et al 1998; Baselga 2004). A
deep knowledge involving crossbreeding parameters for these traits is lacking in
hot climates (Khalil and Afifi 2000; Khalil et al 1995, 2004 and 2005; Al-Saef
et al 2007). Thus, the objective of the present study was to estimate direct
additive and heterotic effects, maternal heterosis, and recombination effects
for litter traits in a crossbreeding program involving one Egyptian Baladi breed
(B) and a Spanish V-line rabbits, that are the founders of the new line
synthesized.

Material and methods

Animals and
crossbreeding program

Four-years crossbreeding project involving
Egyptian Baladi Red rabbits (B) and a Spanish V-line (V) was started in 2003 in
Gimmeza and Shakha Experimental Rabbitries, which belong to Animal Production
Research Institute (APRI), Agriculture Research Center, Ministry of Agriculture.
In this scheme, Baladi Red bucks were mated with V line does to get
F1 of ½B½V, then does and bucks of this F1 were mated to
get F2 of (½B½V)2, followed by two generations of inter se
mating to get a new synthetic line named APRI with genetic structure of
((½B½V)2)2. Litters born in B, V, ½B½V,
(½B½V)2, and ((½B½V)2)2 were 148, 1403, 171,
222, and 840, respectively. The bucks were randomly assigned to mate the does
naturally with the restriction to avoid the matings of animals with common
grandparents. A total of 2784 litters produced by 848 does pedigreed by 477 dams
and 272 sires were used. Data collected were litter size at birth (LSB) and
weaning (LSW), litter weight at birth (LWB) and weaning (LWW), and pre-weaning
litter gain (PLG).

Housing and
feeding

Rabbits of this
work were raised in a semi-closed rabbitries. Breeding females and males were
housed individually in wire cages with standard dimensions of 35 x 35 x 60 cm
arranged in one-tire system allocated in rows along the rabbitry. The cage of
each doe was equipped with a metal nest box for kindling and nursing the progeny
up to weaning at four weeks of age. All cages of does and bucks were provided
with feeders and nipple-drinkers.

Rabbits fed
standard pelleted diet that offered ad libitum. The diet was composed from 32%
barley, 21% wheat bran, 10% soybean meal, 22% hay, 6% berseem straw, 3%
corticated cottonseed meal, 3% molasses, 1% limestone, 0.34% table salt, 0.3
minerals and vitamins, 0.06 methionine and 1.3% anti-coccidian. This diet
provide 16.3% crude protein, 13.2% crude fiber, 2.5 either extract, 0.6 minerals
mixture, 67.4% soluble carbohydrates and 2600 k cal / kg .

Model of analysis
and estimation of crossbreeding genetic effects

For all litter
traits, data were analyzed using a single-trait animal model as:

y= Xb + Zaua +
Zpup + e

where:

y = vector of
records of litter trait,

b = vector of
fixed effects of genetic groups of the doe (five levels), year-season of
kindling (17 levels), and parity (five levels);

ua =
vector of random additive effects of the does and bucks in the pedigree,

up =
vector of random effects of the permanent environment of the doe (permanent
non-additive effect);

X, Za
and Zp = incidence matrices relating records to the fixed effects,
additive genetic effects, and permanent environment, respectively; and

e = vector of
random error.

Variance components of random effects were
estimated by a derivate-free restricted maximum likelihood procedure using
MTDFREML software of Boldmann et al (1995). These estimates were used to solve
the corresponding mixed model equations, obtaining solutions for the genetic
group means and their error variance–covariance matrix, using the PEST program
(Groeneveld 2006). To get the estimates of the crossbreeding genetic parameters
of the lines (Dickerson 1992), a procedure of generalized least squares (GLS)
was applied using the following linear model:

y = Xb + e,   Var(y) =
V

where:

y = vector of estimated
groups means, using the genetic group of Baladi Red as a reference
population;

X
= incidence matrix,

b
= vector of estimable crossbreeding genetic effects,

e
= vector of random error, and

V
= the error variance-covariance matrix of y.

The coefficients relating genetic
crossbreeding parameters to the means of the genetic groups are showed in Table
1 (Dickerson 1992; Wolf et al 1995). Crossbreeding parameters of direct genetic
effects D = DV - DB , direct (HI)
and maternal (HM) heterosis and recombination effect (RI)
were estimated using CBE program of Wolf (1996).

Table 1.  Genetic group of the does and their parents and coefficients of
the matrix relating to the genetic group means of the does with the
crossbreeding parameters

Ordinal

Doe
genetic
group

Sire
genetic
group

Dam
genetic
group

Mean

µ

Coefficients
of the matrix*

DV

DB

HI

RI

HM

1

Baladi (B)

B

B

1

1

0

0

0

0

2

V-line (V)

V

V

1

0

1

0

0

0

3

½B½V

B

V

1

.5

.5

1

0

0

4

(½B½V)2

½B½V

½B½V

1

.5

.5

.5

.25

1

5

((½B½V)2)2

APRI

(½B½V)2

APRI

(½B½V)2

APRI

1

.5

.5

.5

.25

.5

* DV and DB = Direct
additive genetic effects for V-line and Baladi Red breed,
respectively; HI = Direct heterosis;
RI = Direct recombination effect; HM =
maternal heterosis. APRI = New synthetic line referring to Animal
Production Research
Institute.

Results and discussion

Overall
actual means and variation

Means, standard
deviations and minimum and maximum values for litter traits are presented in
Table 2. For crossbreeding programs carried out in the Arabian countries
involving V line rabbits, values reported by Khalil et al (2005) and Al-Saef et
al (2007) in Saudi Arabia were slightly higher than those of the present study,
while the values reported by Iraqi et al (2007) in Egypt were extremely lower.
Consequently, these results could be encouraging factors to involve V-line in
crossbreeding programs in Egypt and other hot climatic countries.

Table 2.
Summary statistics for litter traits
studied

Litter
trait

No.

Mean

SD

Minimum

Maximum

LSB, young

2834

8.77

1.94

1

16

LSW, young

2740

6.09

1.48

1

12

LWB, g

2833

430

85

60

700

LWW, g

2740

3031

601

465

5720

PLG, g

2740

2599

572

145

5325

+LSB= Litter size at birth; LSW= Litter size at weaning; LWB=
Litter weight at birth;
LWW= Litter weight at weaning; PLG=
pre-weaning litter
gain

Genetic additive effects (h2)
and non-additive and permanent environmental effects (p2)

Heritabilities for
litter traits were mostly low and ranging from 0.01 to 0.18 (Table 3).
Estimates of heritability got in
the present study for litter traits are within the ranges cited in the
literature estimated by an animal model (Ferraz et al 1992; Lukefahr et al 1996;
Lukefahr and Hamilton 1997; Rastogi et al 2000; Sorensen et al 2001; El-Deghadi
2005; Khalil et al 2005).

The ratios of permanent environmental
effects (p2) were mostly moderate and ranged from 0.09 to 0.33 (Table
3). Similar estimates were reported by Lukefahr and Hamilton (1997), El-Raffa (2000), Sorensen et al (2001), El-Deghadi
(2005) and Khalil et al (2005) using an animal model.

Table
3.   Estimates
of the proportion of the phenotypic variance due to genetic additive
effects (h2) and to non-additive and permanent environmental
effects (p2) with their standard errors (±SE) for litter traits
studied

Litter trait1

h2±SE

p2±SE

e2±SE

LSB

0.01±0.021

0.33±0.033

0.66±0.02

LSW

0.01±0.022

0.19±0.030

0.80±0.021

LWB

0.13±0.030

0. 11±0.024

0.76±0.02

LWW

0.18±0.005

0.18±0.020

0.64±0.019

PLG

0.05±0.024

0.09±0.023

0.86±0.02

1See Table
2.

Crossbreeding
effects

The main objective of this study was to
estimate the crossbreeding parameters in terms of direct additive, direct
heterosis, maternal heterosis and recombination losses.
Estimation of these crossbreeding parameters were carried out using the
methodology explained in Material and Methods section and some estimates for the
effects of recombination losses were non-expected. Particularly, the structure
of our data was not well conditioned to estimate the recombination losses since
the standard errors of these estimates were somewhat high. For this reason, we
have decided to simplify the model of crossbreeding parameters by eliminating
the effects of recombination losses. Accordingly, the column corresponding to
this effect in Table 1 was eliminated. Consequently, results and discussion
represented here refer to the estimates obtained for crossbreeding parameters
with such simplified model.

In
general, direct additive effects for litter traits studied were in favour of V
line does (Table 4). Differences between line V and Baladi Red in direct
additive effects were significant for two litter traits out of five (LSB and
LWB, Table 4). These results evidenced that genes of line V had better direct
additive effects on litter size and weight at birth.

Table 4.  Estimates of differences between line V and Baladi Red breed in
direct effects and their standard errors
(±SE) for litter traits studied

Litter trait1

Direct additive effects (DV -
DB)

Estimate ± SE

%2

LSB, young

1.78±0.48*

23.0

LSW, young

0.45±0.41 NS

8.1

LWB, g

95±21*

24.2

LWW, g

129±171
NS

4.5

PLG, g

33.5±168
NS

1.4

1 See Table 2, 2 Percentage of the difference
referred to the average of the values for V line and Baladi Red breed, NS
= Non-significant; *
P<0.05

Differences in direct additive effects for
litter size and weight at birth were of considerable importance of 23.0% and
24.2% relative to the average of the founder genetic groups (Table 4). Crossing
line V with Sinai Gabali in Egypt to get F1 showed that line V was
significantly superior to the Sinai Gabali for litter size and weight at birth
(Iraqi et al 2007). In addition, Lukefahr et al (1983), García et al (2000),
Khalil et al (2005) and El-Deghadi (2005) reported significant direct additive
effects on litter traits. Khalil and Afifi (2000) and El-Deghadi (2005) in
crossing experiment between NZW and Gabali rabbits reported that NZW rabbits had
higher estimates of direct additive effects than Gabali rabbits for litter size
and/or litter weight at birth and weaning (P<0.01 or P<0.001).

All estimates of direct heterosis verified
that crossbred does were usually associated with significant and favourable
heterotic effects on litter traits studied; the estimates ranged from 20.0 to
27.7 % (Table 5). All significant estimates were favourable from a production
point of view. Crossbreeding experiments carried out in Egypt (e.g. Khalil et al
1995; Khalil and Afifi 2000; Abd El-Aziz et al 2002; El-Deghadi 2005) reported
significant direct heterotic effects on litter size and weight traits. In
addition, Baselga et al (2003) in an experiment of crossbreeding, involving
three maternal lines, had significant direct heterosis for litter size at birth
in two of the three possible simple crosses obtained. On the contrary, Iraqi et
al (2007) in Egypt found that estimates of direct heterosis for litter size and
weight at birth and weaning were not significant.

Most estimates of maternal heterosis were
significantly unfavourable since the estimates were negative and ranging from
10.0 to 12.3 % relative to the average of the means of V and B (Table 5). The
magnitudes of maternal heterosis are completely opposite to the magnitude of
direct heterosis for these traits. Khalil et al (2004) and Al-Saef et al (2007)
have reported significant maternal heterosis for pre-weaning litter traits.

Table 5.  Estimates of direct and maternal heterosis and their standard
errors (±SE) for litter traits
studied

Doe
trait1

Direct heterosis

Maternal heterosis

Estimate ± SE

%2

Estimate ± SE

%2

LSB, young

1.85±0.48*

23.9

-0.37±0.45
NS

-4.8

LSW, young

1.54±0.41*

27.7

0.10±0.33
NS

1.8

LWB, g

108±21.2*

27.6

-39±17.4*

-10.0

LWW, g

800±171*

27.6

-346±140*

-12.0

PLG, g

495±165*

20.0

-306±135*

-12.3

1 See Table 2, 2 Percentage of the heterosis effects referred to the average of the values
for V line and Baladi breed, NS = Non-significant; *
P<0.05

Conclusions

The use of an exotic line (line V),
highly selected for litter size at weaning, and an Egyptian breed (Baladi
Red), well adapted to hot climates, has led successfully to create a new line
named APRI.

This superiority in such synthetic line
in the present study was verified since the estimates of direct heterosis
obtained were of considerable importance for all litter traits studied.

Acknowledgment

The authors
would like to thank the Spanish Agency of International Cooperation for
supporting the project.

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Received 27 December 2007; Accepted 17 April
2008; Published 4 September 2008

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