Livestock
Research for Rural Development 17 (10) 2005

Guidelines to
authors

LRRD News

Citation of this
paper

Heritabilities and genetic analysis of milk yield and components in crossing
project of Saudi rabbits with Spanish V-line

K A Al-Sobayil, A H Al-Homidan, M H Khalil and M A Mehaia

Department of Animal Production and Breeding, College of Agriculture and
Veterinary Medicine, Al-Qassim University,
Buriedah P.O.Box 1482, Saudi
Arabia
[email-masked]

Abstract

A four-year
crossbreeding project involving Spanish maternal line called V-line (V) and
Saudi Gabali (G) rabbits was carried out to produce six genetic groups of V, G,
½V½G, ½G½V, ¾V¼G and ¾G¼V. Inter se matings for genetic groups of ½V½G, ½G½V,
¾V¼G and ¾G¼V were also practiced. Milk yields (MY) at intervals of 0-7 days
(MY7), 7-21 days (MY21), 21-28 days (MY28), and 0-28 days (TMY) and milk
components (MC) at 14 days of lactation (fat, protein, lactose, ash, and total
solids) were evaluated for 2141 litters of 854 does fathered by 142 sires and
mothered by 351 dams. A repeatability animal model was used to estimate the
corresponding parameters as the heritabilities, the differences between line V
and Gabali in additive direct effects (GIV-G) and maternal
additive effects (GMV-G). The individual (HI)
and maternal (HM) heterosis, and direct recombination effect
(RI) were also estimated.

Heritabilities
for MY traits were moderate, ranging from 0.18 to 0.22, while they were low or
moderate and ranging from 0.09 to 0.28 for MC. The positive estimates of
GIV-G for MY (5.6-14.5%) and MC (4.0-18.7%) were
significantly high and in favour of V-line does. Estimates of
GMV-G were in favour of V-line dams; being 222 g, 0.67%
and -0.08 for MY21, total solids in milk, and fat in milk, respectively. All
estimates of HI for MY and MC were positive and most of them were
significant; ranging from 9.7 to 22.7 % for MY traits (P<0.05-0.001) and 6.0
to 15.8% for MC traits (P<0.05-0.01). Similar to the trend of HI,
the estimates of HM for MY and MC were positively moderate and
ranging from 7.4 to 15.2 % for MY traits and 1.9 to 8.3% for MC. The ranges in
percentages of reduction in direct heterosis were negligible and ranging from
2.2 to 5.3% for MY traits and 3.4 to 9.6% for MC. In practice, crossbred does
and dams involving V-line genes in their constitutions gave favourable heterotic
effects on milk traits and therefore these crossbred does and dams can produce
and lactate efficiently under hot climatic conditions.

Key words: Animal model, crossbreeding,
heritability, milk yield and components, rabbits

Introduction

Genetic diversity of
rabbit breeds in terms of milk production offers the opportunity to increase the
efficiency of doe productivity through crossbreeding. To date, genetic analysis
concerning milk yield (MY) and components (MC) for crossbred rabbits raised in
hot climate countries are scarce. Further, milk production and milk components
are expensive to record. Other traits that are associated with them, are more
directly related with production and are easier to record, such as litter size
at birth or at weaning (Estany et al 1989; Rochambeau et al 1998; Gomez et al
1996; Capra et al 2000; Garcia et al 2000), litter size at weaning and
individual weight at weaning (Moura et al 2001), litter size at weaning and
individual weight gain (Gomez et al 2000), and litter weight at weaning (Salaun
et al 2001; Garreau and Rochambeau 2003). These traits, in a great part, can
replace milk yield as criteria for selection. However, selecting does directly
for yields and components of milk should be of considerable interest and
importance (Garreau and Rochambeau 2003; Baselga 2004; Garreau et al
2004).

The objective of our
study was to estimate direct (GIV-G) and maternal
(GMV-G) additive effects, direct heterosis
(HI), maternal heterosis (HM) and direct recombination
effects (RI), as well as heritabilities, for MY and MC traits in a
crossbreeding project involving Spanish V-line rabbits and Gabali Saudi rabbits.

Materials and
methods

The four-year
crossbreeding project was started in October 2000 in the experimental rabbitry,
College of Agriculture and Veterinary Medicine, El-Qassim region, King Saud
University, Saudi Arabia.

Breeding plan,
management, farm environment and feeding

Rabbits used in this
study represent one desert Saudi breed (Gabali, G) and one exotic breed (Spanish
V-line, V). The breeding plan permitted simultaneous production of ten genetic
groups. Distribution of number of litters weaned in these genetic groups across
different years of kindling is presented in Table 1.

Table 1. Number of litters weaned in different genetic groups
and years of kindling

Sire genetic group

Dam genetic group

Doe genetic group

Ordinal
number

Litters weaned in
year of kindling

Total litters
weaned

2000

2001

2002

2003

V-Line  (V)

V-Line  (V)

V-line (V)

1

39

172

59

36

306

Gabali (G)

Gabali (G)

Gabali (G)

2

36

106

67

39

248

V

G

½V½G

3

33

106

38

20

197

G

V

½G½V

4

23

102

78

32

235

V

½G½V

¾V¼G

5

36

81

33

150

G

½V½G

¾G¼V

6

67

113

27

207

½V½G

½V½G

(½V½G)2

7

42

43

26

111

½G½V

½G½V

(½G½V)2

8

38

63

91

192

¾V¼G

¾V¼G

(¾V¼G)2

9

135

105

240

¾G¼V

¾G¼V

(¾G¼V)2

10

155

100

255

Total

131

669

832

509

2141

A total number of 2541
litters were born by 854 does, fathered by 142 sires and mothered by 351 dams.
The bucks were randomly assigned to mate the does naturally with the restriction
to avoid the matings of animals with common grandparents. Young rabbits were
weaned at four weeks of age. Rabbits were raised in a semi-closed rabbitry.
Breeding does and bucks were housed separately in individual wired-cages. All
cages are equipped with feeding hoppers and drinking nipples. In the rabbitry,
the environmental conditions were monitored; temperature ranged from 20 to about
32 °C, the relative humidity ranged from 20 to 50 % and photoperiod was 16L: 8D.
Rabbits were fed a commercial grower pelleted diet during the whole experimental
period, which lasted 16 weeks of age. On dry matter (DM) basis, the diet
contained 18.5% crude protein (CP), 8.0% crude fiber (CF), 3.0% ether extract
(EE) and 6.5% ash. Feed and water were available ad libitum.

Milk yields and
components

Milk yields (MY) were
recorded during the first seven days (MY7), 7-21 days (MY21), 21-28 days (MY28)
and for the total 0-28 days (TMY). Litter weight at birth (LWB) and litter
weight at weaning (LWW) were also recorded. Milk yield of does was recorded
using weigh-suckle-weigh method. MC of fat, protein, lactose, ash and total
solids (g/100g) were also estimated. In the evening of the day prior to
collection, the kits were separated from their mothers to prevent suckling for a
period of 12 hours before sample collection in the next morning. Milk samples
were collected manually by gently massaging the mammary gland after two minutes
of injection with 0.1 ml of oxytocin hormone to enhance maximum contraction of
myoepithelial cells. Samples were taken per doe per litter in the morning of the
15th day of lactation. The samples were cooled and transferred
immediately to the laboratory for chemical analysis. Milk sample for each litter
born per doe was analysed for total solids, and ash according to procedures
outlined in AOAC (1980). Fat was determined by Gerber method as described by
Case et al (1985), nitrogen by the standard micro-Kjeldahl method (AOAC 1980). A
nitrogen conversion factor of 6.38 was used to calculate protein content.
Lactose was determined by subtraction.

Statistical
analysis

Repeatability animal
model (in matrix notation) used for analysing milk traits was (Boldman et al
1995):

y= Xb +
Zaua + Zpup + e

Where
y = vector of
observed lactation trait for does,
b= vector of fixed effects of genetic
group of doe (ten levels; see Table 1), year-season of kindling (one year season
every three months), and physiological status of the doe (five levels depending
on the parity order and lactation state at the moment of insemination: 1 for
nulliparous, 2 for primiparous lactating, 3 for multiparous lactating, 4 for
primiparous non-lactating, 5 for multiparous non-lactating);
ua=
vector of random additive effect of the does and sires,
up= vector
of random effects of the permanent environment (permanent non-additive
effect);
X, Za and Zp are the incidence matrices
relating records to the fixed effects, additive genetic effects, and permanent
environment, respectively; and e= vector of random residual effects.

Variance components of
direct additive effects, permanent environmental effects and errors were
estimated by DFREML procedure using the animal model (Boldman et al 1995). The
inverse of the numerator relationship matrix (A-1) was considered;
Var(ua)= As2a, Var(up)=
Is2p and Var(e)= Is2e.
Heritabilities for different traits were computed from variance components using
the following equations:

The variance components
estimated before should be used to solve the model and get solutions for the ten
genetic groups (Di, i= 1 to 10) and the corresponding
variance-covariance matrix of the errors. This information should be used to
compute later the estimable functions Di-D2 and their
variance-covariance matrix of errors.

Genetic model and estimation of crossbreeding
effects

The Dickerson's genetic
model (Dickerson 1992) was used to explain the performances of the different
genetic groups. The genetic model take into account the direct additive effects
of the line or breed (e.g. GIG, for Gabali), the maternal
additive effects (e.g. GMV, for line V), the individual
(HI) and maternal (HM) heterosis between Gabali and line V
and the direct recombination effect (RI). Because of linear
dependence between the equations of the fixed factors, estimable functions used
are Di-D2 that allow to estimate the following
combinations of parameters of the Dickerson's genetic model:
GIV-G = GMV -
GIG; GMV-G
=GMV- GMG, HI,
HM and RI. Table 2 shows the coefficients of the previous
combination of parameters for the functions Di-D2 that are
used with their variance-covariance matrix of errors to get generalised least
square estimates of GIV-G, GMV-G,
HI, HM and RI, their standard errors and the
corresponding Student's t-test.

Table 2. Coefficients for genetic effects and interpretations
of the estimable functions (EST) as function of the genetic parameters of
the crossesa

Ordinal number

Doe genetic group

EST1

Direct
Additive,
(GIV-G)

Maternal
Additive,
(GMV-G )

Direct
heterosis
(HI)

Maternal heterosis
(HM)

Recombination
effect,
(RI)

1

V-Line  (V)

D1-D2

1.0

1.0

0.0

0.0

0.0

2

Gabali (G)

D2-D2

0.0

0.0

0.0

0.0

0.0

3

½V½G

D3-D2

0.5

0.0

1.0

0.0

0.0

4

½G½V

D4-D2

0.5

1.0

1.0

0.0

0.0

5

¾V¼G

D5-D2

0.75

0.5

0.50

1.0

0.25

6

¾G¼V

D6-D2

0.25

0.5

0.50

1.0

0.25

7

(½V½G)2

D7-D2

0.5

0.5

0.50

1.0

0.50

8

(½G½V)2

D8-D2

0.5

0.5

0.50

1.0

0.50

9

(¾V¼G)2

D9-D2

0.75

0.75

0.375

0.50

0.375

10

(¾G¼V)2

D10-D2

0.25

0.25

0.375

0.50

0.375

a () defined as the difference between direct
(maternal) additive effects between V-line and Gabali rabbits;
HI = individual heterosis; HM maternal heterosis;
RI = losses of genetic recombination.

1
Di, solution for the ith genetic group of
does.

Results and
discussion

Actual means and
variations

To characterize the
experiment phenotypically, means, standard deviations, minimum and maximum
values for milk traits are presented in Table 3.

Table 3. Actual means, standard deviations (SD) and range of
variation for milk yields (grams) and components (g/100g)

Milk trait

No.

Mean

SD

Minimum

Maximum

MY7

2141

976

328

351

2674

MY21

2141

2438

928

588

6986

MY28

2141

934

332

140

2490

TMY

2141

4331

1344

1449

8533

Fat

1587

12.9

2.3

4.40

23.1

Protein

1587

12.0

1.5

3.84

20.54

Lactose

1587

2.1

0.7

0.29

9.75

Ash

1587

2.2

0.3

0.76

4.32

Total solids

1587

29.1

3.0

17.81

43.57

However, wide
phenotypic variations in all traits were observed. >From producers point of
view, milk yield and milk components showed moderate lactational performances
particularly for hot climate areas. In hot countries, little lower values for
milk yield were reported by Khalil and Afifi (2000) and much lower values by
Lahari and Mahjan (1984), Khalil (1994) and Abd El-Aziz et al (2002). Cowie
(1969) reported that Dutch does (as a small breed) produced less milk in the
first six weeks of lactation than New Zealand White does (3820 gram v. 6940
gram). Lukefahr et al (1983) in USA found that New Zealand White was superior to
Californian rabbits in lactational yield. Lahari and Mahajan (1984) in India
reported that differences in daily milk yield at 21 days of age among Grey Giant
(GG), Soviet Chinchilla (SC), White Giant (WG), New Zealand White (NZW) and
Russian Angora (RA) were not significant but GG had the highest yield (189 g per
day) followed by RA (147g), SC (139g), WG (134g) and NZW (116g). El-Sayiad et al
(1994) with New Zealand White (NZW) and Californian (CAL) rabbits in Egypt
stated that the differences between the two breeds in fat, protein, lactose, ash
and energy of milk were not significant; the estimates were 14.0, 13.6, 1.9,
2.1% and 87.9 kJ/100g in NZW and 14.0, 14.3, 2.0, 2.2% and 89.9 kJ/100g in CAL
for fat, protein, lactose, ash and energy of milk, respectively. Such
discrepancies among reports may be due to the strain of breed used, breed x
environment interaction or different experimental methods.

Total differences
between genetic groups

Deviations of each
genetic group from Gabali (Di-D2) for different milk
traits are presented in Table 4. These deviations are interesting to show the
global performance of the V-line, the Gabali breed and their different crosses
in order to identify their possibilities to be used as pure stock or as a simple
cross or to be used as synthetic line. For all milk traits, V-line rabbits
recorded better lactational performance compared to Gabali rabbits (Table 4).
Clear differences among the ten genetic groups were notified for fat, protein
and total solids in milk.

Table 4. Deviations of each genetic group from Gabali rabbits
(Di-D2) for milk yields (grams) and components
(g/100g)

Milk trait

D1-D2

D3-D2

D4-D2

D5-D2

D6-D2

D7-D2

D8-D2

D9-D2

D10-D2

MY7

17

8

12

38

35

16

91

111

118

MY21

169

175

37

117

165

115

33

170

195

MY28

131

120

180

85

208

113

70

139

123

TMY

328

293

222

194

400

276

236

412

426

Fat

1.1

0.8

0.8

0.7

0.6

0.4

1.1

1.7

2.0

Protein

0.6

0.5

0.3

0.1

0.1

-0.01

0.2

0.8

0.9

Lactose

0.09

0.7

0.6

0.12

0.1

0.34

0.11

0.35

0.36

Ash

-0.02

0.02

0.1

-0.07

-0.01

-0.07

0.05

-0.07

-0.01

Total solids

1.8

2.3

1.6

1.1

0.9

0.5

1.7

3.0

3.5

The highest percentages
of total solids (fat, lactose and protein) were recorded for (¾G¼V)2
group (31.0 %), while the least values were recorded for G group (27.3%). In
most cases (MY7, MY21, MY28 and TMY), genetic group of (¾V¼G)2 or
(¾G¼V)2 gave higher milk yield and components compared to the other
genetic groups (Table 4). The above mentioned results indicate that involving
V-line genes in crossbreeding program with Gabali rabbits was associated with an
improvement in the lactational performance of the crossbred does
obtained.

Additive and permanent environmental effects
and heritability estimates

Ratios of variance
components of direct additive effect (heritabilities, h2) and
permanent environment (p2) to the phenotypic variances are presented
in Table 5.

Table 5. Ratios of variance components for additive effect
(or heritabilities, h2±SE) and permanent environment
(p2±SE) to the total phenotypic variance for milk yields
(grams) and components (g/100g)

Milk trait

h2±SE

p2±SE

MY7

0.20±0.08

0.23±0.06

MY21

0.18±0.07

0.24±0.05

MY28

0.22±0.08

0.28±0.09

TMY

0.21±0.08

0.25±0.07

Fat

0.20±0.08

0.08±0.07

Protein

0.11±0.07

0.11±0.06

Lactose

0.13±0.07

0.12±0.07

Ash

0.09±0.07

0.06±0.08

Total solids

0.28±0.07

0.12±0.07

Heritabilities for
yield traits were moderate, ranging from 0.18 to 0.22, while they were low or
moderate and ranging from 0.09 to 0.28 for milk components (Table 5). However,
the estimates of heritability obtained in the present study for milk traits are
within the ranges of estimates cited in the literature (Lahiri and Mahajan 1984;
El-Maghawry et al 1993; Ayyat et al 1995; Lukefahr et al 1996; Khalil et al
2005).

Similar to the trend of
direct additive effect (heritabilities, h2), the ratios of permanent
environment effects were moderate and ranged from 0.23 to 0.28 for milk yields,
while these ratios were low and ranging from 0.06 to 0.12 for milk components.
However, high contribution of permanent environment to variation of milk traits
may have considerable adverse effects on heterosis of these
traits.

Direct (GI)
and maternal (GM) breed additive effects

Estimates of
GIV-G for most milk yields and components were
significantly moderate or high in favour of V-line rabbits (Table 6). Line V is
a maternal line of rabbits selected for litter size at weaning, being the
animals genetically evaluated by a BLUP methodology under an
animal-repeatability model (Estany et al 1989).

Table 6. Estimates of direct (GIV-G) and
maternal (GMV-G) additive effects and their standard
errors (SE) for milk yields (grams) and components
(g/100g)

Units±SE

GI
%a

Units±SE

GM
%b

MY7

59±32NS

5.6

6±39NS

0.6

MY21

242±89**

9.4

222±111NS

8.6

MY28

122±42*

14.5

18±62NS

2.1

TMY

395±92*

8.8

255±162NS

5.7

Fat

1.24±0.21**

9.9

0.63±0.27NS

5.1

Protein

0.47±0.14*

4.0

0.24±0.17NS

2.0

Lactose

0.38±0.07*

18.7

0.10±0.1NS

4.9

Ash

0.13±0.02*

6.2

0.03±0.03NS

1.4

Total solids

1.22±0.27**

4.3

0.67±0.35NS

2.4

aGI%= [GI in units / (average of
V line and Gabali groups)] x 100
bGM %  =
[GM in units/( average of V line and Gabali groups)] X
100
NS= Non-significant, *= P<0.05, **=
P<0.01.

Estimates of
GIV-G were found to be 59, 242, 122, and 395 grams in MY7,
MY21, MY28, and TMY, respectively. The figures attained for milk components were
1.24, 0.47, 0.38, 0.13 and 1.22 % higher in fat, protein, lactose, ash and total
solids in V-line does compared to G does, respectively. This superiority of
V-line does in GIV-G is in agreement with its long history
of selection for litter size at weaning and its high average for this trait
(Estany et al 1989). This might be due to increased milk production levels in
V-line does compared to G does. Therefore, V-line rabbits could produce and
lactate efficiently under hot climatic conditions of Saudi Arabia. Lukefahr et
al (1983 and 1996) in USA showed that estimates of direct additive effects for
milk yield traits were mostly in favour of New Zealand White rabbits compared to
Californian rabbits. In crossbreeding experiments carried out in Egypt, Abd
El-Aziz et al (2002) found that estimates of direct additive effects for milk
production were mostly in favour of New Zealand White relative to Gabali
rabbits.

Most estimates of
GMV-G for milk yields (MY7, MY28 and TMY) and components
(protein, fat, lactose, and ash of milk) were in favour of V-line dams (Table
6). Estimates of GMV-G were in favour of V-line dams and
found to be 222 g and 0.67% and 0.63 % for MY21, total solids in milk and fat of
milk, respectively. However, most of the Egyptian findings (Khalil et al 1995;
Khalil and Afifi 2000; Abd El-Aziz et al 2002) reported a general trend
indicating that does mothered by exotic breeds (e.g. V-line, Californian,
Chinchilla, etc.) recorded better performance than does mothered by native
breeds (e.g. Baladi and Giza White rabbits). These results do not disagree with
the fact that using V-line as a dam breed could produce high performances in
lactational performance compared to other dam breeds.

Direct (HI)
and maternal (HM) heterosis

Estimates of
HI indicated that crossbred does were associated with heterotic
effects in milk yields and components (Table 7).

Table 7. Estimates of direct (HI) and maternal
(HM) heterosis and their standard errors (SE) for milk yields
(grams) and components (g/100g)

Milk trait

Direct
heterosis

Maternal
heterosis

Units±SE

HI
%a

Units±SE

HM
%b

MY7

109±37*

10.3

150±56*

14.2

MY21

250±70**

9.7

187±58*

7.4

MY28

191±49***

22.7

127±47*

15.2

TMY

550±150**

12.2

449±230*

7.8

Fat

0.97±0.25*

7.8

0.24±0.38 NS

1.9

Protein

0.95±0.16*

8.1

0.89±0.25**

7.6

Lactose

0.32±0.09**

15.8

0.17±0.41**

8.3

Ash

0.13±0.03*

6.0

0.05±0.05 NS

2.2

Total solids

1.91±0.30*

6.8

1.71±0.51**

6.1

aHI%= [HI in units / average of
V line and Gabali groups] x 100
bHM%=
[HMin units / average of V line and Gabali groups] x
100
NS = Non-significant:
* = P < 0.05; ** = P < 0.01 ; *** = P <
0.001.

The estimates of
HI in crossbred does, all significant, were obtained in terms of 109,
250, 191, 550 grams in MY7, MY21, MY28, and TMY and 0.97, 0.95, 0.32, 0.13 and
1.91% in fat, protein, lactose, ash and total solids, respectively. The
estimates of HM were, in general, significant, being 150, 187, 127,
and 449 grams in milk yield traits and 0.24, 0.89, 0.17, 0.05 and 1.71 % in milk
components traits. These results indicate that crossbred does and dams gave
favourable heterotic effects on milk yields and components. Lukefahr et al
(1996) in USA showed that heterotic effect for milk production was 9.2% in
crossing New Zealand White rabbits with Californian. Results of Khalil and Afifi
(2000) revealed that crossing Gabali rabbits with NZW was associated with
negative low non-significant heterotic effects on milk yields during the first
21 days of suckling and the whole period of lactation. Abd El-Aziz et al (2002)
reported that direct heterotic effects on milk production traits were
non-significant (0.12 to 2.4 %).

Direct recombination
effects (RI)

Estimates of
RI for all lactation traits (Table 8) were non-significant and
indicate that epistatic recombination losses for these traits in crossbred does
were negligible.

Table 8: Estimates of direct recombination losses
(RI) and their standard errors (SE) for milk yields (grams) and
components (g/100g)

Milk trait

Recombination
effect

Units±SE

(RI/HI)%

MY7

-2.4±28NS

-2.2

MY21

-6.3±81NS

-2.5

MY28

-10.2±38NS

-5.3

TMY

-13.7±117NS

-2.5

Fat

-0.091±0.19NS

-9.3

Protein

-0.032±0.13NS

-3.4

Lactose

-0.023±0.72NS

-7.1

Ash

-0.012±0.25NS

-9.6

Total solids

-0.083±0.256NS

-4.3

NS =
Non-significant

Moreover, these
estimates of RI were mostly different to estimates of HI
(Table 7). These negligible estimates of RI indicate that there is a
potential advantage to use crossbred does and bucks including V-line genes to
develop parental lines (maternal and paternal lines having more available
heterosis) to be used in hot climate countries. However, informations in the
literature concerning estimates of RI for lactation traits in rabbits
are scarce or not available and consequently no comparison with the present
results was attempted. In general, the two-locus model of heterosis reflects
dominance effect and half additive-by-additive interaction effects whereas the
recombination effect included only half of the additive-by-additive interaction
effects (Dickerson 1992).

Conclusions

Moderate heritabilities
for lactation traits obtained from rabbits raised in the present study lead to
conclude that lactation traits could be practically implemented efficiently (as
selection criteria) in selection programs to synthesize new maternal lines of
rabbits favourable for hot climate.

The favourable
estimates of direct and maternal heterosis for milk production and composition
traits obtained from crossing V-line with Saudi Gabali rabbits would be an
encouraging factor for the rabbit producers in hot countries to use crossbred
does and dams on commercial scale; i.e. crossing V-line with Saudi rabbits was
associated with an improvement in milk production along with a reduction in
conversion ratio of milk to litter gain.

Non significant
recombination effects for most milk yields and components gave an impression to
conclude that crossbred does resulting from crossing V-line with native breeds
of rabbits in hot climate countries could be effective to develop synthetic
maternal lines characterized by high milk production associated with rich
components and consequently higher productivity in does could be
attained.

Acknowledgments

This project
is supported by a great grant (ARP: 18-62) from King Abdulaziz City for Science
and Technology in Saudi Arabia. We are appreciated for the efforts of Mr. M. H.
Abo El-Fadel for collecting, sampling and editing the data and for Mr. S.
El-Khadragy for analyzing chemically the milk samples.

References

Abd El-Aziz M
M, Afifi E A, Bedier Nayera Z, Azamel A A and Khalil M H 2002 Genetic
evaluation of milk production and litter weight traits in Gabali, New Zealand
White rabbits and their crosses in a newly reclaimed area of Egypt. In:
Proceedings of the 3rd Scientific Conference on Rabbit Production in
Hot Climates, Hurghada, 8-11 October 2002, 103-116, Egypt.

AOAC 1980
Official Methods of Analysis. 13th Edition, Association of Official
Agricultural Chemists, Washington, D. C., USA.

Ayyat M S,
Marai I F M and El-Sayiad G H A 1995 Genetic and non-genetic factors
affecting milk production and preweaning litter traits of New Zealand White does
under Egyptian conditions. World Rabbit Science, 3: 119-124.

Baselga M
2004 Genetic improvement of meat rabbits: Programmes and diffusion. In:
Proceedings of the 8th World Rabbit Congress, 7-10 September 2004,
Puebla, Mexico, pp 1-13.

Boldman K G,
Kriese L A, Van Tassell C P and Kachman S D 1995 A manual for use of
MTDFREML. A set programs to obtain estimates of variances and covariance
[DRAFT]. U.S. Department of Agriculture, Agricultural Research Service,
USA.

Capra G,
Blumetto O and Elizalde E 2000 Meat rabbit production in Uruguay. In:
Proceedings of the 7th World Rabbit Congress, Valencia, Spain, 4-7 July 2000,
Volume B: 51-58.

Case R A,
Bradley R L and Williams R R 1985 Chemical and physical methods. In:
Standard Methods for the Examination of Dairy Products. Richardson G H, Editor,
15th Edition, American Public Health Association, Washington, D. C.,
USA, pp.327-402.

Cowie A T
1969 Variations in the yield and composition of the milk during lactation in
the rabbit and the galactopoietic effect of prolactin. Endocrinology
44:28.

Dickerson G E
1992 Manual for evaluation of breeds and crosses of domestic animals, Food
and Agriculture Organization of the United Nations, Rome, PP 47.

El-Maghawry A
M, Soliman A M and Khalil M H 1993 Doe milk production as affected by some
genetic and environmental factors in New Zealand White and Californian rabbits
under Egyptian conditions. Egyptian Journal Rabbit Science 3:
141-150.

El-Sayiad Gh
A, Habeeb A A M and El-Maghawry A M 1994 A note on the effects of breed,
stage of lactation and pregnancy status on milk composition of rabbits. Animal
Production 58:153-157.

Estany J,
Baselga M, Blasco A and Camacho J 1989 Mixed model methodology for
estimation of genetic response to selection in litter size in rabbits. Livestock
Production Science 21: 67-75.

Garcia M L,
Blumetto O, Capra G, Vicente J S and Baselga M 2000 Vitrified embryo of two
selected Spanish rabbit lines to Uruguay. In: Proceedings of the 7th World
Rabbit Congress, Valencia, Spain, 4-7 July 2000, World Rabbit Science, 8 Supp.
1: 139-142.

Garreau H and
Rochambeau H de 2003 La sélection des qualités maternelles pour la
croissance du lapereau. In: 10èmes Journées de la Recherche Cunicole,
Paris, 19-20 Novembre 2003: 61-64.

Garreau H,
Piles M, Larzul C, Baselga M and Rochambeau H de 2004 Selection of maternal
lines: Last results and prospects. In: Proceedings of the 8th World
Rabbit Congress, 7-10 September 2004, Puebla, Mexico, pp 14-25.

Gomez E A,
Rafel O, Ramon J and Baselga M 1996 A genetic study of a line selected on
litter size at weaning. In: Proceedings of the 6th World Rabbit
Congress, Toulouse, France, 9-12 July 1996, 2: 289-292.

Gomez E A,
Rafel O and Ramon J 2000 Preliminary genetic analysis of Caldes line: A
selection experiment for a global objective. In: Proceedings of the
7th World Rabbit Congress, Valencia, Spain, Volume A: 417-423.

Khalil M H
1994 Lactational performance of Giza White rabbits and its relation with
pre-weaning litter traits. Animal Production, 59: 141-145.

Khalil M H
and Afifi E A 2000 Heterosis, maternal and direct additive effects for
litter performance and post-weaning growth in Gabali rabbits and their
F1 crosses with New Zealand White. In: Proceedings of the 7th World
Rabbit Congress, Valencia, Spain, 4-7 July 2000, Volume A: 431-437.

Khalil M H,
Afifi E A, Youssef Y M K and Khadr A F 1995 Heterosis, maternal and direct
genetic effects for litter performance and reproductive intervals in rabbit
crosses. World Rabbit Science, 3(3):99-105.

Khalil M H,
Garcia M L, Al-Dobaib S N, AL-Homidan A H and Baselga M 2005 Genetic
evaluation of pre-weaning litter traits and feed conversion in crossbreeding
project involving Saudi rabbits and spanish V-line. 4th International
Conference of Rabbit Production in Hot Climate, 24-27 February,
Egypt.

Lahari S S
and Mahajan J M 1984 Milk yield and mothering ability in rabbits. Indian
Journal of Animal Science 54(1): 137-138.

Lukefahr S,
Hohenboken W D, Cheeke P R and Patton N M 1983 Characterization of
straightbred and crossbred rabbits for milk production and associative traits.
Journal of Animal Science, 57(5):1100- 1107.

Lukefahr S D,
Cheeke P R and Patton N M 1996 Heritability of milk production and 21-day
litter weight and litter size in purebred and crossbred rabbits using an animal
model. In: Proceedings of the 6th World Rabbit Congress, Toulouse,
France, 9-12 July 1996, 2: 319-324.

Moura A S A M
T, Costa A R C and Polastre R 2001 Variance components and response to
selection for reproductive, litter and growth traits through a multi-purpose
index. World Rabbit Science, 9: 77-86.

Rochambeau H
de, Duzert R and Tudela F 1998 Long term selection experiments in rabbit.
Estimation of genetic progress on litter size at weaning. In: Proceedings of the
6th World Congress on Genetics Applied to livestock Production,
Armidale, NSW, Australia, 11-16 January 1998, Volume, 26: 112-115.

Salaun J M,
Garreau H, Thebault R G, Allain D and Rochambeau H de 2001 Selection pour le
poids total de lapereaux par femelle et par an dans une souche de lapins Castor
Rex. In: 9èmes Journées de la Recherche Cunicole, Paris, 28-29
Novembre 2001: 221-224.

Received 9 June 2005; Accepted 8 July 2005;
Published 1 October 2005

Go to top