Genetic basis and improvement of
reproductive traits
Aynalem Haile and Mourad Rekik (ICARDA)
EIAR-DBARC-ICARDA-ILRI (LIVES)-FAO Training on
Reproduction in Sheep and Goat, Debre Berhan,
Ethiopia, 13-15 October 2014

Reproduction: is a complex composite trait
influenced by many components including puberty,
ovulation, estrus, fertilization, embryo
implantation, pregnancy, parturition, lactation, and
mothering ability.
Breeding and Reproduction---Objectives
• Improved lamb production
• More lambs per lambing
• More frequent lambing
• Increased percent of total sheep nos.
• Reducing death losses

The production systems
• Crop-livestock systems where genetic interventions can
make a difference
• Pastoral & semi-pastoral systems in which adaptation is
critical
3

• Crop-livestock systems
– Medium to high potential areas
– Individual/family enterprises
– Limited land
– Medium to high productivity breeds
• Pastoral & semi-pastoral systems
– Large herds/flocks
– Dictates of climate
– Mobility
– Indigenous breeds
– Strong community values
4

Scenarios
• Fluctuation and poor
quality of the feeding
resources
• Insufficient health
care
• Poor housing
conditions
• Fragile economic
asset
Reproduction is
adversely affected

Consequences for reproduction
Sheep and goat breeds of arid and semi arid zones are often late-maturing
animals, have a delayed puberty, shorter production life-time
later than in more favourable natural conditions.
Productive outputs are limited, within other causes, by long
anoestrus periods and low fertility and prolificacy.
Furthermore, in utero undernutrition, a very common event when
pregnant dams are inadequately fed under arid and semi arid
conditions, contributes to a reduced reproductive fitness of the
progeny

Large genetic differences
Between species
• Goats are more strict
seasonal breeders than sheep
• Goats are in average more
prolific than sheep
Within breed variability
Between breeds
• Late maturing vs. early
maturing breeds
• Existence of natural prolific
strains

Characteristics of the reproductive traits to
be improved
• Economically important (fertility, litter size vs.
return to oestrus)
• Expression at the individual level (litter size vs.
Prolificacy)
• Easiness of measure (litter size vs. ovulation rate)
• Cost of measure
• Existence of variability !!!!!!

Factors affecting reproduction in the
ewe
• Heredity
• Age
• Photoperiod (seasonal)
• Temperature and humidity
• Nutrition and Exercise
• Parturition and lactation
• Disease and parasites
• Fertility of & assoc. with the ram

Factors affecting the reproduction in
the Ram
• Breeding soundness exam
• Palpation of the testicles, epididymis, and
penis and visual appraisal of feet, legs, eyes
and jaws.
• Semen evaluation
• Disease prevention
• Heat stress

Desirable traits for accelerated
lambing
• Ewes can breed year round
• Ewes that can mate while lactacting
• Ewes that have a good lambing rate (ie
twinning)
• Sires that produce a desirable market lamb
and have the libido and fertility for conception
year round

Genetic effects
• Although component traits of reproduction are
under the influence of many genes, a limited number
of major genes associated with separate components
of reproduction have been reported in sheep
• Expressions of the genetic effects on reproduction
are affected by numerous environmental factors such
as season, climatic conditions, management, health,
nutrition, ram to ewe breeding ratio, age of ewe, and
ram libido and fertility. Because genetic and
environmental factors interact, genetic improvement
of reproduction is very complicated.

• Selection for a single component of reproduction
such as ovulation rate, litter size at birth or number
of lambs weaned has commonly been practiced.
However, selection for a single component of a
composite trait does not always result in an overall
improvement of a complex trait such as reproduction
• The relevance of the different reproductive traits is
not the same and also differs among species.
• In meat sheep production, litter size and days to
lambing are two of the most important traits

Sex Expression
Mainly in females
• Age at puberty
• Age at first lambing
• Fertility
• Litter size at lambing
• Litter size at weaning
• Lambing interval
• Productive lifetime
Little attention in males
• Scrotal diameter???
• Libido and sexual
aggressiveness???

Heredity basis of reproductive traits
• For most breeds,
reproductive traits are
quantitative traits:
progress is obtained by
transmission of the
additive effects of genes
• In some breeds or
strains, litter size is
influenced by major
genes: alleles
polymorphism in some
known genes
(≈ Mendelian trait)

Quantitative trait
Composition of the phenotype variance
δ2
P = δ2
G δ2
E δ2
GE
16

2 categories of genetic effects
• Due to the effect of random halving of the genome, we have 2
fundamentally different categories of genetic effects:
• Effects that come into play by mating an individual to a random
sample of the population and are effective as the average of the
offspring (= additive effects).
• Effects determined by specific combination of gametes in a
particular individual, but not the offspring (= dominance and
epistatic effects).
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Splitting the genetic effect
g = ga + do + ep
• ga = "additive" gene effect (relevant for breeding value)
– ga is the part of g, which comes into effect when the individual
is mated to a representative sample of the population in the
average of its offspring.
• do = "dominance effect"
– do is the part of g, not explained by ga and due to interactions
of alleles of the same locus within a particular individual.
• ep = "epistatic effect"
– ep is the part of g, not explained by ga or do and due to
interactions of alleles of different loci within a particular
individual.
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Concept of heritability h2
Heritability is the proportion of variation in a phenotype (trait,
performance) that is thought to be caused by genetic variation
among individuals. The remaining variation is usually
attributed to environmental factors. A measure of
the degree to which the variance in the distribution of
a phenotype is due to genetic causes.
- h2 < 10%: low heritability, low genetic progress by direct
selection
- 10% < h2 < 30% : moderate heritability, slow genetic progress
by direct selection
- h2 > 30% : high heritability, significant progress by direct
selection

Estimates of heritability for basic and
composite traits (Rosati, 2002)
Conception Rate 0,06
Number of lambs born 0,10
Number of lambs born alive 0,05
Number of lambs alive at weaning 0,01
Litter mean weight per lamb born (kg) 0,13
Litter mean weignt per lamb weaned (kg) 0,15
Number of lambs born per ewe exposed 0,09
Number of lambs weaned per ewe exposed 0,07
Total litter weight at birth (kg) 0,4
Total litter weight at weaning (kg) 0,17
Total litter weight born per ewe exposed (kg) 0,13
Total litter weight weaned per ewe exposed (kg) 0,11
Lamb survival at weaning (%) 0,12

Major genes affecting litter size
1. The BMPR 1B (Bone Morphogenetic Protein Receptor
type 1B) gene has been mapped to sheep chromosome 6
(“hyperprolific phenotype” of the Booroola sheep,
Assaf??)
2. The BMP15 (Bone Morphogenetic Protein 15) gene, has
been mapped to sheep chromosome X (Rasa Aragonesa,
Lacaune, Galway)
3. The sheep GDF9 (Growth Differentiation Factor 9) gene
maps to chromosome

The challenge
• Regarding genetic improvement, available work has mainly
focused on phenotypic selection, rather than using
information on specific genetic factors (genotypic information)
affecting these traits.
• Nevertheless, reproductive traits are characterized by low
heritabilities and a complex genetic basis and are thus difficult
to improve using traditional selection methods.
• Moreover, these traits are recordable only in one sex and late
in the animal’s life.
• These limitations have led to a growing interest in the
identification and characterization of specific genes and
genomic regions implicated in the variability and regulation of
reproductive processes.

Breeding structures

Modern Breeding Structures
Breeders
Commercial flocks,
community or base
Breeders
Multipliers
Base flocks
Gene flow (males)
Mueller, 2008
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No breeding structures
– Occurs in low input systems
– Difficult for the breeder to detect the best animals with
high precision
– Difficult to organize a stratified mating in his flock
– Less chance for gene inflow
– Mating is at random within the flock
– Genetic progress is slow, if any
– Difficult to follow
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Nucleus Breeding Structure
Nucleus
Base
Females Males
“Open” to gene flow
in any direction
Mueller, 2008 26

Centralized and dispersed nucleus
central
nucleus
dispersed
nucleus
Participating flocks Participating flocks
Mueller, 2008 27

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The higher the dissemination, the higher
should be the BV and its accuracy
Records
BLUP analyses
Records on
relatives
30%
60%
90%
Genomic
100%
Visual
Random
0%
Performance test
Progeny test
BLP analyses
Sophistication of selection system
Selection accuracy

Thank you