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The topic of today's lecture is the

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genetics of animal reproductive traits.

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This lecture is part of module one,

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Animal Genetics, which is part of the

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ISAGREED project. This

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presentation was supported by an Erasmus

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plus KA2 Partnerships for

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Cooperation grant. Innovating the

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structure and content of curricula in the

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management of animal genetic and food

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resources using digitalization.

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Reproduction is essential for all

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organisms because it is the key to

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survival and evolution.

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Reproductive traits are important for the

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survival of species not only in natural

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populations but also in livestock

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populations, where they have a major

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impact on the economic efficiency of

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breeders and farms.

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Reproductive traits are economically

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important for sustainable food

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production. Reproductive

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traits, especially those related to

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fertility, litter size and pre weaning

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viability, are important components

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to reduce the cost of animal meat

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production. Therefore,

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great efforts are being made to identify

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ways of improving these traits.

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This improvement in reproductive traits

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is related to different areas, with

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management, nutrition and genetics having

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a major impact.

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Fertility is a fundamental biological

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and utilitarian trait of livestock.

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It is a prerequisite for the maintenance

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of the species as well as the production

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of animal products.

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Fertility is generally understood as the

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ability to produce reasonably numerous

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and constitutionally fit offspring.

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Fertility is subject to considerable

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environmental influences, and a

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distinction must therefore be made

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between potential and actual fertility.

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Potential fertility is to be understood

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as the ability of the female to release

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eggs capable of fertilisation, regardless

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of what happens to them next. So it can

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largely be understood as hereditary

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fertility, which is difficult to detect

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without examination. By the action

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of various environmental factors, by

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which we mean not only the internal

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environment of both sexes. But

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also the external environment, hereditary

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fertility in the sense of the above

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definition is considerably reduced, so

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that by actual fertility is to be

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understood the number of live born

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offspring. Potential fertility can

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therefore be considered as an expression

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of the genotype, and actual fertility

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as an expression of the fertility

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phenotype.

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The most significant indicators of female

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fertility include length of gestation,

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number of pups, litter percentage into

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period, length, service period, and

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difficulty of delivery. Male

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fertility indicators may include sperm

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count, incidents of sperm malformations

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and lebo sexualis, which is related to

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sex hormone levels. The

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importance of different reproductive

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traits is not the same and also varies

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between species. In cattle,

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low female fertility has a very negative

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impact on production as it causes

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economic losses by increasing the need

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for additional inseminations, higher

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veterinary costs, significantly longer

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lactations and fewer carves.

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Also, carving ease is closely related

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to reproductive success and viability of

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mother and offspring. In meat sheet

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production, litter size and days to

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estrus are two of the most important

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traits, but their inclusion in selection

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schemes has been limited due to low

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heritability. In pig

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breeding, as in other multipair species

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such as rabbits, litter size is

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probably the most relevant and easily

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measurable reproductive trait that

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receives the most attention. Litter

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size is determined by the interaction of

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many physiological components, such as

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the number of ovulated eggs, which

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determines the maximum number of possible

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offspring and the rate of prenatal

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survival. Age at first

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following is further considered an

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important trait in evaluating the

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reproductive performance of mares, with

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results across the entire equine breeding

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system. As it indicates the

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beginning of the reproductive life of

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individuals. Age at last

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fall is a reproductive trait that is

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considered to be a measure of the

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cessation of reproductive activity of

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individuals, thus indicating the

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reproductive life of the population.

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However, equine reproductive parameters

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related to fertility are complex traits

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influenced by a wide range of genetic,

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environmental and management factors,

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making it difficult to identify the

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underlying factors directly related to

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the animals themselves.

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Factors affecting reproductive traits.

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The reproductive traits of livestock are

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influenced by internal and external

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factors. Internal factors

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are related to the genotype of the

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animal, while external factors are

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related to its environment.

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Ovulation rate and litter size are

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important reproductive traits in

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livestock that have high economic value

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and are genetically controlled.

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Genetic improvement can be achieved by

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identifying polymorphisms in genes

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associated with reproductive traits.

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Non genetic factors can be divided into

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those that have measurable effects such

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as parity, maternal weight and

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carving period, and those that do not

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have measurable effects such as

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infections. Another external

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factor affecting reproductive traits is

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variation in photoperiods, which

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control melatonin secretion.

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Quantitative Genetics.

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Reproductive traits are conditioned by

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polygenes and their inheritance is dealt

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with in quantitative genetics.

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Quantitative genetic studies. The

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inheritance of complex phenotypic traits.

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Its essence is the study of phenotypic

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variation between individuals,

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focusing primarily on traits that take on

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a continuous range of values.

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Any phenotypic expression that has

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different values in different individuals

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and does not follow a pattern of simple

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Mendelian inheritance can be referred to

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as a quantitative trait.

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Quantitative Traits. Are

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conditioned by a large number of small

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effect genes, otherwise called

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polygenes. Environmental

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factors have a large influence on the

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variability of the traits in question.

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They have smooth, uninterrupted

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continuous variability that can be

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objectively measured. In a

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sufficient number of individuals, they

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tend to have a normal distribution of

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phenotypic classes and are ch

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aracterised by a Gaussian curve.

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Their variability is expressed in units

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of measurement and evaluated by

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statistical methods.

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Quantitative traits are measurable. We

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express the phenotype numerically and

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their variability can be characterised

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using statistical quantities.

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With statistical quantities are

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important. The mean?

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The variance or covariance?

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The main error. The standard

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deviation and the coefficient of

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variation.

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Genetic parameters of quantitative

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traits. To study quantitative

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genetic variation, statistical methods

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introduced by Fisher and Wright are used

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to analyse the variance components of

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phenotypic variation and describe the

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similarity between related individuals,

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often without knowledge of the genes

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involved. Genetic parameters

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of quantitative traits can be divided

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into two groups into.

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One primary genetic parameters,

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which we estimate based on biometric

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analysis of the population. They

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represent the individual components of

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the variance partitioned according to the

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source that caused the variance.

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These include. Genetic

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variants. Environmental

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variants. Covariance

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The joint variability of two given

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traits. Two

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secondary genetic parameters are

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calculated as functions of primary

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genetic parameters. These

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include. Heritability.

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Repeatability. And the

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genetic, environmental and phenotypic

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correlations.

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Decomposition of phenotypic variants.

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When assessing the heritability of a

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quantitative trait, it is essential to

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determine to what extent the trait is

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genetically determined and to what extent

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it is environmentally determined.

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The phenotype as an external

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manifestation of a trait is the result of

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the action of complex relationships

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between the genotype and the environment.

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The phenotypic value of an individual

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is the sum of its genotypic value G

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and its environmental value east.

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P = G + E.

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The variance of a phenotype which is

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defined as GE is

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 characterised by the following

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relationships. The value

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V represents the variance of phenotypic

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values. VG represents the variance of

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genotypic values. V represents the

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variance of environmental variance.

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And  represents the covariance between

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genotype and environment.

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Heritability. The most

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common summary statistic in quantitative

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genetics is the calculation of

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heritability. Heritability

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is a measure of the contribution of the

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genotype to the phenotypic re

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lisation of a atrait. It

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determines the proportion of the

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heritable component in the final

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phenotypic expression of a trait.

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Heritability refers only to the

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population and environment in which they

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were measured. Thus, the same

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trait measured in different populations

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may have different heritabilities.

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The mathematical expression of

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heritability is the coefficient of

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heritability H2, which is the

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ratio of genetic variation expressed by

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the variance value to the total

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phenotypic variation also expressed by

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the variance value. Heritability

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coefficient can be expressed in two ways

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this. Heritability

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coefficient in the broad sense.

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Includes all components of genotypic

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variants. Expresses the

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extent to which the phenotype of an

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individual is determined by the genotype.

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Heritability coefficient in the narrow

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sense. Includes the

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component of genotypic variants caused by

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the additive effect of alleles.

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Expresses the extent to which the

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phenotype of individuals is determined by

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two independent sets of genes that they

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acquired from their parents. It

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determines the degree of similarity

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between relatives. The

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coefficient of heritability thus

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determines the degree of similarity

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between related individuals corresponding

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to the general breeding value, the

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proportions due to dominance, D and

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interactions. I indicate

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only how much certain trait combinations

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increase or decrease the value of the

287
00:12:37,563 --> 00:12:40,523
additive effect. The coefficient of

288
00:12:40,533 --> 00:12:42,863
heritability is the most important

289
00:12:42,873 --> 00:12:45,283
genetic parameter for populations of

290
00:12:45,293 --> 00:12:48,163
quantitative traits. It expresses

291
00:12:48,213 --> 00:12:50,563
the extent of variability over which a

292
00:12:50,573 --> 00:12:52,703
population can be influenced.

293
00:12:53,623 --> 00:12:55,593
It is a measure of the efficiency of

294
00:12:55,603 --> 00:12:56,343
selection.

295
00:12:59,413 --> 00:13:01,203
The values of the heritability

296
00:13:01,213 --> 00:13:04,013
coefficient. Heritability

297
00:13:04,023 --> 00:13:06,773
coefficient values vary from zero to

298
00:13:06,783 --> 00:13:08,613
one or from zero to

299
00:13:08,623 --> 00:13:11,243
 100%. What is

300
00:13:11,253 --> 00:13:13,423
important, however, is how the

301
00:13:13,433 --> 00:13:15,563
heritability coefficient value is

302
00:13:15,573 --> 00:13:17,623
practically understood in a particular

303
00:13:17,633 --> 00:13:20,483
case, and what it is then used for in the

304
00:13:20,493 --> 00:13:22,963
selection technique. A

305
00:13:22,973 --> 00:13:25,733
heritability coefficient value close to 1

306
00:13:25,733 --> 00:13:28,003
indicates that most of the observed

307
00:13:28,013 --> 00:13:30,974
variation is due to variation in the

308
00:13:30,984 --> 00:13:33,104
average effects of different alleles.

309
00:13:34,074 --> 00:13:36,904
Conversely, while low heritability means

310
00:13:36,914 --> 00:13:39,404
that VA is small, it tells us little

311
00:13:39,414 --> 00:13:42,364
about VG because the genetic effects may

312
00:13:42,374 --> 00:13:45,204
be largely non additive D and I.

313
00:13:46,254 --> 00:13:48,404
This means that even a trait with the

314
00:13:48,414 --> 00:13:50,684
value of coefficient of heritability

315
00:13:50,734 --> 00:13:53,324
equals zero may still have considerable

316
00:13:53,334 --> 00:13:55,384
genetic variation at locky,

317
00:13:55,834 --> 00:13:57,754
contributing to the observed trait

318
00:13:57,764 --> 00:14:00,734
variability. In general,

319
00:14:00,794 --> 00:14:02,874
the higher the value of the heritability

320
00:14:02,884 --> 00:14:05,234
coefficient I the more

321
00:14:05,244 --> 00:14:07,574
heritability contributes to the overall

322
00:14:07,584 --> 00:14:10,174
variability, the simpler the selection

323
00:14:10,184 --> 00:14:11,494
methods we can use.

324
00:14:12,544 --> 00:14:14,954
Conversely, the lower the value of the

325
00:14:14,964 --> 00:14:17,894
heritability coefficient, IE the more

326
00:14:17,904 --> 00:14:20,154
environmental factors contribute to the

327
00:14:20,164 --> 00:14:22,554
variability of the trait, the more

328
00:14:22,564 --> 00:14:24,784
complicated the selection methods we have

329
00:14:24,794 --> 00:14:27,774
to choose. In practise,

330
00:14:27,774 --> 00:14:29,625
this means that in the case of traits

331
00:14:29,635 --> 00:14:32,325
with high heritability, we can expect the

332
00:14:32,335 --> 00:14:33,965
offspring to have roughly the same

333
00:14:33,975 --> 00:14:35,955
development as the parents for that

334
00:14:35,965 --> 00:14:38,845
trait. The resulting value

335
00:14:38,855 --> 00:14:40,965
of the heritability coefficient is

336
00:14:40,975 --> 00:14:43,895
influenced by. The degree of

337
00:14:43,905 --> 00:14:46,425
variability of the trait under study.

338
00:14:47,435 --> 00:14:50,125
The degree of diversity of genotypes in

339
00:14:50,135 --> 00:14:51,925
the population of interest.

340
00:14:52,965 --> 00:14:55,195
And the degree of diversity of breeding

341
00:14:55,205 --> 00:14:56,015
conditions.

342
00:14:59,115 --> 00:15:02,085
Repeatability. When observing

343
00:15:02,095 --> 00:15:04,465
quantitative traits and characteristics,

344
00:15:04,855 --> 00:15:07,225
it is typical that many of them can be

345
00:15:07,235 --> 00:15:09,405
observed and measured repeatedly in the

346
00:15:09,415 --> 00:15:11,745
same individual throughout his or her

347
00:15:11,755 --> 00:15:14,395
lifetime. Repeatability

348
00:15:14,405 --> 00:15:16,875
refers to the degree of similarity in the

349
00:15:16,885 --> 00:15:19,115
values of repeated traits or

350
00:15:19,125 --> 00:15:21,595
characteristics in a given population.

351
00:15:22,665 --> 00:15:24,915
Repeatability of production traits in

352
00:15:24,925 --> 00:15:27,795
organisms is divided into four groups for

353
00:15:27,805 --> 00:15:30,226
selection and breeding purposes.

354
00:15:31,286 --> 00:15:34,176
Repeatability over time expresses the

355
00:15:34,186 --> 00:15:36,296
extent to which the same trait is

356
00:15:36,306 --> 00:15:38,616
repeated at different ages in the life of

357
00:15:38,626 --> 00:15:41,116
an individual. Partial

358
00:15:41,126 --> 00:15:43,826
repeatability expresses the extent to

359
00:15:43,836 --> 00:15:46,176
which the same performance is repeated at

360
00:15:46,186 --> 00:15:48,316
different periods and over the whole

361
00:15:48,326 --> 00:15:51,276
period of production. Spatial

362
00:15:51,286 --> 00:15:54,146
or topographic repeatability determines

363
00:15:54,156 --> 00:15:56,336
the extent to which the same trait is

364
00:15:56,346 --> 00:15:58,486
repeated on different parts of the animal

365
00:15:58,496 --> 00:16:00,866
's body. Paratype

366
00:16:00,876 --> 00:16:03,606
repeatability expresses the extent to

367
00:16:03,616 --> 00:16:05,926
which the same performance is repeated in

368
00:16:05,936 --> 00:16:07,376
different environments.

369
00:16:10,496 --> 00:16:13,086
Repeatability coefficient Rop.

370
00:16:14,126 --> 00:16:16,656
The measure of repeatability is expressed

371
00:16:16,666 --> 00:16:18,676
numerically by the repeatability

372
00:16:18,686 --> 00:16:21,416
coefficient ROP. The

373
00:16:21,426 --> 00:16:23,696
coefficient of repeatability indicates

374
00:16:23,706 --> 00:16:26,406
the proportion of variability caused by

375
00:16:26,416 --> 00:16:28,557
genetic differences out of the total

376
00:16:28,567 --> 00:16:31,547
phenotypic variability. It

377
00:16:31,557 --> 00:16:33,497
represents the maximum level of

378
00:16:33,507 --> 00:16:36,177
heritability, highlights the additive

379
00:16:36,187 --> 00:16:38,357
component of the genotype, and

380
00:16:38,367 --> 00:16:40,627
expresses the extent to which the same

381
00:16:40,637 --> 00:16:43,077
performance level of performance is

382
00:16:43,087 --> 00:16:45,807
repeated. The higher the value of

383
00:16:45,817 --> 00:16:48,117
ROP, the higher the probability of the

384
00:16:48,127 --> 00:16:50,537
same performance, so the trait is

385
00:16:50,547 --> 00:16:52,337
genetically determined to a higher

386
00:16:52,347 --> 00:16:54,997
degree. It includes the whole

387
00:16:55,007 --> 00:16:57,547
component of genotypic variability,

388
00:16:57,877 --> 00:16:59,967
but also variance conditioned by the

389
00:16:59,977 --> 00:17:02,127
effect of the permanent environment and

390
00:17:02,137 --> 00:17:04,467
variance conditioned by the interaction

391
00:17:04,517 --> 00:17:06,727
between the permanent environment and the

392
00:17:06,737 --> 00:17:07,577
genotype.

393
00:17:10,607 --> 00:17:13,157
Heritability of reproductive traits.

394
00:17:14,207 --> 00:17:16,697
Reproductive performance in both males

395
00:17:16,707 --> 00:17:19,107
and females is the basis of profitable

396
00:17:19,117 --> 00:17:20,917
livestock production systems.

397
00:17:22,037 --> 00:17:24,157
Some of the variation in reproductive

398
00:17:24,167 --> 00:17:27,007
traits is under genetic control, which

399
00:17:27,017 --> 00:17:28,828
means that reproductive traits are

400
00:17:28,838 --> 00:17:31,248
heritable and can help to extend

401
00:17:31,258 --> 00:17:34,238
genetics within a population by improving

402
00:17:34,248 --> 00:17:36,868
the intensity of selection and shortening

403
00:17:36,878 --> 00:17:39,348
the generation interval. The

404
00:17:39,358 --> 00:17:41,688
heritability of reproductive traits is

405
00:17:41,698 --> 00:17:44,378
low to moderate, so that an extensive

406
00:17:44,388 --> 00:17:47,008
record of data is needed to identify

407
00:17:47,018 --> 00:17:48,798
specific selectable traits.

408
00:17:49,888 --> 00:17:52,118
Male reproductive traits, including

409
00:17:52,128 --> 00:17:54,678
ejaculate volume and progressive sperm

410
00:17:54,688 --> 00:17:57,318
motility are moderately heritable

411
00:17:57,488 --> 00:17:59,158
and could be used in selection

412
00:17:59,168 --> 00:18:01,398
 programmes. In

413
00:18:01,408 --> 00:18:04,358
contrast, female reproductive traits are

414
00:18:04,368 --> 00:18:06,868
low heritability and are currently the

415
00:18:06,878 --> 00:18:09,308
limiting factor for genetic improvement.

416
00:18:10,188 --> 00:18:13,088
Litter size and parturition interval are

417
00:18:13,098 --> 00:18:15,178
the main constraints to increasing the

418
00:18:15,188 --> 00:18:18,008
intensity of selection and shortening the

419
00:18:18,018 --> 00:18:20,078
generation interval in a breeding

420
00:18:20,088 --> 00:18:20,738
programme.

421
00:18:23,778 --> 00:18:25,548
The following slides show the

422
00:18:25,558 --> 00:18:27,848
heritability coefficients for selected

423
00:18:27,858 --> 00:18:30,689
parameters for males and females of each

424
00:18:30,699 --> 00:18:31,959
livestock species.

425
00:18:35,009 --> 00:18:37,619
Estimation of heritability of bovine

426
00:18:37,629 --> 00:18:39,579
reproductive traits. Males.

427
00:19:08,809 --> 00:19:11,419
Estimation of heritability of bovine

428
00:19:11,429 --> 00:19:13,529
reproductive traits. Females.

429
00:19:44,520 --> 00:19:46,530
Estimation of heritability of

430
00:19:46,540 --> 00:19:48,580
reproductive traits in pigs.

431
00:21:14,811 --> 00:21:16,801
Estimation of heritability of

432
00:21:16,811 --> 00:21:18,691
reproductive traits in sheep.

433
00:21:49,772 --> 00:21:51,802
Estimation of heritability of

434
00:21:51,812 --> 00:21:53,922
reproductive traits in horses.

435
00:22:39,033 --> 00:22:40,593
Thanks for your attention.