Overview of Breeding Methodologies

[Kvet Forum]

Inheritance of Characteristics

Genes determine the way animals look - the observable trait. Thus the length of ear in sheep is the expression of the genes that regulate ear length. The breeder can only plan according to the trait observed. Repeatability and heritability are two kinds of observation that the breeder can use.

• Repeatability: This refers to the permanence of a type from one observation to the next. It is a measure of the extent to which superiority in any one character is maintained throughout the lifetime. Should sheep in a flock tend to rank in approximately the same order with regard to a certain character, year after year, in spite of environmental changes, the particular character is said to have high repeatability.
• Heritability: This is concerned with the constancy with which the phenotype is passed from parent to offspring. It expresses the proportion of total variance which can be attributed to average effects of the genes. Alternatively, heritability is the degree of inheritance of the trait.
• Selection: Individuals selected for breeding must have desirable characteristics which have good repeatability and heritability and will, therefore, be passed on to offspring. Selection aims to change the gene frequencies in order to improve the animal body types in the following generations.

Selection may be direct or indirect. The direct method selects sheep having the best expression of the trait to be improved. Indirect selection improves a trait by selecting sheep with a related trait. The effectiveness of indirect selection depends upon the correlation between two traits. This is of great importance since animal breeding usually involves more than one trait. An example of indirect selection is given by high growth rate, where selection for this trait is likely to improve early maturity and slaughter weight and also the efficiency of feed conversion.

Breeding Strategies​

Depending on your goals for breeding animals different breeding techniques can be used. The following is a brief overview of some breeding methodologies. The majority are not practical for most people, but for the dedicated animal breeder combinations can be used depending on the breeding strategy.

• Crisscrossing: A continuous program of crossbreeding in which there is an alternate use of males belonging to two breeds. Using two breeds designated as P1 and P2, a crisscrossing program, beginning with the two-breed cross animal (P1 x P2), would begin by backcrossing to one of the parental breeds [(P1 x P2) x P1]. Females resulting from these matings would be bred to a P2 male, [(P1 x P2) x P1] x P2, and so on.
• Genus cross: Mating of animals belonging to different genera (for example, mating of domestic cattle, Bos taurus or Bos indicus, to the buffalo, Bison).
• Grading: Mating of purebred males of a given breed to non-purebred females and the resultant female offspring in successive generations.
• Inbreeding: Mating of animals more closely related to each other than the average relationship within the breed or population concerned.
• Linebreeding: Generally mild form of inbreeding in which animals mated are related to some supposedly outstanding individual.
• Outbreeding: Mating of animals less closely related to each other than the average relationship within the breed or population concerned.
• Species cross: Mating of animals belonging to different species (for example mating of European breed cattle, Bos taurus, to Brahman cattle, Bos indicus).
• Three-breed rotational cross: A continuous program of crossbreeding in which males of three breeds are used on a rotational basis. Using three breeds designated as P1, P2 and P3, the first generation would involve production of two-breed cross animals, P1 x P2. In the second generation, two-breed cross females would be mated to males of the third breed, (P1 x P2) x P3; three-breed cross females would be mated to males of one of the breeds used to produce the two-breed cross animals, [(P1 x P2) x P3] x P1, and so on.

Descriptions in Breeding​

• Progeny = Offspring
• Backcross: Progeny resulting from the mating of a two-breed cross animal to one of the parental breed
• Crossbred: Progeny resulting from the mating of outcross animals belonging to different breeds.
• Inbred line: Line of animals produced by mating related animals.
• Incross: Progeny resulting from the mating of animals from different inbred lines within a breed.
• Incrossbred: Progeny resulting from the mating of animals from inbred lines of different breeds.
• Outcross: Progeny resulting from the mating of unrelated animals within a breed.
• Topcross: Progeny resulting from the mating of animals belonging to different families within a breed.
• Topcrossbred: Progeny resulting from the mating of inbred males to non-inbred females of another breed.
• Topincross: Progeny resulting from the mating of inbred males to non-inbred females of the same breed.
• Two-breed cross: Progeny resulting from the mating of males of one breed to females of another breed.

Breeding Strategies and Plans

Distinct objectives are essential to a breeding plan aiming to improve our livestock breeds for better future profitability such as:

1. Higher milk yield
2. Better milk composition (depends on your market)
3. Good udder or body shape
4. Higher beef/meat quality
5. Higher growth rate (also related to good nutrition)
6. Better disease resistance
7. Better fit to available feed and other circumstances
8. Color preference
9. Polled/non polled etc.

Both quantity and quality must go together for efficient production.
Genes determine the way animals look. For example the coat colour in cows is the phenotypic expression of the genes that regulate coat colour. The breeder can only plan according to the trait observed. Other genes determine whether the udder will be small or large, whether the animal has horns, the size of the body etc.

Some examples of simple breeding strategies we can mention:

1. To increase milk production in zebu cattle: This can be achieved by upgrading the Zebu breed with a proven exotic dairy breed (Jersey, Guernsey, Friesian) upto the fourth generation or the larger and more productive Boran or Sahiwal cow depending on disease pressure in your area.
2. To increase disease resistance in exotic dairy breeds: Introduction of animals with better resistance to disease such as Boran or Sahiwal will improve the disease resistance of the dairy breeds. The cross bred offspring may take more after one parent than the other, but there are very good experiences with such crosses.
3. Better performance within a breed: If natural breeding is practiced - exchange the bull if the offspring consistently have undesirable traits.

If AI is practiced - look carefully at the pictures and specifications of sires offered to determine whether the proposed sire will add better body conformation to the animal offspring. Some AI semen providers will supply pictures of offspring, with strengths highlighted.
N/B: The successive offspring from the initial/ subsequent crossing is the one used for successive matings and not the original dam.


Selection of Individuals:

Individuals selected must possess desirable characteristics which have good repeatability and heritability and will, therefore, be passed on to offspring. Selection aims to change the gene frequencies in order to improve the subsequent generations.
Selection may be direct or indirect. The direct method selects cows having the best expression of the trait to be improved. Indirect selection improves a trait by selecting cows with a related trait. The effectiveness of indirect selection depends upon the correlation between two traits. This is of great importance since animal breeding usually involves more than one trait. An example of indirect selection is given by high growth rate, where selection for this trait is likely to improve early maturity and slaughter weight and also the efficiency of feed conversion.