PROD-400 The Role of Genetics in Wool Production
Wool Production focuses on the characteristics of Merino wool which influence its value, such as fleece weight, average fibre diameter, staple strength, staple length, colour, vegetable matter and style. The impact of genetics, nutrition, environment, physiology and management on these wool characteristics is examined. The interactions between these factors is explored in a range of environments, providing a systems approach to wool production in each and an understanding of the constraints to wool production at a national level, thus allowing the identification and evaluation of options available to the commercial woolgrower for improving productivity and the value of their clip.
Topics within this theme are breeding and genetics in the wool industry, and the genetics of fleece weight and fibre diameter and their importance for inclusion in breeding objectives. The genetics of disease resistance and the notion of breeding for improved resistance to disease in sheep is introduced. Genetic variation in style traits, and skin-based traits are described and systems incorporating these traits into breeding objectives are reviewed.
PROD-400-050 Breeding and Genetics in the Wool Industry
Modules in this topic address various aspects of Merino breeding and genetics. Basic genetic terminology and past to present genetic research are introduced and summarised. Production traits and genetic correlations between these traits, and the repeatability of production traits in Merino sheep are presented. Breeding structures in the stud Merino industry and the breeding objectives and selection strategies utilised are examined. An example of an index-based selection strategy (WOOLPLAN) is introduced.
PROD-400-050-050 Basic genetic terminology as applied to Merino breeding
This module introduces a number of genetic terms, an understanding of which is required to fully grasp the developments in Merino breeding programs towards optimising genetic gains across the industry. These terms are: repeatability, heritability, selection differential, estimated breeding value, genetic correlation and selection index.
PROD-400-050-100 Merino breeding and genetics research: past to present
This module provides a summarised overview of Merino breeding and genetics research undertaken over the last 60 years. This summary is based on two references that provide a very comprehensive history of breeding and genetics in the wool industry: Ponzoni, R.W. (1995). Wool Tech. Sheep Breed. 43:87, and Turner, H.N. (1977). Anim. Breed. Abstr. 45:9.
PROD-400-050-150 An introduction to the genetics of Merino production traits
This module provides an overview of the inheritance of Merino production traits, including wool, body and reproduction traits, as well as some of the important genetic correlations between these traits. It also looks at response to direct and indirect selection for clean fleece weight, as well as selection for increased ewe reproductive performance.
PROD-400-050-200 Repeatability of production traits in Merino sheep
This module looks at the repeatability of production traits in Merino sheep. It highlights the importance of these estimates when consideration is given to the loss in efficiency arising from basing selection decisions on measurements taken at 12 months age, with animals carrying less than 12 months wool. Two-stage selection is outlined as a strategy for overcoming the loss in accuracy associated with early age measurements.
PROD-400-050-250 Breeding structures in the stud Merino industry
This module considers the breeding structure of the stud Merino industry, in terms of gene flow and the implications for genetic progress. The traditional hierarchical structure and genetic lag between tiers are discussed. The value of open nucleus breeding schemes is mentioned, with the Australian Merino Society being used as an example of how such schemes can operate.
PROD-400-050-300 Breeding objectives and selection strategies in the stud Merino industry
This module examines breeding objectives and selection strategies within the stud Merino industry. It is based mainly on a survey of stud practices undertaken by Casey and Hygate (1992). The relative merits of objective measurement and visual assessments are discussed.
PROD-400-050-350 Woolplan
This module introduces WOOLPLAN, an example of an index-based selection strategy for the wool industry. It outlines the breeding objectives and parameter set on which the indexes are based, as well as showing predicted responses to selection based on the various indexes. A summary of issues which contributed to the cessation of the scheme is given.
PROD-400-100 Genetics of Fleece Weight and Fibre Diameter
The genetics of fleece weight and fibre diameter provide the focus of this topic. The importance of fleece weight and fibre diameter as traits for inclusion in breeding programs is emphasised and the genetic variation of these traits between and within flocks is explained.
PROD-400-100-050 The genetics of fleece weight and fibre diameter
This module introduces the importance of fleece weight and fibre diameter as traits for inclusion in the breeding objective, given that these two traits are the main determinants of profit for the commercial breeder. It emphasises that the relative emphasis to be given to each in a breeding program depends on market forces, such that simultaneous selection for improvements in both offers some protection against that risk. It identifies the opportunities for exploiting between- and within- flock variation
PROD-400-100-100 The genetics of fleece weight and fibre diameter: between-flock variation
This module focuses on the genetic variation in fleece weight and fibre diameter that exists between Merino bloodlines, based on data derived from combined wether trials. It highlights the opportunity for simultaneous improvement in fleece weight and fibre diameter through strategic choice of ram source (i.e. bloodline selection).
PROD-400-100-150 The genetics of fleece weight and fibre diameter: within-flock variation
This module focuses on the genetic variation in fleece weight and fibre diameter that exists within a Merino flock. It demonstrates that both traits are heritable and therefore amenable to improvement via selective breeding. It also highlights that there is a genetic antagonism between the two traits as they are positively correlated. However, by reference to the Trangie QPLU$ Project, it demonstrates that simultaneous improvement in fleece weight and fibre diameter can be achieved through strategic choice of the individuals to use for breeding.
PROD-400-150 Genetics of Staple Strength
Sources of genetic variation in staple strength are presented in this topic. Genetic correlations between staple strength and fleece weight and fibre diameter are examined and responses to selection for staple strength are described. The use of CV of fibre diameter as an indirect selection criterion for staple strength is discussed.
PROD-400-150-050 Genetic variation in staple strength
This module examines sources of genetic variation in staple strength, including between strain, between flock and within flock variation. The heritability of staple strength in a number of environments is reported, as are predicted gains in staple strength that could be achieved under single trait selection.
PROD-400-150-100 Staple strength resource flocks
This module describes the AgWA Staple Strength Resource Flocks, established to demonstrate the response to selection for high and low staple strength.
PROD-400-150-150 The genetics of CV of fibre diameter
This module examines sources of genetic variation in CV of fibre diameter and discusses its value as an indirect selection criterion for staple strength.
PROD-400-150-200 Correlated responses in staple strength
This module examines the genetic correlation between staple strength, clean fleece weight and fibre diameter. It shows the predicted correlated changes in staple strength arising from selection for fleece weight and fibre diameter, with varying emphasis on diameter reduction. The use of CV of fibre diameter as a selection criterion to offset negative changes in staple strength is demonstrated.
PROD-400-200 Genetics of Disease Resistance
Breeding for improved resistance to disease in sheep is the focus of this topic. Modules examine genetic variations in disease resistance traits and the genetic correlations that exist between different disease traits and sheep production traits. Breeding for resistance to worms is used as an example of the genetic gains that can be made in disease resistance when genetic variation exists.
PROD-400-200-050 Breeding for disease resistance in sheep
This module introduces the notion of breeding for improved resistance to disease in sheep. Breeding for resistance is one of a range of strategies for controlling disease, and is especially worth considering where conventional measures of control have been either ineffective, unsustainable or uneconomic. It needs to be remembered that it is a long-term strategy and there is a cost in terms of progress in other traits of economic importance. Some of the considerations required when incorporating disease resistance traits into the breeding objective are outlined.
PROD-400-200-100 Genetic variation in disease resistance traits
This module examines genetic variation in the major diseases affecting the sheep industries of Australia. It presents estimates of heritability, sire differences and strain effects. The response to direct selection for resistance to fleece rot is provided as an example.
PROD-400-200-150 Disease resistance: genetic correlations
This module examines genetic covariation between different disease resistance traits, as well as the genetic correlations between these traits and sheep production traits. The impact on genetic gains in fleece weight and fibre diameter when incorporating faecal egg count in the breeding objective is presented, to address the question of how much emphasis should be given to disease resistance in the breeding program.
PROD-400-200-200 Breeding for resistance to worms
This module focuses on breeding for resistance to gastrointestinal worms as an example of the genetic gains that can be made in disease resistance when genetic variation exists. It looks specifically at response to selection in single trait selection lines, where the selection criterion was high or low faecal egg count. Results indicate that selection for resistance to one species of worm confers resistance to other internal worms as well. The benefits arising from breeding for resistance are demonstrated relative to the levels of control afforded by other non-genetic control strategies.
PROD-400-250 Genetics of Style
This topic covers issues such as the genetics of style, the economic value of style and provides background information on the CSIRO Fine Wool Project.
PROD-400-250-050 The genetics of style
This module presents the genetic variation in style traits, both within and between bloodlines. Genetic correlations between assessed and measured style traits are reported, as are the predicted correlated changes in style traits when selecting for simultaneous improvements in fleece weight and fibre diameter. Genetic parameters are presented for fine, medium and broad wool Merino types.
PROD-400-250-100 The CSIRO Fine Wool Project
This module provides background information on the CSIRO Fine Wool Project. In particular, it describes the system used for assessing wool style traits
PROD-400-250-150 The economic value of style
This module considers the economic value of style. The relative importance of style in processing performance and product value is discussed. The price differentials between style grades are also reported, emphasising the interaction between economic importance and fibre diameter.
PROD-400-300 Genetics of growth and carcase specifications
This topic introduces LAMBPLAN, the genetic improvement scheme for the terminal sire and dual-purpose sheep industries of Australia.
PROD-400-300-050 LAMBPLAN: Meeting market specifications
This module introduces LAMBPLAN, the genetic improvement scheme for the terminal sire and dual-purpose sheep industries of Australia. It highlights the need for understanding the range of markets available for sheep meat products and the specifications associated with each. It describes the basic components of the LAMBPLAN system, including estimated breeding values and selection indexes.
PROD-400-300-100 LAMBPLAN: Genetic trends
This module demonstrates the rates of genetic gain being realised by terminal sire breeders, dual-purpose breeders and Merino breeders involved in LAMBPLAN. It also provides a comparison of gains being achieved at an industry level by the dairy, lamb and Merino industries.
PROD-400-350 Skin-based selection
Skin based traits that have been examined as potential selection criteria are defined. The genetic variation and correlations between these traits and those relating to wool production and quality are discussed. Systems and studies based on skin-based traits are introduced and reviewed.
PROD-400-350-025 A definition of skin-based traits
This module describes some of the skin-based traits that have been examined in relation to potential selection criteria for wool production and quality. These traits are: follicle density, S:P ratio, DpDs ratio, follicle depth, follicle evenness and follicle curvature. Simple diagrams are provided to explain each of these traits.
PROD-400-350-050 The genetics of skin-based traits
This module looks at genetic (co)variation in skin-based traits, as well as the genetic correlations between these traits and those relating to wool production and quality. The correlated responses in skin traits to selection for increased fleece weight and the correlated responses in fleece traits to single-trait selection on skin traits are also discussed. The results of a trial looking to establish the contributions made by skin and follicle characteristics to variations in clean fleece weight (CFW) at a given mean fibre diameter of sheep is also discussed.
PROD-400-350-100 Incorporating skin-based traits in the selection index
This module reviews two studies looking at the potential for skin traits to increase genetic gains in the breeding objective, when incorporated into a selection index. One study is based on SA strong wool genetic parameters, the other on fine wool genetic parameters. Both studies compare the outcomes to those achieved when using the index without skin traits being included
PROD-400-350-150 The Soft Rolling Skin System
This module introduces the Soft Rolling Skin (SRS) breeding system, drawing attention to the three components of the system:within flock selection based on skin type, within flock mating strategy based on mate allocation and bloodline substitution (ram source).
PROD-400-350-200 Using skin types as a selection criterion: classing outcomes
This module reviews two experiments looking at the outcomes of selection based on classer assessment of the skin. One experiment reports the average performance of various skin types in terms of wool production traits. The other experiment reports the selection differentials achieved, and compares these to those achieved when index-based selection is practiced.
PROD-400-350-250 South Australian selection demonstration flocks
This module briefly introduces the SA Selection Demonstration Flocks, established to compare the following breeding and selection strategies used throughout the industry: selection based mainly on classer assessment with some use of objective measurement; selection based mainly on performance records with some attention to visual assessment; selection based largely on the SRS-type approach, using skin assessment and mate allocation.