GLOBAL GENETIC EVALUATIONS FOR DAIRY CATTLE

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INTRODUCTION

Achieving genetic improvement involves the identification of those animals with the best breeding values and then ensuring that the selected individuals become parents of the next generation. Artificial insemination (AI) can allow the rapid dissemination of this improvement throughout a population or breed (Bichard, 2002). The importance of accurately estimating breeding values can therefore never be overemphasized.

GLOBAL GENETIC EVALUATIONS FOR DAIRY CATTLE

The genetic evaluation of dairy sires and cows for production traits has for many years been based on the analyses of 305)day lactation yields (Lactation Models). The basis of every 305)day yield is a set of test)day yields taken approximately every 35 days in milk (Figure 1.1). Incomplete lactation records are normally extended to a 305)day basis, following a set of well)defined rules.

TEST-DAY MODELS

The genetic evaluation of dairy cattle using test)day models has been investigated by several research groups in recent years (Swalve, 1995a, 1998, 2000; Freeman, 1998; Misztal et al., 2000 and Jensen, 2001) and some countries have already implemented routine genetic evaluation of large commercial dairy populations using a Test)day Model (Swalve, 2000; Table 1.3).

Types of Test-day Models

Different types of test)day models are used for national dairy cattle evaluations worldwide. A repeatability or fixed regression test)day model was used for German Holstein cattle (Reents & Dopp, 1996; Reents et al., 1998) and is currently used for evaluation of production traits in Slovenia (Potocnik et al., 2001), Estonia and Switzerland (Table 1.3). Random regression test)day models are used in Canada (Schaeffer et al., 2000; Kistemaker, 2003), The Netherlands (De Roos et al., 2001), in Germany for the Holstein and Red breeds (Liu et al., 2001) and in joined evaluations for Simmental and Brown Swiss in Germany and Austria (Emmerling et al., 2002). Finally, a reduced rank random regression model is used in Finland (Lidauer et al., 2000), and is being investigated by The Netherlands (De Roos et al., 2002) and the UK (Mrode et al., 2003). When comparing this literature to the information in Table 1.3, there are some inconsistencies, as the information on the INTERBULL website was probably not yet updated for the relevant countries.

Declaration
Abstract
Acknowledgements
Dedication
CHAPTER 1 – LITERATURE STUDY
1.1 INTRODUCTION
1.2 GLOBAL GENETIC EVALUATIONS FOR DAIRY CATTLE
1.3 TEST-DAY MODELS
1.3.1 Types of Test-day Models
1.3.1.1 Two-Step Test-day Models
1.3.1.2 One-Step Test-day Models
1.3.1.2.1 Fixed Regression Test-day Models (FRM)
1.3.1.2.2 Random Regression Test-day Model (RRM)
1.3.1.2.3 Reduced Rank Random Regression Test-day Model (RRRM)
1.3.1.2.4 Multiple Trait Test-day Model
1.3.1.2.5 Covariance Function Models
1.3.1.2.6 Character Process Models
1.3.1.2.7 Spline Models
1.3.2 Comparison of Models for Genetic Evaluation
1.3.2.1 Test-day Models versus Lactation Models
1.3.2.1.1 Genetic Parameters
1.3.2.1.2 Estimated Breeding Values
1.3.2.1.3 Genetic Trends
1.3.2.1.4 Computation
1.3.2.2 Comparison of different test-day models
1.3.2.2.1 Genetic parameters
1.3.2.2.2 Estimated Breeding Values
1.4 CLOSURE
1.5 AIM OF THE STUDY
1.6 REFERENCES
CHAPTER 2 – CRITICAL ASSESSMENT AND EVALUATION
2.1 INTRODUCTION
2.2 LIMITATIONS AND CHALLENGES
2.3 MODEL INFORMATION
2.3.1 Contemporary Group
2.3.2 Age of the cow at calving
2.3.3 Calving Interval
2.3.4 Regression Function
2.3.5 Permanent Environment
2.3.6 Calving Year
2.4 ADJUSTING FOR HETEROGENEOUS VARIANCES
2.5 PRESENTATION TO THE INDUSTRY
2.6 CRITICAL ASSESSMENT
2.7 CONCLUSIONS
2.8 REFERENCES
CHAPTER 3 – THE USE OF FIXED REGRESSION TEST-DAY MODELS IN THE ESTIMATION OF VARIANCE COMPONENTS FOR SOMATIC CELL SCORE OF SOUTH AFRICAN HOLSTEIN AND JERSEY CATTLE.
3.1 ABSTRACT
3.2 INTRODUCTION
3.3 MATERIALS AND METHODS
3.4 RESULTS AND DISCUSSION
3.5 CONCLUSIONS
3.6 REFERENCES
CHAPTER 4 – TEST-DAY MODELS FOR PRODUCTION TRAITS IN DAIRY CATTLE IN SOUTH AFRICA
4.1 ABSTRACT
4.2 INTRODUCTION
4.3 MATERIALS AND METHODS
4.4 RESULTS AND DISCUSSION
4.5 CONCLUSIONS
4.6 REFERENCES
CHAPTER 5 – TEST-DAY MODELS FOR SOUTH AFRICAN DAIRY CATTLE FOR PARTICIPATION IN INTERNATIONAL EVALUATIONS
5.1 ABSTRACT
5.2 INTRODUCTION
5.3 MATERIALS AND METHODS
5.4 RESULTS AND DISCUSSION
5.5 CONCLUSIONS
5.6 REFERENCES
CHAPTER 6 – COMPARISON OF BREEDING VALUES AND GENETIC TRENDS FOR PRODUCTION TRAITS ESTIMATED BY A LACTATION MODEL AND A FIXED REGRESSION TEST-DAY MODEL
6.1 ABSTRACT
6.2 INTRODUCTION
6.3 MATERIALS AND METHODS
6.4 RESULTS AND DISCUSSION
6.5 CONCLUSIONS
6.6 REFERENCES
CHAPTER 7 – THE IMPACT OF THE ADJUSTMENT OF HETEROGENEOUS VARIANCES AND A CALVING YEAR EFFECT ON A TEST-DAY MODEL FOR NATIONAL GENETIC EVALUATION OF DAIRY CATTLE IN SOUTH AFRICA
7.1 ABSTRACT
7.2 INTRODUCTION
7.3 MATERIALS AND METHODS
7.4 RESULTS AND DISCUSSION
7.5 CONCLUSIONS
7.6 REFERENCES