Optimum Proportion of Bos Taurus 24 Age at First Calving 27 Days Dry and Days Open 29 Calving Interval 30 Lactation Length 33 Milk Production 34 Conclusions 38 DESCRIPTION OF DATA 42 Thai-Danish Dairy Farm, Foundation Cattle and Breeding Policy 42 Feeding and Management 45 Data Preparation 46 Additive genetic effects 55 Heterozygotic and homozygotic coefficients Obtaining additive, heterozygotic, homozygotic and general heterozygotic coefficients Age at calving Season effects 67 Year effects Days open Milk yield iii METHODS OF ANALYSIS 71 RESULTS AND DISCUSSION 77 Means and Standard Errors of Reproduction Traits 84 Means and Standard Errors of Production Traits 86 Model 1. 93 Environmental Effects 93 Breed Group Effects Reproduction Traits 105 Age at calving 105 Days open 106 Lactation length 114 Days dry 115 Calving interval Production Traits Milk yield Conclusions 132 Model 2 133 Model 3 134 Breed additive and nonadditive genetic effects 134 Age at calving 141 Days open Lactation length Days dry Calving interval Milk yield Conclusions Model 4