Genetic improvement of dairy cattle under different herd environments in Kenya

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This thesis contributes to enhancing the efficiency of dairy cattle breeding programs in Kenya by addressing genotype by environment interactions. It focuses on several key objectives: 1) analyzing the breeding structure and estimating trends in genetic variability of the Holstein-Friesian population to identify herds crucial for genetic improvement, 2) evaluating the nature and extent of genotype by environment interactions for milk yield and fertility traits between nucleus and commercial herds, alongside the expected correlated responses to sire selection, 3) assessing genotype by environment interactions for milk yield across different herd environments and the anticipated correlated responses in low opportunity environments to sire selection aimed at increasing milk yield in higher opportunity herds, 4) describing the lactation curve of cows in both herd environments to determine the appropriate polynomial order for additive genetic and permanent environmental curves, and to analyze variance components between environments, and 5) estimating genetic parameters related to lactation persistency and their relationship with milk yield, while assessing the effectiveness of various selection criteria for improving lactation milk yield and persistency.