This study was based on measurements taken from the milk recording scheme of the Agricultural research Council (ARC). In this study the effects of milk urea nitrogen (MUN) on reproduction parameters of dairy cows in South Africa was investigated. The Analysis of Variance (ANOVA) procedure confirmed that MUN has a significant influence on reproduction performance in South African dairy cows. The correlation between MUN and intercalving period (ICP) demonstrated that cows are taking longer to fall pregnant as MUN increases. Other more complex reproduction parameters were also calculated as well as their correlations with MUN. The first is reproduction performance (RP) which was negatively correlated with MUN. The second parameter was reproductive index (RI) which was also negatively correlated with MUN. This means that overall reproduction in dairy cows decline as MUN concentrations are increased. The breeds used in this study were Holstein and Jersey dairy cows. Analysis of variance results confirmed breed differences for the effects of MUN on reproduction parameters. It was found that reproductive success declines with increasing MUN concentrations in Jersey cows regardless the season. Analyses of the interaction between breed and season, indicate that the most important interaction was between Jersey cows in summer. This implies a different urea threshold for Jersey cows between seasons, as well as between Jersey cows and Holstein cows.
Dissertation (MSc (Agric))--University of Pretoria, 2019.