Water and Feed Intake in Dairy Cows – Model Evaluation and Potential for Health Monitoring

Die Dissertation wurde mit dankeswerter finanzieller Unterstützung der Stiftung Schleswig-Holsteinische Landschaft angefertigt. Water is one of the most important foodstuffs of a dairy cow – the average amount of 87% water in 1 kg of milk may confirm this thesis (Winchester and Morris, 1956). To ensure good animal health, performance and welfare status, a sufficient supply of water is essential (Murphy et al., 1983). Furthermore, automatical measuring of water intake and also feed intake has started to be established in diverse test stations and dairy research farms (Coffey et al., 2002, Hüttmann, 2007), whereas the trait milk yield has already been recorded automatically on the majority of farms. In the future, water and feed intake will become more important for dairy management due to their link to the health status of the cow (Lukas et al., 2008) as well as for dairy breeding because of their relationship to the energy status of the cow (Coffey et al., 2002). In addition, in times of increasing costs for feed concentrates it is imaginable to include the trait feed intake into future dairy breeding programmes. Nevertheless, there are only a few sources published in the literature regarding the relationship between water intake, feed intake and milk yield. Generally, random regression models have been postulated to analyse daily yield traits such as milk yield or dry matter intake in order to detect the potential change in the dependencies of these traits within the course of lactation (Koenen and Veerkamp, 1998, Veerkamp and Thompson, 1999). Thus, the aim of Chapter One was to analyse the general relationship between the traits water intake, feed intake and milk yield and to establish whether the relationships remained constant during the course of lactation. To do this, fixed and random regression models were used. Furthermore, the model analysis of daily and hence repeated measures of traits in cows such as milk yield, milk ingredients, water intake and feed intake are becoming more important, since repeated measures are assumed not to be independent and thus they are considered to be moderate autocorrelations between repeated measures of daily yields of dry matter intake. However, in order to obtain valid statistical inference and correct variance components, the use of applicable error covariance structures is necessary to achieve the best model fit this purpose, the aim of the Chapter Two was to compare fixed and random regression models with several error covariance structures. …