IMPROVEMENT OF FEED EFFICIENCY IN DAIRY CATTLE

The improvement of feed efficiency in dairy cattle has traditionally been approached through an increase in production levels. However, the effectiveness of the energy partitioning underlying the dilution of maintenance phenomenon decreases with each successive increment in production relative to body size, and therefore will lose importance in the next years. The selection of more efficient animals (i.e. animals that consume less feed to achieve a fixed production) is limited by the cost and inherent difficulty in recording individual feed intake data, which prove pivotal to improve the accuracy of the estimated breeding values for feed efficiency traits. First aim of my project was to record and collect individual phenotypic data on the dry matter intake of dairy cattle under different dietary conditions and at different production stages. The collected data will become part of a larger collaborative dataset aimed at increasing the prediction power of genomic selection plans including traits related to the feed efficiency. Furthermore, following a multimodal approach essential for an effective improvement of the dairy enterprise efficiency, the effect of feed additives and alternative feed ingredients on the production, health status and efficiency of dairy cattle has been investigated. In the first trial, the effect of camelina cake – a byproduct of camelina oil rich in proteins and unsaturated fatty acids – on milk fatty acid profile was investigated. Results from the study evidenced a higher concentration of n-3 PUFA (p = 0.02) and a lower n-6/n-3 ratio (p = 0.01) in the milk of cows fed camelina compared to control. The analysis of the ruminal content suggested a moderate effect of camelina on the ruminal environment and biochemistry. In the second trial, the effect of Saccharomyces cerevisiae (live yeast) on the ruminal environment and its interaction with the production and health status of dairy cows was investigated. Dietary treatment with S. cerevisiae did not affect the investigated ruminal parameters and had only mild effects on blood biochemistry. However, an effect on the ruminal pH was observed when cows were fed low-quality forages, with higher pH values in cows supplemented with S. cerevisiae compared to control (p < 0.05). In the last trial, the effect of camelina on the ruminal microbial populations and the cumulus-oocyte complexes of growing dairy heifers was evaluated. The inclusion of camelina in the diet was associated with higher expression of all selected molecular markers of oocyte quality (p < 0.05). Moreover, feeding camelina affected the ruminal microbiota, as shown by the significant reduction in the alpha diversity of the treatment group (p < 0.05).