Grazing behaviour and feeding preferences in pastured dairy cows and heifers

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Pasturing is the most natural and welfare friendly way to feed dairy animals, and is a requirement in organic dairying. When given the choice, cows prefer to be on pasture rather than inside in the summer, and their ability to select their own diet is thought to promote their welfare. Achieving high levels of animal performance and health from grazed forage is a key objective within most pasture-based, milk production systems. Over the next five years, I will continue to study dairy cows in pasture-based production systems, with the intent of improving their efficiency, through better cow productivity and health. The long-term goal of this program is to advance our understanding of feeding preference and grazing behaviour of cows in a pasture-based production system. This goal will be achieved by a series of short-term objectives, which aim to determine how feeding preferences and grazing behaviour: 1) are related to health and productivity; 2) can be modified by early experience and learning; 3) are related to forage characteristics. A first experiment will be designed to relate individual differences in feeding preference and grazing behaviour with health and productivity. We predict that cows that fare better on pasture are more efficient grazers and select for optimal energy and protein intake and/or beneficial plants. In a second experiment, we will determine if heifer preference for a bioactive forage, in this case a forage rich in secondary metabolites that are active against parasites is affected by their parasitic load. We predict that heifers with the highest parasitic load will preferentially select forage rich in secondary compounds, and that preference will become more pronounced over time, with the increase in parasitic load. In a third experiment, the development of grazing behaviour and possible long-term benefits of an early introduction to pasture will be studied. We hypothesize that a sensitive period for the acquisition of grazing skills exists, and that heifers learning during this period will become better grazers later in life. In a fourth experiment, the effect of pasturing animals with more experienced ones will be evaluated. We predict that group housing during the milk feeding stage and the presence of an older animal at pasture will help calves learn to graze more efficiently. In a fifth experiment, calves will be exposed to a selection of fresh plant species at the various stages of ruminant digestion, in an attempt to detect a sensitive period for learning of plant characteristics. We hypothesize that heifers learning during the sensitive period will show a preference for these plants later in life. In experiments 6, we will study preferences of dairy cows on experimental pastures containing small plots of various plant species. We predict that cows will show a clear preference for legume species, but that preferences will vary with time of day and stage of maturity of the experimental forages. In experiment 7, preferences of cows for freshly cut plant species will be studied and related to the physicochemical characteristics of the plants. We hypothesize that cow preference or aversion for forage species will be predicted by their physicochemical characteristics such as fibre content, soluble carbohydrates, and secondary compounds. A better knowledge of cow preferences on pasture will help determine optimal pasture composition and pasture management practices to maintain cow performance and health. Understanding the link between grazing behaviour and cow performance will help in our genetic selection of cows that are better adapted to pasture-based systems. Finally, understanding learning mechanisms involved in grazing behaviour will help with the training of cows to become more efficient grazers.