Evaluation of herb pastures for New Zealand dairy systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Sciences at Massey University, Manawatu, New Zealand
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Chicory (Cichorium intybus L.) and plantain (Plantago lanceolata L.) sown in pure swards or both herbs sown with red clover (Trifolium pratense L.) and white clover (T. repens L.) are able to produce large amounts of high-quality forage in summer and autumn, when production and quality of perennial ryegrass (Lolium perenne L.) are often limited. There have been many cases of poor persistence of chicory with current management practices, but there is limited information for plantain and the herb-clover mix pastures when grazed in dairy systems. Additionally, the presence of bioactive compounds in plantain has created interest in their potential effect on rumen fermentation. The objectives of this research were to evaluate the effect of grazing frequency, two and four weeks, on the agronomic characteristics and diet selection of chicory, plantain, and herb-clover mix pastures, with dairy cows during two growing seasons (2011-2012; 2012-2013) and to examine the effect of the bioactive compounds in plantain on in vitro rumen fermentation. Chicory plants grazed every two weeks, rather than every four weeks, did not develop large taproots, and consequently stored less carbohydrate reserves (fructan and fructose) and failed to develop extra shoots. Chicory grazed every two weeks failed to persist, while chicory grazed every four weeks persisted only for the two growing seasons. For plantain the grazing frequency did not affect its plant density nor taproot diameter; however, the number of shoots per plant increased when grazed every two weeks compared to every four weeks. Overall, plantain and herb-clover mix pastures were more productive and persistent than chicory. The three pastures produced high-quality feed for dairy cows. Dairy cows preferred the herb-clover mix pasture, rather than pure chicory or plantain swards, and selected indiscriminately between chicory, plantain, and red clover. The diet selection for chicory and plantain varied between seasons and was affected by the vertical access and horizontal distribution of the species in the swards. The presence of bioactive compounds, aucubin and acteoside in plantain reduced the ammonia concentration during fermentation and probably causes less urea to be excreted in the cow‘s urine when grazing plantain. In conclusion, the herb-clover mix performed best due to its high herbage production and nutritive value and greater grazing preference by dairy cows, plus its potential to reduce the nitrogen lost from dairy systems.