A rumen, animal and farm systems evaluation of fodder beet when used to supplement ryegrass during lactation : A thesis by manuscript submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Content Partner: Lincoln University. The purpose of this thesis was to identify the functional changes at the rumen, individual animal and whole-farm scale when FB is used to supplement a ryegrass-based sward during lactation. A review of the literature (Chapter 2) explored the potential of FB to improve the feed base of the farm system and advance low infrastructure grazing systems which are common to New Zealand. However, the review also suggested greater biological, tactical and financial risk may be associated with growing and feeding FB on the milking platform, and the potential net advantage/disadvantage and had not been well defined in grazing dairy systems. Of primary concern was the incidence of acute and sub-acute ruminal acidosis (SARA) which has been underestimated across the herd in confinement and pastoral dairy systems worldwide. The incidence of SARA in cows transitioned to FB using industry-approved methods, and alternative FB feeding strategies to reduce SARA was highlighted as an area requiring further evaluation. In the first experiment (Chapter 3), the effect of feeding FB during early lactation on milk production and milk fatty acid composition of grazing dairy cows was explored. Sixty Friesian × Jersey cows were blocked into six groups of 10 cows, and groups randomly allocated to three replicates fed either 18 kg DM/day of ryegrass herbage (H), or 14.4 kg DM/day of ryegrass herbage + 4 kg DM of harvested FB bulbs (FBB). There was no advantage to milk production when 30% of a ryegrass-based herbage diet was substituted for FB bulb although, this also indicated that FB might provide an adequate substitute for herbage during periods of feed deficit. Supplementation of herbage with FB increased (P < 0.001) de novo synthesis of saturated fatty acids (particularly; lauric, myristic and palmitic acids) and reduced substrate availability of unsaturated fatty acids for ruminal biohydrogenation which reduced (P < 0.001) the content of long-chain and unsaturated products in milk. While the sward's chemical composition differed between treatments, the fatty acid content of herbage was not different (P > 0.1). The altered biohydrogenation end-products in milk and the high soluble-carbohydrate content of FB compared with herbage indicated altered rumen microbial communities and rumen function. The second experiment (Chapters 4 & 5) was split into two chapters to evaluate two objectives. The first objective was to assess the industry recommended me