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Internal parasitism and growth of farmed deer fed different forage species : a thesis in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University
A series of grazing and indoor experiments were conducted to investigate interactions between internal parasitism and different forage species affecting farmed deer growth, carcass production, voluntary feed intake (VFI) and nutrient digestion. These studies have provided information into aspects of internal parasitism in farmed red (Cervus elaphus) and hybrid (0.75 red:0.25 elk) deer. These studies have also investigated the potential of forage crops with a different plant morphology to perennial ryegrass/white clover (PRG/WC), such as chicory (Cichorium intybus), and those containing condensed tannins (CT) such as sulla (Hedysarum coronarium) and birdsfoot trefoil (Lotus corniculatus), as natural aids in the control of internal parasites of farmed deer. Use of such forage crops could enhance sustainable management systems for deer production with minimal anthelmintic input. This is consistent with the New Zealand Deer Industry's strategy for clean, green, natural products produced using minimal chemical inputs. During 1994, a grazing trial was conducted to evaluate the use of sulla (cv Necton), a new forage legume for deer production. Growth and carcass production from weaning to one year of age on sulla was compared with that on chicory (cv Grasslands Puna) and PRG (Lolium perenne, cv Nui)/WC (Trifolium repens cv Huia) pasture, with all deer receiving three-weekly oral anthelmintic treatment. VFI of deer grazing sulla was greater than for deer grazing chicory in autumn, with pasture being intermediate. Autumn LWG, final liveweight and carcass weight of deer grazing sulla was greater than for deer grazing either pasture or chicory. The proportion of deer reaching 50-65kg carcass weight by one year of age was 100% for sulla and 89% for pasture and chicory. The increased growth and carcass weight of young deer grazing sulla was due to its higher feeding value, particularly during autumn, including increased utilisation of digested nutrients associated with the high CT concentration of sulla (5.1-8.4%). Concurrently, another grazing trial showed that grazing deer on chicory reduced the development of internal parasitism and hence increased deer growth and carcass production, compared with grazing PRG/WC pasture. Deer on the two forages were either treated with anthelmintic three-weekly to control internal parasites, or anthelmintic was withheld until pre-determined trigger-treatment criteria to minimise the welfare risk (to the animal were reached. Chicory and PRG/WC pasture were grazed at the same herbage allowance per animal, but the forages differed in morphology and sward structure, with the broad-leaved chicory sward being taller and more open. Both forages were maintained in the vegetative state, were of high in-vitro digestibility and contained only traces of CT (<0.3%). Untreated deer grazing pasture rapidly developed clinical lungworm infections during the autumn period and required anthelmintic treatment. In contrast, the untreated chicory group required no anthelmintic treatment during the autumn period when grazing chicory, but required treatment 26 days after transfer to pasture during winter. VFI and LWG of untreated deer grazing pasture in autumn was reduced, contributing to lower carcass weights, but anthelmintic treatment had no effect upon the productivity of deer grazing chicory. This experiment also demonstrated limitations of current tools for diagnoses of sub-clinical and clinical internal parasite infections in farmed deer, particularly during the early stages of infection and indicated that further research is needed to investigate the epidemiology, pathogenicity and diagnosis of internal parasite infections. Further research is also needed to partition the effects of plant morphology and plant chemical composition on development of internal parasitism in deer grazing different forage species. Subsequently, a model for sub-clinical parasite infection in deer was established, in a controlled environment, using individually housed deer fed lucerne hay, upon which further evaluation of forage species could be based, allowing individual animal measurement of factors such as VFI, digestion, growth and aspects of parasitology. The initial model investigated the effect of three sub-clinical dose rates of deer-origin lung (Dictyocaulus viviparus) and gastrointestinal (GI) parasite larvae by trickle-infection, relative to an uninfected control group, on deer VFI, liveweight, faecal egg counts (FEC), faecal larval counts (FLC), haematology, serum biochemistry, apparent digestibility, nitrogen (N) retention and digesta N flow at the abomasum and terminal ileum and worm counts at euthanasia. Sub-clinical parasitism reduced liveweight, VFI and serum albumin concentration, elevated serum pepsinogen, gastrin and globulin concentrations and elevated peripheral eosinophil counts, and caused slight haemoconcentration, despite low nematode counts. Reductions in liveweight, N-retention and flow of N at the terminal ileum were shown to be largely due to the reduction in VFI, with no effect of parasite infection on apparent digestibility. This experiment also showed that such studies could be conducted using anthelmintic-treated deer from natural rearing systems as well as artificially-reared deer, thus reducing cost. Finally, the model was used to investigate the effect of feeding forage legumes containing different concentrations of CT on apparent establishment of lung and GI nematodes, VFI, liveweight, FEC, FLC, haematology and serum biochemistry. Fresh, vegetative lucerne (Medicago sativa; 0.1% CT), birdsfoot trefoil (1.9% CT) and sulla (3.5% CT) were compared. This experiment showed a significant negative linear relationship between dietary CT concentration and apparent establishment of abomasal nematodes, particularly T.axei. Deer fed sulla had reduced FLC, higher liveweight gain, carcass weight, dressing-out percentage, serum total protein and albumin concentration and lower serum gastrin concentration, compared with lucerne-fed deer. There were no significant differences in mean VFI between treatment groups during the period of infection, suggesting that the increased liveweight gain of deer fed CT-containing forages was due to an increased efficiency of utilisation of digested nutrients, probably caused by action of CT counteracting protein losses normally associated with parasite infections. It is proposed that the reduced establishment of abomasal nematodes and reduced faecal Lungworm larval count in deer fed sulla containing a high concentration of CT may be due to a direct effect of free CT inactivating nematodes in the GI tract. This study is the first to report and quantify significant reductions in VFI, liveweight gain, N-retention and carcass production in young, farmed deer sub-clinically infected with internal parasites, with most of the reductions being attributable to reduced VFI. Indices for diagnosis of internal parasitism in farmed deer have also been evaluated. Feeding forages containing CT has been shown to reduce apparent establishment of GI nematodes, FLC and increase liveweight gain of parasitised deer. Grazing chicory, a crop of differing plant morphology and sward structure to PRG/WC pasture has also been shown to reduce the development of internal parasitism in farmed deer. The grazing and indoor studies together highlight the potential use of forage crops to increase growth of farmed deer while minimising anthelmintic input. The studies presented in this thesis have great potential significance to the New Zealand Deer Industry. The working model of internal parasitism for deer developed here can now be used to develop further knowledge of deer parasitism and alternative methods of parasite control that are more ecologically sustainable than regular chemical treatment.