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Effects of early grazing on the growth and development of red clover (Trifolium pratense L.) : a dissertation presented in partial fulfilment of the requirements for the degree of Master of AgriScience in Agriculture at Massey University, Palmerston North, New Zealand
(Massey University, 2014) Martin, Tyler John
Developments in red clover cultivars have shown that persistency issues that have limited the inclusion of red clover in New Zealand pastures in the past are now less of a concern. The seasonality of current New Zealand pastures can lead to poor summer production. Red clover (Trifolium pratense L.) offers high drought tolerant pasture along with strong yields and high quality herbage. The objective of this research was to compare recent red clover cultivars with an industry standard red clover cultivar and lucerne (Medicago sativa L.), determining the effects of timing of first grazing and grazing frequency. Two experiments were conducted. The field experiment included two red clover cultivars, Grasslands Relish and Grasslands Sensation, and a lucerne cultivar, Grasslands Torlesse. Treatments consisted of a first grazing 10, 12 and 14 weeks after sowing and a final grazing at 28 weeks after sowing. The species were measured over the experiment for morphological development and production through the establishment period. The second experiment was conducted in a glasshouse which included three red clover cultivars Grasslands Relish, Grasslands Sensation and Grasslands Colenso. Defoliation treatments were applied at 1, 2 and 4 week frequencies while production and development were continuously measured including monthly destructive harvests to further measure total plant biomass content and allocation. The two recent red clover cultivars showed better production than lucerne and the older red clover cultivar, and especially notable production was seen by Grasslands Relish during the field experiment. Grasslands Relish was able to be grazed earlier than Sensation giving more flexibility, as well as maintaining a high plant population from autumn through to spring. Timing of first grazing showed that it substantially affected yield but had no effect on plant populations. High frequency defoliation resulted in less total herbage mass production and suppression of unique cultivar characteristics, such as growth habit, that was shown in red clover cultivars that were defoliated less frequently.
A study of the germination and establishment of lucerne (Medicago sativa L.) oversown on an uncultivated grass sward : a thesis presented in partial fulfillment of the requirements for the degree of Master of Agricultural Science (M. Agr. Sci.) at Massey University
(Massey University, 1977) Kusekwa, Martin Lawrence
In this study on the oversowing of lucerne on an uncultivated sward at Massey, three trials were conducted, two in the field and one box trial under glasshouse conditions during the summer of 1975/76 and the autumn and early winter of 1976. The triars compared the effects of two lengths of ground cover, untreated, suppressed for a longer or shorter period with herbicides and burnt on the early establishment of lucerrne sown as bare or pelleted seed. It was found that small amounts of cover at sowing encouraged lucerne germination under high moisture conditions subsequent establishment and early survival was best on the burnt and chemically desiccated, plots. The cover was most useful where it was short (8 cm) and desiccated by long term paraquat or glyphosate treatments. Dense live cover was harmful to lucerne seedlings and smothered them within 5 weeks after sowing. Where recovery of the resident vegetation and weeds was rapid, as on the burnt and short term herbicide plots, lucerne establishnent and survivar was poor and surviviag plants were small and weak. Weed infestation was heavy both on burnt and herbicide treated plots, pointing to the need to introduce an early weed control programme with oversowing. Weeds were found to respond in a similar manner to lucerne to grass competition. In the autumn and early winter tria1s, slug damage was observed and this problem appeared to be of major importance under wet conditions. The effects of slugs were fourd to be most damaging during the first 4-5 weeks after sowing. Metaldehyde slug bait pellets were effective in reducing slug damage if applied at least twice during the establishment period of lucerne. The implications of these findings are reported and discussed with particular reference to the possibilities of oversowing under East African conditions
An investigation into the mechanisms involved in the depression of ovulation rates in ewes grazing oestrogenic lucerne : a thesis peresented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
(Massey University, 1978) McLeod, Bernard Joseph
The reproductive performance of 123 Romney and Border Leicester x Romney ewes was compared after they grazed oestrogenic lucerne or non-oestrogenic ryegrass/clover pasture. To synchronize oestrus prior to the experimental treatment, progestagen-impregnated intravaginal sponges were inserted in all ewes for 14 days. In Experiment I, which involved 42 Romney and Border Leicester x Romney ewes, the animals grazed treatment pastures for one complete oestrous cycle. Blood samples were taken at intervals throughout the cycle and luteinizing hormone concentrations were determined. Ovulation rates and the numbers of follicles present on the surface of the ovaries were recorded at laparotomy, three days post-oestrus. In Experiment II, which involved 81 Romney ewes, oestrogenic lucerne or non-oestrogenic ryegrass/clover pasture was grazed for a complete oestrous cycle, or treatments were interchanged in mid-cycle. All ewes were slaughtered three days post-oestrus and their reproductive tracts were recovered and individually identified. Ovulation rates and the numbers of follicles on the surface of the ovaries were recorded. After sectioning the ovaries, all follicles of a diameter greater than 2.0mm were recorded. Sections of tissue from the vagina, cervix, uterus and fallopian tubes of each ewe were mounted, stained with haematoxylin and eosin, and the height of their epithelial cells measured. The ingestion of oestrogenic lucerne for one complete oestrous cycle depressed ovulation rates by 29 percent (0.67 ovulations per ewe) in Experiment I and by 22 percent (0.40 ovulations per ewe) in Experiment II. The ingestion of oestrogenic lucerne for part of the oestrous cycle, depressed ovulation rates only if it was consumed for the latter half of the cycle. Oestrogenic lucerne did not significantly influence the secretion of luteinizing hormone over the pre-ovulatory period, or at any other stage of the oestrous cycle. There were no significant differences in the total numbers of ovarian follicles present, in the numbers of follicles on the surface of the ovaries, or in the numbers of large follicles (with a diameter of greater than 3.5mm) present, between the treatment groups. The ingestion of oestrogenic lucerne did not increase significantly, the height of epithelial cells in genital tract tissue, when compared with that in ewes grazing non-oestrogenic ryegrass/clover pasture. Similarly, there was no significant difference in uterine weights. This is in contrast to published data where lucerne is fed to speyed ewes.
Establishment and early regrowth of sheep's burnet (Sanguisorba minor SSP. Muricata (Spach) Briq.) examined multivariately : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
(Massey University, 1991) Douglas, Grant Brodie
Factors affecting establishment and early regrowth of the low growing perennial herb, sheep's burnet (Sanguisorba minor ssp. muricaia (Spach) Briq.), were investigated in field and controlled environment studies. Lucerne (Medicago sativa L.) and sometimes birdsfoot trefoil (Lotus corniculatus L.), were included as dryland standards in the establishment studies. Sheep's burnet emerged more slowly than lucerne and birdsfoot trefoil, but early vegetative growth was similar to that of lucerne and faster than birdsfoot trefoil. Under lower North Island field conditions, spring sown sheep's burnet established and tolerated three partial defoliations (5-7 cm stubble) as well as the legumes and averaged a total of 6.3 t DM ha-1. Regrowth in the autumn indicated that a defoliation frequency of four weeks was suitable. Field emergence of sheep's burnet was influenced markedly by temperature and was 66% on relatively warm, sandy soils at Flock House compared with 27% at Riverside. Seedlings emerged approximately 3-4 days earlier at Flock House. At constant temperatures of 10, 15, 20 and 25°C, final emergences of sheep's burnet were similar and averaged 70.4% but rates of emergence were again faster at higher temperatures. The minimum temperature for satisfactory (50%) emergence of sheep's burnet was 4.9°C and this was discussed in relation to sowing time. Temperature also had a pronounced effect on times to reach various seedling growth stages. Large (>2.8 mm) seeds occasionally provided faster seedling emergence than small (<2.0 mm) and medium (2.0-2.8 mm) seeds, and at constant temperatures, large seeds gave greater emergence (81%) than small seeds (62%). Large and medium seeds also produced a greater proportion of seedling pairs (>50%) per hypanthium ("seed") than small seeds (9%), which may have advantages for rate of ground cover and perhaps earlier provision of forage. Field sowings of unseparated seed averaged 30% seedling pairs. Large seeds frequently produced superior seedlings and seed growers should be encouraged to produce similar seed. Material from Oregon, USA was generally superior to that evaluated in early New Zealand trials but this depended of the evaluation environment, particularly temperature. Foliar regrowth from a range of partially defoliated glasshouse grown plants was superior to that of plants defoliated completely. Reduction in root mass was the most important morphological effect of complete defoliation. The results indicated thet current photosynthates from residual leaves were important in supplying energy for regrowth and this was discussed in relation to possible stand management. Osmotic adjustment was suggested as accounting for satisfactory growth of sheep's burnet in dry environments.
Studies on duration and defoliation in lucerne : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, New Zealand
(Massey University, 1978) Janson, Carroll Garth
A project was conducted to study the influence of grazing duration (GD) on lucerne Medicago sativa L. 'Wairau'. GD was defined as the period of defoliation or grazing before regrowth to the early flowering stage was again permitted. A field trial conducted for eight months from spring to autumn examined three grazing durations (GDs), 2-4, 15 and 30 days, using sheep as the grazing animal. Following this, three studies in controlled environment rooms using simulated grazing techniques allowed a more detailed study of the influence of GD and also provided an insight into the interaction of GD with climate. In both the field and the controlled environments, total herbage production for the full duration of each of the studies was always greatest under the shortest GD (0-3 days) and least under the longest GD (30 days). In the field, total herbage production was reduced by 14% under the 15 day GD system and 29% under the 30 day GD system. However in all the studies the differences in total herbage production were generated almost entirely by differences in stem yield - there were generally no treatment differences in the total production of non-stem (leaf and new shoot) material. The studies in the controlled environment rooms indicated that GD had less effect on lucerne herbage production under dry conditions than under moist conditions favouring rapid growth. Detailed shoot population studies in which large numbers of shoots were individually tagged as they arose, demonstrated the impact of shoot decapitation, the relative contributions of the different shoot types and the importance of the time of shoot appearance in relation to grazing. Differences in the immediate growth rate of the herbage following the different GDs were noted. Maximum herbage growth rates in this period followed the intermediate GDs (10-15 days) with lower growth rates after both the very short (0-3 days) and the very long (30 day) GDs. The initial regrowth inertia following the very short GD was attributed to the low number of basal shoots on this treatment at the start of the regrowth period. However the initially reduced herbage growth rates following the 30 day GDs seemed to result from an 'earlier' partitioning of assimilate to the roots in the first half of the regrowth period following this treatment. It was postulated that this partitioning effect was generated by the 'sink' effect of the depleted root system (lowest root weight, and root TNC and starch concentrations) measured at the end of a 30 day GD. The project has indicated that under active growth conditions, while GDs of 2-4 days will give maximum herbage production, GDs of 10-15 days will have little significant effect on the performance of mature sheep. Under dry conditions, or when grazing young lambs, even longer GDs of up to 30 days are unlikely to seriously affect stock production.
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
(Massey University, 1998) Hoskin, Simone Oriel
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.
Seed production studies in lucerne (Medicago sativa L.) cv. Grasslands Oranga : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science (Seed Technology) at Massey University, New Zealand
(Massey University, 1993) Askarian, Mohsen
Two years of field trials with lucerne (Medicago sativa L.), cv. Grasslands Oranga, were used to determine plant vegetative and reproductive responses to the effects of row spacing and sowing rate, application of two plant growth regulating chemicals, and weed control. For an autumn (March 15) sowing, seedling number per metre of row increased as sowing rate (1 to 12 kg/ha) and row spacing (15 to 60 cm) increased. However the number of seedlings was not directly proportional to the number of seeds sown, and percentage establishment six months after sowing was highest (73%) at the lowest sowing rate of 1 kg/ha. Overall mean establishment for all treatments was 57, 46, and 34% for 1, 6, and 18 months after sowing respectively. Dry matter production at 6 months after sowing was greatest at the 15 and 30 cm row spacings and 12 kg/ha sowing rate, but there were no significant differences in dry matter among treatments at later assessments. In the first year seed yield from the 15 cm row spacing was significantly lower than from the 30, 45 and 60 cm row spacings, while sowing rate had no effect on seed yield. In the second year, row spacings did not significantly affect seed yield, but the seed yield from the 1.0 kg sowing rate was significantly increased because harvestable racemes/m2 and thousand seed weight were significantly increased. Seed yield over the two years of the experiment was highest at the 1 kg/ha sowing rate and for the 30 and 45 cm row spacings. The average seed yield for all treatments was 127.2 and 186.9 kg/ha for the first and second year respectively. Neither row spacing nor sowing rate had any effect on the quality of harvested seed. There were no interactions between row spacing and sowing rate for plant establishment, dry matter production, or seed production. In the 1991/1992 season, the effect of two plant growth regulators, paclobutrazol at 1.0 kg a.i/ha (applied on 1 November or 1 December), and cycocel at 3.0 kg a.i/ha (applied on 1 December, 23 December, 1991 or 1 January 1992), on vegetative and reproductive growth was examined. Paclobutrazol applied during active vegetative growth (1 November) significantly altered vegetative shoot development by inhibiting apical dominance, thus inducing lateral branches which subsequently increased reproductive sites, and increased seed yield by 37%. This seed yield increase was due to an increased number of racemes/m2 (+36%) and pods per raceme (+72%). Paclobutrazol applied at first flower bud appearance (1 December) had no effect on seed yield or seed yield components because it did not alter shoot production or the number of racemes. Cycocel application did not retard plant height or increase racemes per unit area. However while application on 23 December (at first flowering) had no significant effect on seed yield, cycocel applied in early December (first flower bud appearance) or early January (at peak flowering) significantly decreased seed yield, because of a reduction in the number of flowers/m2 and/or harvestable racemes/m2. In the following season (1992/93), paclobutrazol at 0.5 kg a.i/ha and 1.0 kg a.i/ha was applied during active vegetative growth on 25 October 1992. Both rates significantly reduced plant height by 8 weeks after application, but this effect had disappeared by final harvest. As in the previous year, paclobutrazol at 1.0 kg a.i/ha significantly increased seed yield, but the increase (+153%) was much greater than in the previous year. This increase in seed yield was associated with an increase in the number of harvestable racemes/m2 (+126%), pods per raceme (+36%) and thousand seed weight (+11%). Paclobutrazol at 0.5 kg a.i/ha had no significant effect on seed yield. In 1992/1993 the effect of hand weeding and the application of three herbicides (hexazinone 1.0 kg a.i/ha, simazine 2.25 kg a.i/ha plus paraquat 0.6 kg a.i/ha) on seed yield in a second year crop was investigated. Hand removal of weeds, predominantly white clover but also Poa annua L. and broad leaved species increased seed yield from 0.7 to 21.3 g/m2, mainly because racemes increased from 89 to 1230/m2. Increases in pods per raceme and seeds per pod were also recorded. Hexazinone applied during active vegetative growth in early spring eliminated white clover from lucerne plots and increased seed yield to 14.3 g/m2. However this treatment did not control Rumex obtusifolius L. Simazine plus paraquat applied in winter before active spring growth controlled many annual weeds but, although initially checking white clover, did not control it. As a consequence, seed yield did not differ from that of the untreated control. Although hexazinone effectively removed white clover from a second year lucerne seed crop, it is recommended for use only on mature stands. Harvested lucerne seed viability did not differ among treatments, but hand weeding and herbicide treatments significantly reduced the percentage of hard seed.
Effects of RDI on apple tree (cv. Royal Gala) growth, yield and fruit quality in a humid environment : a thesis presented in partial fulfilment of the requirements for the degree of Doctor in Philosophy in Horticulture at Massey University
(Massey University, 1990) Durand, Gladys
The feasibility of using Regulated Deficit Irrigation in the humid environment of New Zealand was evaluated on trees of apple cv. Royal Gala (Malus domestica Borkh.). The study was carried out in a glasshouse experiment and a field experiment. In the glasshouse experiment, it was evaluated the pattern of soil water extraction by the winter mutant of lucerne (Medicago sativa sensu lato) ASR13R from a 'synthetic' soil layered in the same way that it occurs in the research orchard, under trickle and sprinkler irrigation. Results indicated that lucerne extracted soil water at a high rate and explored deep areas of soil. The field experiment was conducted during two consecutive seasons (1987-1989). Lucerne as under tree cover and black polyethylene mulch were compared with conventional herbicide strip to control excess of water in the root zone of the crop that would otherwise promote vegetative growth. These treatments were applied in combination with an irrigation schedule divided into three Phases. In Phase I, water was withheld, in Phase II RDI was compared with full irrigation, and during Phase III which coincided with the rapid fruit growth, all treatments received the full irrigation rate. During the first season, RDI and full irrigation treatments were based on 25% and 100% replacement EPS (evaporation in the planting square) respectively. In the second season, after a 50% of the soil water content in the top 600 mm of soil, between Drainage Upper Limit and me Lower Limit was reached, full irrigation treatments were replenished to the DUL, while RDI treatments received 25% of that amount. Results showed that under the conditions of this study evaluation of crop water requirements based on soil moisture measurements was more reliable than those based on pan evaporation. The degree of reduction of summer pruning obtained under lucerne X RDI treatment, reflected levels of soil and plant water deficit similar to those obtained in arid environments. Results confirmed my hypothesis that by using lucerne as under tree cover, a RDI strategy can be used in this environment. In contrast, black plastic mulch appeared to maintain soil moisture rather than prevent its accumulation. Nevertheless, effects were obtained which reflected positively in fruit growth and yield. Similar results were obtained under the control treatment, although it was less effective for in reducing tree vigour. The latter treatment, however, can be implemented in most orchards at no cost and generate important savings. Apple fruit growth proved to be relatively insensitive to water deficit imposed during early stages of growth, whereas vegetative growth was checked. Restoring full irrigation to coincide with rapid fruit growth stimulated growth of RDI fruits resulting in higher yield under control and plastic X RDI. Lucerne showed higher rates of water use that were not compensated by the irrigation which affected fruit growth and size. Results showed that fruits from RDI treatments were firmer, accumulated higher T.S.S. and had lower bruise susceptibility than fruits from fully irrigated treatments. Fruit quality remained higher after 10 weeks of cool storage.
The influence of diet and intake level on hepatic ammonia metabolism and ureagenesis by the ovine liver : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
(Massey University, 2001) Greaney, Kenneth Barry
The New Zealand agricultural industry is based on the efficient utilisation of fresh forages, a characteristic of which is a high soluble protein content. A large proportion of the ingested protein is highly soluble in the rumen. A significant proportion of the ingested N is removed from the rumen as ammonia with the bulk of this ammonia being removed from the venous blood by the liver for detoxification to urea. Hepatic urea-N production, or ureagenesis, typically exceeds the rate of hepatic ammonia-N extraction, consequently it has been suggested that the shortfall in N required for ureagenesis is contributed by amino acid-N (Parker et al. 1995; Lobley et al., 1995). This study tested the hypothesis that elevated hepatic ammonia extraction would require a concomitant increase in hepatic amino acid catabolism to supply the additional N required for ureagenesis. In order to evaluate the level of rumen ammonia production and consequently the rates of hepatic ammonia extraction, ureagenesis and amino acid catabolism. the following feeding regimens were tested in sheep held indoors in metabolism crates in three separate experiments; Firstly, lucerne pellets (Medicago sativa) were compared with fresh white clover (Trifolium repens), secondly fresh white clover was offered at either a low or high intake and finally the daily allowance of fresh white clover was fed in two 2 hour periods per day. In each experiment, silicone based catheters were surgically inserted into the posterior aorta and the mesenteric (2), portal and hepatic veins. Following a ten day dietary adjustment period and a ten day nitrogen balance, the sheep were infused with para-aminohippurate (pAH) and 15NH4Cl via the mesenteric vein. The pAH was infused to allow the blood flow across the splanchnic tissues to be estimated, whilst the 15NH4Cl was infused to trace hepatic ammonia metabolism to urea. Blood samples were collected to determine the ammonia, urea, oxygen and amino acid concentrations in the mesenteric, portal and hepatic veins, as well as the posterior aorta. Despite similar DM intakes, the nitrogen intake of the sheep fed fresh white clover was 60% higher (P < 0.001) than that of the same animals fed lucerne pellets. The difference in rumen protein fermentation in these two contrasting diets resulted in higher (P < 0.001) rumen ammonia production in the animals offered fresh white clover. There was, however, only a trend (P = 0.072) toward elevated hepatic ammonia extraction in these animals and urea production was not significantly different to the animals fed lucerne pellets. Hepatic amino catabolism was not elevated in the sheep fed fresh white clover, nor was there a significant difference in the proportion of ME intake that was utilised for ureagenesis between the two groups. In the second experiment the DM intakes of the two groups were different (P < 0 001), with the sheep offered the low intake of fresh white clover consuming 807 g DM/d whilst the high intake group consumed 1118 g DM/d. Even with these differences in intake, portal vein ammonia and urea concentrations were similar. Therefore the rate of hepatic ammonia extraction and urea production were also similar between the two intake groups. However, hepatic extraction of 15N-ammonia was higher (P = 0.033) in the high intake group compared to the low intake group. There was no evidence to suggest that the level of hepatic amino acid catabolism increased with intake level, consequently the proportion of ME intake attributed to urea synthesis was similar for the two intake groups When the experimental animals were restricted to two 2 hour feeding periods per day the DM and N intake decreased by 31% from that of the low intake group in the second experiment. There was no significant effect of time after the onset of feeding on portal ammonia or urea concentrations, hepatic ammonia extraction or hepatic urea production. However portal ammonia concentration and consequently hepatic ammonia extraction and urea production tended to be higher 4-6 hours after ingestion of fresh white clover. However this trend was not observed when the 15N tracer data was used to calculate the hepatic ammonia transfer rate. The ammonia, urea and amino acid hepatic transfer values in this experiment were largely comparable to those recorded for the low and high intake treatments in the second experiment. In these studies, there was no evidence of elevated hepatic amino acid catabolism occurring in response to elevated rates of hepatic ammonia extraction and hence ureagenesis. Additionally there was no suggestion that ammonia provided both of the N atoms of the urea molecule. It is concluded that the liver adapted to the changes in dietary nitrogen supply without incurring significant increases in the metabolic cost of ammonia detoxification to urea. However the nutritional challenges presented to the liver may not have been severe enough to induce measurable changes in hepatic ammonia metabolism. A possible mechanism to account for these observations may be that the liver adapted to the changes in nitrogen supply by altering the activity of the primary regulator of the rate of ureagenesis, carbamoyl phosphate synthetase (CPSI).
Determination of digestion parameters to develop and evaluate forage mixtures for pasture-fed ruminants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
(Massey University, 2004) Burke, Jennifer Leighann
Animal production can be improved by lessening the dependence on ryegrass-based pastures as the sole source of nutrients for production. Ryegrass varies in quality and availability and supplementation with appropriate forages will maintain or improve production. This thesis defines the nutritive characteristics of a range of forages, including temperate and tropical grasses, legumes with and without condensed tannins, herbs and silages, in terms of chemical composition, products of degradation and rates of digestion using in sacco and in vitro methods. The forages assessed varied in crude protein concentration (CP; 7.6 - 29.9 % of dry matter; DM) and neutral detergent fibre (NDF; 22.4 - 57.8% DM), with commensurate net appearance of plant N as ammonia (0 to 49%) and in sacco DM, CP and NDF degradation rates (%/h) from 3 - 26, 3 - 19 and 4 - 28, respectively. The Cornell Net Carbohydrate Protein System (CNCPS) was used to evaluate the ability of forages to meet the energy and protein requirements of dairy cows. Data suggested sulla (Hedysarum coronarium), lucerne (Medicago sativa), red clover (Trifolium pratense) and white clover (Trifolium repens) as potential forages for feeding with medium to low quality pasture. Lambs were fed pasture, white clover, lucerne and sulla alone or in mixtures and production, rumen digestion parameters and estimates of protein synthesis were measured. Lambs fed white clover, sulla, lucerne:sulla and white clover:sulla had the highest daily intakes (1.47 - 1.54 kg DM) and liveweight gains (281 - 308 g) compared to lambs fed pasture (1.10 kg DM; 116 g). Sulla had potential for feeding with pasture and lucerne, but energy limited production. Protein synthesis between lambs fed lucerne, sulla and lucerne:sulla were similar (162 - 180 g/day) and greater than pasture (93 g/day). In a trial with dairy cows fed pasture (P), supplementation with maize silage (M) or sulla (S) did affect in sacco degradation and the maize silage lowered in sacco DM degradation rates (P, 7; M, 4; S, 16; P:M; 5; P:S, 11 and P:M:S, 6 %/h). The work presented provides a foundation for formulating mixed forage rations to meet cow nutrient requirements and improve productivity in ryegrass-based pasture systems. Animal trials demonstrated synergistic effects of dietary components on both animal production and rumen microbial function.

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