Experimental Paddocks Research Articles

Germination and population structure of spear thistle Cirsium vulgare in relation to experimentally controlled sheep grazing.

The size and number of rosettes of Cirsium vulgare were censused in a 4 ha sheep grazing trial on lowland calcareous grassland in paddocks receiving controlled winter, spring and summer grazing treatments. Spring grazing significantly increased thistle rosette numbers, and there were always fewer rosettes in size classes 250mm-300 mm under the heavier grazing treatments. The emergence of seeds of Cirsium vulgare sown by hand into each of the grazing treatments was monitored and showed a positive effect of spring grazing. When the percent emergence of sown seeds was used as a covariate in the analysis of rosette numbers in the experimental paddocks, it was found to account for 77% of the variance in thistle numbers. It was concluded that the main effect of grazing on thistle rosette numbers is an indirect one exercised through the effects of grazing on germination conditions. Seeds of Cirsium vulgare were sown into artificial gaps at another grassland site, to determine the effect of gap-size upon seedling emergence. Germination was poor, but significantly more seedlings emerged in gaps 10-20 cm diameter, than in 5 cm gaps or in control plots without a gap. A computer simulation model was used to explore the relationship between gap density and thistle population dynamics. A threshold density of gaps was found to exist, below which thistle populations went extinct, and above which the thistle population grew geometrically. The degree of aggregation of dispersed seeds did not alter the threshold gap-density for plant extinction, but did affect the rate of increase of the thistle population when the threshold gap-density was exceeded. It is concluded that strategies for controlling Cirsium vulgare populations by grazing manangement will be most effective if aimed at reducing suitable sites for establishment in spring. The success of such attempts will depend upon the soil fertility of the site, and sudden outbreaks of Cirsium vulgare infestation can be expected if a sward gradually deteriorates through over-grazing.

The ecology of infective larvae of bovine gastrointestinal trichostrongylids in dry season contaminated pastures in the Nigerian derived savanna.

Five experimental grass paddocks were sequentially contaminated with fresh bovine faeces containing known numbers of eggs of predominantly Haemonchus and Cooperia spp. during the 1984/85 dry season (November to March). Faecal, herbage and soil samples were examined at regular intervals between November and June in order to determine the rate of development and mortality of infective larvae (L3) in faeces, the pattern of herbage infestation with L3 and the role of faeces and soil as reservoirs of L3 during the dry season and early rains. L3 first appeared in faeces approximately 4 days post contamination (PC) and peak counts were obtained 28, 14, 7 and 14 days PC in the paddocks contaminated in December, January, February and March, respectively. The counts initially declined linearly at the rate of approximately 7535 L3/week and 10,947 L3/week in P2 and P4 respectively, due primarily to mortality but later there was an accelerated fall in the counts as the surviving L3 moved out of the faecal pads onto herbage. The overall trend of faecal larval populations in each paddock was therefore distinctly curvilinear. Although large numbers of L3 were present inside dry faecal pads in most paddocks throughout the dry season, none migrated on to herbage at that time of the year. Translation of L3 to herbage was very rapid and occurred simultaneously in all the paddocks 24 hours following the first heavy rainfall in late March. Consequently peak herbage infestations in all paddocks were coincident and occurred a few days after commencement of larval migration. The closer to the end of the dry season the contaminations were carried out, the larger were the subsequent early rains rise and the peak herbage infestation and the longer this infestation survived on herbage. No L3 were recovered from soil throughout the study, which suggests that faecal pads were the sole reservoir of L3 during the dry season and hence the source of the early rains herbage infestation.

THE EFFECTS OF RESTRICTING OR STOPPING FERTILISER APPLICATION TO WAIKATO DAIRY PASTURES

Waikato dary pastures were developed through large inputs of superphosphate and potassium chloride. Many farmers have continued to apply similarly large amounts of fertiliser in post-development situations. Trials to study the effects on the production of dairy pastures to restricting or stopping fertiliser application were started in 1978 and have continued to the present. The tria1s were conducted on 6 commercial dairy farms throughout the Waikato region selected for high milkfat production and past fertiliser applications. Each trlal included 3 fertiliser treatments: 1000, 500 and 0 kg fertiliser (30% potassic superphosphate)/ha/year. Pasture production was estimated through a trimming technique designed to cause minimal interference with management and use of the experimental paddock by the farmer and in later years through calibrated visual assessments and electronic probe readings of pasture dry matter. Pastures receiving 500 kg fertiliser/ha/year produced on average 2.5% less over an 8 year period than pastures receiving 1,000 kg fertiliser. Applying no fertiliser caused a slow reduction in pasture production in 3 of the trials but an immediate reduction of more than 10% in the other three trials. The latter effect could be partly explained by low soil test levels and high stocking rate. Keywords: Yellow-brown loams, gley soils, maintenance fertiliser, phosphorus, potassium.

A prediction model for parasitic gastro-enteritis in lambs

Paton G., Thomas R. J. and Waller P. J. 1984. A prediction model for parasitic gastroenteritis in lambs. International Journal for Parasitology 14: 439–445. The parasite Ostertagia circumcincta is a major cause of parasitic gastro-enteritis in lambs in temperate countries. A prediction model is described, based on a mathematical representation of the external and internal stages of the life-cycle. The model is used to predict the numbers of infective larvae on a permanent experimental paddock grazed by ewes and lambs in 1973 and 1974. The “moisture status” of the surface layer of the pasture was found to be of fundamental importance for the successful prediction of the development and survival of the pre-infective larval stages. For the years studied the contribution to the summer wave of infection by lamb derived larvae was particularly significant.

Grassland dynamics under sheep grazing in an Australian Mediterranean type climate

Grassland dynamics in a degraded disclimax grassland dominated by Danthonia caespitosa Gaudich. are examined using both demographic and multivariate approaches in an experiment designed to determine the effect of grazing intensity and exclosure on pasture dynamics. The experiment ran for 20 years from 1949 to 1968, using permanent quadrats at 3 grazing intensities and within exclosures. Demographic studies of some perennial grass species demonstrated markedly different responses to grazing; Danthonia caespitosa was unaffected by grazing but responsive to seasonal rainfall differences. Enteropogon acicularis survived only on protected sites. Numerical classification of total species set (121 species) for six observation periods demonstrated that community types were sensitive to differences in winter rainfall, and time since the start of experiment. Principal component analysis of permanent quadrat observations for individual years demonstrates quadrat trajectories which confirm this and indicate progressive divergence of the successional trends of the grazed and ungrazed quadrats. Repeated analysis on grazed quadrats only, shows that three components of pasture dynamics can be recognized; these are trend (succession?) and seasonal differences, each of which account for about 20% of the variance, and differences due to soil heterogeneity in the experimental paddock (8% of variance accounted for). No effect of grazing intensity was detected. Multivariate techniques can provide a clear partitioning of types of dynamic behaviour present in grassland communities. It is concluded that partitioning of environmental heterogeneity prior to demographic studies would increase their sensitivity.

The influence of shape of paddock, type of fence and stocking rate on grazing behaviour and social facilitation in Merino sheep

The results indicate that grazing patterns adopted by sheep in small experimental paddocks are likely to be affected by daylength, lack of grass and rate of loss of liveweight. Grazing behaviour of groups of two sheep was not different when compared to four or five sheep over the summer period. Differences which showed up with time were more related to change of liveweight than to any suggestion that two sheep in a flock behaved in a way which was substantially different to sheep in the larger flocks. There was little substantial evidence for social facilitation affecting grazing times. Grazing patterns of sheep in square paddocks did not appear to be affected by the ability to see sheep in neighbouring plots. However, there was the possiblity of social inhibition occurring in sheep grazing in adjoining rectangular paddocks and the tendency to more uniform grazing behaviour in plots with wire fences suggested that vision may have been important in this connection.

The veld condition score: An evaluation in situations of known past management

Abstract The method of assessing veld condition which has been developed in Natal by Foran has given a reasonable separation of the veld in ten experimental paddocks which varied widely in condition both from the broad ecological viewpoint and in relation to their agricultural value for grazing animals. There are still, however, aspects which give rise to concern and it would be advisable to develop the method further before its adaptation for general use.

Vaccination of lambs against Taenia ovis infection using antigens collected during in vitro cultivation of larvae: passive protection via colostrum from vaccinated ewes and the duration of immunity from a single vaccination

Fifty Merino-cross ewes were vaccinated approximately four weeks before parturition with antigens collected during in vitro cultivation of Taenia ovis larvae. A further 50 pregnant ewes were sham-vaccinated at the same time. When the first 20 lambs from each group of ewes were one to two weeks old they were placed, with the ewes, on an experimental paddock heavily contaminated with T ovis eggs. After six weeks the lambs were killed and their total carcase musculature and hearts examined for cysticerci. The results showed that the ewes vaccinated in late pregnancy had conferred a very high degree of transcolostral immunity upon their lambs against the T ovis challenge infection. Eighty T ovis-free Merino-cross weaner lambs, four months old, were divided into two groups of 40. One group was vaccinated with T ovis culture antigens and the other group was sham-vaccinated. At intervals of one, four, eight and 12 months after vaccination 10 lambs from each group were allowed to graze on the plot contaminated with T ovis eggs. After six weeks the lambs were killed and examined for cysticerci of T ovis. The results indicated that the single vaccination had stimulated a high level of immunity which persisted for at least 12 months.

Feed analyses and mineral contents of lupins associated with lupinosis of sheep in Western Australia

Lupin components from 25 experimental paddocks in the Gingin-Dandaragan area were analysed for standard feed components and trace elements in 1961 and 1962-63. Lupinosis had occurred in all the experimental paddocks. Much of this area is deficient in trace elements and lupinosis appeared in 1948 soon after copper-ore topdressing was introduced and the use of superphosphate greatly expanded. The analyses were related to soil types, past dressings of copper and zinc, and compared with general lupin analyses in the district. Protein and calcium in the leaf and seed and calcium to phosphorus ratios in the leaf were high. Cobalt was often below the critical range for sheep health, iron was very high (815-2400 p.p.m. in leaves), organic sulphate was low (mean 0.2 per cent) and manganese was high (mean 326 p.p.m. in leaves). Molybdenum varied widely and was related to past copper and zinc topdressing. It was high in lupin seed where copper-ore topdressings were applied. Copper was marginal for sheep health (3-6 p.p.m.) in leaf and seed and deficient in stems and in associated grasses. Copper was lower and molybdenum higher on paddocks where lupinosis was severe.

Vitamin B12 and cobalt concentrations in livers from healthy and cobalt-deficient lambs.

DURING field investigations into cobalt deficiency we collected pasture samples from experimental paddocks at intervals for cobalt analyses, and at the end of the trials made comparisons of the vitamin B12 and cobalt concentrations in the livers of healthy lambs not given cobalt, cobalt-dosed lambs, and other groups showing various stages of cobalt-deficiency disease. Results are shown in Table 1.