Removal Of Cattle Research Articles

Avian Responses to Late-Season Grazing in a Shrub-Willow Floodplain.

Riparian vegetation in western North America provides important habitat for breeding birds and valuable forage for grazing livestock. Whereas a number of studies have documented the response of riparian vegetation to the removal of cattle, few have experimentally evaluated specific grazing systems. We evaluated the responses of vegetation and breeding birds to two cycles of late-season (August-September) grazing followed by 34 months of rest on the Arapaho National Wildlife Refuge, Colorado. We used a before-and-after control-impact (BACI) design, with two control (ungrazed) and two treatment ( grazed) pastures composing the experimental units. Vegetation characteristics and bird densities were quantified on sample plots prior to and following two cycles of the treatment. We found no statistical differences in vegetation change and few differences in bird-density change among pastures. Inspection of means for pastures, however, suggests that changes in shrub vigor and spatial pattern differed among ungrazed and grazed pastures and that changes in population density for three of the nine bird species and three guilds studied differed among pastures. Our results suggest that habitat for grazing-sensitive birds may be restored while still allowing late-season grazing, although the rate at which species are recovered will be slower than if all cattle are removed.

Serological Evaluation of Five Unvaccinated Heifers as a Method for Detecting Herds Infected with Bovine Viral Diarrhea Virus

Cattle persistently infected (Pl) with bovine viral diarrhea virus (BVDV) are the major reservoir of infection within and between herds. The key to eradicating BVDV is the identification and removal of all PI cattle. This requires testing all cattle within a herd, which is costly and labor-intensive for the producer. It would be desirable to accurately identify herds infected with the virus prior to committing the resources necessary for whole-herd screening. The objective of this study was to determine if the evaluation of BVDV antibody titers in five randomly selected unvaccinated heifers (sentinel heifers) was an accurate way to predict if a herd was infected with the virus.

Irrigated Wheat Grazing and Tillage Effects on Subsequent Dryland Grain Sorghum Production

Use of conservation tillage has improved sorghum [Sorghum bicolor (L.) Moench] grain yield 10 to 20% in ungrazed wheat (Triticum aestivum L.)–fallow–sorghum production systems. Our objective in this 2‐yr field study was to develop tillage guidelines for systems where the wheat was grazed. Grazing duration on winter wheat and tillage during the fallow period preceding dryland grain sorghum were treatments on Pullman clay loam (Torrertic Paleustoll). Grazing increased surface soil compaction and reduced wheat residues. Surface soil (0–5 cm) penetration resistance was 0.36, 0.52, 0.75, and 0.92 Mpa, and wheat residue in 1996 was 6.0, 4.8, 3.5, and 1.2 Mg ha for ungrazed and early, normal, and late cattle removal dates, respectively. As a result, sorghum grain yield in 1996, an exceptionally wet season, was 7.9, 7.5, 7.0, and 3.8 Mg ha−1, respectively, with no tillage (NT). In 1997, a dry season with low runoff, only the late cattle removal with NT had reduced yield (3.4 Mg ha−1 compared with 3.9 Mg ha−1 for ungrazed NT). Use of one‐time sweep tillage early in fallow resulted in an increase in sorghum grain yield of 1.9 Mg ha−1 in 1996 for the late cattle removal treatment compared with NT, but it had no effect on yield with the normal cattle removal treatment. In 1997, one‐time sweep tillage increased yield by 0.3 Mg ha−1 with late removal. When wheat residue was ≤2.4 Mg ha−1 following grazing, sweep tillage reduced surface compaction, increased soil water at planting an average of 26 mm over 2 yr, and improved grain yield of sorghum compared with NT. If wheat residues were ≥3.5 Mg ha−1 after grazing, NT was as effective as any tillage treatment. Results agree with conservation tillage guidelines developed on ungrazed wheat.

Comparison of grassland management systems for beef cattle using self-contained farmlets: effects of contrasting nitrogen inputs and management strategies on nitrogen budgets, and herbage and animal production

Past research on nitrogen (N) inputs, losses and surpluses focused on separate components of grassland management, i.e., grazed or cut swards and the impact of fertiliser or slurry applications. In practice, however, grassland is both grazed and cut for conservation, and N fertiliser is supplied from both organic and inorganic sources. A whole systems approach was used to evaluate the effects of combinations of management strategies designed to reduce N losses on N budgets, and herbage and animal production in South West England. Three systems with contrasting N inputs were compared: CN, conventional mineral N application and broadcast slurry; TN, tactical mineral N application with slurry injection and the early housing of cattle; GC, a mixed grass/white clover sward with no mineral N addition and slurry injection. Comparisons were made on two contrasting soil types: a freely-draining sandy loam (Gleysol, Site 1), and a poorly drained clay (Luvisol, Site 2). 1 ha farmlets were grazed to a target sward height by beef cattle for a 5-year (Site 1) or a 4-year (Site 2) period. Herbage surplus to grazing requirements was cut for silage. On average, 185 kg N ha −1 was applied annually to treatment TN compared with 280 kg N ha −1 for CN. An additional 76, 102 and 67 kg N ha −1 was applied in slurry to treatments CN, TN and GC, respectively. Substantial reductions in N surpluses were achieved for both treatments TN and GC compared with treatment CN (N surpluses ha −1: 254, 168 and 119 kg at Site 1, and 247 kg, 190 and 73 kg at Site 2, for CN, TN and GC, respectively). The highest N input for treatment CN was associated with the greatest animal and herbage production. More land was required for grazing on treatment GC and less herbage was cut for silage so that self-sufficiency was not attained for winter fodder on this treatment. The early removal of cattle on treatment TN did not result in a significant increase in the amount of herbage cut for silage. It was concluded that the combinations of mitigation options used were successful in reducing N surpluses compared with the conventional N management system, but animal and herbage production was reduced.

Forage Removal and Grazing Time of Cattle on Small Paddocks

Animals used in grazing trials with small paddocks usually have not been exposed to the experimental site and related research procedures. Grazing trials conducted in May and August 1996 on smooth bromegrass (Bromus inermis L e y s s . ) quantified forage removal and grazing time of heifers adapted or not adapted to small paddocks. Treatments consisted of adapting heifers for 4 days to small paddocks (0.054 ha) and a control treatment of heifers continuously stocked in larger paddocks (>16 ha). On day 5, each group of heifers was moved to similar small paddocks and forage utilization and cattle grazing times were measured after 4 and 24 hours of grazing. In May, when sward structure was comparable in the large and small paddocks, tiller height reduction, leaf length reduction, herbage bio mass reduction, and grazing time were similar (P > 0.10) for experienced and inexperienced heifers after 4 and 24 hours of exposure to day-5 paddocks. In August, when sward structure differed between the large and small paddocks, leaf length reduc tion after 4 hours was greater (P < 0.10) by experienced cattle than inexperienced cattle. Herbage reduction in August by expe rienced cattle was 435 kg ha -1 greater (P < 0.05) than by inexperi enced cattle after 24 hours. Cumulative grazing time was 76 min utes (P < 0.10) greater at 4 hours for the experienced cattle than the inexperienced cattle. Grazing animals appear to adapt imme diately to small paddocks but other unfamiliar grazing conditions, e.g., sward structure, may require short adaptation periods for experimental animals.

Evaluating control strategies for outbreaks in BHV1-free areas using stochastic and spatial simulation

Several countries within the EU have successfully eradicated bovine herpesvirus type I (BHV1), while others are still making efforts to eradicate the virus. Reintroduction of the virus into BHV1-free areas can lead to major outbreaks — thereby causing severe economic losses. To give decision-makers more insight into the risk and economic consequences of BHV1 reintroduction and into the effectiveness of various control strategies, we developed the simulation model InterIBR. InterIBR is a dynamic model that takes into account risk and uncertainty and the geographic location of individual farms. Simulation of a BHV1-outbreak in the Netherlands starts with introduction of the virus on a predefined farm type, after which both within-farm and between-farm transmission are simulated. Monitoring and control measures are implemented to simulate detection of the infection and subsequent control. Economic consequences included in this study are related to losses due to infection and costs of control. In the simulated basic control strategy, dairy farms are monitored by monthly bulk-milk tests and miscellaneous farms are monitored by half-yearly serological tests. After detection, movement-control measures apply, animal contacts are traced and neighbour farms are put on surveillance. Given current assumptions on transmission dynamics, we conclude that a strategy with either rapid removal or vaccination of infected cattle does not reduce the number of infected farms compared to this basic strategy — but will cost more to control. Farm type with first introduction of BHV1 has a considerable impact on the expected number of secondarily infected farms and total costs. To limit the number of infected farms and total costs due to outbreaks, we suggest intensifying the monitoring program on farms with a high frequency of cattle trade, and monthly bulk-milk testing on dairy farms.

Forage removal and grazing time of cattle on small paddocks

Animals used in grazing trials with small paddocks usually have not been exposed to the experimental site and related research procedures. Grazing trials conducted in May and August 1996 on smooth bromegrass (Bromus inermis Leyss.) quantified forage removal and grazing time of heifers adapted or not adapted to small paddocks. Treatments consisted of adapting heifers for 4 days to small paddocks (0.054 ha) and a control treatment of heifers continuously stocked in larger paddocks (&gt;16 ha). On day 5, each group of heifers was moved to similar small paddocks and forage utilization and cattle grazing times were measured after 4 and 24 hours of grazing. In May, when sward structure was comparable in the large and small paddocks, tiller height reduction, leaf length reduction, herbage bio-mass reduction, and grazing time were similar (P &gt; 0.10) for experienced and inexperienced heifers after 4 and 24 hours of exposure to day-5 paddocks. In August, when sward structure differed between the large and small paddocks, leaf length reduction after 4 hours was greater (P &lt; 0.10) by experienced cattle than inexperienced cattle. Herbage reduction in August by experienced cattle was 435 kg ha-1 greater (P &lt; 0.05) than by inexperienced cattle after 24 hours. Cumulative grazing time was 76 minutes (P &lt; 0.10) greater at 4 hours for the experienced cattle than the inexperienced cattle. Grazing animals appear to adapt immediately to small paddocks but other unfamiliar grazing conditions, e.g., sward structure, may require short adaptation periods for experimental animals.

Ponderosa Pine Aboveground Growth after Cattle Removal of Terminal Tissue

Mismanagement of livestock can result in herbivory on Pinus seedlings with potential for growth loss. From 1986 to 1990 on a conifer plantation in the Mixed-Conifer Zone of southwestern Oregon we measured the aboveground growth of ponderosa pine (Pinus ponderosa Douglas ex Lawson &C. Lawson var. ponderosa) seedlings that had sustained (1) removal of terminal stem or bud tissue by cattle, and (2) no removal (control). In 1990 (year 5 of the plantation), cumulative, absolute height and stem volume on seedlings that sustained terminal tissue removal were similar to control seedlings. In 1988, relative height growth was comparable between control seedlings and seedlings sustaining tissue removal in May 1987. In contrast, 1988 relative height growth was -22% (P < 0.05) for seedlings sustaining tissue removal in August 1987, compared with control seedlings. Relative stem volume growth in 1988 ranged from -21 to -26% (P < 0.05) for seedlings sustaining tissue removal in (1) August 1987, (2) April or May 1988, and (3) 1987 and 1988, compared with control seedlings. Reduced relative growth was short-term. Relative growth rates for seedlings sustaining tissue removal were comparable to control by the first or second year after removal. Seedlings sustaining tissue removal before winter bud set (April and May) were more likely to recover by the first year than seedlings sustaining tissue removal after winter bud set (August). We propose that if silviculturists prescribe cattle grazing early in the growing season and terminal tissue is removed at that time, they can still achieve understory vegetation control and enhanced soil water availability without jeopardizing long-term aboveground growth of ponderosa pine. The lack of spatial replication of treatments (terminal tissue removal dates) limits spatial extrapolation of our findings. The credibility of our findings should be tested with additional research on the growth response of ponderosa pine seedlings subsequent to actual live-stock herbivory, conducted with spatially replicated treatments.

Nitrogen and Phosphorus Cycling in Grazed and Ungrazed Plots in a Temperate Subhumid Grassland in Argentina

The distribution and dynamics of N and P were studied for two adjacent grazed and ungrazed areas of native grassland in the Flooding Pampa, Argentina, over the winter-spring season of maximum primary production. We evaluated how grazing effects on vegetation structure altered patterns of nutrient cycling at the ecosystem level. Nutrient transfers were estimated from element concentrations measured in plant and soil pools at minimum and peak standing crop and from previous work in the study area. Total nutrient amounts in vegetation (9.4-12.6 g m -2 N and 0. 50-0.76 g m -2 P) did not differ consistently between grazed and ungrazed grassland, but nutrient location reflected the effect of cattle on phytomass structure and species composition. Plant pools of N and P were mainly located in below-ground organs, to the extent of 80-90% in grazed and 63-75% in ungrazed vegetation. Nutrients in above-ground green material from grazed prairie were 50% of the content for ungrazed prairie. At peak standing crop the grazed grassland contained more than 50% N and P in forb biomass, whereas protected vegetation had most nutrients in graminoids. Nitrogen concentration in live shoots declined through the season while it was increasing in roots, indicating preferential below-ground allocation. Seasonal patterns of plant N were amplified by continuous grazing. Phosphorus allocation appeared to be closely regulated in this grassland. Although changes in shoot P concentrations were subtle, P allocation to shoots seemed higher in ungrazed grassland. Shoot N:P ratios suggested that vegetation was relatively more P-limited in early winter, but more N-limited in late spring. In general, N and P contents tended to increase in living vegetation and to decrease in dead plant compartments over the season studied. Nutrient uptake by roots was 30-50% higher in the grazed plot, in correspondence with enhanced mineralization rates. Concentrations of N and P in graminoid live shoots were also higher under grazing, although grazing decreased the overall translocation of N to shoots. Livestock consumption represented more than 40% of above-ground nutrient translocation, and thus grazing increased nutrient flow through the below-ground plant pathway. Strong demand from underground sinks in grazed vegetation probably contributed to increased root uptake. Grazing did not affect soil-available nutrients, although it did accelerate nutrient cycling rates, mostly of P. Ammonia volatilization and N exports through cattle removal were of similar magnitude (0.22 g m -2 year -1 N), and were 60% of wet deposition. Therefore, N tended to accumulate in this grassland. Annual P outputs in animal biomass produced a small net loss of P from the managed ecosystem.

Effects of breed type and accelerated fat removal on subprimal yields and carcass values

Nine Brown Swiss and nine English crossbred steers representing the industry standard were slaughtered to determine the effects of cattle type and hot fat removal on subprimal yields and carcass value. After dressing, cod fat, kidney, pelvic, and heart fat (KPHF), and subcutaneous fat thicker than .6 cm was removed from the right side of each carcass (HFT). The left side was not hot-fat trimmed (NFT). Both sides were fabricated into subprimal cuts with no more than .6 cm of subcutaneous fat. Carcass side values were adjusted to a 300-kg chilled carcass weight basis. All comparisons were made for the carcasses using a USDA Select quality grade end point. English crossbred steer carcasses had more (P < .05) subcutaneous fat on the loin and chuck and more (P < .05) total hot fat trim, when KPHF was not included, than Brown Swiss steers (P < .05). Brown Swiss steers had more (P < .05) KPHF. Hot-fat trimmed sides had higher (P < .05) percentage yields from the chuck, brisket, foreshank, rib, plate, round primal cuts, and most of the subprimal cuts than NFT sides, but the primal loin percentage was higher (P < .05) in the NFT sides. The total subprimal cuts yield was approximately 5% higher for the HFT sides than for the NFT sides, and the total fat trim during fabrication was more than 6% less. When the value of the sides was calculated from unadjusted weights, the NFT sides were approximately $26.50 more valuable than the HFT sides.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of grazing on the abundance and diversity of annual plants in Chihuahuan desert scrub habitat.

We assess the impact of release from cattle grazing on the abundance and diversity of both winter and summer annual plant communities at an upper Chihuahuan Desert scrub site in south-eastern Arizona. In contrast to previous studies, we found that removal of herbivores (cattle) had little impact on ephemeral plant assemblages at our site. The total number of summer annual individuals per quadrat did not differ significantly, but there were significantly more winter annual plants on ungrazed quadrats. The number of species per quadrat, however, did not differ significantly between sites exposed to, or protected from, grazing in either season. Of 79 annual species recorded (34 in winter, 45 in summer), only 2 species, 1 in each season, responded significantly to the removal of cattle: Stephanomeria exigua and Polygala tweedyi were more abundant on ungrazed plots. Three additional species, Eriastrum diffusum and Cryptantha micrantha in winter, and Mollugo cerviana (summer), approached statistical significance. Differences in the effect of cattle grazing on annual plants between our results and those at other sites in the arid southwest most likely reflect differences in the speed of response by annuals in different areas. Comparisons of this with other studies underscores recent calls for studies at broader spatial and greater temporal scales.

Studies on the Decline of Bovine Virus Diarrhoea Virus (BVD V) Maternal Antibodies and Detectability of BVDV in Persistently Infected Calves

Persistently infected (PI) animals play a significant role in spread and transmission of bovine virus diarrhoea virus (B VD V) (Duffell & Harkness 1985). The identification and removal of PI cattle from the herd is of great importance in the control of BVDV. Although PI animals often show various degrees of growth retardation and unthrifty appearance, a significant proportion is clinically normal. PI animals are often seronegative (Duffell & Harkness 1985), but calves may be tested seropositive because of the presence of maternal immunity (Meyling & Jensen 1988). The passively derived BVDV antibodies may interfere with the ability to detect virus. Considering the importance of early recognition of PI calves, it is essential to determine the earliest time when PI animals can safely be diagnosed in the herd.

Litter decomposition in an Indian monsoonal wetland overgrown withPaspalum distichum

After the removal of domestic cattle and water buffalo in 1982, the monsoonal wetlands of the Keoladeo National Park, India were rapidly overgrown by the grassPaspalum distichum L. We studied the decomposition of above-ground litter ofPaspalum distichum and that of ten submersed, floating-leaved, free-floating and emergent species, including the dominants in these wetlands prior to 1982. The only species that had decomposition rates as low as those ofPaspalum were the emergents,Pseudoraphis spinescens (R. Br.) Vickery andTypha angustata Bory & Chaub, which had very restricted distributions both before and after 1982. All the previous dominants had much higher decomposition rates. The turnover time forPaspalum litter was estimated to be greater than one year, while litter of the previous dominants all had turnover times of less than one year. Thus, a permanent litter layer could develop in these wetlands that had not been present previously.

Epidemiology of paramphistomosis in cattle

Rolfe P. F., Boray J. C., Nichols P. and Collins G. H. 1991. Epidemiology of paramphistomosis in cattle. International Journal for Parasitology 21: 813–819. The epidemiology of paramphistomosis in cattle was studied using tracer calves in a subtropical location in eastern Australia. Two species of paramphistomes were present; Calicophoron calicophorum and Paramphistomum ichikawai. The former species was the most abundant. Gyraulus scottianus and Helicorbis australiensis acted as intermediate hosts, respectively. Paramphistome burdens varied seasonally and were dependent upon the number of infected host snails. Peak fluke burdens and clinical paramphistomosis occurred in late summer in year 1 and early winter in year 2. The peak fluke burdens coincided with prolonged inundation of the grazing areas resulting in rapid multiplication and infection of host snails, and the period after the inundated areas dried out. The prevalence of infection in snails was high in both years, peaking at 98% in year 1 and 58% in year 2. The main host snail, G. scottianus, aestivated and retained infection for at least 24 weeks in soil, and in vegetable debris on the surface of the soil, resulting in rapid reappearance of host snails and infective metacercariae after the onset of seasonal rain. Metacercariae survived on herbage for up to 12 weeks, depending on the environmental conditions. Paramphistome burdens in calves could be predicted from the prevalence of infection in the host snail, the water levels and an index of surface water on the grazing site. Control of paramphistomosis during and after flooding may be achieved by removal of susceptible cattle from pasture or regular treatment during these periods. Strategic treatment during the dry season may reduce contamination of snail habitats and infectivity of the pasture in the following wet season.

Vegetation dynamics and seed banks of a monsoonal wetland overgrown with Paspalum distichum L. in northern India

Wetlands in the Keoladeo National Park, Bharatpur, India, have been dominated by the grass Paspalum distichum L. since the removal of cattle and water buffalo from the park in the early 1980s. The mean water depth was lowest just before the onset of monsoon, highest immediately after it, and then declined slowly over the winter and spring. The mean cover of P. distichum was also lowest just prior to the onset of the monsoon (e.g. 19% in June 1984), increased after the monsoon (e.g. 35% in October 1985) and did not reach its maximum until late winter (e.g. 49% in March 1985). There was relatively little change in the species composition of the vegetation over an annual cycle. Because of the poor monsoon in 1986, water depths were much lower during the post-monsoonal period than normal. The cover of P. distichum was also reduced during this period and fell to only 2% by March 1987. The seed banks of areas dominated by Paspalum and four other emergent species contained a total of 55 species and between 1100 and 3100 seeds m −2. Seeds of P. distichum were found in all vegetation types. Paspalum-dominated areas grazed by geese had a seed bank that contained 44 species and a mean of about 1000 seeds m −2. Only goose droppings collected in November contained viable seeds, of which 90% were Paspalum seeds. Paspalum litter (6 cm or more) reduced recruitment from the seed bank by about 80% and the number of species recruited by about 50%. Only 12 species (total seedling density < 1 seedling m −2) became established in openings created in the grass mat by geese during a summer drawdown. In an area where Paspalum was removed with bulldozers, the post-monsoonal vegetation was dominated by submersed and floating-leaved species. Paspalum was initially present at very low cover (0.1%) and increased to 4.6% in the next 9 months.

Endophyte-free tall fescue improves cattle production

A fungal endophyte was discovered infecting over 95% of tall fescue swards in the U.S. and also in European swards. This asymptomatic intercellular parasite appears to be transmitted only vertically, through infected seed. The fungus is associated with decreased animal performance. Specific toxin(s) produced by the fungus or by the fescue plant in response to the fungus has not been identified. Signs of toxicosis in cattle include increased body temperature, harsh hair coat, reduced serum prolactin, impaired reproduction, decreased rate of gain and/or milk production. Upon removal of cattle from toxic fescue to feedlots, performance is impaired 6 weeks or more. Replacement of infected fescue swards with new endophyte-free varieties greatly improves animal performance.

Yield and Quality Trends of Tall Fescue Grazed with Different Subdivisions of Pasture1

AbstractSubsequent to a grazing experiment which showed average daily gains of growing cattle on N‐fertilized tall rescue (Festuca arundinacea, Schreb.) to be similar whether grazed continuously or in a two‐paddock grazing round baled hay aftermath system, a study was done to determine short‐term changes in the quantity and quality of herbage‐on‐offer for pastures with 0, 2, or 4 subdivisions of grazing. The objective of this experiment was to provide possible explanations for the lack of differences in rate of gain in the on‐going grazing trial. Six groups of three weaner calves grazed replicated pastures of N‐fertilized tall rescue (0.256 ha/group) for 80 days in spring‐summer and 40 days in fall. Cattle were used as defoliators, and animal performance data are not presented. During each grazing cycle, cattle were continuously grazed on pastures with no subdivisions, rotated every 20 days with 2 subdivisions and every 10 days on pastures with 4‐subdivisions. At 5‐day intervals, herbage samples (10 × 0.26 m2) were cut to ground level from each subdivision under grazing. These samples were later analyzed for in vitro dry matter disappearance (IVDMD), N, and mineral composition. Residual herbage samples were also obtained following the completion of the second and third grazing cycles.In the spring and summer (20 May to 7 August), subdivision treatments did not differ in average amount of herbage‐on‐offer/ha. On removal of cattle on 7 August when the no‐subdivision treatment was fully grazed, amount of residual herbage among treatments was nearly the same. Percent IVDMD declined curvilinearly in all treatments from an average of 64% in May to 49% in mid‐July, followed by a 2.5 percentage unit increase in August.In the fall (17 September to 27 October), average amount of herbage‐on‐offer/ha ranged from 800 to 1,000 kg/ha higher with 4 subdivisions than with the other treatments. Fall digestibilities ranged from 62 to 43% IVDMD. Low values occurred at the end of the grazing cycle, especially in the 4 subdivision treatment where the most residue (trampled herbage) was observed.Composited herbage samples from the no‐ and 4‐subdivision treatments showed little difference between the spring‐summer and fall grazing cycles in range of concentrations for N and eight minerals.The results indicate that subdividing pastures for rotational grazing did not have a marked effect on average quantity and quality of tall rescue during the spring and summer. However, pastures with 4 subdivisions did provide more herbage growth in the fall. These findings may partially explain why cattle daily gains in another on‐going grazing trial have not been different.

The Effects of Killing or Removal of Animals Affected with Foot-and-Mouth Disease on the Amounts of Airborne Virus Present in Looseboxes

Pigs or cattle which had been infected with foot-and-mouth disease virus were held in looseboxes and the amount of virus present in the air after killing or removal of the animals was measured. Killing or removal of pigs led to a reduction of twenty-five fold or more in virus recovered but virus persisted in the looseboxes for at least 24 hours although only to 1/5000th of that originally present. Removal of cattle from the box did not lead to any significant fall in virus recovery. Epithelium was collected from lesions on pigs’ feet at intervals up to 24 hours after killing, but no fall in titre was found. These results are discussed in relation to the source of airborne virus from the animal, and to the measures taken in the field in the control of disease by slaughter. Les cochons ou le bétail infectés par le virus de la fièvre aphteuse étaient gardés dans des box et on a mesuré la quantité de virus presents dans l’air après abbatage ou enlèvement des animaux. L’abattage ou l’enlèvement des cochons provoquait une réduction de 25 fois ou plus du nombre de virus mais les virus persistaient dans les box 24 heures au moins quoiqu’à raison de 1/5000 ème seulement de ceux présents à l’origine. L’enlèvement du bétail du box ne provoqua aucune diminution significative de la quantité de virus récupérés. On préleva l’épithelium des lésions des pieds de cochons à intervalles allant jusqu’à 24 heures après abattage, mais on ne constata aucune diminution du titre. Ces résultats sont discutés par rapport à la source de virus d’origine atmosphèrique provenant de l’animal et en fonction des mesures prises au champ pour contrôler la maladie par abattage. Schweine oder Rinder, die mit Maul- und Klauenseuche-Virus infiziert waren, wurden in “loose-boxes” gehalten und die Menge der in der Luft suspendierten Viren nach Schlachtung oder Entfernung der Tiere gemessen. Schlachtung oder Entfernung von Schweinen führte zu einer 25 fachen oder grösseren Verminderung der Virusmenge, doch waren Viren in den “loose-boxes” für wenigstens 24 Stunden nachweisbar, obwohl nur in 1/5000 der ursprünglichen Menge. Entfernung von Rindern führte zu keiner signifikanten Verminderung der gefundenen Viren. Von erkrankten Stellen an den Füssen der Schweine wurde Epithel entnommen, bis zu 24 Stunden nach der Schlachtung, doch wurde keine Verminderung des Titers gefunden. Diese Ergebnisse werden in Beziehung auf die in der Luft suspendierten Viren und ihre Herkunft von den Tieren erörtert. Die vorbeugenden Massnahmen gegen die Krankheut in Form von Tötung der Tiere werden besprochen. Los cerdos y ganado vacuno que habían sido infectados por los virus de la fiebre aftosa fueron mantenidos en sus establos y se procedió a la medida de virus presentes en el aire después de sacrificar ο retirar a los animales de dichos establos. El sacrificio ο retirada de los cerdos condujo a una reducción del orden del 25 por ciento ó más de los virus recogidos, aunque los virus persistieron en los establos por lo menos durante 24 horas, aunque sólo a 1/5000 de las cifras originales. La retirada del ganado vacuno de los establos no condujo a ninguna reducción significativa en la recogida de virus. Se recogieron muestras del epitelio procedente de lesiones en las patas de los cerdos a intervalos de 24 horas después de haber sacrificado a los animales, sin obtenerse ninguna reducción en el título. Se discuten estos resultados en relación al origen de los virus aereos procedentes de los animales y a las medidas tomadas en el campo en el control de la enfermedad por el sacrificio de los animales.

THE EFFECTS OF LEVEL OF NITROGEN FERTILIZER ON BEEF PRODUCTION FROM GRAZED PERENNIAL–RYEGRASS/WHITE–CLOVER PASTURES

The treatments in this summer–grazing experiment were designed as a 2 × 3 factorial, there being two levels of nitrogenous fertilizer (nitro–chalk), supplying 0 and 336kg of N/ha per annum (NO and N3, respectively) and three stocking rates. The fertilizer was applied in 7 dressings at approximately three–weekly intervals. The animals used were Hereford x Friesian steers; these were slaughtered at the end of the grazing season. The stocking rates were calculated on the basis of expected herbage production. The experiment was laid out in 6 randomized blocks which were grazed in rotation. Two blocks were cut for conservation before grazing each year; up to the end of June only 4 blocks were used for grazing.There was little contamination of the swards with unsown species. With the NO swards the clover contents declined each year, but remained fairly high at over 20% in 1965. Clover contents also declined each year in the N3 swards and by 1965 were only 2 to 4%.The quantities of herbage cut for conservation were higher from the swards receiving N. The live–weight gains of the cattle (per head) were higher at the lower stocking rates, the effect of stocking rate being more noticeable in the July to Oct. period. Live–weight gains per ha increased at the higher stocking rates. In 1963 and 1965, as stocking rates increased carcass weights per animal decreased and carcass quality, as indicated by the commercial grades, was poorer. In 1964, a dry spell from July to Oct. necessitated the removal of cattle from the experiment and the effects of treatment on carcass weight and quality were not apparent.