Reaudit letter to the City of Ottumwa for the period July 1, 2005 through June 30, 2006, as well as certain issues applicable to the year ended June 30, 2005 and subsequent periods

Reaudit letter to the City of Ottumwa for the period July 1, 2005 through June 30, 2006, as well as certain issues applicable to the year ended June 30, 2005 and subsequent periods

Some like it hot: temperature and acidification modulate larval development and settlement of the sea urchin Arbacia lixula

We studied the effects of temperature and pH on larval development, settlement and juvenile survival of a Mediterranean population of the sea urchin Arbacia lixula. Three temperatures (16, 17.5 and 19 °C) were tested at present pH conditions (pHT 8.1). At 19 °C, two pH levels were compared to reflect present average (pHT 8.1) and near-future average conditions (pHT 7.7, expected by 2100). Larvae were reared for 52-days to achieve the full larval development and complete the metamorphosis to the settler stage. We analyzed larval survival, growth, morphology and settlement success. We also tested the carry-over effect of acidification on juvenile survival after 3 days. Our results showed that larval survival and size significantly increased with temperature. Acidification resulted in higher survival rates and developmental delay. Larval morphology was significantly altered by low temperatures, which led to narrower larvae with relatively shorter skeletal rods, but larval morphology was only marginally affected by acidification. No carry-over effects between larvae and juveniles were detected in early settler survival, though settlers from larvae reared at pH 7.7 were significantly smaller than their counterparts developed at pH 8.1. These results suggest an overall positive effect of environmental parameters related to global change on the reproduction of A. lixula, and reinforce the concerns about the increasing negative impact on shallow Mediterranean ecosystems of this post-glacial colonizer.

Soil phosphorus fractions in sandy soils amended with cattle manure for long periods

Phosphorus fractions were determined in soil samples from areas fertilized or not with farmyard cattle manure (FYM) and in samples of FYM used in the semi-arid region of Paraiba state, Brazil. Soil samples were taken from the 0-20; 20-40 and 40-60 cm layers of 18 cultivated areas, which, according to interviews with farmers, had been treated with 12 to 20 t ha-1 FYM annually, for the past 2 to 40 years. Soil samples were also collected from four unfertilized pasture areas as controls. Phosphorus in the soil samples was sequentially extracted with water (Pw), resin (Pres), NaHCO3 (Pi bic and Po bic), NaOH (Pi hid and Po hid), H2SO4 (Pacid) and, finally, by digestion with H2SO4/H2O2 (Presd). Nine FYM samples were extracted with water, resin, Mehlich-1, H2SO4, NaOH or digestion with H2SO4/H2O2, not sequentially, and the extracts analyzed for P. The sampled areas had homogeneous, sandy and P-deficient soils; increases in total soil P (Pt) above the mean value of the control areas (up to 274 mg kg-1 in the 0-20 cm layer of the most P-enriched samples) were therefore attributed to FYM applications, which was the only external P input in the region. Regression analysis was used to study the relationship between soil P fractions and Pt. The Pacid fraction, related to Ca-P forms, showed the greatest increases (p < 0.01) as a result of FYM applications, rising from 8.4 mg kg-1 in a non-fertilized sample to 43.8 mg kg-1 in the sample with the highest Pt content. The sum of Pw, Pres and Pi bic, considered as labile P, showed comparable increases with Pacid, while Pi hid showed the smallest increase due to FYM applications. Organic P forms also increased, more so the fraction Po hid, considered less labile, than the more labile one, Po bic. The residual P fraction was practically half of Pt, independently of the Pt value. Increases in labile P, Pacid and organic P were justified by the high average concentration of Pw (36 %), Pacid (34 %), and Po hid (30 %) in the FYM. Significant changes in the proportion of P forms among soil layers indicated the downward movement of P in organic forms.

Report on a review of selected general and application controls over the Iowa Department of Administrative Service’s (DAS) Human Resource Information System (HRIS), Payroll, Integrated Information for Iowa (I/3) and E-Payment Engine Systems for the periods April 13, 2009 through May 15, 2009 and April 5, 2010 through May 7, 2010

Report on a review of selected general and application controls over the Iowa Department of Administrative Service’s (DAS) Human Resource Information System (HRIS), Payroll, Integrated Information for Iowa (I/3) and E-Payment Engine Systems for the periods April 13, 2009 through May 15, 2009 and April 5, 2010 through May 7, 2010

Phosphorus extracted by ion exchange resins and mehlich-1 from oxisols (latosols) treated with different phosphorus rates and sources for varied soil-source contact periods

Despite the large number of studies addressing the quantification of phosphorus (P) availability by different extraction methods, many questions remain unanswered. The aim of this paper was to compare the effectiveness of the extractors Mehlich-1, Anionic Resin (AR) and Mixed Resin (MR), to determine the availability of P under different experimental conditions. The laboratory study was arranged in randomized blocks in a [(3 x 3 x 2) + 3] x 4 factorial design, with four replications, testing the response of three soils with different texture: a very clayey Red Latosol (LV), a sandy clay loam Red Yellow Latosol (LVA), and a sandy loam Yellow Latosol (LA), to three sources (triple superphosphate, reactive phosphate rock from Gafsa-Tunisia; and natural phosphate from Araxá-Minas Gerais) at two P rates (75 and 150 mg dm-3), plus three control treatments (each soil without P application) after four contact periods (15, 30, 60, and 120 days) of the P sources with soil. The soil acidity of LV and LVA was adjusted by raising base saturation to 60 % with the application of CaCO3 and MgCO3 at a 4:1 molar ratio (LA required no correction). These samples were maintained at field moisture capacity for 30 days. After the contact periods, the samples were collected to quantify the available P concentrations by the three extractants. In general, all three indicated that the available P-content in soils was reduced after longer contact periods with the P sources. Of the three sources, this reduction was most pronounced for triple superphosphate, intermediate for reactive phosphate, while Araxá phosphate was least sensitive to the effect of time. It was observed that AR extracted lower P levels from all three soils when the sources were phosphate rocks, while MR extracted values close to Mehlich-1 in LV (clay) and LVA (medium texture) for reactive phosphate. For Araxá phosphate, much higher P values were determined by Mehlich-1 than by the resins, because of the acidity of the extractor. For triple superphosphate, both resins extracted higher P levels than Mehlich-1, due to the consumption of this extractor, particularly when used for LV and LVA.

Physical quality of an Oxisol after different periods of management systems

Management systems may lead to a loss of soil physical quality as a result of removal of the plant cover and excessive agricultural mechanization. The hypothesis of this study was that the soil aggregate stability, bulk density, macro- and microporosity, and the S index and saturated hydraulic conductivity may be used as indicators of the soil physical quality. The aim was to study the effects of different periods and managements on the physical attributes of a medium-textured Red Oxisol under soybean and corn for two growing seasons, and determine which layers are most susceptible to variations. A completely randomized experimental design was used with split plots (five treatments and four layers), with four replications. The treatments in 2008/09 consisted of: five years of no-tillage (NTS5), seven years of no-tillage (NTS7), nine years of no-tillage (NTS9), conventional tillage (CTS) and an adjacent area of native forest (NF). The treatments were extended for another year, identified in 2009/10 as: NTS6, NTS8, NTS10, CTS and NF. The soil layers 0-0.05, 0.05-0.10, 0.10-0.20 and 0.20-0.30 m were sampled. The highest S index values were observed in the treatment CTS in the 0-0.05 m layer (0.106) and the 0.05-0.10 m layer (0.099) in 2008/09, and in the 0-0.05 m layer (0.066) in 2009/10. This fact may be associated with soil turnover, resulting in high macroporosity in this treatment. In contrast, in the NTS, limiting macroporosity values were observed in some layers (below 0.10 m³ m-3). Highest aggregate stability as well as the highest saturated hydraulic conductivity (Kθ) values were observed in NF in relation to the other treatments. In 2009/10, the Kθ in NF differed only from NTS10. This study showed that the use of the S index alone cannot be recommended as an absolute indicator of the soil physical quality, even at values greater than 0.035.

Temporal and spatial dynamics of benthic invertebrate communities in an alpine glacier-fed alluvial system

Summary The present thesis work focused on the ecology of benthic invertebrates in the proglacial floodplain of the Rhone in the Swiss Alps. The main glacial Rhone River and a smaller glacial tributary, the Mutt River, joined and entered a braiding multi-thread area. A first part concentrated on the disruption of the longitudinal patterns of environmental conditions and benthic invertebrate fauna in the Rhone by its tributary the Mutt. The Mutt had less harsh environmental conditions, higher taxonomic richness and more abundant zoobenthos compared to the Rhone upstream of the confluence. Although the habitat conditions in the main stream were little modified by the tributary, the fauna was richer and more diverse below the confluence. Colonisation from the Mutt induced the occurrence of faunal elements uncommon of glacial streams in the upper Rhone, where water temperature remains below 4°C. Although the glacial Rhone dominated the system with regard to hydrology and certain environmental conditions, the Mutt tributary has to be seen as the faunal driver of the system. The second part of the study concerned the spatio-temporal differentiation of the habitats and the benthic communities along and across the flood plain. No longitudinal differentiation was found. The spatial transversal differentiation of three habitat types with different environmental characteristics was successfully reflected in the spatial variability of benthic assemblages. This typology separated marginal sites of the flood plain, left bank sites under the influence of the Mutt, and the right bank sites under the influence of the Rh6ne. Faunistic spatial differences were emphasized by the quantitative structure of the fauna, richness, abundances and Simpson index of diversity. Seasonal environmental variability was positively related with Simpson index of diversity and the total richness per site. Low flow conditions were the most favourable season for the fauna and November was characterized by low spatial environmental heterogeneity, high spatial heterogeneity of faunal assemblage, maximum taxonomic richness, a particular taxonomic composition, highest abundances, as well as the highest primary food resources. The third part studied the egg development of three species of Ephemeroptera in the laboratory at 1.5 to 7°C and the ecological implications in the field. Species revealed very contrasting development strategies. Baetis alpinus has a synchronous and efficient egg development, which is faster in warmer habitats, enabling it to exploit short periods of favourable conditions in the floodplain. Ecdyonurus picteti has a very long development time slightly decreasing in warmer conditions. The high degree of individual variation suggests a genetic determination of the degree-days demand. Combined with the glacial local conditions, this strategy leads to an extreme delay of hatching and allows it to develop in very unpredictable habitats. Rhithrogena nivata is the second cold adapted species in Ephemeroptera. The incubation duration is long and success largely depends on the timing of hatching and the discharge conditions. This species is able to exploit extremely unstable and cold habitats where other species are limited by low water temperatures. The fourth part dealt with larval development in different habitats of the floodplain. Addition of data on egg development allowed the description of the life histories of the species from oviposition until emergence. Rhithrogena nivata and loyolaea generally have a two-year development, with the first winter passed as eggs and the second one as larvae. Development of Ecdyonurus picteti is difficult to document but appears to be efficient in a harsh and unpredictable environment. Baetis alpinus was studied separately in four habitats of the floodplain system with contrasting thermal regimes. Differences in success and duration of larval development and in growth rates are emphasised. Subvention mechanisms between habitats by migration of young or grown larvae were demonstrated. Development success and persistence of the populations in the system were thus increased. Emergence was synchronised to the detriment of the optimisation of the adult's size and fecundity. These very different development strategies induce a spatial and temporal distribution in the use of food resources and ecological niches. The last part of this work aimed at the synthesis of the characteristics and the ecological features of three distinct compartments of the system that are the upper Rhone, the Mutt and the floodplain. Their particular role as well as their inter-dependence concerning the structure and the dynamics of the benthic communities was emphasised. Résumé Ce travail de thèse est consacré à l'écologie des invertébrés benthiques dans la zone alluviale proglaciaire du Rhône dans les Alpes suisses. Le Rhône, torrent glaciaire principal, reçoit les eaux de la Mutt, affluent glaciaire secondaire, puis pénètre dans une zone de tressage formée de plusieurs bras. La première partie de l'étude se concentre sur la disruption par la Mutt des processus longitudinaux, tant environnementaux que faunistiques, existants dans le Rhône. Les conditions environnementales régnant dans la Mutt sont moins rudes, la richesse taxonomique plus élevée et le zoobenthos plus abondant que dans le Rhône en amont de la confluence. Bien que les conditions environnementales dans le torrent principal soient peu modifiées par l'affluent, la faune s'avère être plus riche et plus diversifiée en aval de la confluence. La colonisation depuis la Mutt permet l'occurrence de taxons inhabituels dans le Rhône en amont de la confluence, où la température de l'eau se maintient en dessous de 4°C. Bien que le Rhône, torrent glaciaire principal, domine le système du point de vu de l'hydrologie et de certains paramètres environnementaux, l'affluent Mutt doit être considéré comme l'élément structurant la faune dans le système. La deuxième partie concerne la différentiation spatiale et temporelle des habitats et des communautés benthiques à travers la plaine alluviale. Aucune différentiation longitudinale n'a été mise en évidence. La différentiation transversale de trois types d'habitats sur la base des caractéristiques environnementales a été confirmée par la variabilité spatiale de la faune. Cette typologie sépare les sites marginaux de la plaine alluviale, ceux sous l'influence de la Mutt (en rive gauche) et ceux sous l'influence du Rhône amont (en rive droite). Les différences spatiales de la faune sont mises en évidence par la structure quantitative de la faune, la richesse, les abondances et l'indice de diversité de Simpson. La variabilité saisonnière du milieu est positivement liée avec l'indice de diversité de Simpson et la richesse totale par site. L'étiage correspond à la période la plus favorable pour la faune et novembre réunit des conditions de faible hétérogénéité spatiale du milieu, de forte hétérogénéité spatiale de la faune, une richesse taxonomique maximale, une composition faunistique particulière, les abondances ainsi que les ressources primaires les plus élevées. La troisième partie est consacrée à l'étude du développement des oeufs de trois espèces d'Ephémères au laboratoire à des températures de 1.5 à 7°C, ainsi qu'aux implications écologiques sur le terrain. Ces espèces présentent des stratégies de développement très contrastées. Baetis alpinus a un développement synchrone et efficace, plus rapide en milieu plus chaud et lui permettant d'exploiter les courtes périodes de conditions favorables. Ecdyonurus picteti présente une durée de développement très longue, diminuant légèrement dans des conditions plus chaudes. L'importante variation interindividuelle suggère un déterminisme génétique de la durée de développement. Cette stratégie, associée aux conditions locales, conduit à un décalage extrême des éclosions et permet à l'espèce de se développer dans des habitats imprévisibles. Rhithrogena nivata est la seconde espèce d'Ephémères présentant une adaptation au froid. L'incubation des oeufs est longue et son succès dépend de la période des éclosions et des conditions hydrologiques. Cette espèce est capable d'exploiter des habitats extrêmement instables et froids, où la température est facteur limitant pour d'autres espèces. La quatrième partie traite du développement larvaire dans différents habitats de la plaine alluviale. Le développement complet est décrit pour les espèces étudiées de la ponte jusqu'à l'émergence. Rhithrogena nivata et loyolaea atteignent généralement le stade adulte en deux ans, le premier hiver étant passé sous forme d'oeuf et le second sous forme de larve. Le développement de Ecdyonurus picteti est difficile à documenter, mais s'avère cependant efficace dans un environnement rude et imprévisible. Baetis alpinus a été étudié séparément dans quatre habitats de la plaine ayant des régimes thermiques contrastés. La réussite et la durée du développement embryonnaire ainsi que les taux de croissance y sont variables. Des mécanismes de subvention entre habitats sont possibles par la migration de larves juvéniles ou plus développées, augmentant ainsi la réussite du développement et le maintien des populations dans le système. L'émergence devient synchrone, au détriment de l'optimisation de la taille et de la fécondité des adultes. Ces stratégies très différentes induisent une distribution spatiale et temporelle dans l'usage des ressources et des niches écologiques. La dernière partie synthétise les caractéristiques écologiques des trois compartiments du système que sont le Rhône amont, la Mutt et la zone alluviale. Leurs rôles particuliers et leurs interdépendances du point de vue de la structure et de la dynamique des communautés benthiques sont mis en avant.

Stability of soybean yield through different sowing periods

Soybean yield is highly affected by sowing period and there are significant productivity losses when sowings are done outward a relatively restricted period in many regions of Brazil. Breeding cultivars less sensitive to photoperiod and to temperature variations is desirable for adaptation to wider sowing period and wider latitude range and also make irrigated soybean cultivation possible during the fall-winter seasons in frost free regions. The possibility of selecting high yielding and stable lines for yield during various sowing periods was studied by analyzing the behavior of 100 non-selected advanced lines (F9 and F10), from each one of all possible biparental crosses involving the genotypes BR85-29009, OCEPAR 8, FT-2, and BR-13. Experiments were set up in a completely randomized design with single-plant hill plots and received supplementary irrigation. Sowing was on Sept 27, Oct 20, Nov 17, and Dec 17 in 1993/94 and Sept 20, Oct 20, Nov 17, and Dec 14 in 1994/95 at Londrina, PR, Brazil. Procedures of regression analysis and minimum variance among planting date means were efficient for selecting stable lines during the four sowing seasons. It was possible to select stable and high yielding genotypes through the four sowing periods in all the crosses. No specific cross was clearly better to produce a greater number of stable genotypes.

Changing patterns of cancer incidence in the early- and late-HAART periods: the Swiss HIV Cohort Study.

BACKGROUND: The advent of highly active antiretroviral therapy (HAART) in 1996 led to a decrease in the incidence of Kaposi's sarcoma (KS) and non-Hodgkin's lymphoma (NHL), but not of other cancers, among people with HIV or AIDS (PWHA). It also led to marked increases in their life expectancy. METHODS: We conducted a record-linkage study between the Swiss HIV Cohort Study and nine Swiss cantonal cancer registries. In total, 9429 PWHA provided 20,615, 17,690, and 15,410 person-years in the pre-, early-, and late-HAART periods, respectively. Standardised incidence ratios in PWHA vs the general population, as well as age-standardised, and age-specific incidence rates were computed for different periods. RESULTS: Incidence of KS and NHL decreased by several fold between the pre- and early-HAART periods, and additionally declined from the early- to the late-HAART period. Incidence of cancers of the anus, liver, non-melanomatous skin, and Hodgkin's lymphoma increased in the early- compared with the pre-HAART period, but not during the late-HAART period. The incidence of all non-AIDS-defining cancers (NADCs) combined was similar in all periods, and approximately double that in the general population. CONCLUSIONS: Increases in the incidence of selected NADCs after the introduction of HAART were largely accounted for by the ageing of PWHA.

Effects of parental larval diet on egg size and offspring traits in Drosophila.

If a mother's nutritional status predicts the nutritional environment of the offspring, it would be adaptive for mothers experiencing nutritional stress to prime their offspring for a better tolerance to poor nutrition. We report that in Drosophila melanogaster, parents raised on poor larval food laid 3-6% heavier eggs than parents raised on standard food, despite being 30 per cent smaller. Their offspring developed 14 h (4%) faster on the poor food than offspring of well-fed parents. However, they were slightly smaller as adults. Thus, the effects of parental diet on offspring performance under malnutrition apparently involve both adaptive plasticity and maladaptive effects of parental stress.

Manejo da pastagem de azevém, contaminação larval no pasto e infecção parasitária em ovinos

O objetivo deste trabalho foi avaliar o efeito do manejo da pastagem de azevém sobre o risco de reinfecção parasitária. Foram utilizadas duas ofertas (10 e 20 kg de matéria seca por 100 kg de peso vivo) em dois métodos de pastejo (lotação contínua e intermitente). A infestação parasitária no mantilho e nos diferentes estratos da forragem foi avaliada nos estratos: acima de 15, 10-15, 5-10, 2,5-5 e 0-2,5 cm; a carga parasitária no animal foi avaliada por exames coproparasitológicos; e a seletividade da dieta foi avaliada com afilhos marcados. Independentemente do método, a densidade larval aumentou do topo para a base do dossel forrageiro. No entanto, entre os estratos aptos ao pastejo foram observadas diferenças na oferta de 20% do peso vivo. A oferta influenciou o número de larvas recuperadas na forragem e a infecção no animal para ambos os gêneros de parasitas Haemonchus spp. e Trichostrongylus spp. A maior oferta proporcionou maior contaminação larval e infecção nos ovinos, porém na oferta de 10% do peso vivo, a quantidade de larvas presentes no pasto foi menor em lotação contínua, mas a carga parasitária no animal foi semelhante à da lotação rotacionada, independentemente do método de pastejo.

Evolution and functional characterisation of the IR chemosensory receptors in the Drosophila larval gustatory system

Chemosensory receptor gene families encode divergent proteins capable of detecting a huge diversity of environmental stimuli that are constantly changing over evolutionary time as organisms adapt to distinct ecological niches. While olfaction is dedicated to the detection of volatile compounds, taste is key to assess food quality for nutritional value and presence of toxic substances. The sense of taste also provides initial signals to mediate endocrine regulation of appetite and food metabolism and plays a role in kin recognition. The fruit fly Drosophila melanogaster is a very good model for studying smell and taste because these senses are very important in insects and because a broad variety of genetic tools are available in Drosophila. Recently, a family of 66 chemosensory receptors, the Ionotropic Receptors (IRs) was described in fruit flies. IRs are distantly related to ionotropic glutamate receptors (iGluRs), but their evolutionary origin from these synaptic receptors is unclear. While 16 IRs are expressed in the olfactory system, nothing is known about the other members of this repertoire. In this thesis, I describe bioinformatic, expression and functional analyses of the IRs aimed at understanding how these receptors have evolved, and at characterising the role of the non-olfactory IRs. I show that these have emerged at the basis of the protostome lineage and probably have acquired their sensory function very early. Moreover, although several IRs are conserved across insects, there are rapid and dramatic changes in the size and divergence of IR repertoires across species. I then performed a comprehensive analysis of IR expression in the larva of Drosophila melanogaster, which is a good model to study taste and feeding mechanisms as it spends most of its time eating or foraging. I found that most of the divergent members of the IR repertoire are expressed in both peripheral and internal gustatory neurons, suggesting that these are involved in taste perception. Finally, through the establishment of a new neurophysiological assay in larvae, I identified for the first time subsets of IR neurons that preferentially detect sugars and amino acids, indicating that IRs might be involved in sensing these compounds. Together, my results indicate that IRs are an evolutionarily dynamic and functionally versatile family of receptors. In contrast to the olfactory IRs that are well-conserved, gustatory IRs are rapidly evolving species-specific receptors that are likely to be involved in detecting a wide variety of tastants. - La plupart des animaux possèdent de grandes familles de récepteurs chimiosensoriels dont la fonction est de détecter l'immense diversité de composés chimiques présents dans l'environnement. Ces récepteurs évoluent en même temps que les organismes s'adaptent à leur écosystème. Il existe deux manières de percevoir ces signaux chimiques : l'olfaction et le goût. Alors que le système olfactif perçoit les composés volatiles, le sens du goût permet d'évaluer, par contact, la qualité de la nourriture, de détecter des substances toxiques et de réguler l'appétit et le métabolisme. L'un des organismes modèles les plus pertinents pour étudier le sens du goût est le stade larvaire de la mouche du vinaigre Drosophila melanogaster. En effet, la principale fonction du stade larvaire est de trouver de la nourriture et de manger. De plus, il est possible d'utiliser tous les outils génétiques développés chez la drosophile. Récemment, une nouvelle famille de 66 récepteurs chimiosensoriels appelés Récepteurs Ionotropiques (IRs) a été découverte chez la drosophile. Bien que leur orogine soit peu claire, ces récepteurs sont similaires aux récepteurs ionotropiques glutamatergiques impliqués dans la transmission synaptique. 16 IRs sont exprimés dans le système olfactif de la mouche adulte, mais pour l'instant on ne connaît rien des autres membres de cette famille. Durant ma thèse, j'ai effectué des recherches sur l'évolution de ces récepteurs ainsi que sur l'expression et la fonction des IRs non olfactifs. Je démontre que les IRs sont apparus chez l'ancêtre commun des protostomiens et ont probablement acquis leur fonction sensorielle très rapidement. De plus, bien qu'un certain nombre d'IRs olfactifs soient conservés chez les insectes, d'importantes variations dans la taille et la divergence des répertoires d'IRs entre les espèces ont été constatées. J'ai également découvert qu'un grand nombre d'IRs non olfactifs sont exprimés dans différents organes gustatifs, ce qui leur confère probablement une fonction dans la perception des goûts. Finalement, pour la première fois, des neurones exprimant des IRs ont été identifiés pour leur fonction dans la perception de sucres et d'acides aminés chez la larve. Mes résultats présentent les IRs comme une famille très dynamique, aux fonctions très variées, qui joue un rôle tant dans l'odorat que dans le goût, et dont la fonction est restée importante tout au long de l'évolution. De plus, l'identification de neurones spécialisés dans la perception de certains composés permettra l'étude des circuits neuronaux impliqués dans le traitement de ces informations.

Dual-purpose wheat grain and animal production under different grazing periods

The objective of this work was to evaluate the influence of different grazing periods on beef animal production and on wheat forage and grain yield. The experiment was carried out in Pato Branco, PR, Brazil. Six grazing periods were evaluated (0, 21, 42, 63, 84, and 105 days) on dual-purpose wheat cultivar BRS Tarumã. Purunã steers, with average live weight of 162 kg and ten months of age, were kept under continuous grazing using a variable stocking rate, in order to maintain the established sward height of 25 cm. Greater increases in total animal gain (TAG) occurred with longer grazing periods. However, there was little increase after 63 days (490 kg ha-1), and TAG decreased from 552 to 448 kg ha-1 between 84 and 105 days. Grain yield decreased from 2,830 to 610 kg ha-1 when the grazing period increased from 0 to 105 days, but there was little change after 63 days (750 kg ha-1). Cultivar BRS Tarumã shows excellent animal production potential, and the decision on how long wheat pastures should be grazed must be based on relative prices of grain and livestock.