West and northwest of Logan City there are approximately 2,372 acres of land irrigated by water from the Logan Cow Pasture Water Company irrigation system. This company is a nonprofit corporation organized by a group of land owners for the purpose of arranging conveyance of water ta their farms and ranches.

Asthma is a chronic respiratory disease characterized by reversible airway obstruction, persistent airway hyperresponsiveness, chronic airway inflammation, and chronic airway remodeling. Most adult asthmatics have neutrophilic airway inflammation that correlates to increasing disease severity, and fail to respond to corticosteroid therapies that mitigate other asthma endotypes. Accordingly, there is a need to investigate the molecular mechanisms responsible for neutrophilic asthma. Pasture heaves, a respiratory disease affecting horses housed on pasture in conditions of high heat and humidity, shares the aforementioned characteristics of human asthma, including neutrophilic inflammation. The cause is undetermined, but genetic propensities for reactivity to seasonally inhaled, pasture-associated, aeroallergens are presumed. Complexities of diseases like asthma and pasture heaves, that include temporal interactions between environmental and genetic factors, lend themselves to exploration using -omics technologies. An emergent paradigm in disease pathogenesis views disease as the result of imbalances in a biological system of thousands of proteins that maintain eukaryotic homeostasis. Consistent with this paradigm, this dissertation describes systematic efforts to identify groups of proteins in the bronchoalveolar lavage fluids of horses with pasture heaves that are altered in a manner that influences neutrophilic airway inflammation, and are similarly changed in human asthma. This is the first use of -omics technologies to investigate pasture heaves. This was accomplished first by improving functional annotation of the equine genome by providing functional annotation for an equine oligoarray, thereby facilitating future functional modeling of equine gene products. Next, through comparative modeling of protein functions in normal bronchoalveolar lavage fluid (BALF) proteomes from horse, human, and mouse, we demonstrated conservation of protein functions in lung fluids across these species. Finally, comparative modeling of pasture heaves-affected and non-diseased BALF proteomes demonstrated that proteins in diseased BALF favor airway neutrophilic inflammation by increasing neutrophil migration, chemotaxis, adhesion, detachment, transmigration, and degranulation, while reducing activation, cell spreading, infiltration, phagocytosis, respiratory burst, apoptosis, and clearance. Collectively, these molecular events contribute to airway neutrophilic inflammation in pasture heaves, and are conserved in human asthma. This method further validates pasture heaves as a robust model for human neutrophilic asthma, and highlights proteins of potential clinical and therapeutic relevance.

Understanding the particularities of pasture inclusion on cows' diets and their subsequent impact on the digestive processes, together with possible differences in the nutrient utilization of cows managed under grazing conditions, are challenges that must be elucidated in order to design strategies to improve the cows' productive performance. The objectives of this dissertation were: 1) to review the existing literature on ration formulation for dairy cows in pasture-based systems, identifying limitations and potential improvement areas, 2) to evaluate the adequacy of the Molly model predictions of ruminal fermentation, nutrient digestion, and performance from cows consuming fresh ryegrass-based diets, identifying mechanisms that could be used to direct further model improvements, 3) to evaluate the model predictions of milk, fat and protein production using data from Holstein-Friesian and Jersey cows from Chile managed under pasture-based systems, identifying mechanisms that could be used to direct further model improvements, 4) to identify the different dairy breeds and their crosses that are used in the Chilean dairy population, determining if there are specific breed and heterosis effects on productive and some functional traits, and 5) to characterize the ruminal degradation dynamics of crude protein (CP) and individual amino acids (AA) from ryegrass (Lolium perenne) at vegetative stage, generating information to improve the ration formulation in dairy cows in pasture-based systems. From the literature revision in objective 1, different factors that could help to create a more specific classification of dairy pasture-based systems were identified. Maximizing grass inclusion seems to leads to an oversimplification of diets, potentially limiting the performance of medium and high producing cows. Despite the low N use efficiencies reached in pasture-based systems, there is a lack of information in studies that delve into the ruminal degradation of CP and AA, as well as their intestinal absorption, and subsequent post-absorptive utilization. Advances in the understanding of these areas could help to create strategies to face this problem. There is evidence suggesting that cows can perform different under different productive systems, but various breeds, strains, and crossbreds are used in pasture-based systems, being needed first a better characterization of them. To achieve the second objective, a total of 25 studies (n = 115 treatments) including dairy cows consuming ryegrass predominant diets, published from 1970 through 2020, were collected from the literature and used to assess the model accuracy and precision based on root mean squared errors and concordance correlation coefficients (CCC). Predictions of protein and fiber digestion and fiber and organic matter fecal excretion were improved after model reparameterization, while body weight and body condition score predictions were improved after model modifications and reparameterization. Although digestion of nutrient was better represented by the new set of parameters derived, the accuracies of milk, protein, and fat production remained low (CCC of 0.13, 0.12, and 018, respectively), with moderate slope bias. To achieve the third objective, a dataset including 180 group cows' diets (153 from Holstein Friesian and 27 from Jersey cows) from 18 commercial dairy farms with different inclusion of ryegrass was compiled. Chemical composition of feeds ingredients, group intakes and animal performance records, were provided by the Chilean cooperative Colun. Separately model mammary reparameterization of Holstein Friesian and Jersey cows' data, improved both milk production (CCC values of 0.69 and 0.90, respectively) and milk solids predictions (CCC values of 0.68 and 0.92 for milk protein and 0.65 and 0.80 for milk fat, for Holstein Friesian and Jersey cows, respectively). This indicates that there seems to be some differences in mammary cells and cells activity between breeds evaluated, translated into different lactation curves and milk solids synthesis patters. To achieve the fourth objective, a dataset considering 1,429,132 records from 586,624 cows that calved between 1998 and 2018 was compiled. Pedigree information, milk, milk protein, and milk fat, as well as somatic cell score and calving interval records were provided by the Chilean cooperative COOPRINSEM. The proportion of each breed according to the different country origin (strain) was calculated for all the animals, being identified eight genetic strains with enough information to perform separated genetic evaluations: Chilean Friesian, French Holstein-Friesian, US-Holstein, US-Jersey, French Montbeliarde, New Zealander Holstein-Friesian, Swedish Red and White, and British Friesian. Four different genetic models, increasing in complexity (considering breed or strain classification, crossbreeding proportion, and heterosis effects) were tested. Specific effects for some genetic strains, as well as heterosis effects between some strains with Chilean Friesian were identified, so these effects should be considered when performing genetic evaluations in the Chilean dairy population. Also, they can be used to direct future selection programs. To achieve the last objective, an in situ study using three cannulated cows was carried out at the Agricultural Research Station of the Austral University of Chile (Valdivia, Chile). Samples from a perennial ryegrass pasture were collected during winter, spring and summer at vegetative stage. Duplicate bags were ruminally incubated for 4, 8, 12, 24, and 96 h. CP and AA profile of original samples and from incubation residues were determined. Ryegrass samples presented a high crude protein content (averaging 25.8%), however, the RUP content was ~15 to 20% of CP. Significant differences were observed for ryegrass CP and individual AA ruminal degradation kinetics, this seems to be associated to some specific AA. / Doctor of Philosophy / The used of pasture-based systems in dairy production are an important alternative in countries were local environmental and climatological conditions, as well as soil properties are suitable for the growth of high-quality grasslands. The main advantages attributed to the use of pasture-based system are the reduction in the production costs, and potentially improving the nutrition quality of dairy products as well as the cows' welfare. However, they have some important limitations as the natural variation in the quantity and quality of available herbage. Also, there is a lack of information on fundamental nutrition of pasture nutrients digestion and utilization by the cows manage and selected under these environmental conditions. The first two objectives of this dissertation consisted in using the Molly nutritional model, which represents the biology of the whole cow, in order to identify key aspects to better understand the cows manage under pasture-based systems and develop strategies to precise their nutrition. Particularly, topics such as prediction of ruminal fermentation and digestive processes, mobilization of body reserves, mammary glands metabolism, and potential differences between Holstein-Friesian and Jersey cows were analyzed. Overall, work on these objectives resulted in improvements to the Molly model for making predictions of diets that include grass. The diversity of breeds and their country of origin, as well as different crosses in the Chilean dairy population were explored. A more comprehensive genetic model was proposed in this work to precise the calculation of breeding values in the country. Furthermore, our findings could be used as inputs to direct future selection programs. The last objective explored the ruminal degradation of crude protein and each individual amino acid in ryegrass. We demonstrate that indeed there are differences in the degradation parameters for some amino acids. Due to the high degradability of fresh ryegrass, there could be some potential limitations in the supply of some essential amino acids, especially in high producing cows consuming predominant ryegrass diets.

An experiment was conducted to evaluate the effects of pasture finishing versus high-concentrate finishing, over time, on fatty acid metabolism in Angus crossbred (n = 24) beef steers. Ruminal fluid, serum, and adipose tissue biposies were obtained on d 0, 28, 84, and 140. Pasture forages and diet ingredient samples were obtained at 14 d intervals to determine nutritive value and fatty acid composition. The high-concentrate diet consisted of corn silage, cracked corn, soybean meal, and a vitamin and mineral supplement. The pasture-finished steers grazed sequentially on triticale (Triticale hexaploide)/annual ryegrass (Lolium multiflorum), alfalfa (Medicago sativa)/orchardgrass (Dactylis glomerata), and a cool-season grass/legume mixture. The high-concentrate diet consisted of 57 % linoleic acid and 7 % linolenic acid (of total fatty acids). The pasture forages contained an average 9 % linoleic acid and 66 % linolenic acid (of total fatty acids). Adipose tissue concentrations of 18:2 cis-9, trans-11 CLA were higher (P < 0.05) in the pasture-finished steers than high-concentrate finished steers. Concentrations of 18:2 cis-9, trans-11 CLA declined in the high-concentrate finished steers (P < 0.05) from d 0 to 28 and d 28 to 84. In the pasture-finished steers concentrations peaked (P < 0.10) on d 28, and remained high throughout the duration of the study. Concentrations of linolenic acid were higher (P < 0.05) in adipose tissue, ruminal fluid, and serum of the pasture-finished steers, compared to the high-concentrate finished steers. In the pasture-finished steers linolenic acid concentrations peaked (P < 0.05) on d 28, and remained high throughout the study. Concentrations of linolenic acid gradually decreased (P < 0.05) over time within the high-concentrate finished steers. Thus, it appears that only a short time is needed to alter the omega-3 and CLA composition of adipose tissue in cattle finished on pasture. / Ph. D.

Version 2.0 of the P Index for Virginia uses coefficients describing the risk of P losses for different manure sources applied to fescue pasture that have not been verified on Virginian soils. In the first experiment, four sources of manure (dairy slurry, piggery waste, beef solids, and poultry litter) and triple superphosphate (TSP) were applied iso-nitrogenously to pasture plots (1.5 m2, 10% slope) with 31 ppm Mehlich 1-P soil test. The P treatments were amended in spring at a rate of 62.7 kg P2O5/ha and compared against a no-P-amended control. Forage was cut and removed monthly (n=5). Five rainfall simulations (65-70 mm/h) were conducted at three occasions (June, August, and October); the soil moisture was below field capacity at two events. Continuous surface runoff was collected for 30 min from each plot in accordance with the protocol of the National P Research Project. Data were statistically analyzed using Proc Mixed of SAS with rain event or cutting used as the repeated measure. Runoff concentrations of total P (TP) and dissolved reactive P (DRP) did not vary by treatment. The control showed less TP (0.126 mg/l) and DRP (0.068 mg/l) concentration than all other treatments (ranges 0.190 to 0.249 mg TP/l and 0.129 to 0.182 mg DRP/l) in runoff during the first event (40 d after treatment). The control had the lowest (0.118 mg/l) and TSP the highest (0.248 mg/l) TP concentration during the second event 24 h later. Samples taken at 5-min intervals during the second simulation showed a significant decrease in TP and DRP concentrations over time for all treatments but the control. Treatments did not affect edge-of-the-field losses of TP, DRP, or TKN. Soil test P and water-extractable P measured after the fifth and final rainfall simulation did not correlate to P concentrations in runoff. Forage yields and their N and P concentrations were not impacted. Results indicated a decreasing impact of manure, spring-applied to fescue pasture, on runoff P concentrations throughout the season. Highest TP concentrations were found during the first pair of simulated rainfalls from the TSP treatment. In a second experiment, indoor runoff boxes were used to simulate management intensive rotational grazing. Commercial fertilizer TSP and manure application increased runoff TP concentration from 0.146 mg/l to 0.245 mg/l and DRP concentration from 0.105 mg/l to 0.183 mg/l. Runoff P did not differ between organic or inorganic P treatments, possibly due to the small area of the boxes. However, application of manure increased runoff TKN overall, with a linear decrease as the time increased between application and rain simulation. / Master of Science

The lack of consistent summer pasture supply is a major limitation to livestock production in the mid-Atlantic region. Perennial warm-season grasses might provide a solution if managed for high quality. Experiments were conducted on separate well-established stands of Caucasian bluestem and 'Cave-in-Rock' switchgrass at the Kentland Farm near Blacksburg, VA. Stages of grass maturity at harvest simulating pasture and hay systems were tested. Six interseeded legume species and two grass monoculture checks, one with 56 kg N/ha applied in spring and after each harvest, the other with no N, were imposed as sub-plots. Legume species included alfalfa, red clover, sericea lespedeza, annual lespedeza, Illinois bundleflower, and purple prairieclover. Inter-seeded legumes contributed a significant amount to yield and quality of perennial warm-season grasses in the legume-establishment year. In the year after establishment, grass mixtures with alfalfa, red clover, and, for switchgrass, sericea lespedeza yielded as much forage as N-fertilized grasses. Alfalfa and red clover altered the distribution of yield of the grasses, and may not be as compatible with perennial warm-season grasses as sericea lespedeza in the long-term. Interseeded legumes improved quality considerably in the second year. / Master of Science

Measurements of runoff quantity and quality from three cattle stocking treatments applied to pastureland in southwestern Virginia indicate the need for further research to determine treatment effects. Three cattle stocking treatments (1) Continuous, 2) Rotational, and 3) Mob) were applied to three pastures at the Virginia Tech Prices Fork Research Farm. Rainfall simulations were performed over replicated plots in each treatment to induce runoff for collection of runoff quantity and quality data during the 2012 grazing season. Additionally, rainfall simulations were performed prior to applying the grazing treatments to establish initial conditions. Monitored runoff quantity and quality response variables included runoff depth, mean nutrient concentrations, and nutrient mass loss. Response variables were compared among the three pastures for initial conditions and among treatments for post-treatment conditions. Additionally, the trends in response variables within the 2012 season were compared among treatments. Plot and rainfall conditions that were expected to influence responses were also collected and analyzed in relation to response variables. Analyses of the response variables suggested that the variability within treatments likely muted any treatment effect on the response variables. Therefore, we concluded that further research is needed to determine treatment effects on runoff quantity and quality. / Master of Science

Climate change and global warming affect both humans and nature in many ways. One of the sectors that is most affected is the agricultural industry because both drought and excessive rainfall pose significant problems. Agricultural lands, especially meadows and pastures, are among the most species-rich environments. Due to changing land use such as exploitation and a challenging economic situation, many farmers choose to terminate their businesses. In Jämtland County, Sweden, the number of notifications to take their agricultural land out of production is increasing, resulting in a decrease in the agricultural land area, which in turn means negative consequences for biodiversity. This study therefore examines the consequence of declining agricultural land areas (pasture land) for a species strongly linked to these environments – the violet copper butterfly (Lycaena helle). The hypothesis is that the violet copper has decreased in occurrence in the last 20 years (2003–2023) as pasture land areas have been reduced in Jämtland. To investigate this, correlation analyzes were made between species observations in Jämtland over the last 20 years (2003–2023) and data for pasture land areas for the same period. The correlation analysis was carried out for species observations from the Swedish Species Observation System (SLU Artdatabanken) and from the Swedish Butterfly Monitoring (Svensk Dagfjärilövervakning) to compare whether the outcomes were different depending on the data source. None of the statistical tests showed any significant positive correlation (p &gt;0.05), which meant that the hypothesis was not correct. In contrast, the correlation results for the two different data sources implied different trends: Swedish Species Observation System's findings shows a negative correlation (r= -0.408; p = 0.074; 2-tailed) indicating an increasing population size and the Swedish Butterfly Monitoring data shows a positive correlation (r= 0.449; p = 0.225; 2-tailed) indicating a decreasing population size. However, estimating total population size is challenging, so targeted repeated inventories on the same sites over a long period of time are recommended (similar to the Swedish Butterfly Monitoring program) to obtain accurate and reliable datasets for analyses. It is difficult to determine whether climate change is directly affecting the violet copper, but the indirect effects such as land use change, exploitation and abandoned agricultural land most likely do. This study further recommends research on the isolation effects on the Swedish population (genetic variation), further consequences of land use change and the species' habitat requirements (ecology). / Klimatförändringarna och den globala uppvärmningen påverkar både människan och naturen på många sett. En av de sektorer som drabbas hårdast är jordbruksverksamheten eftersom dels torka, dels för hög nederbörd innebär stora problem. Jordbruksmarker, framför allt ängs- och betesmarker är en av de artrikaste miljöer som existerar. På grund av förändrad markanvändning som exploatering och en utmanande ekonomisk situation väljer många jordbrukare att lägga ned sina verksamheter. I Jämtland ökar antalet anmälningar att ta sin jordbruksmark ur produktion vilket resulterar i att jordbruksarealen minskar vilket i sin tur innebär negativa konsekvenser för den biologiska mångfalden. Den här studien undersöker därför konsekvensen av minskande jordbruksarealer (betesmarker) för en art som är starkt kopplad till dessa miljöer – violett guldvinge (Lycaena helle). Hypotesen är att violett guldvinge har minskat i förekomst de senaste 20 åren (2003–2023) i takt med att betesmarkarealerna reducerats i Jämtlands län. För att undersöka detta gjordes korrelationsanalyser mellan artfynd i Jämtland de senaste 20 åren (2003–2023) och data för betesmarksarealer för samma period och område. Dels gjordes korrelationsanalysen med fynd från SLU Artdatabanken, dels från Svensk Dagfjärilsövervakning för att jämföra om utfallet blev annorlunda beroende av datakälla. Ingen av de statistiska testerna visade någon signifikant positiv korrelation (p &gt;0,05), vilket innebar att hypotesen inte stämde. Däremot antydde korrelationsresultaten mellan de två olika datakällorna olika trender: SLU Artdatabankens fynd visar en negativ korrelation (r= -0,408; p = 0,074; 2-tailed) vilket indikerar på en ökande population medan Svensk Dagfjärilsövervakning visar en positiv korrelation (r= 0,449; p = 0,225; 2-tailed) vilket indikerar på en minskande population. Att uppskatta populationsstorlekar är dock utmanande, så riktade inventeringar på återkommande lokaler under lång tid rekommenderas (i likhet med Svensk Dagfjärilsövervakning) för att få ackurata och trovärdiga dataset att analysera. Det är svårt att avgöra om klimatförändringarna direkt påverkar den violetta guldvingen, men de indirekta effekterna som förändrad markanvändning, exploatering och övergivna jordbruksarealer gör det sannolikt. Studien rekommenderar vidare forskning kring det svenska beståndets isoleringseffekter (genetisk variation), ytterligare konsekvenser av förändrad markanvändning och artens habitatkrav (ekologi).

O objetivo foi avaliar, por meio de uma abordagem meta-analítica, quais os principais fatores que influenciam no desempenho produtivo e reprodutivo de novilhas e vacas primíparas de corte. Para tanto, foram utilizados, de forma agregada, dados de 3.933 novilhas e vacas primíparas de corte, provenientes de 29 estudos (dissertações e teses) e 43 experimentos. As informações relacionadas à metodologia e aos resultados de cada trabalho foram tabuladas em planilha, constituindo a sistematização dos dados. Por meio dos dados disponibilizados, três artigos foram realizados. No primeiro deles, as variáveis independentes analisadas foram: idade das novilhas (14 ou 24 meses de idade) e vacas primíparas (24 ou 36 meses de idade) no momento em que foram expostas à reprodução, tipo de pastagem (pastagens de ciclo hiberno-primaveril ou natural) e tipo racial (taurinas ou mestiças). As variáveis respostas foram os pesos e escores de condição corporal ao início e final do período reprodutivo e a taxa de prenhez. Maiores pesos corporais ao início do acasalamento e taxa de prenhez foram observados nas novilhas expostas à reprodução aos 24 meses (325,25±1,55 kg e 73,84±1,41%), nas mestiças (321,41±2,15 kg e 70,88±1,63%) e nas que pastejaram pastagens de ciclo hiberno-primaveril no pré-acasalamento (318,34±2,01 kg e 82,43±1,60%). Maiores pesos corporais foram observados nas vacas primíparas expostas à reprodução aos 36 meses de idade (376,09±1,55 kg), nas mestiças (373,56±1,54 kg) e nas que pastejaram pastagens de ciclo hiberno-primaveril (377,80±2,29 kg). A maior prenhez foi observada nas primíparas aos 24 meses de idade (83,44±3,03%, nas taurinas (88,53±2,61%) e nas que pastejaram pastagens de ciclo hiberno-primaveril (77,68±1,93%). No segundo trabalho, a taxa de prenhez foi considerada a variável resposta. Foram realizadas análises de sub-grupos entre categoria animal (novilhas e vacas primíparas), idade das fêmeas no momento em que foram expostas à reprodução (14, 24 ou 36 meses de idade), tipo de pastagem (pastagens de ciclo hiberno-primaveril ou natural) e tipo racial (taurinas ou mestiças). Novilhas e vacas primíparas, expostas à reprodução apresentaram maior taxa de prenhez (80,24%). No terceiro trabalho, a variável resposta foi a taxa de prenhez.Fatores explanatórios foram categoria animal (novilhas ou vacas primíparas), peso corporal ao início do período reprodutivo, ganho médio diário durante a reprodução, tipo racial (taurinas e mestiças) e taxa de lotação. O peso ao início da reprodução influenciou 93,1% da taxa de prenhez. Por meio da presente meta-análise, a idade à qual as fêmeas foram expostas à reprodução, a raça, o tipo de pastagem utilizada no pré-acasalamento, o peso corporal ao início da reprodução e a taxa de lotação são fatores que influenciam o desempenho produtivo e reprodutivo de novilhas e vacas primíparas de corte no sul do Brasil. / The aim was to evaluate, through a meta-analytical approach, the main factors that influence the productive and reproductive performance of heifers and primiparous cows. We used, in aggregate, data from 3,933 heifers and primiparous cows from 29 studies (dissertations and theses) and 43 experiments. The information related to the methodology and the results of each work were tabulated in a spreadsheet, constituting the systematization of the data. Through the available data, three articles were made. In the first one, the independent variables analyzed were: age of heifers (14 or 24 months of age) and primiparous cows (24 or 36 months of age) at the time they were exposed to reproduction, type of pasture (winter-spring cycle or natural pasture) and breed (Taurine or crossbred). The variables responses were the weight and body condition scores at the beginning and end of the reproductive period and the pregnancy rate. Larger body weights at the beginning of the breeding season and pregnancy rate were observed in heifers exposed to reproduction at 24 months (325.25±1.55 kg and 73.84±1.41%), in crossbreed (321.41±2,15 kg and 70.88±1.63%) and in those that grazed winter-spring cycle pastures in pre-mating (318.34±2.01 kg and 82.43±1.60%). Higher body weights were observed in the primiparous cows exposed to the breeding season at 36 months of age (376.09±1.55 kg), in the crossbreed (373.56±1.54 kg) and in those that grazed hiberno-spring cycle (377.80±2.29 kg). The highest pregnancy was observed in the primiparous cows at the 24 months of age (83.44±3.03%), in the taurine (88.53±2.61%) and in those that grazed winter-spring cycle pastures (77.68±1.93%). In the second study, the pregnancy rate was considered the response variable. Was evaluated analysis of subgroups between animal categories (heifers and primiparous cows), age of females at the time of the breeding season (14, 24 or 36 months of age), type of pasture (winter-spring cycle or natural pasture) and breed (Taurine or crossbreed). Heifers and primiparous cows, exposed to reproduction, had a higher pregnancy rate (80.24%). In the third study, the response variable was the pregnancy rate. Explanatory factors were animal category (heifers or primiparous cows), body weight at the beginning of the breeding season, average daily gain during the breeding season, breed (Taurine and crossbreed) and stocking rate. Through the present meta-analysis, the age at the which females were exposed to the breeding season, breed, type of pasture used in pre-mating, body weight at the beginning of the breeding season and stocking rate are factors that influence productive performance and reproductive performance of heifers and primiparous beef cattle in southern Brazil.

O trabalho conduzido na Fazenda Rancho Santa Zelina, Júlio de Castilhos/RS, avaliou o desenvolvimento corporal e o desempenho produtivo de 64 novilhas de um rebanho comercial Angus da concepção aos 13/15 meses de idade, submetidas a quatro sistemas alimentares durante a gestação: pastagem de Brachiaria com suplementação + pastagem natural no terço final de gestação (BRACS-PN}, pastagem natural com suplementação+ pastagem natural no terço final de gestação (PNCS-PN), pastagem de Brachiara + pastagem cultivada de aveia preta e azevém no terço final de gestação (BRA-PC}, pastagem natural + pastagem cultivada de aveia preta e azevém no terço final de gestação (PN-PC). O delineamento experimental foi o inteiramente casualizado, quatro sistemas alimentares e duas repetições de área, sendo cada potreiro considerado uma unidade experimental. Para as variáveis de desempenho dos bezerros, cada bezerro foi considerado uma unidade experimental. Ao final dos sistemas alimentares de verão/outono (02/06/2012), as novilhas do BRACS-PN eram mais pesadas (392,0 kg) do que as do BRA-PC (375,5 kg), as quais igualmente superiores as do PNCS-PN (355,0 kg) e PN-PC (354,5 kg). No inverno, novilhas em pastagem natural (BRACS-PN e PNCS-PN) perderam peso, enquanto as em pastagem cultivada ganharam peso e condição corporal. Novilhas do BRA-PC (421 ,O kg) e PN-PC (377,0 kg) tiveram maior peso ao parto, porém as do PN-PC não diferiram do BRACS-PN (323,5 kg) e estas não diferiram das PNCS-PN (306,5 kg). O auxílio ao parto foi maior nas BRA-PC e PN-PC (37,5%), mas não diferiram das PNCS-PN (18,8%). O peso corporal das BRA-PC foi maior (417,4 kg) ao início da monta, mas não diferiru das PN-PC (392,0 kg) e BRACS-PN (351 ,8 kg}, os quais não diferiram das PNCS-PN (329,8 kg). As novilhas do PN-PC tiveram a maior prenhez (100,0%), mas não diferiram das BRA-PC (87,5%) e BRACS-PN (66,0%), os quais não diferiram das PNCS-PN (62,0%). Os bezerros filhos das vacas dos PN-PC e BRA-PC tiveram maiores ganhos de peso até o desmame. Conclui-se da necessidade de desenvolver mais estudos com objetivo de ter maior desenvolvimento das novilhas prévio o terço final de gestação, para aumentar o conhecimento sobre a oferta e o manejo da pastagem natural para minimizar perdas de peso ao final da gestação e para identificar tempo de pastejo pré-parto em pastagem cultivada, que minimizem auxílios e perdas ao parto. Possivelmente, a antecipação da primeira prenhez, através de melhor recria de bezerras, possibilite inicialmente um menor período pré-parto em pastagem cultivada, reduzindo problemas ao parto e, após, um longo período pós-parto em pastagem cultivada. / The work conducted at Rancho Santa Zelina Farm, Júlio de Castillos/RS, evaluated lhe grow and productive performance of 64 heifers of a commercial Angus herd since the conception to 13/15 months of age under four feeding systems during the gestation: Brachiaria pasture with supplementation + natural pasture in the final third of gestation (BRACS-PN), natural pasture with supplementation + natural pasture in the final third of gestation (PNCSPN), Brachiaria pasture + cultivated pasture (oat and ryegrass) in the final third of gestation (BRA-PC), natural pasture + cultivated pasture in the final third of gestation (PN-PC). The experimental design was completely randomized, four food systems and two plots, each paddock considered an experimental unit. For lhe performance variables of the calves, each calf was considered an experimental unit. At lhe end of the feeding summer/fall systems (06/02/2012), lhe heifers of BRACS-PN were heavier (392.0 kg) than lhe BRA-PC (375.5 kg), which were heavier than PNCS-PN (355.0 kg) and PN-PC (354.5 kg). During the winter, heifers on natural pasture (BRACS-PN and PNCS-PN) lost weight, while heifers on cultivated pasture gained weight and body condition. Heifers BRA-PC (421.0 kg) and PN-PC (377.0 kg) were heavier at calving, but the PNPC did not differ from BRACS-PN (323.5 kg) and these ones of PNCS-PN (306.5 kg). The aid to calving was higher in BRA-PC and PN-PC (37.5%) without differ of PNCS-PN (18.8%). The body weight of BRA-PC at the beginning of reproduction was higher (417.4 kg), without differ of PN-PC (392.0 kg) and BRACS-PN (351.8 kg), which ones did not differ of PNCS-PN (329.8 kg). Heifers of PN-PC had the highest pregnancy rale (100.0%), without differ of BRA-PC (87.5%) and BRACS-PN (66.0%), which ones did not differ of PNCSPN (62.0%). Calves of PN-PC and BRA-PC cows had higher weight gain until weaning. This results underscores lhe need for further studies in arder to identify higher growth of heifers prior the final third of gestation, to increase the know about the availability and management of natural pasture to minimize weight loss in late pregnancy and to identify grazing time on cultivated pasture pre calving to minimize tosses and aids to calving. Probaly, earlier first pregnancy through better rearing and genetics of calves initially enables a lower pre-partum period on cultivated pasture, reducing calving problems and, after, a long postpartum grazing on cultivated pasture.