Degradabilidade in situ de híbridos de milho e de capim-elefante colhidos em quatro estádios de maturidade

Dentre as forragens, a silagem de milho é amplamente utilizada pelos fazendeiros que visam explorar o máximo do potencial genético dos animais. No entanto, outros volumosos tropicais como o capim-elefante (Pennisetum purpureum) são mais produtivos e, portanto, mais baratos do que a silagem de milho. Nosso objetivo foi comparar a degradabilidade in situ do capim-elefante com a degradabilidade de híbridos de milho, colhidos em quatro estágios de maturidade. O experimento seguiu um delineamento de blocos ao acaso com sub-parcelas. Dois híbridos de milho: AG5011 e ZN8392 foram colhidos com 25, 30, 35 e 40% matéria seca (MS) na planta toda e separados na fração colmo + bainha + folhas e espigas. Capim elefante foi colhido 30, 40, 50 e 60 dias após o corte de nivelamento. As amostras secas e trituradas foram incubadas no rúmen por 0, 6, 12, 24, 48 e 72 h para cálculo da cinética da degradação ruminal da MS e da fibra em detergente neutro (FDN). O avanço da maturidade aumentou os teores de FDN e fibra em detergente ácido (FDA) do capim elefante e reduziu a degradabilidade da MS. Entretanto, a maturidade teve pouco efeito sobre os teores de fibra e a degradabilidade da MS da fração planta dos híbridos de milho. O capim elefante apresentou maior degradabilidade da FDN do que híbridos de milho, e não houve efeito da maturidade sobre a degradabilidade da FDN das duas espécies. A degradabilidade da fibra de capim-elefante não é pior do que a de híbridos de milho e, portanto a escolha da forragem deve ser feita com base em análises econômicas ao invés de assumir um menor potencial de produção em dietas a base de capim elefanteAmong tropical forages, corn silage is largely used by farmers trying to explore the maximum genetic potential from the animals. However, other tropical forages, such as elephant-grass (Pennisetum purpureum), are more productive and therefore cheaper to use than corn silage. Our objective was to compare the in situ degradability of elephant-grass with that from corn hybrids, all harvested at four stages of maturity. The experimental design followed a randomized block design with nested subplots. Two corn hybrids: AG5011, ZN8392 were harvested with 25, 30, 35, and 40% dry matter (DM) in the whole plant, and separated in stem + leaf sheath + leaf blade (stover), and cobs. Elephant-grass was harvested with 30, 40, 50 and 60 days after a leveling cut. Dried and ground samples were incubated in nylon bags inside the rumen for 0, 6, 12, 24, 48 and 72 h to estimate the kinetics of ruminal DM and neutral detergent fiber (NDF) degradation. The advance of maturity increased the NDF and acid detergent fiber (ADF) content in elephant-grass, and reduced its DM degradability. However, maturity had little or no effect on fiber content and DM degradability of corn stover. Elephant-grass had a higher NDF degradability than corn stover, and there was no effect of maturity on NDF degradability of either elephant-grass or corn stover. Fiber degradability of elephant-grass was not worse than that of corn stover, and therefore the choice of forage should be made on economical analysis rather than assuming an intrinsic low production potential for elephant-grass based diet

Impacto do teor e da qualidade da forragem sobre o desempenho de bovinos em crescimento e terminação

Os organizadores autorizam a reprodução total ou parcial deste trabalho, para qualquer meio convencional ou eletrônico, para fins de estudo e pesquisa, desde que citada a fonte

Novos desafios da pesquisa em nutrição e produção animal.

Os organizadores autorizam a reprodução total ou parcial deste trabalho, para qualquer meio convencional ou eletrônico, para fins de estudo e pesquisa, desde que citada a fonte

Efeito de níveis crescentes de uréia na dieta de vacas leiteiras sobre a composição e rendimento de fabricação de queijos minas frescal

O objetivo do trabalho foi avaliar a substituição do farelo de soja por níveis crescentes de uréia na dieta de vacas leiteiras e os seus efeitos sobre a composição e o rendimento de fabricação de queijo Minas Frescal. Para a fabricação dos queijos, foram utilizados 15 kg de leite, provenientes de nove vacas Holandesas em lactação, distribuídas em três quadrados latinos 3x3. Foram utilizadas três dietas: A) controle, formulada para suprir 100% das exigências de proteína bruta, proteína degradável no rúmen (PDR) e proteína não degradável no rúmen (PNDR), utilizando farelo de soja como principal fonte protéica; B) com a inclusão de 0,75% de uréia, em substituição parcial ao farelo de soja, e C) com inclusão de 1,5% de uréia, em substituição parcial ao farelo de soja. Todas as dietas foram isoenergéticas (1,53 Mcal/kg de energia líquida de lactação) e isonitrogenadas (16% de PB) e utilizaram cana-de-açúcar como volumoso. Quando analisados por regressão polinomial simples, os resultados da composição e da fração nitrogenada do leite pasteurizado não foram influenciados pelo nível de uréia na dieta, o mesmo ocorrendo com a composição (pH, umidade, gordura, matéria mineral, cloreto de sódio, proteína bruta, nitrogênio solúvel em pH 4,6 e em TCA 12%) e o rendimento de fabricação dos queijos. Com base nos resultados deste estudo, concluise que o uso de até 1,5% de uréia na alimentação de vacas em lactação não alterou a composição do leite pasteurizado, bem como a composição e o rendimento de fabricação de queijo Minas Frescal.The aim of this study was to evaluate the substitution of soybean meal for increasing levels of dietary urea on the composition and yield of Minas cheese. For each cheese making process, 15 kg of milk were collected from nine lactating Holstein cows that were arranged in 3 Latin squares. Three diets with sugar cane as roughage were fed for cows and consisted of: A) control diet formulated to provide 100% of the requirements of crude protein (CP), rumen undegradable protein (RUP) and rumen degradable protein (RDP), using soybean meal; B) urea inclusion at 0.75% of dry matter in substitution for soybean meal crude protein equivalent; C) urea inclusion at 1.5% of dry matter in substitution for soybean meal crude protein equivalent. Energy and protein levels of rations comply with NRC (2001), and were isoenergetic and isonitrogenous. When the data were analyzed by simple polynomial regression, no effect of treatments were observed on pasteurized milk composition and milk nitrogen fractions, as well as for cheese composition (pH, moisture,fat,ash, sodium cloride, crude protein, soluble nitrogen in pH 4,6 and in TCA 12%) and cheese yield. Based on the results of this study, it can be concluded that the addition of urea up to 1.5% in dry matter basis in substitution for soybean meal in the diet of Holstein cows did not alter cheese composition and yield

Composição bromatológica e digestibilidade de cana-de-açúcar colhida em duas épocas do ano

Objetivou-se com este estudo avaliar o efeito da época de corte sobre a composição bromatológica e digestibilidade in vitro de genótipos de cana-de-açúcar, comparar a composição bromatológica e digestibilidade in vitro das frações colmo e folhas, e estabelecer possíveis correlações entre composição química e digestibilidade in vitro da planta inteira de genótipos da cana-de-açúcar. Nove genótipos foram colhidos em maio e setembro de 2006. Em maio, somente a fração planta inteira foi analisada, em setembro foram separados em colmos, folhas ou planta inteira para determinação da composição bromatológica, sacarose (POL) e digestibilidade in vitro. Colmos apresentaram menor teor de fibra em detergente neutro (FDN) e lignina na MS, e maior digestibilidade in vitro da matéria seca (DIVMS) do que folhas. Em contrapartida, apresentaram menor digestibilidade in vitro da FDN (DIVFDN), maior teor de lignina na FDN e menor concentração de proteína bruta (PB). Houve redução no teor e digestibilidade da FDN com o avanço da maturidade, enquanto que DIVMS, POL e lignina aumentaram. A DIVMS se mostrou negativamente correlacionada com FDN e FDN/POL, porém não houve correlação entre DIVFDN e FDN ou FDN/POL. Conclui-se que o avanço da maturidade promoveu redução na DIVFDN e aumento na DIVMS, não existindo correlação genética entre acúmulo de açúcar e digestibilidade in vitro da fibra. Os dados deste artigo indicam não ser esperado que a seleção de genótipos com maior DIVFDN do colmo altere o teor de açúcar do mesmo.The objectives of this study were to evaluate the effect of time of harvest on chemical composition and in vitro digestibility of sugarcane genotypes, to compare chemical composition and in vitro digestibility of the stem and leaf fractions, and to determine possible correlations between chemical composition and in vitro digestibility of the whole plant in sugarcane genotypes. Nine genotypes were harvested in May and September of 2006. In May, only the whole-plant fraction was analyzed, in September the genotypes were separated in stems, leaves or whole-plant for determination of chemical composition, sucrose (POL) and in vitro digestibility. Stems had lower neutral detergent fiber (NDF) and lignin in the DM, and greater in vitro dry matter digestibility (IVDMD) than leaves. However, stems had lower in vitro NDF digestibility (IVNDFD), higher lignin in the NDF and lower crude protein (CP). The NDF and IVNDFD were reduced with advanced maturity, while IVDMD, POL and lignin were increased. IVDMD was negatively correlated with NDF and NDF/POL, however there was no correlation between IVFDND and NDF or NDF/POL. It can be concluded that with the advance in maturity the IVNDFD was reduced and IVDMD was increased, and there was no genetic correlation between accumulation of sugar and in vitro fiber digestibility. Data from this study indicate that it is not expected that selection of genotypes with greater stem IVNDFD would alter the sugar content of the plant

In situ degradability of corn stover and elephant-grass harvested at four stages of maturity

Among tropical forages, corn silage is largely used by farmers trying to explore the maximum genetic potential from the animals. However, other tropical forages, such as elephant-grass (Pennisetum purpureum), are more productive and therefore cheaper to use than corn silage. Our objective was to compare the in situ degradability of elephant-grass with that from corn hybrids, all harvested at four stages of maturity. The experimental design followed a randomized block design with nested subplots. Two corn hybrids: AG5011, ZN8392 were harvested with 25, 30, 35, and 40% dry matter (DM) in the whole plant, and separated in stem + leaf sheath + leaf blade (stover), and cobs. Elephant-grass was harvested with 30, 40, 50 and 60 days after a leveling cut. Dried and ground samples were incubated in nylon bags inside the rumen for 0, 6, 12, 24, 48 and 72 h to estimate the kinetics of ruminal DM and neutral detergent fiber (NDF) degradation. The advance of maturity increased the NDF and acid detergent fiber (ADF) content in elephant-grass, and reduced its DM degradability. However, maturity had little or no effect on fiber content and DM degradability of corn stover. Elephant-grass had a higher NDF degradability than corn stover, and there was no effect of maturity on NDF degradability of either elephant-grass or corn stover. Fiber degradability of elephant-grass was not worse than that of corn stover, and therefore the choice of forage should be made on economical analysis rather than assuming an intrinsic low production potential for elephant-grass based diets.Dentre as forragens, a silagem de milho é amplamente utilizada pelos fazendeiros que visam explorar o máximo do potencial genético dos animais. No entanto, outros volumosos tropicais como o capim-elefante (Pennisetum purpureum) são mais produtivos e, portanto, mais baratos do que a silagem de milho. Nosso objetivo foi comparar a degradabilidade in situ do capim-elefante com a degradabilidade de híbridos de milho, colhidos em quatro estágios de maturidade. O experimento seguiu um delineamento de blocos ao acaso com sub-parcelas. Dois híbridos de milho: AG5011 e ZN8392 foram colhidos com 25, 30, 35 e 40% matéria seca (MS) na planta toda e separados na fração colmo + bainha + folhas e espigas. Capim elefante foi colhido 30, 40, 50 e 60 dias após o corte de nivelamento. As amostras secas e trituradas foram incubadas no rúmen por 0, 6, 12, 24, 48 e 72 h para cálculo da cinética da degradação ruminal da MS e da fibra em detergente neutro (FDN). O avanço da maturidade aumentou os teores de FDN e fibra em detergente ácido (FDA) do capim elefante e reduziu a degradabilidade da MS. Entretanto, a maturidade teve pouco efeito sobre os teores de fibra e a degradabilidade da MS da fração planta dos híbridos de milho. O capim elefante apresentou maior degradabilidade da FDN do que híbridos de milho, e não houve efeito da maturidade sobre a degradabilidade da FDN das duas espécies. A degradabilidade da fibra de capim-elefante não é pior do que a de híbridos de milho e, portanto a escolha da forragem deve ser feita com base em análises econômicas ao invés de assumir um menor potencial de produção em dietas a base de capim elefante

The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment

The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in operation since July 2014. This paper describes the second data release from this phase, and the fourteenth from SDSS overall (making this, Data Release Fourteen or DR14). This release makes public data taken by SDSS-IV in its first two years of operation (July 2014-2016). Like all previous SDSS releases, DR14 is cumulative, including the most recent reductions and calibrations of all data taken by SDSS since the first phase began operations in 2000. New in DR14 is the first public release of data from the extended Baryon Oscillation Spectroscopic Survey (eBOSS); the first data from the second phase of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2), including stellar parameter estimates from an innovative data driven machine learning algorithm known as "The Cannon"; and almost twice as many data cubes from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous release (N = 2812 in total). This paper describes the location and format of the publicly available data from SDSS-IV surveys. We provide references to the important technical papers describing how these data have been taken (both targeting and observation details) and processed for scientific use. The SDSS website (www.sdss.org) has been updated for this release, and provides links to data downloads, as well as tutorials and examples of data use. SDSS-IV is planning to continue to collect astronomical data until 2020, and will be followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14 happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov 2017 (this is the "post-print" and "post-proofs" version; minor corrections only from v1, and most of errors found in proofs corrected

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Evaluation of nutritional and agronomic characteristics of corn hybrids for silage

Estudou-se as características agronômicas, composição química da fração volumosa (haste+folhas) e da silagem, e a digestibilidade "in situ" da matéria seca e da fibra em detergente neutro da fração volumosa de 28 híbridos de milho em 1996, e de 21 híbridos de milho em 1997, com o objetivo de se estabelecer as relações existentes entre os parâmetros analisados. Dos 21 híbridos de milho selecionados em 1997, 13 fizeram parte do experimento em 1996. Em 1996, foram confeccionadas silagens em tambores de 200 L dos híbridos estudados. Foi utilizado o modelo de McDonald (1981) para se avaliar a cinética de degradação "in situ" da MS, e o modelo descrito por Mertens & Loften (1980) para se analisar a cinética de degradação "in situ" do FDN. No experimento de campo (características agronômicas e composição química), o delineamento experimental utilizado foi o de blocos ao acaso com 3 repetições. No experimento de digestibilidade "in situ", o delineamento utilizado foi o de parcelas subdivididas, onde os períodos constituíam os blocos (3 períodos), os tempos de incubação ruminal as parcelas e os híbridos de milho as sub-parcelas. Os dois anos experimentais foram analisados em conjunto para se determinar o efeito ambiental (ano) e a interação efeito genético (híbrido) e ambiental (ano) sobre os parâmetros analisados. Observou-se a existência de variabilidade genética para todos os parâmetros analisados. A produção total e a porcentagem de grãos não se mostraram correlacionadas com a digestibilidade da porção volumosa, indicando a possibilidade de um programa de seleção conjunto para produção e digestibilidade. Os constituintes da parede celular (FDN, FDA, lignina, celulose e hemicelulose) se mostraram negativamente correlacionados com a digestibilidade da MS da porção fibrosa, sendo que dentre eles, o FDA foi o parâmetro que melhor se relacionou com a degradabilidade efetiva da MS durante os dois anos experimentais, indicando que doravante, deva ser utilizado como indicador da digestibilidade da fração volumosa usando-se a equação desenvolvida: Deg.ef = 100,6077 - 1,4085 * FDA (R2=0,86). A porcentagem de espigas na MS se mostrou positivamente correlacionada com o teor de FDN e FDA da fração volumosa em 1996, e com o teor de FDA em 1997, indicando um possível efeito de translocação de carboidratos da planta para os grãos. Houve grande efeito ambiental sobre os parâmetros de qualidade dos híbridos de milho. A interação híbridoXano experimental foi significativa para as características agronômicas, bem como para a digestibilidade da fração volumosa, indicando que o efeito ambiental exerceu grande influência sobre a expressão genética dos híbridos, porém a interação não foi significativa para o teor de FDA da fração volumosa. A ocorrência de estresse hídrico (1996) diminuiu a produção total de MS e a participação das espigas na MS, porém aumentou a digestibilidade "in situ" da MS da fração volumosa dos híbridosThe agronomic characteristics, stover and silage chemical composition, and the dry matter (DM) and neutral detergent fiber (NDF) "in situ" digestibility of 28 corn hybrids in 1996, and 21 corn hybrids in 1997, was measured with the objective of establishing relationships among this analyzed variables. From the 21 corn hybrids selected in 1997, 13 were hybrids already tested in 1996. In 1996, silages were made with the selected hybrids in 200 L plastic barrels. The mathematic model described by McDonald (1981) was used to describe the DM "in situ" digestibility kinetics, and the model described by Mertens & Loften (1980) to analyze the digestibility kinetics of the NDF fraction. The experimental design utilized in the agronomic experiment was the randomized blocks with 3 plots. In the digestibility trial, the split-plot design was utilized, where the periods were the blocks (3 periods), the ruminal incubation times were the plots, and the corn hybrids were the split-plots. Both the years were analyzed together to determine the environmental effect (year) and the environmental (year) x genetic (hybrids) interactions over the analyzed variables. The occurrence of genetic variability was observed for all the analyzed variables. The total DM production and the cob percentage were not correlated with the stover digestibility, showing the possibility for a selection program based on productivity and digestibility. The cell wall constituents (NDF, ADF, lignin, cellulose and hemicellulose) were negatively correlated with the stover DM digestibility, and among them, ADF was the variable best correlated with effective DM degradability (Deg.ef) during both experimental years, showing that from now on should be utilized as a stover digestibility indicator using this equation: Deg.ef = 100,6077 - 1,4085*ADF (R2=0,86). The cobs DM percentage were positively correlated with the stover NDF and ADF content in 1996, and with the stover ADF content in 1997; possibly a reflection of a soluble carbohydrates translocation from the stover to the grains. There was a greatest environmental effect over the corn hybrid quality variables. The hybrid X year interaction was significant for the agronomic characteristics, as well as for the stover digestibility, showing that the environment had great influence upon the genetic behavior of the corn hybrids, however the interaction were not significant for the stover ADF content. The occurrence of water stress (1996) reduced the DM total production and the percentage of cobs, however improved the com hybrids stover digestibilit

Evaluation of nutritional and agronomic characteristics of corn hybrids for silage

Estudou-se as características agronômicas, composição química da fração volumosa (haste+folhas) e da silagem, e a digestibilidade "in situ" da matéria seca e da fibra em detergente neutro da fração volumosa de 28 híbridos de milho em 1996, e de 21 híbridos de milho em 1997, com o objetivo de se estabelecer as relações existentes entre os parâmetros analisados. Dos 21 híbridos de milho selecionados em 1997, 13 fizeram parte do experimento em 1996. Em 1996, foram confeccionadas silagens em tambores de 200 L dos híbridos estudados. Foi utilizado o modelo de McDonald (1981) para se avaliar a cinética de degradação "in situ" da MS, e o modelo descrito por Mertens & Loften (1980) para se analisar a cinética de degradação "in situ" do FDN. No experimento de campo (características agronômicas e composição química), o delineamento experimental utilizado foi o de blocos ao acaso com 3 repetições. No experimento de digestibilidade "in situ", o delineamento utilizado foi o de parcelas subdivididas, onde os períodos constituíam os blocos (3 períodos), os tempos de incubação ruminal as parcelas e os híbridos de milho as sub-parcelas. Os dois anos experimentais foram analisados em conjunto para se determinar o efeito ambiental (ano) e a interação efeito genético (híbrido) e ambiental (ano) sobre os parâmetros analisados. Observou-se a existência de variabilidade genética para todos os parâmetros analisados. A produção total e a porcentagem de grãos não se mostraram correlacionadas com a digestibilidade da porção volumosa, indicando a possibilidade de um programa de seleção conjunto para produção e digestibilidade. Os constituintes da parede celular (FDN, FDA, lignina, celulose e hemicelulose) se mostraram negativamente correlacionados com a digestibilidade da MS da porção fibrosa, sendo que dentre eles, o FDA foi o parâmetro que melhor se relacionou com a degradabilidade efetiva da MS durante os dois anos experimentais, indicando que doravante, deva ser utilizado como indicador da digestibilidade da fração volumosa usando-se a equação desenvolvida: Deg.ef = 100,6077 - 1,4085 * FDA (R2=0,86). A porcentagem de espigas na MS se mostrou positivamente correlacionada com o teor de FDN e FDA da fração volumosa em 1996, e com o teor de FDA em 1997, indicando um possível efeito de translocação de carboidratos da planta para os grãos. Houve grande efeito ambiental sobre os parâmetros de qualidade dos híbridos de milho. A interação híbridoXano experimental foi significativa para as características agronômicas, bem como para a digestibilidade da fração volumosa, indicando que o efeito ambiental exerceu grande influência sobre a expressão genética dos híbridos, porém a interação não foi significativa para o teor de FDA da fração volumosa. A ocorrência de estresse hídrico (1996) diminuiu a produção total de MS e a participação das espigas na MS, porém aumentou a digestibilidade "in situ" da MS da fração volumosa dos híbridosThe agronomic characteristics, stover and silage chemical composition, and the dry matter (DM) and neutral detergent fiber (NDF) "in situ" digestibility of 28 corn hybrids in 1996, and 21 corn hybrids in 1997, was measured with the objective of establishing relationships among this analyzed variables. From the 21 corn hybrids selected in 1997, 13 were hybrids already tested in 1996. In 1996, silages were made with the selected hybrids in 200 L plastic barrels. The mathematic model described by McDonald (1981) was used to describe the DM "in situ" digestibility kinetics, and the model described by Mertens & Loften (1980) to analyze the digestibility kinetics of the NDF fraction. The experimental design utilized in the agronomic experiment was the randomized blocks with 3 plots. In the digestibility trial, the split-plot design was utilized, where the periods were the blocks (3 periods), the ruminal incubation times were the plots, and the corn hybrids were the split-plots. Both the years were analyzed together to determine the environmental effect (year) and the environmental (year) x genetic (hybrids) interactions over the analyzed variables. The occurrence of genetic variability was observed for all the analyzed variables. The total DM production and the cob percentage were not correlated with the stover digestibility, showing the possibility for a selection program based on productivity and digestibility. The cell wall constituents (NDF, ADF, lignin, cellulose and hemicellulose) were negatively correlated with the stover DM digestibility, and among them, ADF was the variable best correlated with effective DM degradability (Deg.ef) during both experimental years, showing that from now on should be utilized as a stover digestibility indicator using this equation: Deg.ef = 100,6077 - 1,4085*ADF (R2=0,86). The cobs DM percentage were positively correlated with the stover NDF and ADF content in 1996, and with the stover ADF content in 1997; possibly a reflection of a soluble carbohydrates translocation from the stover to the grains. There was a greatest environmental effect over the corn hybrid quality variables. The hybrid X year interaction was significant for the agronomic characteristics, as well as for the stover digestibility, showing that the environment had great influence upon the genetic behavior of the corn hybrids, however the interaction were not significant for the stover ADF content. The occurrence of water stress (1996) reduced the DM total production and the percentage of cobs, however improved the com hybrids stover digestibilit