Massa de forragem, composição morfológica e valor nutritivo de capim-braquiária submetido a níveis de sombreamento e fertilização / Herbage mass, morphological composition and nutritive value of signalgrass, submitted to shading and fertilization levels

Características produtivas e nutricionais de Brachiaria decumbens, submetida a condições de sombreamento (sol pleno, 20% e 70% de sombreamento), sem e com uso de fertilização (80 kg.ha-1 de N e K2O e 60 kg.ha-1 de P2O5), foram avaliadas no delineamento de blocos casualizados, com quatro repetições. As parcelas sombreadas foram alocadas em um sistema silvipastoril, enquanto aquelas a pleno sol foram avaliadas em um monocultivo de B. decumbens. O sombreamento severo promoveu reduções de 54% na massa seca verde, 59% na massa seca total e 58% na densidade volumétrica de forragem. Aumentos da massa de forragem e da densidade volumétrica em resposta ao fertilizante foram observados somente nas condições de sol pleno e sombreamento moderado. A adubação não influenciou nas características nutricionais da forragem, mas o sombreamento severo promoveu aumentos de 20 e 51% nos teores de clorofila e de proteína bruta, respectivamente. Reduções dos teores de fibra em detergente neutro e fibra em detergente ácido foram observadas com o sombreamento. Os teores de lignina e a digestibilidade in vitro da matéria seca não variaram com nenhum fator estudado (médias de 6,0 e 60,9%, respectivamente). A adubação de B. decumbens com dose moderada de NPK é recomendada para dosséis cultivados no sol pleno e sombreamento moderado, mas deve ser evitada em pastos severamente sombreados, pois não reflete aumento de massa de forragem nem melhorias de seu valor nutricional.(AU)

Productive and nutritional traits of Brachiaria decumbens, submitted to shading conditions (full sun, 20% and 70% shading) and fertilization levels (without or with 80 kg.ha-1 of N and K 2 O and 60 kg.ha-1 of P 2O5), were evaluated in a randomized complete block design, with four replications. The shading were allocated in a silvopastoral system, while full sun was obtained in an exclusive B. decumbens pasture. The severe shading reduced the green dry mass in 54%, total dry mass in 59% and the forage bulk density in 58%. Increases in the forage mass and forage bulk density in response to fertilization were observed only in full sun and moderate shade. The nutritional traits did not vary with fertilization, but the chlorophyll and crude protein contents increased 20 and 51% with severe shading, respectively. The neutral detergent fiber and acid detergent fiber reduced with shade. The lignin content and in vitro dry matter digestibility did not vary with factors (average values of 6.0 and 60.9%, respectively). Fertilization with moderate dose of NPK is recommended to B. decumbens in full sun and moderate shading, but should be avoided in severely shaded pasture, because not reflected in improvement of forage mass and its nutritional traits.(AU)

Valor nutritivo e cinética de degradação in vitro de genótipos de capim-elefante (Penissetum purpureum Schumach) sob dois intervalos de desfolhação e duas alturas de resíduo pós-pastejo / Nutritive value and in vitro kinetics degradation of elephant grass genotypes (Penissetum purpureum Schumach) under two intervals of defoliation and two post-grazing heights

O experimento foi conduzido na Embrapa Gado de Leite, em Coronel Pacheco, MG, com o objetivo de avaliar o valor nutritivo e a cinética de degradação in vitro de genótipos de capim-elefante submetidos ao pastejo, usando-se a técnica de mob-grazing. Utilizou-se a combinação fatorial (2x2x2), sendo dois genótipos de capim-elefante (BRS Kurumi e CNPGL 00-1-3), duas interceptações luminosas (IL) à entrada dos animais nos piquetes (90 e 95%) e duas alturas de resíduo pós-pastejo (30 e 50cm), dispostos num delineamento inteiramente ao acaso, com três repetições. Para o pastejo, foram usadas 24 novilhas mestiças Holandês x Zebu, com 190kg. O genótipo BRS Kurumi apresentou maior teor de PB (15,65%), menor teor de FDN (60,35%), maior coeficiente de digestibilidade (70,04%) e mais alta taxa de degradação (2,62% h1) em relação ao outro genótipo, quando manejados a 90% IL. O manejo a 95% de IL e resíduo de 30cm favoreceu mais altos teores de PB (14,04%) e coeficientes de DIVMS (69,81%) e mais baixos teores de FDN (60,61%), independentemente do genótipo. Assim, recomenda-se a utilização do genótipo Kurumi, manejado a 90% de IL e resíduo de 30cm, quando se leva em consideração o valor nutritivo da forragem.(AU)

The experiment was conducted at Embrapa Gado de Leite, Coronel Pacheco, MG, to evaluate the nutritive value and the in vitro kinetics of degradation of elephant grass genotypes under rotational grazing. The treatments consisted of a factorial combination (2x2x2), two genotypes of elephant grass (BRS Kurumi and CNPGL 00-1-3), two light interceptions (LI) at initiation of grazing (90 and 95%) and two post-grazing heights (30 and 50cm), arranged in a completely randomized design with three replications. Grazing animals were 24 Holstein Zebu crossbred heifers with 190kg BW. The genotype BRS Kurumi has a higher CP content (15.65%), lower NDF content (60.35%), higher digestibility (70.04%) and higher rate of degradation (2.62% h-1) in relation to CNPGL 00-1-3 when managed under 90% of LI. The management based on 95% of LI and 30cm of residual height promote higher CP content (14.04%) and coefficient of IVDMD (69.81%), as well as lower NDF content (60.61%), regardless of genotype. Thus, taking into account the nutritional value of forage, it is recommended to use the genotype BRS Kurumi managed under 90% of LI and 30cm of post-grazing residue.(AU)

Sward characteristics and performance of dairy cows in organic grass-legume pastures shaded by tropical trees.

The silvopastoral system (SPS) has been suggested to ensure sustainability in animal production systems in tropical ecosystems. The objective of this study was to evaluate pasture characteristics, herbage intake, grazing activity and milk yield of Holstein×Zebu cows managed in two grazing systems (treatments): SPS dominated by a graminaceous forage (Brachiaria decumbens) intercropped with different leguminous herbaceous forages (Stylosanthes spp., Pueraria phaseoloides and Calopogonium mucunoides) and legume trees (Acacia mangium, Gliricidia sepium and Leucaena leucocephala), and open pasture (OP) of B. decumbens intercropped only with Stylosanthes spp. Pastures were managed according to the rules for organic cattle production. The study was carried out by following a switch back format with 12 cows, 6 for each treatment, over 3 experimental years. Herbage mass was similar (P>0.05) for both treatments, supporting an average stocking rate of 1.23 AU/ha. Daily dry matter intake did not vary (P>0.05) between treatments (average of 11.3±1.02 kg/cow per day, corresponding to 2.23±0.2% BW). Milk yield was higher (P0.05) in subsequent years. The highest (P0.05) milk yields. Low persistence of Stylosanthes guianensis was observed over the experimental period, indicating that the persistence of forage legumes under grazing could be improved using adapted cultivars that have higher annual seed production. The SPS and a diversified botanical composition of the pasture using legume species mixed with grasses are recommended for organic milk production.

Perfil de ácidos graxos no leite de vacas holandês em pastagens tropicais suplementadas com dois níveis de concentrado / Milk fatty acids profile of Holstein cows grazing tropical forages supplemented with two concentrate levels

Milk fatty acids profile was evaluated using 12 Holstein cows producing 15 kg/day of milk with 4.0% of fat. The animals were assigned to four treatments in a 2 x 2 factorial arrangement (two tropical grasses - Brachiaria brizantha cv. Xaraés and Panicum maximum cv. Tanzania, supplemented with two concentrate levels - 3 and 6 kg/cow/day) in a completely randomized block design. There was no effect of forage and concentrate level (P>0.05) on concentrations of rumenic, vaccenic, (C18: 1 trans-11) and oleic acids in milk fat (mean values of 1.01, 1.79, and 22.55 g/100 g of total fatty acids, respectively). The concentrations of lauric (C12:0), myristic (C14:0), and palmitic (C16:0) acids were also unaffected by treatments (mean values of 2.63, 9.77, and 27.44g/100g of total fatty acids, respectively). Overall, the results illustrate the potential of tropical grasses in producing milk containing a more desirable fatty acids profile in terms of human health.

Substitution of crude cell wall for neutral detergent fibre in the equations of the Cornell Net Carbohydrate and Protein System that predict carbohydrate fractions: application to sunflower ( Helianthus annuus L.).

Prediction of carbohydrate fractions using equations from the Cornell Net Carbohydrate and Protein System (CNCPS) is a valuable tool to assess the nutritional value of forages. In this paper, these carbohydrate fractions were predicted using data from three sunflower (Helianthus annuus L.) cultivars, fresh or as silage. The CNCPS equations for fractions B2 and C include measurement of ash and protein-free neutral detergent fibre (NDF) as one of their components. However, NDF lacks pectin and other non-starch polysaccharides that are found in the cell wall (CW) matrix, so this work compared the use of a crude CW preparation instead of NDF in the CNCPS equations. There were no differences in the estimates of fractions B1 and C when CW replaced NDF; however, there were differences in fractions A and B2. Some of the CNCPS equations could be simplified when using CW instead of NDF. Notably, lignin could be expressed as a proportion of DM, rather than on the basis of ash and protein-free NDF, when predicting CNCPS fraction C. The CNCPS fraction B1 (starch + pectin) values were lower than pectin determined through wet chemistry. This finding, along with the results obtained by the substitution of CW for NDF in the CNCPS equations, suggests that pectin was not part of fraction B1 but present in fraction A. We suggest that pectin and other non-starch polysaccharides that are dissolved by the neutral detergent solution be allocated to a specific fraction (B2) and that another fraction (B3) be adopted for the digestible cell wall carbohydrates.

Influência da diferença cátion-aniônica da dieta sobre o balanço de cálcio, fósforo e magnésio em ovinos / Influence of the dietary cation-anion difference on calcium, phosphorus and magnesium balance in sheep

O efeito do balanço cátion-aniônico da dieta (BCAD) no balanço macromineral (cálcio, fósforo e magnésio), no pH urinário e fecal, na concentração sérica de cálcio, fósforo e magnésio foi estudado utilizando-se 16 carneiros machos, da raça Santa Inês, por um período de 26 dias, sendo sete de adaptação. O delineamento experimental foi em blocos ao acaso, com quatro tratamentos. Para a manipulação do BCAD foram adicionados cloreto de cálcio e bicarbonato de sódio, obtendo-se os seguintes tratamentos: -12; +30; +76 e +133mEq/kg MS da ração. Não foram encontradas diferenças (P>0,10) no pH fecal, pH urinário, balanço de fósforo e magnésio. Com o aumento do BCAD houve decréscimo da absorção e retenção de cálcio, e aumento da excreção fecal. A manipulação do BCAD interferiu no metabolismo de macrominerais, principalmente no de cálcio.