Rodrigo Amorim Barbosa

Avaliação de Três Cultivares de Panicum maximum Jacq. sob Pastejo: Composição Química e Digestibilidade da Forragem

A study was conducted to evaluate three cultivars of Panicum maximum Jacq. under rotational grazing for the nutritive value,where the estimates of crude protein, neutral detergent fiber, acid detergent fiber, lignin, cellulose, silica, and in vitro digestibility of the organic material were performed in samples of leaves and stems. Additional nitrogen was applied in cv. Tanzania at the end of the rainny season. Samples were taken in June, September, and October 1998 and in March 1999. Some differences among treatments were observed. In general, cv. Massai showed a lower nutritive value with lower crude protein and digestibility, and higher neutral detergent fiber, acid detergent fiber, and lignin, either in samples of leaves or in stems. Therefore, its utilization as a forage option should be based on other agronomic characteristics. The cv. Mombaca exhibited higher concentrations of silica and its nutritive value was not affected by nitrogen fertilization at the end of the rainny season, except for an increase in the percentage of crude protein and a reduction in the amount of lignin and silica in March. The nutritive value of the stems was inferior to the leaves. The nutritive value was highest in all treatments at the beginning of the rainny period.

Avaliação de três cultivares de Panicum maximum Jacq. sob pastejo: composição da dieta, consumo de matéria seca e ganho de peso animal

Three varieties of Panicum maximum Jacq. were evaluated by measuring the botanical and chemical composition of the diet, and the dry matter intake and weight gain of the animal under rotational grazing, before and after a period of grazing. The treatments were: 1) v. Tanzânia + 50 kg N/ha, 2) v. Tanzânia + 100 kg N/ha, 3) v. Mombaca + 50 kg N/ha, and 4) v. Massai + 50 kg N/ha. Of the diets selected by the animals, v. Massai tended to show lower values for digestibility and crude protein, and higher values for neutral detergent fiber; however, in general, the diets containing v. Mombaca had higher values for silica. The animals selected an average of 92.4% green leaves, independent of treatment and season of sampling. The animals consumed similar quantities of forage on the diverse treatments, with average intakes of 1.9, 2.8, 3.4, and 2.3 kg DM/100 kg BW, respectively, for June, September and November of 1998 and March of 1999. Low weight gains of the animals on v. Massai were verified, but due to the higher availability of forage during the rainy season, the weight gains per hectare were higher than for v. Mombaca + 50 kg N/ha and v. Tanzânia+ 50 kg N/ha. Factors which had the most positive influence on weight gain of the animals were quantity of leaves, height of the pasture, crude protein content of the diet selected by the animals, and size of the bite.

Avaliação de três cultivares de Panicum maximum Jacq. sob pastejo: disponibilidade de forragem, altura do resíduo pós-pastejo e participação de folhas, colmos e material morto

Three cultivars of Panicum maximum Jacq. under rotational grazing were evaluated for one year, before and after grazing, when measurements were made of the availability of total dry matter, height, residual dry matter, forage density, leaf dry matter, participation of leaves, stems and dead material, and ratios of leaf:stem and leaf:dead plant material. The treatments were 1) v. Tanzania + 50 kg N/ha, 2) v. Tanzania + 100 kg N/ha, 3) v. Mombaca + 50 kg N/ha, and 4) v. Massai + 50 kg N/ha. The Mombaca cultivar presented the poorest results, lowest production of leaves and the highest proportion of stems. However, the cv. Massai deservers attention for characteristics such as higher density of DM and higher leaf lamina:stem ratio; however, it presented a lower ratio of leaves:dead material. There were no significant differences in percentage of leaves among the cultivars. In the cv. Tanzania, nitrogen fertilization at the end of the rainy period had beneficial effects only in March when there was an increase in the leaf:stem and leaf:dead plant material ratios. The residual dry matter correlated positively with the height of the forage. The animals grazed 41% of the height of the pasture in the dry period, and 47% in the rainy period.

Avaliação de três cultivares de Panicum maximum Jacq. sob pastejo: comportamento ingestivo de bovinos

Three varieties of Panicum maximum Jacq. were evaluated by measuring ingestive behavior components (bite size, grazing time, and rate of eating) for one year under rotational grazing. The treatments were: 1) v. Tanzânia + 50 kg N/ha, 2) v. Tanzânia + 100 kg N/ha, 3) v. Mombaca + 50 kg N/ha, and 4) v. Massai + 50 kg N/ha. The values for bite size were probably overestimated, even so, values lower than 300 g DM/bite size were observed, a critical consideration, in the dry period. There was a tendency for smaller size bites with v. Massai during the dry period, probably due to distribution of leaves and dead material present in the pasture. There were no differences in time of pasturing among treatments and between seasons of evaluation, but the standard of distribution for time spent grazing along with the day was modified by the different seasons. Few differences in rate of eating were observed among the varieties. The rate of eating tended to increase with the length of time in the plots. Among the components of ingestive behavior the only significant correlation observed was between time of pasturing and bite size (r = -0.45).

Morphogenetic characteristics and forage accumulation of Tanzania grass (Panicum maximum Jacq.) in two post-graze stubbles

This trial was conducted at National Beef Cattle Research Center of Brazilian Agricultural Research Corporation (Embrapa Beef Cattle), to evaluate the morphogenetic characteristics of leaves and tiller, green dry matter yield and growth index of Tanzaniagrass in two post-graze stubbles (high post-graze stubble (HPS) ¾3.6 t of DM/ha and low post-graze stubble (LPS) ¾ 2.3 t of DM/ha) until 35 days after grazing. The experimental design was a complete randomized block, with treatments assigned to a split plot design, with three replicates. Differences between post-graze stubble (PS) in the tiller dynamics only occurred to new basal tiller. The appearance of new basal tillers and new aerial tillers linearly decreased during the days after grazing. There was no difference between the post-graze stubble and the new and remaining tillers for the leaf elongation rate and leaf senescence. On the other hand, the leaf duration of elongation was lower in the low PS and the new tillers, producing leaves with lower fully length. There was interaction in the leaf appearance rate between PS and kind of tillers, with a higher one for low PS in the remaining and new tiller. There was no difference among the post-graze stubbles for green dry matter yield, with mean values of 61.4 and 47.9 kg/ha.day, for low and high PS, respectively. There was also no difference between high and low PS for the relative growth rate and leaf area index (LAI). However, the LAI increased, as a function of to the days after grazing.

Aspectos quantitativos do processo de reciclagem de nutrientes pelas fezes de bovinos sob pastejo em pastagem de Brachiaria decumbens na Zona da Mata de Minas Gerais

The experiment was carried out at the experimental station of EMBRAPA/National Dairy Research, at Coronel Pacheco, in the Zona da Mata region of Minas Gerais, to evaluate the qualitative aspects of the nutrients recycling through the feces of grazing bovines. A 110 square meter plot was located in a previous established pasture of Brachiaria decumbens. There were significant differences on the nitrogen and magnesium concentrations of forage, for 10 weeks, apparently reflecting amounts in the forage. There were no variation of the other nutrients in the forage and feces. The average frequency defecation was of 9.84 defecations/animal per day and the average weight of the feces at each defecation was of 200.5 g dry matter. It was verified, by means of some data estimates, that the nutrients recycling in the feces, so 93.28% N, 76.68% P, 1.99% K, 72.93% Ca and 62.54% Mg, that was ingested by the animal returned to the pasture as feces, the same as 18.09% N, 35.46% P, 5.47% K, 30.26% Ca and 15.43% Mg, available as primary production, returned to the pasture through feces.

Eficiência bionutricional de animais Nelore e seus mestiços com Simental e Aberdeen Angus, em duas dietas

This experiment was carried out for two years with the objective of evaluating the performance of genetic groups with different genetic potentials for growth, such as Nellore (N), ½ Angus - ½ Nellore (AN) and ½ Simmental - ½ Nellore (SN).This study is part of an ample project, which has as principal goal, to evaluate the efficiency of production of systems composed by animals with different mature sizes (Projeto cruzamento Embrapa 1). Using a bivariate analysis involving the variables average daily gain and dry matter intake, it was determined the first discriminant canonical function which was used for estimating performance indexes that were denominated bio-nutritional efficiency. The data were obtained from 72 animals under two diets, one composed by Tanzânia hay plus 600 g of ground soybean (diet A), provided ad libitum, and other where this hay was combined with a concentrate ration (diet B). The bio-nutritional efficiency was significantly affected by the interaction between genetic group (GG) and diet (D). Thus, the least square means were compared by four different contrasts. These contrasts were, on diet B: C1) Nellore versus average of crossbreds and, C2) ½ Angus - ½ Nellore versus ½ Simmental - ½ Nellore. And on diet A: C3) Nellore versus crossbreds and, C4) ½ Angus - ½ Nellore versus ½ Simmental - ½ Nellore. The analyses of these contrasts revealed that, independently on diet, Nellore animals had a worst performance than the average observed for the F1s. The average of bio-nutritional efficiencies were equal to 429.74 and 490.46 for Nellore and crossbred animals, respectively, on diet B and, in the same sequence, 299.70 and 376.10 on diet A. Relatively to the F1 animals, their performances were dependent on diet. On diet A, the ½ Angus - ½ Nellore and ½ Simmental - ½ Nellore presented the same bio-nutritional efficiency (376.10) while on diet B, the ½ Angus - ½ Nellore were superiors (529.84 versus 451.09).

Steer performance on Panicum maximum (cv. Mombaça) pastures under two grazing intensities

The objective of this study was to evaluate animal performance in Mombaca guineagrass (Panicum maximum Jacq.) pastures under intermittent grazing associated with two post-grazing heights (30 and 50 cm) and a pre-grazing height of 90 cm. A completely randomised block experimental design was employed, with two treatments and three replicates. The pastures were evaluated pre- and post-grazing grazing, to determine the herbage mass, percentage of leaf, stem and dead material and nutritive value. The stocking rate (expressed in animal unit, AU = 450 kg liveweight) was adjusted twice a week, and the animals were weighed every 28 days. The average grazing frequencies were 33 and 40 days, respectively, for 50 cm and 30 cm of residue pastures to reach the pre-grazing target (90 cm). The forage accumulation rate and pre-grazing herbage mass were similar for pastures with post-grazing heights of 30 and 50 cm. However, 50 cm of residue in the pasture resulted in greater pre-grazing leaf percentage and nutritive value and a lower percentage of dead material than did 30 cm of residue, and, consequently, a greater herbage intake (2.6 and 2.0 kg of dry matter/100 kg liveweight, respectively). The stocking rate was greater in the pastures with 30 cm of residue (6.7 AU/ ha) than in those with 50 cm (5.1 AU/ha). However, the average daily gain was greater for the 50-cm (655 g/steer.day) than for the 30-cm (390 g/steer.day) post-grazing height, resulting in a greater animal production of 1070 versus 635 kg/ha, respectively. Thus, under intermittent grazing, Mombaca guineagrass should be managed using a 50-cm post-grazing height.

Consumo, composição botânica e valor nutritivo da dieta de bovinos em pastos tropicais consorciados sob três taxas de lotação

The effects of three stocking rates on intake, botanical composition, and nutritive value of the diet of cattle on pastures of Brachiaria decumbens with Stylosanthes guianensis cv. Minerao and B. brizantha cv. Marandu with S. guianensis cv. Mineirao were evaluated. The experimental design was a randomized complete block with two field replications. The treatments were arranged as a 2 x 3 factorial with 2 grasses (B. decumbens and B. brizantha cv. Marandu) in association with S. guianensis cv. Minerao, three stocking rates (0.8, 1.2, and 1.6 AU/ha), and two sampling periods (July and October 1998, corresponding to the early and late dry season; and January and April 1999, corresponding to the mid and late rainy season). Weaned Nellore steers with an average initial weight 138 kg were used. There was no effect of stocking rate on the variables studied. Daily consumption of forage dry matter was higher on pastures with B. brizantha in October (late dry season) and in April (late rainy season). However, it was observed diets with higher nutritive value in B. decumbens pastures. More than 80% of the diet was composed of live grass leaves while legumes represented 2.1% of the diet, with a selection index of 0.08, indicating low contribution of this forage component to the grazing animals.