Desempenho de bovinos Tabapuã e seus cruzados em pastagens de braquiária no estado da Bahia / Performance of straightbred and crossbred Tabapuã cattle on brachiaria pasture in Bahia state

Comparou-se o desempenho de bovinos de diferentes grupos genéticos quanto a algumas características produtivas da desmama até o abate. Os dados são referentes a 827 bovinos machos oriundos do cruzamento de vacas Tabapuã com touros Tabapuã (TAB), Red Angus (REDTAB), Santa Gertrudis (STATAB), e das fêmeas TabapuãxRed Angus com touros Santa Gertrudis (STAREDTAB) (nascidos entre 1999 e 2001 e criados em pastagens de braquiária, no Estado da Bahia). Foram analisados o peso à desmama ajustado aos 205 dias (PD205), o peso ao abate (PA), o ganho médio diário da desmama ao abate (GMD) e a idade ao abate (IA). O grupo contemporâneo (GC), o grupo genético (GG) e a interação entre GC e GG influenciaram as características avaliadas (P<0,05). O REDTAB apresentou superioridade entre os GG para GMD no primeiro ano do GC (1GC), com média de 0,552kg (P<0,05). Os cruzados STATAB e STAREDTAB não apresentaram diferenças significativas para as médias de GMD (P>0,05); entretanto, apresentaram médias inferiores às do grupo REDTAB e TAB. Em condição de ambiente mais favorável, o REDTAB pode ser mais precoce, obtendo maior GMD e PA com menor IA, sendo superior ao Tabapuã e aos cruzados da segunda geração (F2). Os cruzados F2 não demonstraram vantagem em relação ao cruzado F1 e à raça pura.

The aim of this study was to compare the different genetic groups performances from weaning to slaughter. The d ata are referred to 827 male calves of Tabapuã c ows crossed with Red Angus (REDTAB) and Santa Gertrudis sires and from Tabapuã x Red Angus cows crossed with Santa Gertrudis sires , born from 1999 to 2001 and raised in Brachiaria pastures, in Bahia state , Brazil. The w eaning weight was adjusted to 205 day s (WW205), slaughter weight (SW ), average daily gain from weaning to slaughter (ADG) and age slaughter (AG), were analyzed. The contemporary group (CG), genetic group (GG) and the interaction between CG and GG influenced the parameters (P<0.05). The REDTAB showed superiority between GG for ADG in 1CG, with an average of 0.522 kg (P<0.05). The cro s sbreed STATAB and STAREDTAB weren 't different to ADG (P>0.05), however, ha d lower averages than REDTAB and TAB. In more favorable environment al conditions, REDTAB s hould get higher ADG and SW and lower AG , being superior than Tabapuã and to the second generation's crossbr ed (F2). The crossbr ed F2 show ed no advantage over F1crossbr ed and straightbred.

Physiological and bromatological aspects of Brachiariahumidicola / Aspectos fisiológicos y bromatológicos de Brachiaria humidicola / Aspectos fisiológicos e bromatológicos de Brachiaria humidicola

Brachiaria humidicola was brought to Colombia in order to improve forage production and poor acid soils wherethere was no fodder adapted to these conditions in which this species could be an excellent alternative. However,work to compile aspects and qualitative physiological characteristics are scarce, for this reason, a brief review botanyand morphophysiological of this species also present results of various studies that show the values of quality foragesuch as content protein, neutral detergent fiber (NDF) and acid detergent fiber (FDA), in vitro digestibility of dry matter and lignin content among others. The review took into account the behavior of Brachiaria in environments of special interest such as: soil, nutrients and water.

Brachiaria humidicola, fue traída a Colombia con el propósito de mejorar la producción de forraje en suelos ácidos y pobres donde no se contaba con forrajes adaptados a estas condiciones, en las cuales esta especie pudiera ser una excelente alternativa. Sin embargo, trabajos que compilen aspectos relacionados con sus características fisiológicas y bromatológicas son escasos; por tal motivo se realizó una breve revisión botánica y morfofisiologíca de estaespecie, además se presentan resultados de diversas investigaciones que muestran valores de calidad de este forraje tales como contenido proteico, fibra en detergente neutra (FDN) y fibra en detergente acida (FDA), digestibilidad in vitro de la materia seca y contenido de lignina entre otros. En la revisión se tuvo en cuenta el comportamiento de Brachiaria en ambientes de especial interés como son: suelos, nutrientes y agua.

Brachiaria humidicola, foi trazida para a Colômbia com um propósito de melhorar a produção de forragem emsolos ácidos e pobres onde não se contava com forragens adaptadas a estas condições, nas quais esta espécie pudesse ser uma excelente alternativa. Contudo, trabalhos que juntem aspectos relacionados com as suas característicasfisiológicas e bromatológicas são escassos; por tal motivo foi realizada uma breve revisão botânica e morfofisiológicadesta espécie, ademais são dados resultados de diversas pesquisas que mostram valores de qualidade desta forragem tais como conteúdo proteico, fibra em detergente neutra (FDN) e fibra em detergente acida (FDA), digestibilidade in vitro da matéria seca e conteúdo de lignina entre outros. Na revisão foi tido em conta o comportamento de Brachiariaem ambientes de interesse especial como: solos, nutrientes e água.

Microsporogenesis in Brachiaria dictyoneura (Fig. & De Not.) Stapf (Poaceae: Paniceae)

icrosporogenesis was analyzed in five accessions of Brachiaria dictyoneura presenting x = 6 as the basic chromosome number. All accessions were tetraploid (2n = 4x = 24) with chromosome pairing in bi-, tri-, and quadrivalents. The recorded meiotic abnormalities were those typical of polyploids, including precocious chromosome migration to the poles, laggard chromosomes, and micronucleus formation. The frequency of these abnormalities, however, was lower than those reported for other polyploid accessions previously analyzed for other Brachiaria species. Cell fusion and absence of cytokinesis were also recorded in some accessions, leading to restitutional nucleus formation in some cells. Genetically unbalanced microspores, binucleate, and 2n microspores were found among normal meiotic products as results from these abnormalities. The limitation in using these accessions as pollen donor in interspecific crosses with sexual species with x = 7 or x = 9 in breeding programs is discussed.

Evidence of allopolyploidy in Brachiaria brizantha (Poaceae: Paniceae) through chromosome arrangement at metaphase plate during microsporogenesis

In the hexaploid (2n = 6x = 54) accession B176 of Brachiaria brizantha, one cytological characteristic differentiated it from the other accessions previously analyzed with the same ploidy level. Nearly 40% of meiocytes displayed the chromosome set arranged at two metaphase plates at the poles of the cell, close to the membrane. In these cells, both metaphase plates were arranged in an angle to form a typical tripolar spindle. Therefore, cells did not show normal chromosome segregation at anaphase I. Only nine univalent chromosomes migrated from each plate to the opposite pole with the remainder staying immobile on the plate. As a result of such spindle orientation and chromosome behavior, trinucleate telophases I were recorded. After telophase, cytokinesis eliminated the small nuclei into a microcyte. The second division proceeded normally, with the presence of microcytes in all phases. The origin of such an abnormality was explained on the hexaploid level of the accession which could have resulted by chromosome doubling of a triploid derived from species that did not display the same behavior for spindle organization. The high percentage of meiotic abnormalities recorded in this accession compromises fertility and renders it inadequate for the breeding program.

Microsporogenesis in tetraploid accessions of Brachiaria nigropedata (Ficalho & Hiern) Stapf (Gramineae)

The genus Brachiaria (Trin.) Griseb. has achieved considerable importance to cattle production systems, as a result of the good production and adaptation of a few cultivars to poor and acid soils of the Brazilian savannas. Many of its species and accessions are polyploid and apomictic, which limits direct hybridization. To assist the breeding program, cytogenetic characterization has been undertaken on the accessions of Brachiaria collection at the Embrapa Beef Cattle Research Center. In this study, chromosome number and meiotic behavior are reported for the Brachiaria nigropedata (Ficalho & Hiern) Stapf collection. The 20 available accessions are tetraploid (2n = 4x = 36). Chromosomes paired preferentially as bivalents, but quadrivalents were found in high frequencies in some cells. Meiotic behavior was, in general, irregular, and varied among accessions. Most accessions presented more than 20% of abnormal tetrads. The most common meiotic abnormalities were those related to irregular chromosome segregation due to polyploidy, leading to micronuclei formation in the tetrad stage. A low frequency of other meiotic abnormalities such as the absence of cytokinesis, chromosome stickiness, cell fusion, anaphase bridges, and chromosome transfer among microsporocytes were also recorded in some accessions. Limitations of these accessions for use in hybridization programs are discussed.