The degree of genetic polymorphism at the DRB3 locus in the major histocompatibility complex (Mhc) of the North American bison was investigated by PCR and DNA sequence analysis. Nine different alleles were characterized in a selected sample of 20 animals. The genetic distances between alleles were as large as usually found at highly polymorphic Mhc loci in other species. A comparative analysis of the DRB3 polymorphism in bison and cattle revealed an extensive sharing of sequence motifs. The result clearly shows a transspecies persistence of DRB3 allelic lineages in the two species. Consequently a significant amount of Mhc polymorphism has been maintained through the population bottleneck that bison experienced in the late nineteenth century. An analysis of the pattern of sequence polymorphism among bison and cattle DRB3 alleles strongly suggested that interallelic recombination has contributed significantly to the generation of allelic diversity at this locus.
RESUMO -Objetivou-se verificar a existência de variação genética entre cultivares de capim-colonião quanto ao efeito da maturidade sobre a composição química e a digestibilidade, e classificar os genótipos de acordo com características produtivas e de qualidade nutricional. Utilizou-se o delineamento de blocos ao acaso, com parcelas subdivididas e três repetições, considerando parcelas as datas de corte e subparcelas, os genótipos. A produção de MS diferiu entre os genótipos somente aos 90 dias de crescimento, mas a porcentagem de folhas, colmos e material morto variou tanto aos 60 como aos 90 dias de crescimento. Ao contrário do observado para as folhas, a composição química e a digestibilidade do colmo fiber, acid detergent fiber, and lignin, and lower values of crude protein, when compared to the leaves. It also presented higher digestibility of dry matter at 60 days of growth, and higher digestibility of neutral detergent fiber at 30, and at 60 days of growth. Clustering of the cultivars identified the PM39 and PM47 genotypes as the most promising ones in the breeding program, because they showed high productivity and high nutritional quality. Maturity has little effect on leaf digestibility when compared to the stem. When participation of the stem increases in the total of dry matter, this component becomes the major factor limiting quality of forage plants. Therefore, breeding program must consider, in addition to leaf:stem ratio, the in vitro digestibility of neutral detergent fiber of the stem when selecting genotypes. IntroduçãoNo Brasil, a produção de bovinos de corte ocorre predominantemente a pasto, onde as pastagens tropicais são as principais fontes de alimento para os ruminantes, sendo sensivelmente mais econômica em relação aos concentrados (Aguiar et al., 2000). O Panicum maximum é uma das espécies de plantas forrageiras mais importantes R. Bras.
Rapid decline in cell-wall digestibility hinders efficient use of warm-season grasses. The objective of this study was to identify genes whose expressions are related to the slope of decline in cell-wall digestibility. Eleven guineagrass genotypes were harvested at three ages and classified according to fibre digestibility. Extreme genotypes were separated into groups with either FAST or SLOW decline in fibre digestibility. Expression of transcripts from six genes from the lignin synthesis pathway was quantified by real-time PCR. Fast decline in fibre digestibility was associated with higher DM yield after 90 d of regrowth. Apart from lower fibre digestibility and higher lignin content for the FAST group, there were no other differences between the two groups for the chemical composition of stems and leaves. Maturity affected differently the expression of two of the six genes, cinnamate 4-hydroxylase and caffeoyl-CoA O-methyltransferase (C4H and CCoAOMT). Genotypes with fast decline in fibre digestibility had greater increase in the expression of C4H and CCoAOMT from 30 to 60 d of regrowth, than genotypes with slower decline. Expression of C4H and CCoAOMT appears to be related to the decline in cell-wall digestibility with advance in maturity of guineagrass.
Polymerase chain reaction (PCR) primers specific to exon 2 of the bovine lymphocyte antigen (BoLA)-DRB3 gene were successfully used to amplify the equivalent region in 469 American bison (Bison bison). In domestic cattle, alleles of DRB3 are assigned through a restriction fragment length polymorphism (RFLP) analysis of the patterns of fragment lengths observed after digestion with the restriction enzymes RsaI, BstYI and HaeIII. In bison, using the same procedure, the observed RFLP patterns provided evidence for the strong conservation of restriction sites previously reported in cattle.
Resumo -O objetivo deste trabalho foi avaliar o efeito da maturidade da planta sobre a qualidade nutricional do colmo de híbridos de milho, para definir critérios de seleção em programas de melhoramento de milho para ensilagem. Foram avaliados 15 híbridos de milho, do programa de melhoramento do Instituto Agronômico, em Campinas, SP, colhidos com 90, 120 e 150 dias após a germinação, em experimento com delineamento de blocos ao acaso, com três repetições. O quarto e o quinto internódios do colmo foram retirados para determinação da composição bromatológica e digestibilidade in vitro. Com o avanço da maturidade, houve queda no teor de fibra e aumento no de lignina de ambos os internódios. Observou-se aumento na digestibilidade da matéria seca do quinto internódio, mas não houve mudanças na do quarto internódio. A maturidade também reduziu a digestibilidade da fibra em detergente neutro (DIVFDN) do quarto internódio, mas não a do quinto. A DIVFDN do quarto internódio pode ser utilizada como parâmetro de seleção para aumento da qualidade nutricional de híbridos de milho. Nas três idades de corte, houve grande variabilidade genética dos parâmetros de qualidade, o que realça a possibilidade de implantação de programas de melhoramento genético para qualidade nutricional do milho para ensilagem.Termos para indexação: Zea mays, degradabilidade, lignina, melhoramento genético, parede celular. Stalk nutritive value of corn hybrids harvested at three maturity stagesAbstract -The objective of this work was to evaluate the effect of plant maturing on the stalk nutritional quality of corn hybrids, in order to define selection criteria in breeding programs of maize for silage. Fifteen hybrids from the Instituto Agronômico breeding program in Campinas, SP, Brazil, harvested at 90, 120 and 150 days after germination, were evaluated in a randomized block design, with three replicates. The fourth and fifth stalk internodes were removed for determination of chemical composition and in vitro digestibility. In both internodes, fiber content decreased and lignin content increased as maturity advanced. Dry matter digestibility of the fifth internode increased with maturity, while there was no change in the fourth internode. Maturity reduced neutral detergent fiber digestibility (DIVFDN) of the fourth internode but not of the fifth one. The forth internode DIVFDN can be used as a selection criterium for nutritional quality improvement of corn hybrids. There was great genetic variability of quality parameters, among harvested hybrids at the three maturity stages, which highlights the possibility of implementing breeding programs for nutritional quality of corn for silage.
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