RESUMEN

Principal component analysis was applied to evaluate the variability and relationships among univariate breeding values predicted for 9 weaning and yearling traits, as well as suggest functions of the traits that would promote a particular breeding objective. Phenotypic and pedigree information from 600,132 Nelore animals was used. Genetic parameters and breeding values were obtained from univariate analyses of birth to weaning weight gain; weaning to yearling weight gain; conformation, finishing precocity, and muscling scores at weaning and at yearling; and yearling scrotal circumference. The principal component mainly associated with maturity (precocious vs. late animals) was used as a pseudophenotype in bivariate analyses with either adult weight or adult height of cows. Direct heritability estimates ranging from 0.19 ± 0.01 to 0.41 ± 0.01 indicate that these 9 traits are all heritable to varying degrees. Correlations between the breeding values for the various traits ranged from 0.14 to 0.88. Principal component analysis was performed on the standardized breeding values. The first 3 principal components attained the Kaiser criterion, retaining 48.06%, 18.03%, and 12.97% of the total breeding value variance, respectively. The first component was characterized by positive coefficients for all traits. The second component contrasted weaning traits with yearling traits. The third component represented a contrast between late maturity animals (better for weight gain and conformation) and early maturity animals (better for finishing precocity, muscling, and scrotal circumference). Thus, the first 3 components represent 3 different potential selection criteria. Selecting for the first principal component would identify animals with positive breeding values for all studied traits. The second principal component may be used to identify animals with higher or lower maturation rates (precocity). Animals with negative values in the third principal component are regarded as early maturing. Genetic correlations between maturity (third principal component) with adult weight and adult height were 0.19 ± 0.02 and 0.32 ± 0.02, respectively. These results showed that the weaning and yearling bovine maturity is genetically associated with the adult size of the cows used in reproduction.

Asunto(s)

Bovinos/fisiología , Modelos Estadísticos , Reproducción , Animales , Peso Corporal , Cruzamiento , Bovinos/genética , Bovinos/crecimiento & desarrollo , Femenino , Masculino , Linaje , Fenotipo , Análisis de Componente Principal , Carne Roja , Escroto , Destete , Aumento de Peso

RESUMEN

The global invasion of non-native aquatic ecosystems by Nile tilapia (Oreochromis niloticus) is well documented and coincides with their increased use as an aquaculture species. Aquaculture can be defined as the farming of fish or other aquatic organisms and it varies considerably in terms of production practices. Generally, freshwater finfish, such as Nile tilapia, are reared in inland ponds (closed systems). However, in several countries, floating cages are increasingly used to rear Nile tilapia in open water bodies. In such systems, escape is inevitable. The Nile tilapia is considered an omnivorous species and it ingests zooplankton, phytoplankton, or debris present in rivers. As a consequence, the release of Nile tilapia into non-native aquatic ecosystems may result in competition for food and space, thereby damaging native species. The wide environmental tolerance and high reproductive rate of Nile tilapia facilitate its use for aquaculture, but also render the species highly invasive. Here, we review the high frequency of Nile tilapia in non-native biodiversity and indicate the existence of the species under feral conditions in every country in which it has been introduced through farming systems.

Asunto(s)

Cíclidos/fisiología , Ecosistema , Especies Introducidas , Animales , Acuicultura , Biodiversidad , Agua Dulce , Fitoplancton/metabolismo , Ríos , Contaminantes Químicos del Agua/química , Zooplancton/metabolismo

RESUMEN

A hyphenated technique for coupling a spectrophotometric detector to a gas chromatograph with a packed column is described. The packed column was connected directly to the flow cell (path length 1 cm) which was placed in a UV-visible molecular absorption spectrophotometer with diode array detector. This detection system was employed for separating and determining benzene, toluene, 1,4-xylene, 1,2-xylene and mesitylene. Molecular absorption spectra of all the separated compounds have also been obtained. A new possibility for coupling capillary gas chromatography and gas phase molecular absorption spectrometry is currently being tested. In this new case, two fibre optics are used and the measurement is performed in the capillary column.

RESUMEN

A method for the simultaneous determination of sulphide and sulphite is described, which involves continuous H(2)S and SO(2) generation, preconcentration in a liquid nitrogen trap and measurement of the molecular absorption spectra of volatiles in the gas phase in 190-220 nm range. Under the recommended conditions (sample flow: 50 ml/min and concentrated sulphuric acid flow: 12 ml/min; generation time: 4 min) linear response ranges from 0.05 mug/ml for S(2-) and 0.20 mug/ml SO(2-)(3) are obtained with detection limits of 0.05 and 0.20 mug/ml respectively. Synthetic mixtures of the two components have been solved and a comparative study of different calculation methods has been made. In conclusion, multiwavelength methods offer better precision and accuracy.