Dissertação
Meta-análise para estimativas de parâmetros genéticos para características de crescimento em ovinos
Fecha
2023-01-27Autor
Evangelho, Lavínia Aires
Institución
Resumen
With a growing demand for sheep meat, those produced have increased their productivity and
beliefs of genetic parameters such as heritability (direct and maternal) and genetic, phenotypic
and environmental correlations are commonly evaluated in domestic animals, including
sheep. The aim of this study was to perform a meta-analysis for estimates of direct, maternal
and total heritability and genetic correlations for weight gain traits and growth assessments at
different ages in beef sheep and to evaluate through a meta-regression the impact of
secondary variable on the observed heterogeneity between studies. A search was carried out
in the literature of scientific articles published between the years 2012 to 2022 on the digital
platforms PubMed, Scielo, Web of Science and ScienceDirect. The random effects model was
used to obtain estimates of the combined effects. The effect sizes were evaluated by means of
the average of the values published in the literature for the heritabilities and genetic
correlations between the evaluated traits. Heterogeneity was reduced using Cochran's I2
and Q
statistics. A total of nine traits related to weight gain and growth in sheep were evaluated. A
meta-regression was conducted to assess the influence of secondary variables that occurred on
the evaluated parameters. After cleaning the data, a total of 118 articles remained for the
meta-analysis, which generated 504 heritability estimates and 74 genetic correlation
estimates. Pooled heritability estimates across studies ranged from 0.07 to 0.29 for weaning
weight and 9-month weight, respectively. The year of data collection, the method and
statistics (uni, bi or multivariate) explained the greater proportion of the variability observed
between studies. There was a trend towards increased direct heritability for animal weight
when the measure was evaluated in older animals, ranging from 0.18 for birth weight to 0.26
for weight at 12 months of age, while maternal heritability decreased with age and ranged
from 0.16 to 0.12, for weight at birth and at 6 months of age, respectively, an expected result,
given the decrease in the importance of the maternal effect with advancing age, whereas the
total heritabilities there was little variation from 0.18 to 0.21 for birth weight and weight at 9
months and for weight at 6 months, respectively. Genetic correlations showed a low variation
of 0.45 to 0.53 for birth weight, weaning weight and weight at 9 and 12 months, respectively.
The presented results confirm that the growth traits in sheep are subject to selection, being
more important at the beginning of the animal's life, which reinforces the hypothesis that it is
important to observe, in addition to the effect of the animal's direct genetics, the maternal
genetics to carry out more efficient selection, especially for traits measured at younger ages.
Moderate correlations suggest a good response to indirect selection, which can be a tool to
select traits with lower heritability.