Interação genótipo ambiente devido ao estresse térmico durante o final da gestação sobre caraterísticas de crescimento de bovinos de corte
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Data
2021-02-25
Autores
Alves, Mariana Stucki
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Universidade Federal de Mato Grosso
Resumo
The effect of thermal stress on production traits has been widely
studied in cattle. However, the effect of heat stress that females undergo during
pregnancy can compromise embryonic nutrition, fetal and placental development,
cause a reduction in gestation length, and impair calves' postnatal performance.
Thus, this study aimed to estimate genetic parameters associated with thermal
stress during late pregnancy for birth weight (BW) and average daily weight gain
from birth to weaning (ADG) of Braford and Brangus cattle. The data refer to
73,383 animals of the Braford breed and 45,120 of the Brangus breed, with birth
dates between 1974 and 2017. The calves were weighed at birth and at the time
of weaning, which occurred around 205 days of age. The average temperature
and humidity index (ITU) was calculated over the last days of gestation (60, 70,
80, and 90) for each animal in the analysis. The mean ITU of the final pregnancy
period (ITUg) was included in the fixed linear model. The least-squares means
(LSM) were calculated for BW and ADG on each ITUg variable to be evaluated.
A regression model was applied on the LSM to assess the BW and ADG
response pattern in the function of each ITUg. For Braford and Brangus, the fixed
model considering the ITUg calculated over 60 days and 70 days before calving,
respectively, presented the highest R2
. During the final gestation period, heat
stress significantly reduced both the BW and the ADG of the Braford and
Brangus cattle. The ADG was reduced by -00021 and -0,0013 kg/ day / ITUg for
Braford and Brangus, representing an expressive productive and economic loss
for the studied populations. The heritability estimates for the direct effect for BW
varied for Braford from 0,35 to 0,62 with an average of 0,45. For Brangus, the
estimates were from 0,26 to 0,52 with an average of 0,37. For the maternal
effect, they ranged from 0,06 to 0,17 for Braford and 0,07 to 0,35 for Brangus,
with a mean of 0,10 and 0,16 respectively. The heritability estimates for direct
and maternal effects were 0,07 to 0,27, with a mean of 0,14, and 0,11 to 0,19,
with an average of 0,14, respectively for ADG of Braford cattle. These estimates
demonstrate substantial heterogeneity of genetic variances along the
environmental gradient. The genetic correlations between the same trait in
adjacent ITUg values were of high magnitude. However, among extreme and
opposite ITUg they were low or even negative, especially for BW. Therefore, the
inclusion of this effect in genetic evaluations to identify and select animals
genetically more tolerant to thermal stress becomes justified due to its reflexes
on the animal's future performance.
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ALVES, Mariana Stucki. Interação genótipo ambiente devido ao estresse térmico durante o final da gestação sobre caraterísticas de crescimento de bovinos de corte. 2021. 36 f. Dissertação (Mestrado em Zootecnia) - Universidade Federal de Mato Grosso, Campus Universitário de Rondonópolis, Instituto de Ciências Agrárias e Tecnológicas, Rondonópolis, 2021.