trabalho completo - 52ª Reunião Anual da Sociedade Brasileira de

52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
Parâmetros genéticos para perímetro escrotal ajustado para características de crescimento e correlação com
idade ao primeiro parto1
Bárbara Mazetti Nascimento2, Laila Talarico Dias3, Rodrigo de Almeida Teixeira3
1
Parte do projeto de iniciação científica do primeiro autor, financiado pelo CNPq
Mestranda do Programa de Pós-Graduação em Zootecnia – UFPR, Curitiba, Brasil, e-mail: [email protected]
Professor adjunto, Departamento de Zootecnia - UFPR. e-mail: [email protected]; e-mail: [email protected]
2
3
Resumo: Os objetivos deste trabalho foram estimar a herdabilidade (h²) e a correlação genética (rg) para idade ao
primeiro parto (AFC) e perímetro escrotal ajustado para idade (SCa), idade e peso (SCaw) e para conformação
(SCc), precocidade (SCp) e musculatura (SCm) em bovinos da raça Nelore, pertencentes ao grupo Aliança Nelore.
No modelo foi considerado, como fixo, o efeito de grupo contemporâneo e os efeitos linear e quadrático de idade ao
sobreano, peso ajustado aos 500 dias de idade, conformação, precocidade, musculatura e idade da mãe como
covariáveis, utilizadas de forma específica para cada uma das análises. As h² estimadas para AFC variaram entre
0,21 e 0,22. Já para os perímetros ajustados, o ajuste para conformação proporcionou maior estimativa h² entre
todos os perímetros analisados (0,55), enquanto que o ajuste simultâneo para idade e peso (SCaw) resultou em
menor estimativa de h² (0,50). As rg entre AFC e os perímetros escrotais ajustados foram negativos e de mediana
magnitude, variando de -0,28 a -0,34. Os resultados obtidos permitem afirmar que o ajuste da medida de perímetro
escrotal para conformação, assim como o ajuste para idade e, idade e peso, também pode ser uma alternativa para a
identificação de reprodutores para precocidade sexual.
Palavras–chave: conformação, correlação genética, herdabilidade, musculatura, precocidade sexual
Genetic parameters of scrotal circumference adjusted to growth traits and age at first calving
Abstract: The aim of this study were to estimate heritability (h²) and the genetic correlation (rg) to age at first
calving (AFC) and scrotal circumference adjusted for age (SCa), age and weight (SCaw), conformation (SCc),
precocity (SCp), musculature (SCm), belong to Aliança Nelore. The model considered as fixed effect the
contemporary group, and as covariates, used specifically for each trait, the linear and quadratic effects of age at post
weaning, weight adjusted to 500 days old, conformation, precocity, musculature and age of dam. The h² estimates
for AFC varied between 0.21 and 0.22. The adjusted for conformation promoted the higher value for scrotal
circumference h² estimate (0.55), while the simultaneous adjust for age and weight leaded to a 0.50 h2 estimate. The
rg between AFC and adjusted scrotal circumference were negative and have medium magnitude, range from -0.28
to -0.34. Results showed that the conformation adjustment maybe an alternative, as the adjustment for age, and age
and weight, to use as selection criteria to identify sires for sexual precocity.
Keywords: conformation, heritability, musculature, post weaning age, post weaning weight, precocity
Introduction
Scrotal circumference is usually a selection criteria in beef cattle breeding programs, due to the ease of
measure, the magnitude of heritability coefficient and because it is genetically correlated to growth and
reproductive traits.
According to Ortiz Peña et al. (2000), scrotal circumference adjusted to age is useful in selection to growth
precocity, and the simultaneous adjustment to age and body weight identifies sires to sexual precocity. However, it
is notice that animals with the same weight, age and scrotal circumference can have different biotypes.
The age at first calving is the most used trait to evaluate reproductive efficiency in dams, because it is easily
measured and it is relate to the potential longevity of them (Azevêdo et al., 2006). Besides, the scrotal
circumference has genetic correlation with age at first calving, and animals with higher scrotal circumference has
progenies with younger age at first calving (Boligon et al., 2007), which is desirable.
Therefore, the aim of this study were to estimate heritability and genetic correlation to age at first calving
and scrotal circumference adjusted for age, age and weight, conformation, precocity, musculature in Nelore cattle.
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52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
Material e Methods
Data from 108,040 animals born between 1990 and 2009, belong to Aliança Nelore breeders group were
used. The statistical model considered contemporary group (CG) as fixed effect. The GC effect for sires was
composed by: farm, year and birth station, weaning and post weaning management group, weaning and post
weaning evaluation date. For dams the weaning variables were not considered in GC effect, totaling 3,927 and 779
groups, respectively. The linear and quadratic effect of age at post weaning (APW), weight adjusted to 500 days old
(W500), conformation (C), precocity (P), musculature (M) and age of dam (AD) were considered as covariates,
according the trait as dependent variable. For example, when the scrotal circumference was adjusted for age, the
age was not considered as covariate.
The post weaning weight was standardized to 500 days old (W500), using the formula:
𝑃𝑊𝑊 − 𝑊205
𝑊500 = (
) ∗ 295 + 𝑊205
𝑃𝑊𝐴 − 205
Which; PWW is post weaning weight, W205 is weaning weight adjusted to 205 days and PWA is post
weaning age.
The regression coefficients to PWA, W500, C, P and M were estimated using the GLM procedure of SAS
(SAS/STAT 9.3, 2011), using the models:
𝑆𝐶𝑎 = 𝛽0 + 𝐶𝐺1𝑖 + 𝛽1(𝐴𝑖𝑗 ) + 𝛽2(𝐴𝑖𝑗 )2 + 𝑒𝑖𝑗
𝑆𝐶𝑎𝑤 = 𝛽0 + 𝐶𝐺1𝑖 + 𝛽1(𝐴𝑊𝑖𝑗 ) + 𝛽2(𝐴𝑊𝑖𝑗 )2 + 𝑒𝑖𝑗
𝑆𝐶𝑐 = 𝛽0 + 𝐶𝐺1𝑖 + 𝛽1(𝐶𝑖𝑗 ) + 𝛽2(𝐶𝑖𝑗 )2 + 𝑒𝑖𝑗
𝑆𝐶𝑝 = 𝛽0 + 𝐶𝐺1𝑖 + 𝛽1(𝑃𝑖𝑗 ) + 𝛽2(𝑃𝑖𝑗 )2 + 𝑒𝑖𝑗
𝑆𝐶𝑚 = 𝛽0 + 𝐶𝐺1𝑖 + 𝛽1(𝑀𝑖𝑗 ) + 𝛽2(𝑀𝑖𝑗 )2 + 𝑒𝑖𝑗
Which: SCa, SCaw, SCc, SCp and SCm are the scrotal circumference (SC) observations adjusted to post
weaning age, post weaning age and weight, conformation, precocity and musculature, respectively; CG1i is the
effect of i-th contemporaty group of sires; β0, β1 and β2 are, respectively, the intercept and the linear and quadratic
regression coefficient of SC; Aij is the effect of age from the j-th animal belonging to the i-th CG; AWij is the
effect of age and weight from the j-th animal belonging to the i-th CG; Cij is the effect of conformation from the jth animal belonging to the i-th CG; Pij is the effect of precocity from the j-th animal belonging to the i-th CG; Mij
is the effect of musculature from the j-th animal belonging to the i-th CG; eij is the aleatory error associated to each
observation.
Results and Discussion
The Table 1 shows the estimatives of genetic parameters to age at first calving (AFC) and the scrotal
circumference adjusted to age (SCa), age and weight simultaneously (SCaw), conformation (SCc), precocity (SCp)
and musculature (SCm).
Table 1. Estimatives of (co)variance and genetic parameters of age at first calving (trait 1) and scrotal
circumference adjusted to growth traits (trait 2): post weaning age (SCa), post weaning age and weight
(SCaw), conformation (SCc), precocity (SCp) and musculature (SCm)
Age at first calving (AFC)
Parameter
SCa
SCaw
SCc
SCp
SCm
σ²a 1
1513,23
1498,07
1513,98
1517,71
1527,31
σ²a 2
3,32
2,60
3,48
3,28
3,44
σ²a 1, 2
-23,92
-21,26
-24,59
-19,53
-21,20
σ²e 1
5503,87
5514,70
5503,95
5508,55
5493,35
σ²e 2
3,12
2,65
2,84
3,09
3,11
h² 1
0,22 ± 0,02
0,21 ± 0,02
0,22 ± 0,02
0,22 ± 0,02
0,22 ± 0,02
h² 2
0,52 ± 0,02
0,50 ± 0,02
0,55 ± 0,02
0,52 ± 0,02
0,53 ± 0,02
rg
-0,34 ± 0,05
-0,34 ± 0,05
-0,34 ± 0,05
-0,28 ± 0,05
-0,29 ± 0,05
σ²a 1 = genetic variance to the trait 1; σ²a 2 = genetic variance to trait 2; σ²a 1, 2 = genetic covariance between traits
1 and 2; σ²e 1 = environmental variance to trait 1; σ²e 2 = environmental variance to trait 2; h² 1 = heritability to the
trait 1; h² 2 = heritability to trait 2; rg = genetic correlation between traits 1 and 2.
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52a Reunião Anual da Sociedade Brasileira de
Zootecnia
Zootecnia: Otimizando Recursos e Potencialidades
Belo Horizonte – MG, 19 a 23 de Julho de 2015
It is possible to observe that the heritabilities estimated to AFC were moderate (Table 1). Similar results
were related by Pereira et al. (2001) that justified the AFC heritability magnitude by the high dependency on age
that the dams were exposed to the sire.
Regardless of adjustment factor the heritabilities for scrotal circumference were high, indicating that all
traits enable selection response. These results differs in magnitude of the estimated values from Gressler et al.
(2000) and Boligon at al. (2007), 0.33 and 0.34, respectively, both with Nelore cattle.
The genetic correlation between AFC and the adjusted SC (Table 1) were negative and presented moderate
magnitude, similar to the values estimated by Pereira et al. (2001) and Boligon et al. (2001), -0.24 and -0.23,
respectively. The authors concluded that the SC measured at 18 months old could be a selection criterion for the
reduction of AFC.
Conclusion
Results showed that the conformation adjustment maybe an alternative, as the adjustment for age, and age
and weight, to use as selection criteria to identify sires for sexual precocity.
Acknowledgements
To Gensys Consultores Associados S/C Ltda. by the data concession and CNPq by scholarship.
Referencies
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Zootecnia, v.35, n.3, supl., p.982-987, 2006
BOLIGON, A. A., RORATO, P. R. N., ALBUQUERQUE, L. G. Correlações genéticas entre medidas de perímetro
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v.36, n.3, p.565-571, 2007.
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