Estimativa de parâmetros genéticos da habilidade de permanência aos 48, 60 e 72 meses de idade em vacas da raça Caracu

Abstract

RESUMO -Objetivou-se estimar a herdabilidade da característica habilidade de permanência (HP) em um rebanho de bovinos da raça Caracu visando sua utilização como critério de seleção. A característica em estudo foi definida como a probabilidade de a vaca estar presente no rebanho aos 48 (HP48), aos 60 (HP60) e aos 72 (HP72) meses, desde que possuíssem registros de pelo menos duas lactações nas específicas idades. Observações binárias, com zero (0 = fracasso) e um (1 = sucesso) foram designadas aos animais. Para análise da HP, foram utilizados dados de 5.487, 4.947 e 4.308 animais aos 48, 60 e 72 meses, respectivamente. Os componentes de variância e as herdabilidades foram estimados mediante inferência Bayesiana, via amostragem de Gibbs, pelo programa MTGSAM -threshold, utilizando-se um modelo touro. Foram utilizadas como variáveis explanatórias grupo de contemporâneos, classe de produção de leite na primeira lactação, classe de idade ao primeiro parto e sua interação. As análises forneceram estimativas médias de herdabilidade iguais a 0,28 ± 0,07 para HP48, 0,27 ± 0,07 para HP60 e 0,23 ± 0,07 para HP72. Os resultados evidenciaram que a característica HP apresentou variação aditiva em todas as idades estudadas e, portanto, pode ser empregada como critério de seleção para longevidade produtiva. Palavras-chave: característica de limiar, dupla-aptidão, longevidade Estimation of genetic parameters of stayability in Caracu cattleABSTRACT -The aim of this study was to estimate the heritability of stayability (HP) in Caracu cattle in order to evaluate its usage as a selection criterion for longevity. Stayability was defined as the probability of a cow to be producing in the herd at the ages of 48 (HP48), 60 (HP60) and 72 (HP72) months. Binary observations indicating failure (zero) or success (one) were assigned to records on 5487, 4947 and 4308 cows with at least two lactations at the ages of 48, 60 and 72 months, respectively. Variance components and heritability for HP48, HP60 and HP72 were estimated using a sire model including the fixed effects of contemporary group, classes of milk yield at first calving, classes of age at first calving and the interaction between milk yield and age at first calving classes by Gibbs sampling with the MTGSAM for threshold program. Average heritability estimates for HP48, HP60 and HP72 were 0.28 ± 0.07, 0.27 ± 0.07 and 0.23 ± 0.07 respectively. These results indicate that HP can be used as selection criterion for longevity in Caracu cattle.

Analysis of culling probability in dairy buffalo using survival models

“…Therefore, culling can be used to penalize less productive females. Queiroz et al (2007) studying Caracu cattle, reported higher frequencies of success for ST in cows with higher first-lactation milk yields, in agreement with this study.…”

“…Studying Charolaise cows, Phocas and Ducrocq (2006) observed that 49.3% of the right-censored records remained until 48 months of age and 33.8% remained until 96 months. Queiroz et al (2007), studying ST in a Caracu herd, reported that 60% of the cows remained until 48 months of age, 52% until 60 months, and 55% of the herd had been culled at 72 months of age. We found no studies reporting mean ST values for buffaloes.…”

“…In a study involving a Holstein herd, Pü ski et al (2002) concluded that that there is a negative correlation between milk production and ST. However, Queiroz et al (2007) observed higher frequencies of success for ST in cows with higher first-lactation milk yields. For Murrah buffaloes reared in Bulgaria, Peeva and Ilieva (2007) showed that low milk yield is the second cause of culling, after reproductive problems.…”

Genetic Association Between Herd Survival and Linear Type Traits in Holstein Cows Under Tropical Conditions

“…Studies with other breeds in Brazil also reported higher values than those of the present study. Queiroz et al (2007) reported average value of 0.27 and 0.23 in Genetic association survival-type traits Caracu cattle for Long1_60 and Long1_72, respectively. In Sweden, Ahlman et al (2011), also using a threshold model in Holstein cows, obtained a low posterior heritability for the ability to remain in the herd to the first (0.05) and second lactation (0.08), and a moderate value to remain until the third lactation (0.20).…”

“…Only 34.77 and 28.32% of the cows survived until 48 to 54 months from the first calving, respectively. According to Queiroz et al (2007), this decrease in survival rate demonstrates the difficulties found by farmers for maintaining cows with good productive and reproductive performance over time.…”