Tendência genética para pesos padronizados aos 205, 365 e 550 dias de idade de bovinos Nelore da região norte do Brasil

Abstract

Pesquisas efetivas que avaliam a eficiência dos rebanhos bovinos na região Norte do Brasil são insipientes. Por isso, objetivou-se avaliar as mudanças genéticas aditivas diretas e maternais dos pesos padronizados para 205 (P205), 365 (P365) e 550 (P550) dias de idade, de animais da raça Nelore, criados a pasto, nascidos entre 1997 e 2007 na região Norte do Brasil. As estimativas dos componentes de (co)variâncias utilizadas no cálculo dos valores genéticos foram obtidas pelo método de máxima verossimilhança restrita livre de derivadas (REML), usando o aplicativo MTDFREML. As tendências genéticas dos efeitos genéticos direto e maternal foram estimadas pela regressão, ponderada, das médias anuais dos valores genéticos dos animais. As estimativas das herdabilidade para P205, P365 e P550 foram 0,33; 0,51 e 0,41, com ganhos genéticos de 0,494, 1,229 e 1,500 kg ano-1 , respectivamente. Em virtude da variação genética existente, verificou-se que a seleção do rebanho na região Norte do Brasil tem enfatizado principalmente a seleção para peso pós-desmama, ressaltando-se que a seleção para estes pesos pode gerar ao longo dos anos, aumento nos custos de produção, da idade ao abate e acabamento dos animais, havendo assim, necessidade de seleção mais criteriosa para estas características. Palavras-chave: (co)variância, ganho genético, herdabilidade, zebu. Genetic trend for adjusted weight at 205, 365 and 550 days of age of Nellore cattle from Northern Brazil ABSTRACT. Effective researches assessing the efficiency of cattle herds in Northern Brazil are incipient. This study aimed to evaluate the direct additive and maternal genetic trends of weights adjusted to 205 (P205), 365 (P365) and 550 (550) days of age in Nellore animals raised on pasture, born between 1997 and 2007, from Northern Brazil. Estimative of (co)variance components used in the prediction of breeding values were obtained by derivative-free restricted maximum likelihood method (REML) using the MTDFREML program. The genetic trends of direct and maternal genetic effects were obtained by the regression of the annual average of predicted breeding values. The heritability estimates for P205, P365 and P550 were 0.33, 0.51 and 0.41, with genetic gain of 0.494, 1.229 and 1.500 kg year-1 , respectively. The genetic variance evidenced that the selection of cattle herds from Northern Brazil has mainly emphasized the selection for post-weaning. Along years, this selection for these weights can generate increase in production costs, of age at slaughter, and dressing of these animals. Therefore, there are need more judicious selection for these characteristics.

Genetic parameters of growth traits in Nellore cattle

“…Average birth weights ranged from 29.5 kg to 32.8 kg in previous reports (HOLANDA et al, 2004;MENEZES et al, 2013;ARAÚJO et al, 2014), for Nellore herds in Midwestern and Northeastern Brazil, compared to 37.6 kg in this study. The same was true for the adjusted 120-day weight 138.4 kg, compared to 119.1-129.0 kg in GARNERO et al, 2010;SOUZA et al, 2011), for the adjusted 205-day weight compare Table 1 to SANTOS et al, 2012;AMARAL et al, 2014;ARAÚJO et al, 2014), and for adjusted 365-day and 550-day weights, compare Table 1 with the study by (RIBEIRO et al, 2001;GARNERO et al, 2010).The high birth weight measured in this study might result from the selection criteria adopted for the analysis, which included birth weight in the calculations of adjusted weights at weaning. In addition, the higher 365-day and 550-day weights observed here could be due to the intense selection for weight traits practiced at the ranch, which included periodic culling of animals not meeting performance expectations.…”

“…On the other hand, the weaning weight at 205 days of age is an important trait in selection programs, because it is an estimate of the milking and mothering abilities of the dam and the growth potential of the calf (MALHADO et al, 2005). In addition, weaning weight is important in production system because preweaning gains have lower costs than postweaning gains (SANTOS et al, 2012). All calf weight traits measured had considerable direct additive genetic variability (Table 2), and thus can be used in breeding programs for selection for birth weight.…”

Genetic study of skin thickness and its association with postweaning growth in Nellore cattle: estimation of the genetic parameters

“…Generally, the non-genetic factors that affect postweaning weight gain are related to the calf sex, year, and season of birth (Silva et al, 2004) and herd and feeding regimen (Santos et al, 2012), as well as, good nutritional management and health of the herd. Considering the environmental correlation between ST and PWG550, the non-additive factors that influence PWG550 should not affect ST, suggesting that the differences in ST between animals may not be affected during the postweaning period.…”

Bayesian estimates of genetic parameters for reproductive traits in Nellore cows raised on pasture in tropical regions

“…Gunawan et al (2011b) considered that this might be partly a correlated response to selection for increased daily gain. A possible cause of the undesirable trend in gestation length and of the marked fluctuation of values observed for AFC, CI, and DO could be the intense selection to increase productive traits (Lopes et al, 2011;Santos et al, 2012;Lopes et al, 2013), without giving attention to reproductive traits.…”