Objetivos de seleção para sistemas de produção de gado de corte em pasto: ponderadores econômicos

Abstract

RESUMOForam desenvolvidos objetivos de seleção para gado de corte criado nas condições de produção típicas do Brasil Central. As características consideradas foram: número de bezerros desmamados por vaca/ano (NBD), peso da carcaça (PC), peso à desmama (PD) e consumo de alimento. Foram adotados dois sistemas de produção, um que considerava somente a cria e outro, o ciclo completo (cria, recria e engorda). No primeiro, as receitas foram a venda de bezerros à desmama, novilhas excedentes e vacas de descarte. No segundo, a receita foi a venda das novilhas excedentes, vacas de descarte e novilhos para o abate. Em ambas as situações, o lucro (USD/vaca/ano) foi estimado pela diferença entre receita e despesa. Os valores econômicos estimados foram expressos em dólar por unidade de mudança na característica, calculados na base vaca/ano. O valor econômico foi calculado avaliando-se a alteração ocorrida no lucro quando a característica era incrementada de uma unidade, permanecendo as demais inalteradas. A característica que apresentou maior valor bruto do ponderador econômico foi o NBD, seguida pelo consumo, PC e PD. Quando se considerou o valor econômico, em unidades de desvio-padrão genético-aditivo, a ordem de importância foi consumo, PC, NBD e PD.Palavras-chave: bovino de corte, objetivo de seleção, ponderador econômico ABSTRACT Breeding objectives were developed for beef cattle production under typical economic and environmental conditions of central Brazil. The traits considered were: calves weaned per cow/year (NCW), weaning weight (WW), carcass weight (CW) and food intake. In the study, two systems were examined, a cowcalf system (surplus calves sold after weaning) and a cow-calf enterprise (in which surplus calves are raised for slaughter). In the first, income is from the sale of male calves and surplus heifers after weaning and of culled cows. In the second, the income is from the sale of steers, surplus heifers and culled cows. For both situations, the profit (US$/cow/year) was estimated by the difference between revenue and costs. The economical values (EV) were calculated as the change in profit resulting from a unit change in each trait, as other traits remained unchanged. The trait with greatest economic value was NCW, followed by food intake, CW and WW. The order of importance when values were in additive genetic standard deviation units were feed intake, CW, NCW and WW.

Breeding objectives for a Nellore cattle rearing system

“…Bittencourt et al (2006) The economic weight of CP in the second scenario was the second largest in terms of absolute EV. Consequently, when comparing the two proposed scenarios, the selection gain is enhanced using CP and it also provides higher revenue than the direct selection based on WW.…”

“…This was done because, although the female calves are not sold at weaning, the production costs for this category should still be computed, as they represent a portion of the cost of the system up to that age. (1) Weaning rate, adult mortality rate, and carcass yield according to Oliveira et al (2006); replacement rate according to Bittencourt et al (2006); and mean weight at weaning, weight of adult cows, mean weight of yearling heifers, and mean cumulative productivity according to Associação Nacional de Criadores e Pesquisadores (2014) and to Anualpec (Estatísticas, 2008(Estatísticas, , 2009(Estatísticas, , 2010(Estatísticas, , 2011(Estatísticas, , 2012. Two scenarios were evaluated in the simulated rearing system, considering that the breeding objectives were to increase the fertility of the herd and to increase the selling weight of the animals.…”

“…Alternative production scenarios were considered in the sensitivity analysis, and the effects of variations in the cost and revenue component prices on the EVs were evaluated as in Bittencourt et al (2006): sale price of beef, 20% increase or decrease; price per kilogram of dry matter forage, 20, 30, and 50% increase or decrease; and dry matter consumption, 20% increase or decrease.…”

“…The definition of selection objectives for a combination of economically important traits should be the first step in implementing a breeding program (Bittencourt et al, 2006;Laske et al, 2012;Pravia et al, 2014). After defining these objectives, the traits that will constitute the selection criteria must be chosen and subjected to genetic evaluations (Áby et al, 2012;Pravia et al, 2014).…”

“…Despite the increasing concerns on the economic efficiency of production systems, few studies have been conducted to evaluate the importance of breeding objectives for different breeding programs of Nellore herds in Brazil, similar to those developed by Bittencourt et al (2006) andJorge Júnior et al (2007), which could assist in improving the financial performance of various farms. Moreover, new traits are constantly being sought for inclusion in breeding programs, and multifactorial traits such as the cumulative productivity of dams, proposed by Schwengber et al (2001), have not yet been assessed as to their economic values for breeding systems.…”