Abstract
The objectives of this study were to define breeding objectives and derive economic weights for production traits in family-based beef cattle systems, assess the sensitivity of these weights to changes in market and husbandry indicators and estimate the expected genetic changes in the selection criteria proposed. Based on data from the production systems, farms revenues and expenses, obtained from interviews and meetings with producers, a bioeconomic model was derived, relating biological traits of animals with the financial result of the production system based on calf-crop, selling male calves and culling cows for finishing. Traits considered in the model as breeding goals were weaning rate, weaning weight and cow weight. The economic weights, obtained by the partial derivative of the bioeconomic model with respect to the trait in question, assessed on the average value of the remaining traits, were R$ 73.21% for weaning rate, R$ 17.07/kg for weaning weight and R$ 4.75/kg for cow weight. An index for joint selection of these three criteria would allocate 89.5% of importance to weaning rate, 6.9% for weaning weight and 3.6% for cow weight. In this way, for every R$ 100.00 of genetic gain in this index, there would be an increase of 1.4% in weaning rate, but with reduction of 0.004 kg in weaning weight and 0.665 kg in cow weight due to negative genetic association between these traits. The proposed index and the relative importance identified for the economic traits can guide the selection decisions of smallholders, both in the choice of their animals and in the acquisition of bulls, cumulatively increasing the productivity of their herds.
Highlights
Animal improvement aims to increase the frequency of favorable gene combinations in economically important traits for a given production system and, thereby, increase profitability, which is determined in part by the emphasis given on each trait included in the breeding objectives (Smith, 1983).The definition of breeding objectives must be the first step in the outset of a genetic improvement program (Urioste et al, 1998; Smith, 1985; Ponzoni, 1986; Fewson, 1993), and traits considered in the breeding objective are the basis for the formulation of a profit function from which economic values are derived (Vercesi Filho, 1998)
The economic importance of biological traits to be included in a breeding objective is assessed by their economic weights, defined as the expected increase in herd annual profit resulting from a unit increase in a trait due to selection (Jorge Júnior et al, 2007)
The largest gains for these low input beef cattle systems can be obtained by selection for weaning rate, followed by weaning weight and by the cow weight
Summary
Animal improvement aims to increase the frequency of favorable gene combinations in economically important traits for a given production system and, thereby, increase profitability, which is determined in part by the emphasis given on each trait included in the breeding objectives (Smith, 1983). The definition of breeding objectives must be the first step in the outset of a genetic improvement program (Urioste et al, 1998; Smith, 1985; Ponzoni, 1986; Fewson, 1993), and traits considered in the breeding objective are the basis for the formulation of a profit function from which economic values are derived (Vercesi Filho, 1998). The genetic improvement of low input cattle from smallholders must be treated differently from traditional elite seedstock breeding programs, considering, besides environmental production system and market aspects, their cultural way of life and production (Laske et al, 2009). Fertility, weaning weight and adaptation have been recognized as the most important traits for these systems (Laske et al, 2009)
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