Caracterização da pecuária familiar e objetivos e critérios para o melhoramento genético do rebanho bovino de corte

Abstract

In the Rio Grande do Sul State extensive beef cattle ranching has major economic, social and cultural. Family based smallholds derived from ranch division by inheritance or by acquisition of small areas, being the main source of income for a large portion of the small ranchers of this region. The objectives of this study were: 1) to characterize the production systems of family based smallholds in the southern half of the state of Rio Grande do Sul, and 2) to derive breeding objetives and selection criteria for genetic improvement of their beef cattle herds. The study was conducted in three locations: the Cerro da Jaguatirica in Manoel Viana, located in a region of sandstone soil type Santa Barbinha in the city of Caçapava do Sul, and Palmas in Bage, both on basaltic soils. The survey involved interviews using a semistructured questionnaire in 30 production units, covering a total of 110 people, and participatory meetings of researcher of Embrapa Pecuária Sul e Emater/RS and producers. This survey focused on social characteristics and the production system, comprising a set of essential information for understanding the production and survival logics of these families. The family are relatively small, with two to six members, where most people have a low education level, having only finished elementary school. The properties have basic infrastructure including homes with electricity and running water, barns and pens. The production systems are strictly based on extensive livestock (cattle and sheep), and the sale of calves and culling cows as the main income. The properties have on average 90 hectares of total surface, showing a wide range on properties’ areas (minimum 10 ha, maximum 290 ha), and herd around 59 animals, mostly females, with a weaning rate of 47%. The pasture is the predominantly native and cultivated pastures, where they exist, are basically oat and ryegrass during winter sown on native or small areas of summer crop residue fields. From the data collected a bio-economic model has been developed linking the biological traits of animals with the financial result of the production system, based on cow-calf operation, sale of male calves and culling. In this model, traits that affect the economic results are weaning weight (WW), weaning rate (WR) and mature weight of dam (CW), which could be measured at ranch level and adopted as selection criteria. The economic weights for these selection criteria, obtained by the partial derivative of the bio-economic model with respect to the trait in question, assessed on the average of other criteria, were R$ 73.21 to WR, R$ 17.07 for WW and R$ 4.75 for CW. An index to the joint selection of these three criteria would allocate 89% of importance to WR, 7% for WW and 4% for CW. This relative importance was little sensitive to changes in market and herd performance indicators, demonstrating that despite the low heritability, WR is the trait that should receive greater emphasis in the genetic improvement in order to increase the profitability of cow-calf systems of family based smallholds.