Meyer, Paulo H. Brazil is the world's largest beef exporter with the world's largest commercial cattle herd; however, the production cycle needs to be more efficient to supply internal and external demands in the future. Feedlot operations are currently a reality for the Brazilian beef cattle industry; nonetheless the beef cattle industry in Brazil is still based on grass-fed animals in which the Nellore breed predominates. Brazilian packing plants regulate the use of antibiotics, especially ionophores used as growth promoters, on farms certified to export beef to European countries. In addition, the use of any implant or beta-agonist for cattle is forbidden in Brazil.
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E-mail: caiovictor3 gmail. The objective of this work was to define the traits that should be included as breeding objectives for Nellore cattle, according to simulations with a bio-economic model for rearing systems. To determine the impact of each selection on the revenue system, two scenarios were simulated based on the traits being selected.
In the second scenario, the cumulative productivity CP of dams was used as an indirect evaluation of the performance of calves, with all the other traits included, except WW. The meat price paid to the producer is the factor with the greatest impact on the EVs of all examined traits. The basic premise of any industry is the generation of efficient, productive results that lead to maximized economic returns.
Increased efficiency in raising beef cattle in Brazil is likely to be achieved by improving the genetic quality of livestock through selection Brumatti et al. 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.
In a beef cattle production system, several traits affect the economic and productive performance of the herd as a whole.
The traits with most impact in rearing production systems can be separated into two groups: reproductive and growth. According to Formigoni et al. 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.
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.
In order to specify the rearing production and marketing system, a deterministic model for herd simulations was used, which described an extensive rearing system typical of the central region of Brazil, i. The adopted stocking rates were 2. It was assumed that the animals consumed 2. As to the specifications of the reproductive system, the simulated commercial herd was considered to have a fixed number of 1, dams in reproduction age until the sixth parturition , including month-old heifers Figure 1.
The age distribution and the specification of the number of members in the herd, as well as of the number of animals needed for replacement and of the number of animals available for sale, were all used for EV calculations. For simulation purposes, all male calves under one year of age were sold after weaning, and the females remained on the property until they reached an average age of days. Surplus heifers were then marketed, considering the same carcass yield applied to cows.
The biological parameters used for the herd simulation are shown in Table 1. Therefore, the economic data covered 5 years, which correspond to a period of change in the Brazilian and global economic environments, including changes in the values of the components involved in the production costs and in the prices passed on to the producer Hall et al. The total costs of ownership consisted of sanitary control medications and vaccines , mineral supplementation, training, and pasture maintenance.
Revenues were derived from the sales of calves after weaning, of surplus heifers after the breeding season, and of cows removed from the production system. The identification of the sources of revenue and expenses is necessary to subsequently assemble the profit equations of the proposed model. Information on the cost and revenue components used for the simulation, as well as the compilation of the total costs by animal category in the herd, is shown in Table 2.
The primary objective of the rearing system is to produce and sell weaned calves, intended for fattening and meat production. Therefore, their weaning weight is very important economically. Besides that, the estimation of the EV of a multifunctional trait, in this case of the cumulative productivity of dams CP Schwengber et al. The CP was proposed by Schwengber et al.
Therefore, CP constitutes a complete and suitable selection criterion for use in herd breeding, since it includes both productive and reproductive traits. The weaning rate is another trait directly linked to the production of calves that was evaluated. Therefore, the EVs were assessed for the breeding weight at a designated age of heifers, standardized to days of age, and for the adult weight of cows.
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. 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.
In the first scenario, the selection criteria included WW, YW, MCW, and WR, which were represented in the total profit equation P total by including the fraction of profit attributed to P calf1 , explained by an increase in the criterion when selecting for WW. In the second scenario, the CP was used as an estimate of the production kg of calves in relation to the production of dams, but YW, mature cow weight MCW , and WR were also assessed.
The influences of these criteria on the total profit equation P total were estimated with the fraction of profit attributed to P calf2 , which represents this contribution to the system's profits associated with improvements achieved from selecting for CP.
The bio-economic model used Microsoft Excel spreadsheets for calculating the productive performance, costs, and revenues of the traits included in the selection criteria.
Because the traits are expressed in different units, Hietala et al. The relative importance, or marginal EV, was standardized by multiplying the EV by the additive genetic standard deviation obtained in the literature for Nellore cattle in Brazil: 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.
The positive impact of WR on the economic returns of production systems has also been pointed out by Laske et al. The EV reported by Laske et al. Although the estimates of the relative importance of WR were lower for both scenarios Table 3 , they had the largest values found for the considered system, followed by YW, also in both scenarios. The higher value attributed to WR was probably due to the greater number of calves produced with its increased performance, i.
The EV of WW, as well as its relative importance, was the lowest among the assessed selection criteria, in the first scenario. Bittencourt et al. The values obtained in the present study are consistent with the EVs reported in the literature, in which WW contributes positively to the profits of the herd, but with a low economic weight.
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.
Therefore, as the estimation of CP encompasses other traits, its effectiveness in indirectly selecting for calf weights and for reproductive performance of dams is significant.
Significant economic importance in production systems has been attributed to WR and CP reproductive traits, as observed in the present study. Pravia et al. As for the economic importance of YW and MCW, their EVs had positive contributions to the studied systems, with a relatively similar level of importance in both scenarios. Brumatti et al.
These values, as well as those calculated here, indicate positive contributions to the economic returns of the studied systems. The difference between the estimated EV of MCW in the present study and those reported in the literature may be attributed to differences in the number of dams in the systems. In the other studies, MCW was found to be a trait of minor importance, which differs from the results obtained here.
This difference may be due to the cow value in the market during the evaluated years, given that the increase in adult weight was of no economic interest because excessively large animals have an increased demand for food, raising production costs. The value of the pastures varied over the years because of the increased costs of forming and maintaining them. This variable, however, did not have a large impact on the production system costs, since the dry matter DM production is relatively high, approximately This value is consistent with those obtained by Bittencourt et al.
These conflicting results may be attributed to the costs of forming and maintaining pastures in the different years and regions, as well as to the mean productivity of the forage species evaluated in each study. These results may also be explained by the low value per kg of pasture, which ultimately does not increase production costs even in situations with significantly increased forage consumption.
Although they did not change the EVs of the traits, variations in the pasture costs are expected to exert some influence on the economic weight in contrasting production situations, such as with prolonged drought, which may affect the productivity and quality of pastures, or with increased input price for forming and maintaining the pastures.
The weaning rate has the greatest economic impact on the Nellore cattle rearing production system, followed in relative importance by the yearling weight and the mature cow weight. The cumulative productivity of damns should be considered as a selection criterion for beef cattle breeding programs.
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Journal of Dairy Science, v. Breeding objectives and economic values for traits of low input family-based beef cattle production system in the State of Rio Grande do Sul. Washington: National Academy Press, Developing breeding objectives for Australian beef cattle production. Animal Production, v. Identification of breeding objectives using a bioeconomic model for a beef cattle production system in Uruguay.
Breeding objectives for pasture-fed Uruguayan beef cattle. Journal of Animal Breeding and Genetics, v. Strategies for defining traits when calculating economic values for livestock breeding: a review. Animal, v. This is an open-access article distributed under the terms of the Creative Commons Attribution License. Services on Demand Journal.
Abstract: The objective of this work was to define the traits that should be included as breeding objectives for Nellore cattle, according to simulations with a bio-economic model for rearing systems. Introduction The basic premise of any industry is the generation of efficient, productive results that lead to maximized economic returns. Conclusions The weaning rate has the greatest economic impact on the Nellore cattle rearing production system, followed in relative importance by the yearling weight and the mature cow weight.
Progress in the Brazilian cattle industry: an analysis of the Agricultural Censuses database
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