Improving beef production in Brazil using selection and crossbreeding : a thesis presented in partial fulfillment of the requirements for the degree of Master of Applied Science in Animal Science at Massey University, Palmerston North, New Zealand
Beef industry is an important sector of the Brazilian economy. Brazilian beef production is very dependent on pasture, which, in all most its totality, is constituted by tropical forages characterized by abundance during the rain season and low quality and quantity during the dry season. Therefore, efficient beef production systems would include breeding adapted genotypes rather than attemptig large changes in the environment. As a result, animal breeding becomes a very important agent within beef production. This project intended to investigate throughout computer modeling the effects of different breeding schemes applied to a hierarchical integrate beef production system, involving a three straight bred herds nucleus and a three-breed terminal crossing commercial herd. The study simulated a tropical system of production based on common Brazilian management practices and parameters published in the literature related to beef production on tropical and subtropical climates. A deterministic procedure was applied to develop a model for a hierarchical integrated beef production system involving a crossbred commercial herd and three straight-bred nucleus herds and it was developed on an annual basis using a Microsoft Excel spreadsheet. Economic selection index methodology was applied to develop different selection indexes. The model was used first to estimate economic values for biological traits affecting returns and costs. A breeding objective was established based on economic values of traits that would significantly affect profitability of the production system. Basically there were two different scenarios that were tested. One scenario investigated the results of 20 years of selection taking in account the use of progeny tested bulls while the other scenario would investigated the outcomes of selection based only on individual selection of the bulls. Subsequently, the model was used to investigate which economic values would maximize profit per animal unit. The two selection indexes that included information of progeny into the selection criteria were the best ones when compared to the selection indexes using individual selection independently of the relative economic values applied. The maximizing profit AU relative economic value selection index presented the best improvement in profit per AU, which was also followed by a higher profit per hectare and return rates. Economic selection index proved to be an efficient tool to change profit since breeding schemes improved profit in all scenarios independent from the relative economic value applied or if information from progeny was included or not in the index. The adoption of progeny testing in breeding programs proved to be more effective than individual selection on a long-term basis. The advantage of selection indexes including progeny was to promote a greater increase in dressing out percentage and a lower change on mature size of the breeding cows.