Sustainability Implications of Alternative Feedlot Management Practices and On-ranch Genetic Evaluations in Beef Cattle.

摘要

The demand on agriculture to produce healthy and wholesome products will increase along with the growing world population. The social movement towards sustainability has also applied pressure on agriculture to produce food in a manner that is more efficient, better for the environment, and satisfies societal needs. Sustainability in agriculture has broad goals (USDA, 2007), and encompasses three main aspects: environmental wellbeing, economic sufficiency, and human social needs. However, it is difficult to satisfy all three aspects of sustainability due to the conflicting nature of those aspects (Heitschmidt et al., 1996). Alternative production practices (e.g., natural and organic) have been proposed as a more sustainable option to conventional practices. Often these alternative practices rely less heavily on modern technological inputs and rely more on "natural" inputs (e.g., integrated pest management instead of chemical pesticides, manure application in place of synthetic fertilizer). Technologies such as metabolic modifiers offer efficiency enhancement in beef production (Preston, 1999) and DNA-based technology offers an opportunity to improve the accuracy of genetic evaluations and response to selection (Pollak, 2005).;Increasing attention is being given to the environmental implications of animal agriculture, especially as they relate to greenhouse gas ( GHG) emissions. Carbon dioxide, methane, and nitrous oxide are the GHG of great importance to global warming, with the latter two being most relevant in animal agriculture. Animal calorimetry and digestive modeling offer methods to measure and predict GHG emissions, respectively (Kebreab et al., 2006).;Conventional feedlot management systems often utilize metabolic modifiers (growth promoting implants, beta-adrenergic agonists, and ionophores) to improve efficiency and profits. In contrast, Never Ever 3 is a feedlot management system where cattle never receive growth promotants, antibiotics, or animal fed by-products and as such is representative of a "natural" production system. System-based research is needed to determine the contributions of conventional and alternative systems to the goals of sustainability.;Genetic evaluations have allowed for the genetic improvement of beef cattle through increased accuracy of selection and response to selection. Expected progeny differences (EPD) are the expected performance values of an offspring based on performance records and pedigree expressed as a deviation from the population mean (Bourdon, 2000). Goals of genetic evaluation and the use of EPDs include selection of high performance animals for economically-relevant traits with the objective of ultimately improving the profitability of beef operations (Enns and Garrick, 2003). Breed associations are responsible for the production of these EPDs. The American Angus Association (AAA) is the association that generates EPDs for the Angus breed. While breed association EPDs offer great benefits towards genetic improvement, they do not take into account the environmental effects associated with a specific ranch. According to Pollak (2005) breed association EPDs may not translate perfectly to use on the commercial ranch due to the fact that the data used for EPD generation is often collected at the purebred level and the fact that few carcass data are collected. Therefore commercial producers may benefit from the production of ranch-specific EPDs. Paternity determination based on DNA marker technology has enabled pedigree determination and thus generation of EPDs when multiple-sire breeding pastures are used, which is often the case in commercial operations. On-ranch EPDs offer benefits including sire evaluation based on performance specific to that ranch and evaluation of traits not included in breed association evaluations. Therefore comparison of the performance of AAA EPDs to on-ranch EPDs is needed to evaluate the benefits associated with the generation of the ranch specific evaluations.