The use of selection to improve sow longevity
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The objective of this dissertation was to evaluate multiple approaches to incorporating sow longevity or lifetime sow productivity into a selection program. Sow longevity can be selected for using indicator traits, such as structural soundness and lameness. In the first study, objective measurements to detect sow lameness were examined. Lameness was chemically induced for a short time period in multiparous sows and their weight distribution and walking gait were objectively measured in the days following lameness induction. Using a classification tree analysis, it was determined that the mean weight being placed on each leg was the most predictive measurement when determining whether the leg was sound or lame after injection. The weight distribution measures had a greater predictive ability compared to the walking gait indicators. These measures could be used to select sows that are less likely to become lame and be removed from the breeding herd. While reducing the lameness instances in a herd would improve sow longevity, direct selection for longevity would be desirable. In the second study, genetic correlations between purebred and crossbred sow longevity were estimated. Most genetic improvement programs are based on an assumed relationship between purebred performance in a nucleus herd and their relatives' crossbred performance in a commercial herd; however, this study found that there was little to no genetic correlation between purebred and crossbred sow longevity for this population. While longevity is heritable at both the nucleus and commercial levels, results from this study indicate that little improvement would be made in crossbred longevity if selection relies solely on purebred information. One way to select for sow longevity would be to estimate purebred genomic breeding values using records from a related crossbred population. A spreadsheet for estimating the total costs associated with incorporating genome-enabled selection into a swine breeding program was developed as the final part of this dissertation. This tool will aid producers in estimating the economic viability of incorporating genome-enabled selection into their specific breeding program. Based on the results from these projects, it is recommended that a commercial test herd be implemented as part of a selection program to improve longevity or sow productive lifetime. If a genetic company can succeed in improving sow longevity through an effective breeding program, production efficiency and profitability can be improved for commercial swine operations.