Use of serial pig body weights for genetic evaluation of daily gain

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Abstract
This study examined the utility of serial weights from FIRE (Feed Intake Recording Equipment, Osborne Industries, Inc., Osborne, KS, USA) stations for an analysis of daily gain. Data included 884 132 body weight records from 3888 purebred Duroc pigs. Pigs entered the feeder station at age 77-149 days and left at age 95-184 days. A substantial number of records were abnormal, showing body weight close to 0 or up to twice the average weight. Plots of body weights for some animals indicated two parallel growth curves. Initial editing used a robust regression, which was a two-step procedure. In the first step, a quadratic growth curve was estimated assuming small or 0 weights for points far away from the curve; the process is iterative. In the second step, weights more than 1.5 SD from the estimated growth curve were treated as outliers. The retained body weight records (607,597) were averaged to create average daily weight (170,443) and then used to calculate daily gains (152,636). Additional editing steps included retaining only animals with >or=50 body weight records and SD of the daily gain <or=2 kg, followed by removing records outside 3 SD from the mean for given age, across all the animals - the resulting data set included 69,068 records of daily gain from 1921 animals. Daily gain based on daily, weekly and bi-weekly intervals was analysed using repeatability models. Heritability estimates were 0.04, 6 and 9%, respectively. The last two estimates correspond to heritability of 28% for a 12 week interval. For daily gain averaged weekly, the estimate of heritability obtained with a random regression model varied from 0.07 to 0.10. After extensive editing, body weight records from automatic feeding stations are useful for genetic analyses of daily gain from weekly or bi-weekly but not daily intervals.

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