Backtest
Piglets born in the November seasons of 2008 and 2009
as well as piglets born in the July 2008 season were
evaluated using a standard backtest as described
(Hessing et al., 1993). Piglets were evaluated once 2 d after
weaning, at approximately 24 d of age before actual
transfer to the nursery. The backtest was performed on
2–6 piglets within a litter selected to represent the
complete range of day 1 activity scores within each litter.
Approximately equal numbers of gilts and barrows were
phenotyped within each litter and use of cross-fostered
piglets was avoided. A similar number of piglets were
phenotyped for each sire used in that breeding season.
Twelve sires were represented in the January 2008 season.
A different set of 12 sires produced the next two groups of
pigs (July 2008 and January 2009).
Piglets were placed on their backs and the testing
began immediately after the animal became calm. The test
lasted for 60 s, or until the animal became calm if they
were actively struggling at the end of the 60 s test. All
animals were evaluated by the same observer for the
entire study. Traits analyzed were time until the initial
struggle or latency time (LT), number of struggle events
(#S) and total time spent struggling (ST)