Correlated responses in performance test traits were estimated for populations of Large White (LW) and British 
Landrace (LR) pigs to four generations of divergent selection for lean growth rate (LGA), lean food conversion 
(LFC) and daily food intake (DFI) with ad-libitum feeding. Totals of 3537 LW and 2642 LR pigs were 
performance tested in Edinburgh and Wye, respectively. Selection for lean growth rate, in LW and LR pigs, 
increased growth rate (54 and 101 g/day), but reduced backfat (-3.9 and -2.0 mm), food conversion ratio (
0.23 and -0.25) and total food intake (-11.8 and -12.6 kg). There was no change in daily food intake in LW pigs 
(-19 g/day), but daily food intake increased in the LR pigs (69 g/day). With selection for lean food conversion 
in LW and LR pigs, there was no response in growth rate (9 and 9 g/day), but backfat (-4.1 and -2.1 mm), total (- 
6.6 and -11.8 kg) and daily food intake (-90 and -172 g) were reduced, as animals had tower food conversion 
ratios (-0.13 and -0.22). LW and LR pigs selected for daily food intake ate more food in total (6.8 and 5.9 kg) 
and on a daily basis (314 and 230 g), grew faster (94 and 51 g/day) and had higher food conversion ratios 
(0.12 and 0.13). Backfat was increased in LW pigs (3.7 mm), but not in LR pigs.
In general, efficiency of lean growth was improved by increasing growth rate, with negligible change in daily 
food intake given selection for lean growth rate, but was primarily due to reduced daily food intake given 
selection on lean food conversion.

N. D Cameron, M. K Curran

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 19. Selection and quantitative genetics; growth; reproduction; lactation; fish; fiber; meat., , 83–86, 1994
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