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Responses in gilt post-farrowing traits and pre-weaning piglet growth to divergent selection for components of efficient lean growth rate
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Responses in gilt post-farrowing traits and pre-weaning piglet growth to divergent selection for components of efficient lean growth rate
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Responses in gilt liveweight, backfat depth and food intake during lactation and in pre-weaning piglet growth rate were examined after seven generations of divergent selection for daily food intake (DFI), lean food conversion (LFC) or lean growth rate (LGA) on ad-libitum feeding or lean growth on restricted feeding (LGS). There were 242 Large White gilts in the study.
Selection for low DFI resulted in gilts with less backfat (25.7 v 30.7 mm, s.e.d. 2.2) at farrowing and a substantially lower food intake (129 v 146 kg, s.e.d. 5) during lactation, but similar reductions in liveweight (42 kg, s.e.d. 6) and backfat depth (8.4 mm, s.e.d. 1.7) than with selection for high DFI. Therefore, the lower piglet growth (167 v 195 g/day, s.e.d. 11) with selection for low DFI compared to selection for high DFI was primarily due to lower food intake of the gilts, as energy for milk production from food was reduced. In contrast, selection for high LFC resulted in relatively smaller changes in liveweight (37 v 48 kg, s.e.d. 5) and backfat depth (7.6 v 8.9 mm, s.e.d. 1.3) than selection for low LFC, which combined with a lower food intake (132 v 148 kg, s.e.d. 4) during lactation, resulted in lower piglet growth (181 v 200 g/day, s.e.d. 11).
The higher food intake of high LGA gilts (137 v 121 kg, s.e.d. 4) compensated for the relatively lower reductions in liveweight (41 v 46 kg, s.e.d. 5) and backfat depth (5.5 v 6.7 mm, s.e.d. 1.3) during lactation compared to the low LGA line, such that piglet growth was similar (195 v 189 g/day, s.e.d. 11) in the two selection lines. In the high and low LGS selection lines, piglet growth was similar (195 v 186 g/day, s.e.d. 11), as was gilt food intake (125 v 117 kg, s.e.d. 5) and the changes in liveweight (39 v 41 kg, s.e.d. 6) and backfat depth (8.1 v 7.7 mm, s.e.d. 2.2) during lactation. An examination of the daily energy used in litter gain and the energy available from gilt food intake and mobilisation of body lipid indicated that one equation to predict the amount of body lipid mobilised during lactation was not appropriate for different genotypes.
Responses in gilt food intake and the changes in liveweight and backfat during lactation were selection strategy dependent. However, in general, the selection strategies which reduced gilt voluntary food intake during lactation or resulted in lower liveweight and backfat depth at farrowing were detrimental to piglet growth rate.
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