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Genotype with nutrition interaction for protein and lipid deposition in pigs
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Genotype with nutrition interaction for protein and lipid deposition in pigs
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Testing different pig genotypes on a single diet may constrain protein and lipid deposition or reduce the efficiency of nutrient utilisation by under- or over-supply of nutrients. If the ranking of genotypes is dependent on the diet used when performance testing animals, then genotype-specific nutritional regimes may be required by breeding companies to identify animals of high genetic merit and by producers to realise the benefits obtained by genetic improvement programmes.
There were 320 Large White pigs in the study. In each of the eight selection lines from the Edinburgh lean growth experiment, 30 pigs were ad-libitum fed one of three isoenergetic (14.0 MJ DE/kg) diets differing in lysine : energy (0.40, 0.76 and 1.12 g ileal lysine/MJ DE). The study also included 80 control line pigs, which were fed the 0.40 and 0.76 lysine diets. Two pigs from each selection or control line-diet subclass were slaughtered at either 30, 45, 60, 75 or 90 kg with subsequent chemical analysis of carcass and non-carcass components. Animals were performance tested in four batches, with a batch consisting of a pair of high and low selection lines and 20 animals from the control line. The control line was represented in each batch for estimation of non-genetic differences between the batches. Rates of tissue deposition were estimated in residual maximum likelihood analyses. The model for protein or lipid weight in the carcass included fixed effects of selection and control lines, diet, sex and the line-diet interaction and random effects of litter and batch, with litters nested in batches. Days on test was fitted as a covariate separately for each line-diet subclass, from which tissue deposition rates were determined.| Figure 1. Protein deposition (g/day) | Figure 2. Lipid deposition (g/day) |
In Figure 1 (or Figure 2), estimated protein (or lipid) deposition rates from a model containing the selection line-diet
interaction (X axis) are plotted against estimated protein (or lipid) deposition rates from the additive model,
omitting the selection line with diet interaction, (Y axis). If estimates from the additive and interaction models
were similar, such that there was no interaction, then points would lie on the line Y = X (as indicated).
The significant (P<0.05) selection line with diet interaction for protein deposition rate was primarily due to
the high (H) LGS line, which had higher protein deposition on the 0.76 lysine diet than estimated from the additive
model. The significant (P<0.05) selection line with diet interaction for lipid deposition rate resulted from
high lipid deposition in the LGS lines on the 0.76 lysine diet, particularly the low (L) LGS line. When the high
LGS line was excluded, the correlation between estimates for protein deposition rate from the interaction and
additive models of 0.85 (s.e. 0.21) was not significantly different from unity. The correlation between estimates
from the two models for lipid deposition rate was 0.89, when the high and low LGS lines were excluded; again not
significantly different from one.
There was no evidence of a genotype with nutrition interaction for protein or lipid deposition, excluding the
LGS lines, such that ranking of the selection lines will be similar irrespective of the performance test diet.
It may not be necessary to performance test pigs on diets substantially higher than 0.8 g ileal lysine/MJ DE,
given the similar rates of protein and lipid deposition of pigs fed diets containing 0.76 and 1.12 g lysine/MJ DE.
The selection strategy-diet combination of high LGS and 0.76 g ileal lysine/MJ DE provides an efficient and
high protein deposition rate.
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