Genotype with nutrition interaction for performance test traits in pigs selected for lean growth rate


BSAS Annual Meeting, Scarborough 1997, paper no. 29

The genotype with nutrition interaction for performance test traits was examined by testing genotypes which had been divergently selected for lean growth rate on ad-libitum (LGA) or restricted (LGS) feeding for nine generations in the Edinburgh lean growth selection experiment. Within each selection line, there were 100 pigs and there were also 100 control line pigs. Animals were tested from 30 kg for a fixed time of 12 weeks, with individual penning, on either ad-libitum or restricted (0.75, 0.81, 0.88, and 0.94 g/g of daily ad-libitum food intake) feeding, on isoenergetic (14.0 MJ DE/kg) diets, differing in lysine content (0.40, 0.58, 0.76, 0.94 and 1.12 g lysine/MJ DE). Protein content of the diets was 160, 185, 210, 235 and 260 g CP/kg. There were 25 diet-ration combinations in the experiment, with four animals of each genotype tested on each combination. On each diet, growth rate of the high LGS line was greater than for the high LGA line and similarly for the low lines. Growth rate of the control line was similar to the high LGA line, on all diets. For diets included in the study, growth rate in the high and control lines was highest with the 0.58 g lysine/MJ DE diet, but growth rate of the low selection lines was insensitive to changes in diet. The greater variation for mean growth rate for diet-ration subclasses of the high lines compared to the low lines indicated that the genotype with nutrition interaction was due to the high selection lines.

Ranking of the selection lines for protein conversion ratio (g CP/ kg weight gain) (PCR) was consistently opposite to the ranking for growth rate. Responses in PCR to increased dietary lysine content were linear in the low selection lines, but in the high selection lines, responses were only linear when the diet contained more than 0.58 g lysine/MJ DE.

The genotype with nutrition interaction study demonstrated a greater sensitivity of the high lean growth selection lines to different nutritional inputs, than in the low lean growth lines. Non-linear responses in growth rate and PCR to increased dietary lysine in the high lines indicated that dietary lysine of 0.58 g/MJ DE was sufficient, while in the low selection lines, diets containing more than 0.4 g lysine/MJ DE over-supplied nutrients. The higher growth rate and more efficient use of protein in the high LGS line than in the high LGA line implied that selection on restricted feeding emphasised efficiency, while there was relatively less emphasis on efficiency with selection on ad-libitum feeding, as genetic merit for "appetite" was combined with genetic merit for efficiency.



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