A NOTE ON THE RESPONSE OF GROWING-FINISHING PIGS TO INCREASING THE THREONINE TO LYSINE RATIO OF DIETS WITH REDUCED LYSINE CONTENT
M.K. O’Connell, P.B. Lynch and J.V. O’Doherty

Abstract
Threonine is the second limiting amino acid in most barley and wheat based pig diets. This experiment was carried out to determine the effect on pig performance of increasing the threonine to lysine (THR:LYS) ratio when the lysine content of the diet was reduced. Single-sex groups (n=40) of thirteen pigs (37.8 ? 2.2 kg), were allotted at random to one of five treatments in eight blocks. All pigs were fed a control diet until 58 kg (12 g lysine (lys) per kg diet, THR:LYS ratio of 0.60). From 58 kg until slaughter, the dietary treatments were: (A) control diet, (B) 9.5 g lys per kg, 0.60 THR: LYS ratio, (C) 9.5 g lys per kg, 0.70 THR:LYS ratio, (D) 8.0 g lys per kg, 0.60 THR:LYS ratio, (E) 8.0 g lys per kg, 0.70 THR: LYS ratio. Pig groups were slaughtered at an average liveweight of 94.0 ? 5.2 kg. Average daily liveweight gain was reduced (P<0.01) and feed conversion ratio deteriorated (P<0.01) when the lysine content was reduced from 12.0 g/kg to 9.5 g/kg, at THR:LYS ratio of 0.60 (Trt B) and when the lysine content was reduced from 12.0 g/kg to 8.0 g/kg at THR:LYS ratio of either 0.60 or 0.70 (Trts D and E). However, increasing the THR: LYS ratio to 0.70 at 9.5 g of lysine/kg, resulted in similar (P>0.05) daily liveweight gain and feed conversion ratio to Trt A. Daily carcase growth rate was higher and carcase feed conversion ratio was better for pigs on treatments A and C compared to pigs on treatment D (P<0.01). These results indicate that the THR:LYS ratio should be increased to 0.70 when the lysine content is reduced from 12.0 to 9.5 g/kg. Reducing the lysine content from 12.0 to 8.0 g of lysine per kg, in the later stages of growth, negatively affected pig performance at both THR:LYS ratios.

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