Amino acid requirements of growing pigs. 7. The response of pigs from 25 to 55 kg live weight to dietary ideal protein

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Abstract
One hundred and twenty pigs were used in a 3 × 8 factorial design. The factors were sex, 40 trios of littermate boars, castrated males and gilts, and dietary lysine, eight concentrations from 7×5 to 14×5 g/kg diet with 1 g/kg diet intervals of lysine with corresponding crude protein (CP) concentrations from 114 to 226 g/kg diet. Increases in dietary lysine were associated with concomitant increases in the other essential amino acids so as to provide an ideal protein. All diets had similar digestible energy values (13·65 MJ/kg). Pigs were fed once daily on a restricted scale from 25 to 55 kg live weight. For growth and carcass characteristics there was a range of linear response followed by a plateau. The inflexion points of dietary lysine for growth characteristics were at 11·1, 10·2 and 10·9 g/kg diet (171, 157 and 168 g CP per kg diet) together with daily intakes of 18·0, 16·7 and 17·6 g (daily intake of 277, 257 and 271 g CP) for boars, castrated males and gilts respectively. The equivalent points for carcass characteristics were 10·4, 9·7 and 10·1 g/kg (160, 149 and 156 g CP per kg diet) with daily intakes of 16·9, 15·9 and 16·4 g lysine (daily intakes of 260, 245 and 252 g CP). Blood urea data gave good support for these observations.