Protein, lysine and feed intake level effects on pig growth: I. Main effects

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Abstract
SUMMARY: A total of 512 pigs were given from 50 lb live weight one of 16 diets, i.e. with 4 lysine levels at each of 12, 14, 16 and 18% protein, at one of 4 levels of intake. They were killed at 100, 150, 200 or 250 lb live weight.Live-weight gain was not improved significantly by increasing the protein level above 16, 14, 12and 12%, respectively, for the 50–100, 100–150, 150–200and200–2501bstages. However, conversion of feed to live-weight gain was improved significantly during the 50–100 lb stage by increasing the protein to 18%. Gain in lean meat and in the efficiency of conversion of feed to lean meat were improved by increasing the above protein levels slightly.Live-weight gain was not improved significantly by increasing the lysine level above 1·04, 0·74, 0·70 and 0·59%, respectively, for the 50–100, 100–150, 150–200 and 200–250 lb stages. However, conversion of feed to live-weight gain was improved significantly during the 50–100 lb stage by increasing the lysine level to 1·22%. Raising the lysine level at each level of protein had no significant effect on the rate and efficiency of lean meat gain.Live-weight gain was significantly improved by increasing the level of feed intake almost to ad libitum levels for the 50–100, 100–150 and 150–200 lb stages. There was a suggestion of a similar effect in the 200–250 lb pigs although it was not statistically significant. Conversion of feed to live-weight gain was improved in the 50–100 lb pigs only by increasing the level of feed intake: in the older pigs increasing the level of feed intake caused a worsening in feed conversion ratio. Increasing the level of feed intake gave a significant improvement in rate of lean meat gain but a significant worsening in the efficiency of conversion of feed to lean meat during all stages up to 200 lb.Interaction effects of these factors and sex, on growth performance, are described.