Effect of protein source on performance and nitrogen metabolism of pigs weaned at 21 days of age

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Abstract
The effects of source of protein on performance and nitrogen metabolism were studied in pigs weaned at 21 days of age. All diets contained 190 g crude protein and 14·6 MJ digestible energy per kg, and had a similar essential amino acid composition. Sources of protein were a combination of soya bean meal, fish meal and dried skim milk which was compared with soya bean meal alone, or in combination with either fish meal or dried skim milk. Seven groups of pigs (four pigs per group) received each diet ad libitum until 56 days of age. Performance was similar with the combinations of sources of protein, but with soya bean meal alone, food intake and growth rate were reduced (P < 0·05), but food conversion efficiency was not affected. Nitrogen metabolism was studied in seven pigs per diet given a restricted intake. Under these conditions, protein source had no effect on performance or retention and apparent digestibility of nitrogen. Nitrogen retention increased (P < 0·05) between 35 and 49 days of age, and was affected by the duration of the balance period (P < 0·01). In a second experiment, imparting a fish-like odour to the diet with soya bean meal as the sole source of protein by the addition of a fish oil did not affect food intake or performance.These results indicate that a mixture of protein supplements in the diet of pigs weaned at 21 days of age may be unnecessary.