1.Forty pigs between 23 and 51 d of age were given ad lib. diets containing wheat and one of five protein concentrates: meat meal A, meat meal B, soya-bean meal, milk and lupins (Lupinus augustifolius). Twenty of these pigs were given indigestible markers from 51 to 56 d of age and were killed at 56 d of age.
2.The diets containing meat meals A and B, soya-bean meal and milk contained 2.3 g total methionine/kg and the diet containing lupins contained 2.1 g/kg.
3.A further forty pigs of the same age were given the same diets supplemented with 1 g synthetic methionine/kg.
4.The weight gains and feed conversion ratios of the pigs given the diets containing 2.1–2.3 g methionine and 3.1–3.3 g methionine/kg were not significantly different.
5. The weight gains of the pigs given lupins (2.1 g methionine/kg) were less than those of the pigs given the diets containing 2.3 g methionine/kg.
6. The apparent digestibility of dry matter (DM) and nitrogen was less for the diets containing the meat meals (0.75 and 0.78 respectively) than for those containing the other protein concentrates (0.80 and 0.84).
7.The retention times in the large intestine of the diets containing soya-bean meal and lupins were 965 and 1083 min which were greater than those of the diets containing the other protein concentrates, mean 732 min.
8. The major site of N digestion and absorption for the diet containing milk was the area of the small intestine 25–50% of total length from the pylorus, while for the other protein concentrates the major site was 50–75% of its total length from the pylorus.
9. The digestion and absorption of N in the large intestine was less (3.4%) for the diet containing milk than for those containing the other protein concentrates (7.5–11.3%).
10. The apparent digestibility of the methionine to the ileum for the five diets ranged from 0.74 to 0.86 while the calculated retention of the apparently-absorbed methionine was 1.00. It was suggested that methionine digestibility could be used as an indicator of availability.
11. The calculated retention of apparently absorbed N in the carcass was 0.71 for the pigs given the diet containing milk and 0.51–0.58 for the pigs given the other diets.