An evaluation of total and digestible lysine as a predictor of lysine availability in protein concentrates for young pigs.

Forty pigs between 23 and 51 d of age were given, ad lib., diets containing 7.9 g lysine/kg. The diets contained wheat and one of five protein concentrates: milk, peanut (Arachis hypogaea) meal, cotton-seed (Gossypium herbaceum) meal, meat meal or lupins (Lupinus augustifolius). Twenty of the pigs were given an indigestible marker, 103Ru-labelled Tris-(1,10-phenanthroline)-ruthenium(II) chloride, between 51 and 56 d of age and were killed at 56 d of age. A further forty pigs, between 23 and 51 d of age, were given the same diets supplemented with 3 g L-lysine hydrochloride/kg. The weight gains of the pigs given the diets containing 7.9 g lysine/kg (95-153 g/d) were significantly less (P less than 0.05) than those of the pigs given the diets containing 10.9 g lysine/kg (274-340 g/d). Weight gains of pigs given the diets containing meat meal were less than those of pigs given diets containing milk, peanut meal or lupins. Feed conversion ratios decreased and N balances increased with increasing lysine content of the diets. Apparent digestibilities of dry matter (DM) and nitrogen of the diets containing meat meal and cotton-seed meal were less than those of the other three diets, but there was no effect of lysine content of the diets on these indices. The major site of DM and N absorption for the diet containing milk was the duodenum while for the other four protein concentrates the jejunum and ileum were the major absorption sites. Apparent digestibility of lysine from the five diets ranged from 0.54 to 0.75. The retention of the apparently absorbed lysine in weight gain was 0.86-0.94, and there was no significant (P greater than 0.05) difference between diets which suggested that the apparent digestibility of lysine could be an indicator of its availability.