Comparison of total tract digestibility and nitrogen balance between Cinta Senese and Large White pigs fed on different levels of dietary crude protein

The work aimed to study the digestive capacity and nitrogen balance of Cinta Senese pig fed diets with different crude protein (CP) content. Twelve castrated male pigs (6 Cinta Senese and 6 Large White), of the same body weight (on average 62.7 kg), were submitted to 8 subsequent trials of total tract digestibility and nitrogen balance. The pigs were kept in metabolism cages allowing collection of faeces samples and total urine. The diets, of exclusive vegetal origin, were formulated to contain four protein levels 70, 100, 130 and 160 g/kg as fed (named CP7, CP10, CP13 and CP16, respectively) assured mainly by soybean meal. Total tract nutrient apparent digestibility did not differ (P>0.05) between breeds. Apparent digestibility of CP increased (P<0.01) with increasing dietary CP (from 0.756 to 0.874 for Cinta Senese and from 0.742 to 0.868 for Large White), as consequence of faecal endogenous nitrogen which underestimates the digestibility of protein in inverse proportion with its amount in the diet. Nitrogen balance showed that breed differences (P<0.01) emerged for the urinary N and the total excreted N, with higher emission in Cinta Senese than in Large White breed. The difference was not significant at CP7 diet (excreted N: 19.4 vs. 17.1 g/d for Cinta Senese and Large White) but became progressively more important (P<0.01) in the diets with higher CP content (excreted N at CP16 diet: 39 vs. 35.4 g/d for Cinta Senese and Large White). Consequently, Large White retained more nitrogen than Cinta Senese (about +2.6; +3.0; +3.4; +3.8 g/d with CP7; CP10; CP13; CP16 diet, respectively; P<0.01). So, the efficiency of N utilization (retained N/absorbed N), favoured the Large White in all the tested diets (P<0.01). These results suggest to limit the CP content in diets for Cinta Senese breed, to reduce nitrogen pollution in the environment.