Statistical evaluation of the discrepancy between analysed and formulated crude protein content in commercial feed mixtures for pigs

The analysed (Kjeldahl) crude protein (CP) content in four standardised formulated feed mixtures for pigs (with calculated means of: Sw1, 185 g CP kg−1; Sw2, 145 g kg−1; Sw3, 165 g kg−1; SwP, 390 g kg−1, respectively) from 11 factories was compared with the nominal guaranteed level. The sampling period was 8 years. Samples with analysed CP values outside the statutory range were counted as faulty. Percentages of samples that were faulty were: 14.1, 8.9, 10.5 and 23.5 for Sw1, Sw2, Sw3 and SwP, respectively. The correlation between the percentage of faults and the nominal protein level in the mixtures was high and significant (P = 0.02). The percentage of faults in mixtures for pigs was found to have a magnitude of 56% of the CP percentage. On average, 97% of all faulty samples were deficient in CP, with only 3% having a higher protein content than declared. In spite of recent high levels of innovation and investment at the factories, there was no decreasing tendency for the percentage of faults during the period for any of the mixtures (P > 0.05). There were, however, significant (P < 0.01) differences between regions, i.e. in some regions the mixtures were almost without faults; in other regions, the faults were quite frequent.