Phosphorus digestibility and metabolizable energy concentrations of contemporary cereal grain varieties fed to growing pigs

Cereal grains are a major feedstuff in pig nutrition across the world. Due to their high starch content and their high inclusion rates, they supply the majority of energy in diets for pigs. At the same time they also provide a major part of phosphorus (P). Because most P in plant seeds is present in the form of phytate-P, which is only poorly digestible by pigs, excess excretion of P occurs primarily via faeces. To minimize P excretion an exact knowledge of digestible P (dP) content is indispensable for diet formulation. A rapid and cheap in vitro system for exact estimation of dP content of single batches of different feedstuffs is of great importance in practice.
Because there can be larger differences of P-digestibility between different types of cereal grains and within one type of grain, the extent of differences of P-digestibility and metabolizable energy (ME) concentrations were evaluated. Eight genotypes each of barley, rye, triticale and wheat were analyzed for apparent total tract digestibility (ATTD) of P and ME concentrations. This was done using the difference method with quantitative collection of excreta from fattening pigs.
The mean in vivo ATTD of P was 0.444 for barley, 0.449 for rye and 0.504 for triticale. Highest mean ATTD of P was observed for wheat (0.573). Within one grain type, significant differences for ATTD of P were found for triticale. No significant differences were found within the eight genotypes of barley, rye and triticale. Highest mean ME concentrations were found for triticale and wheat (16.1 and 16.2 MJ ME/kg dry matter (DM), respectively). Mean ME concentrations for barley (14.9 MJ ME/kg DM) and rye (14.8 MJ ME/kg DM) were significantly lower. Within one type of grain there were significant differences for barley, triticale and wheat.
For prediction of dP-values the 32 cereal grains and further 22 feed samples were analyzed for their content of hydrolyzable P (hP). The same samples were used for determination of dP content. Regression analysis showed strong correlation between dP and hP-values. By determination of hP the dP content could be predicted with a coefficient of determination (R²) of 0.88. [(r = 0.809): dP (g/kg DM) = –0.125 (P > 0.10) + 1.482 (P < 0.01) × hP (g/kg DM)]. With precise knowledge of dP content, diet formulation can be made to match requirements closely. Supplementation with mineral P can be minimized, which has an impact on the world’s reserves of rock phosphate. At the same time, P excretion via excreta can be reduced and the negative environmental effects of the P content in manure will be minimized.