While Environmental Protection Agency regulations limiting the amount of phosphorus (P) in swine effluent have driven research towards finding ways to reduce the excretion of P by pigs, the increased cost of dietary inorganic P sources has continued to motivate producers to reduce the levels of inorganic P added to swine diets.

In a recent study conducted by Dr Chad Stahl and his colleagues, the impact of a single nucleotide polymorphism (SNP) on dietary P utilisation was examined.

The SNP in the calcitonin receptor gene (CALCR) had been previously identified by Dr Stahl’s group as being associated with bone integrity in young pigs, so in this study they examined whether there was an interaction between dietary P level and this SNP.

Pigs were separated based on genotype and fed either a P-adequate diet (meeting NRC P requirements) or a 20 per cent P-deficient diet from weaning until completion of the study 14 weeks later.

While there was no impact of genotype or dietary P on growth performance parameters, there were significant interactions between CALCR genotype and dietary P concentrations on measures of bone integrity (Figure 1).

Bones of pigs fed the P-deficient diet had reduced bone strength and mineral content. Interactions between CALCR genotype and dietary P levels were observed in bone modulus and ash percentage. The metacarpals of pigs with the 11 genotype exhibited greater decreases in bone rigidity (modulus) during P restriction when compared with pigs having the 12 or 22 genotype.

The effect of the CALCR genotype on the loss of bone integrity due to dietary P deficiency seemed to be additive, with pigs of the 11 genotype having a greater loss of bone rigidity and mineral content than those having the 22 genotype, and the 12 genotype being intermediate and not different from the other genotypes. The allele 2 of this CALCR SNP was associated with reduced sensitivity to dietary P restriction, with the bones of the pigs homozygous for this allele not being affected by dietary P deficiency.

Because proper bone health plays a major role in the economic viability of swine production, utilisation of this data may offer possible management strategies based on the interaction of the CALCR polymorphism and diet to improve sow longevity and gilt development. Although selecting for this particular genotype may not be economically plausible, it may be beneficial to alter the diets fed to animals based on genotype to maximize muscle and skeletal growth potential.

This research is reported in its entirety as ‘A calcitonin receptor (CALCR) single nucleotide polymorphism is associated with growth performance and bone integrity in response to dietary phosphorus deficiency.’ J. Anim. Sci. 2010. 88:1009–1016.

November 2010