Efficiency of energy and protein deposition in swine measured by dual energy X-ray absorptiometry (DXA)

Abstract. A series of studies were conducted using dual energy X-ray absorptiometry (DXA) to measure energy and protein deposition in pigs. In an initial validation study DXA was compared directly with slaughter analysis as a method for measuring energy deposition in pigs. During growth from 30 to 60 kg the mean value for carcass energy deposition measured by DXA was 251 MJ compared to 249 MJ by chemical analysis (R²=0.94). Subsequently it was shown that both compensatory growth and the addition of ractopamine to the diet resulted in an improvement in efficiency of protein deposition (PE), however, ractopamine also resulted in a reduction in the efficiency of energy deposition (k_g). Another study was conducted to compare the efficiency of utilization of dietary energy and protein by control and IGF-I transgenic pigs in response to dietary conjugated linoleic acid (CLA). Addition of CLA to the diet resulted in a reduction in k_g, though there was no difference in k_g based on genotype or sex. The PE was higher (P<0.05) in the IGF-I transgenic pigs. DXA was also used to assess energy deposition in pigs that were either homozygous stress non-sensitive (NN), heterozygous (Nn) or homozygous stress sensitive (nn). During growth from 30 to 60 kg or 60 to 90 kg there were no differences in the efficiency of either energy or protein deposition. In conclusion, DXA can be used to replace the comparative slaughter technique for measuring energy and protein deposition in pigs, thus this approach is useful for identifying differences in energy and protein deposition in pigs of different genotypes or when subjected to various dietary treatments.