DUAL-ENERGY X-RAY ABSORPTIOMETRY (DXA) ANALYSIS OF GROWTH AND COMPOSITION OF PIGS OF DIFFERENT RYANODINE RECEPTOR GENOTYPES

Dual energy x-ray absorptiometry (DXA) was used to evaluate live body composition of homozygous stress nonsensitive (NN, 27 pigs), heterozyg ous (Nn, 28 pigs) and homozygous stress sensitive pigs (nn, 18 pigs). The pigs were anesthetized and scanned by DXA at 10, 30, 60 and 90 kg live body weight. From each weight group, pigs were slaughtered (10 kg , 22 pigs; 30 kg, 19 pigs; 60 kg, 15 pigs; and 90 kg, 17 pigs) and car cass composition determined by chemical analysis. DXA and carcass anal ysis results were compared for all pigs. DXA instrument readings for p ercent fat were lower than results obtained by carcass analysis, howev er predicted values based on DXA results were quite close to carcass v alues (16.16% +/- 0.59 versus 16.39% +/- 0.63, respectively). The DXA predicted value for percentage of protein was slightly less than obtai ned by carcass analysis (18.9% +/- 0.15 versus 19.7% +/- 0.23, respect ively). DXA predicted percentage of water was significantly (P<0.05) m ore than the percentage determined by carcass analysis (65.0% +/- 0.7 versus 63.2% +/- 0.6, respectively). The DXA measurement of total body bone mineral content was less than the amount estimated from total ca rcass ash (2.38% +/- 0.03 versus 2.58% +/- 0.06, respectively). DXA me asurements of percentage of fat and lean revealed no differences among genotypes for the 10 kg pigs. At 30, 60 and 90 kg, NN pigs were obser ved to have more fat and less lean (P<0.05) than the nn pigs while the Nn pigs were intermediate with respect to both fat and lean percentag es. DXA measurements of bone mineral content revaled no differences am ong genotypes for any weight group. Calculations of fat and lean growt h, based on DXA measurements for the period of growth from 30 to 90 kg live weight, revealed that differences in body composition were the r esult of differences in fat accretion (more in the NN pigs followed by the Nn and mt pigs), but not accompanied by differences in lean growt h.