Prediction of fat-free mass of pigs from 50 to 130 kilograms live weight

Seventy-two Duroc x Hampshire x Yorkshire pigs were used to evaluate bioele ctrical impedance procedures to predict fat-free mass of live pigs. Pigs we re allotted by sex, ancestry, and weight. Pigs (12 gilts and 12 barrows) av eraging 50 +/- 2.4 kg were slaughtered-to establish a baseline for body com position. A pen-of six gilts and a pen of six barrows were randomly selecte d for slaughter when the pen averaged either 70, 90, 110, or 130 kg. Pigs w ere weighed, then a four-terminal plethysmograph was used to measure resist ance (Omega) and reactance (Omega), and length (cm) was measured between de tector terminals. Pigs were slaughtered 12 h later, and carcasses were chil led for 24 h. The right side was ground twice and mixed and samples were fr ozen for later analyses of fat content. Actual fat-free mass (ActFFM) was d etermined from the weights and percentage of fat. Predicted fat-free mass ( PredFFM) was calculated using the following equation: Pred FFM = .486 (live weight) - .881 (resistance) + .48 (length) + .86 (reactance) + 7.959. The correlation coefficients between ActFFM and PredFFM ranged from .66 to .91 overall. Correlation coefficients approximating slaughter weight (90 kg) we re .94 (P < .02). Fat-free mass was underestimated by the prediction equati on at all slaughter weights, but the predicted fat-free mass was highly cor related to the actual fat free mass, except for the 110-kg gilts (r = .68, P = .15) and the 130-kg barrows (r = .65, P = .16). The data support the us e of bioelectrical impedance to measure fat-free mass over a wide range of weights for finishing pigs.