Estimating intramuscular fat content and fatty acid composition in live and post-mortem samples in pigs

Repeated muscle sampling (n=732) on 216 pigs was performed to evaluate the effect of live sampling and sample size on intramuscular fat (IMF) content and fatty acid (FA) composition. The sampling scheme consisted of 1-3 biopsies of longissimus dorsi (LM), a small and a big post-mortem sample of LM, and a big post-mortem sample of gluteus medius (GM). IMF was determined by quantitative gas chromatography after direct transesterification. Data on LM were jointly analyzed using a mixed model on age with heterogeneous residual variances across sampling methods. Biopsies overestimated IMF and polyunsaturated FA content and underestimated monounsaturated FA content with decreasing sample size. Potential for bias and not sampling variance is the major limitation of using live samples for assessing changes in IMF with age. Small post-mortem samples of LM were as informative as big samples of GM for inferring IMF content but not IMF composition.