Evaluation of equations to estimate fat content in soft tissues of carcasses and viscera in sheep based on carbon and nitrogen content
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2019 Elsevier B.V. The objective of the present study was to evaluate equations for estimating fat content (%) of soft tissues of carcass (muscle and adipose tissues, n = 28) and viscera (n = 28) samples of adult ewes based on nitrogen (N, %), carbon (C, %) and dry matter (DM, %) composition. The following equations reported by Brouwer (1965) and Kuhla et al. (2004) were tested: ether extract (EE, %) = 1.3038 C (%) 4.237 N (%) (eq. 1), EE (%) = 1.2948 C (%) 4.407 N (%) (eq. 2) and EE (%) = 31.23 + 1.9677 DM (%) (eq. 3). A fourth equation for estimating EE was also tested: EE (%) = 1.3039 ( 0.017) C (%) 3.9949 ( 0.218) N (%) (eq. 4). A final equation including DM content was also developed and tested in the present study: EE (%) = 1.3820 ( 0.025) DM (%) (eq. 5). The correlation coefficients (r) between EE and C and between EE and N were 0.90 and 0.97, respectively (P < 0.001). All of the equations presented high precision (r2> 0.91), except equations (3) and (5), and high accuracy according to the bias correction factor (Cb > 0.95), confirming their good reproducibility and concordance with the observed data (CCC > 0.94). The modelling efficiency factor (MEF) indicated moderate to high efficiency of prediction (from 0.63 to 0.91) for all equations except equation (3). The coefficient of model determination (CD) ranged from 0.59 to 1.25, indicating high variability in the predicted data. The null hypothesis (intercept = 0 and slope = 1) was only accepted for equations (1), (4) and (5). Equations (1) and (4) had high precision (r2 = 0.92) and accuracy (Cb = 0.99), with a reproducibility index of 0.95. Hence, we conclude that equations (1) and (4) could be used to predict the percentage of EE in sheep soft tissues of carcasses and viscera based on the C and N contents (%). These equations could be applied in the future to determine the composition of the soft tissues of carcass and viscera of animals to estimate their energy requirements under different production levels.