Evaluation of the precision and accuracy of equations to predict backfat iodine value (IV) in pork carcasses of pigs fed diets containing distillers dried grains with solubles (DDGS)

Abstract Text:

Iodine value (IV) is a common measurement of fat quality that determines the concentration of unsaturated fatty acids in pork carcass fat depots. Equations have been developed to predict backfat IV based on the amount and composition of dietary lipids fed to growing-finishing pigs. The objective of this study was to evaluate 8 published equations for predicting backfat IV of pigs using dietary fatty acid composition and intake of 8 diets fed in 2 similar experiments. Pigs (n = 432/experiment, initial BW = 23.9 ± 4.1 kg, 9 pigs/pen, 12 pens/treatment) were fed diets consisting of corn and soybean meal or corn-soybean meal diets containing 40% DDGS from 7 different sources (ether extract content ranged from 5.6 to 16.0%) in a 4-phase feeding program. The IV product (IVP) of diets ranged from 24.0 to 82.1 g/100g. Pigs were harvested (BW = 114.6 ± 7.9 kg), and backfat at the midline of the last rib were sampled from 2 pigs in each pen (24 pigs/treatment) with BW closest to the pen mean. Backfat samples were analyzed for fatty acid composition, and IV was calculated from the AOAC (1998) equation and analyzed using Proc Mixed of SAS with pen as the experimental unit. Calculated backfat IV ranged from 57.7 to 82.3 g/100g. Precision (low prediction error; PE) and accuracy (deviation of predicted means from observed means; bias) were calculated for each equation using predicted backfat IV compared with calculated backfat IV of pigs fed the 8 dietary treatments. Backfat IV was predicted poorly using equations based on percentage of DDGS in the diet, but using equation: 52.4 + (0.315 × diet IVP) resulted in the best estimates for backfat IV due to the least PE and low bias.

Reference	Equation	PE	Bias
Benz et al. (2011)
Equation 1	35.458 + 14.324 × Diet 18:2n6, %	8.18	0.42
Equation 2	51.946 + 0.2715 × Diet IVP1	6.46	-5.07
Bergstrom et al. (2010)	57.89 + 0.18 × Diet IVP	6.18	-4.24
Boyd et al. (1997)	52.4 + 0.315 × Diet IVP	4.60	-2.18
Madsen et al. (1992)	47.1 + 0.14 × IVP/day, kg	6.44	-4.98
Cromwell et al. (2011)	64.5 + 0.432 × % DDGS in diet	8.26	7.10
Restrepo et al. (2013)
Equation 1	70.06 + 0.29 × % DDGS in diet	9.19	8.00
Equation 2	60.13 + 0.27 × Diet IVP	5.03	3.03
1IVP = dietary IV × % dietary lipids × 0.10.

Keywords:

backfat IV, prediction equations, DDGS, growing-finishing pigs