The objectives of this study were two fold. The first objective was to analyze existing data to develop predictive equations to determine the iodine value of three economically relevant adipose depots in finishing pigs. These equations would be developed using parameters such as dietary iodine value product, withdrawal period, carcass characteristics, etc. The second objective was to validate these equations in a live-animal finishing trial. In addition to examining the direct effect of these diets on iodine value in these depots, molecular analyses were conducted to investigate the biological mechanisms that govern or explain the observed phenotypic responses.
Overall, adding fat to swine diets throughout the finishing period increased ADG and improved feed efficiency compared to pigs fed a diet without fat for a portion of the finishing phase. Additional fat also increased backfat which consequently tended to reduce the carcass percent fat free lean. As previous data suggests, as soybean oil was added to diets, dietary C18:2 increased which caused an increase in PUFA. As dietary PUFA’s increased, IV increased within each fat depot. Conversely, as soy bean oil was added to diets dietary C18:1 was driven down, which lowered MUFA’s for all individual fat depots. Blended diets were similarly affected, however, not to the extent of the pigs fed soy bean oil. Jowl fat, unlike the other two depots, did not show a period affect for IV when additional fat was provided in the diet. Interestingly, tallow did not affect SFA levels in fat depots. Because neither MUFA nor PUFA were significantly impacted by tallow compared to a control diet, IV values were not significantly altered by tallow. Therefore feeding tallow can improve rate of gain as well as feed efficiency while not impacting IV. Feeding soy bean oil can also improve both ADG and feed efficiency, but it negatively impacts fatty acid composition and IV. This negative impact can be improved by utilizing a withdrawal strategy, but IV levels remain above controls even after long term withdrawal of 42 d.
The jowl depot appeared to be least responsive to withdrawal periods indicating a differential response between adipose depots. This is supported by previous studies that indicate that the jowl depot is weakly correlated to other economically relevant depots. This should be taken into consideration as a standard location and procedure for assessing IV in pig carcasses are developed.
Producer bottom line:
• Essential fatty acids (C 18:2 and C 18:3) content of diets can be used to predict iodine value in back, belly, and jowl fat depots in finishing swine using the equations generated herein.
• Equations incorporating the appropriate factors to estimate carcass fat IV will allow producers to feed their pigs appropriately to avoid monetary discounts associated with IV that are higher than acceptable at harvest.
• While a number of different factors were evaluated, dietary EFA, NE content, and backfat thickness exhibited the greatest influence on predicting IV of 3 distinct fat depots.
• Duration of feeding and composition of dietary fat affects the effectiveness of withdrawal time:
o Adding fat to swine diets throughout the finishing period increased ADG and improved feed efficiency compared to pigs fed a diet without fat for a portion of the finishing phase.
o Feeding tallow can improve rate of gain as well as feed efficiency while not negatively impacting IV.
o Feeding soy bean oil can improve both ADG and feed efficiency, but it negatively impacts fatty acid composition and IV. This negative impact can be improved by utilizing a withdrawal strategy, but IV levels remain above controls even after long term withdrawal of 42 d.
• Specific diets fed during different periods and for different durations induce depot specific changes in the individual genes involved in the lipid assimilation and metabolism.
