#18-118

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When pork loin quality is evaluated by pork processors, evaluations are conducted on the ventral surface of a whole boneless loin, and general estimations about the amount of marbling are assigned to the entire loin without regard to variability in marbling based on anatomical location. However, when boneless pork chops are evaluated by consumers at retail, each chop from a given loin is independently evaluated based partially on marbling to make purchasing decisions. Because of this, it is possible the quality assigned to the entire loin based on the color and marbling estimation of the ventral side is not representative of all the chops that are produced from that loin. Due to differences in variability in anatomical location, sex of pigs, and genetic lines used by producers, it is also possible that loins classified as high quality at the processing facility may not necessarily produce consistently high quality chops at retail or provide a high quality eating experience. Our previous work identified that in addition to differences in the amount of marbling produced by barrows and gilts or by pigs from two different genetic lines, the variability of that marbling was also different. Therefore, it was critical to characterize differences in the amount of marbling and the variability of marbling throughout a loin and to determine how that variability is influenced by sex and genetic line. In order to establish scenarios by which producers can consistently produce high quality pork and be rewarded for it, a better understanding is needed regarding the amount of marbling deposited throughout the loin, its variability of the marbling and the underlying cellular mechanisms that influence its deposition.

For this experiment, 196 pigs (10 weeks of age) were raised in a 98 day growth study. Pigs were fed in a university finisher barn in pens of 4 pigs each. Equal numbers of barrows and gilts sired by boars targeting meat quality or lean growth were used. Pigs were all fed the same corn-soybean diet that met or exceeded nutrient requirements based on the 2012 NRC of swine, for a 3 phase feeding program. At 10, 15, 20, and 24 weeks of age, all pigs were ultrasonically scanned to estimate marbling and backfat. A limited number of pigs were slaughtered at each of these time points to validate the ultrasound procedure. At 24 weeks of age, all pigs were slaughtered and loins were collected. Bone-in loins were sliced into one inch chops. Chops from the 6th rib, 10th rib, last rib and 4th lumbar vertebrae were analyzed for visual marbling, intramuscular fat (IMF) and tenderness (Warner-Bratzler Shear Force).

Results:
1) Determination of marbling from ultrasound images in this trial was not an accurate indicator of marbling deposition throughout the growing phase. Ultrasonic values overestimated marbling in young pigs and reported a smaller range of values than was actually observed in market weight pigs. This could be due to technician error or the inadequacy of the technology for smaller pigs. While data from the serial slaughter of young pigs did not validate ultrasonic marbling estimates, it did provide valuable information about marbling deposition. The pattern of marbling with highs and lows present along the length of the loin at early ages mimicked the pattern observed in market weight pigs. Therefore, while intramuscular fat is often thought of as a “late developing” tissue, the differences in marbling deposition along a loin are present even at very young ages.
2) The applied meat quality portion characterized variability of marbling throughout the loin. IMF was the greatest at the front and back chop location while it was intermediate at the 10th rib and the poorest at the last rib. Chops from the 6th rib location were the most tender while chops from the last rib area were the least tender. There were also significant differences in color, marbling score, firmness, moisture, and cook loss across the different locations. Therefore, marbling and tenderness does vary between locations in a pork loin.
3) Sex and sire line play a role in the cellular mechanisms controlling marbling. Analysis of the genes and transcripts crucial to marbling in loins is underway. Sex, sire line and location along the loin were able to account for 47% of the total variability in marbling. However, these factors only explained 14% of the variability in tenderness.

From these results the following conclusions can be made:
• Marbling is present and variable in pigs from a very young age, however exact quantification of marbling deposition throughout the growing period is difficult to obtain. Ultrasound imaging of a young pig is not ideal to identify animals with a potential to be highly marbled.
• Marbling does vary from location to location in a loin but these difference do not correspond to differences in tenderness. Therefore, while marbling is variable how this might contribute to variability in eating experience warrants more investigation
• As overall quality of a loin improves its variability also increases. As a producer improves meat quality they will also be increasing variability. This is not necessarily a bad thing if there is incentive for improved meat quality, but is important to be aware of when selecting for increased marbling.
Contact Information: Dr. Anna Dilger, University of Illinois. adilger2@illinois.edu

Key Findings:
• Marbling is present and variable in pigs from a very young age, however exact quantification of marbling deposition throughout the growing period is difficult to obtain. Ultrasound imaging of a young pig is not ideal to identify animals with a potential to be highly marbled.
• Marbling does vary from location to location in a loin but these difference do not correspond to differences in tenderness. Therefore, while marbling is variable how this might contribute to variability in eating experience warrants more investigation
• As overall quality of a loin improves its variability also increases. As a producer improves meat quality they will also be increasing variability. This is not necessarily a bad thing if there is incentive for improved meat quality, but is important to be aware of when selecting for increased marbling.