Reducing Muscle Glycogen in Swine Through Diet Manipulation and Transport to Improve Pork Muscle Quality

The objective of both studies contained in this thesis was to improve pork muscle quality by lowering muscle glycogen levels prior to harvest. The first study involved feeding an ultra-high protein/low carbohydrate (HIPRO) diet to lower the glycogen stores in pork muscle in order to improve pork muscle quality. Forty-eight crossbred barrows at a live weight of 92 ± 18 kg were assigned across five treatments and two reps (four or five pigs per treatment by rep combination). All barrows were fed a control diet (13.1 % CP; com-soybean meal diet) until their assigned treatment began. Treatment was defined as the number of days barrows were fed the HIPRO diet prior to harvest (0, 2, 4, 7, and 14 d). The HIPRO diet (35.9% CP) was 97% extruded soybeans. Daily feed disappearance and weekly body weights were recorded for all barrows. At-death blood glucose levels were determined. Muscle pH, temperature and electrical impedance were measured in the longissmus lumborum and semimembranosus muscles at 45 min, 3 h and 24 h postmortem. Glycolytic potential, Minolta L *a*b* values, visual scores for color, firmness and marbling, water-holding capacity traits (drip loss, purge loss and cooking loss) and Wamer-Bratzler shear force values were determined in the longissmus thoracis et lumborum. Weight gain per day decreased the longer the pigs were fed the HIPRO diet (P \u3c 0.05). Daily feed intake decreased during the first week on the HIPRO diet, but returned to near-control levels during the second week, which when coupled with the continued decreases in daily gain, resulted in substantial decreases in feed conversion during the second week on the HIPRO diet (P \u3c 0.05). Blood glucose levels and glycolytic potentials were not decreased by feeding the HIPRO diet (P \u3e 0.05); and therefore, no differences in rate of pH decline or ultimate pH among dietary treatments were found (P \u3e 0.05). Likewise, there were no differences among dietary treatments in any of the measured meat quality attributes (P \u3e 0.05). Feeding barrows the HIPRO diet for a time period prior to slaughter decreased feed disappearance, rate of gain, and feed efficiency, and was not effective at lowering glycolytic potential or improving pork muscle quality. The objective of this study was to determine the interaction effects of fasting and length of transport prior to harvest on pork muscle quality. Pigs (n = 177) from two different genetic sources were used in the study. The study design was a 2 x 2 x 3 factorial, which involved two genetic sources, fasting (F) or not fasting (N) of pigs 48-h prior to harvest, and three different transport times (0.5, 2.5 or 8.0 h) on the semi-trailer to the packing plant. Genetic source was a significant source of variation (P \u3c 0.05) for composition and muscle quality variables. Fasting reduced hot carcass weight by 3.6% (P \u3c 0.05), whereas length of transport did not affect hot carcass weight (P \u3e 0.05). There were no differences (P \u3e 0.05) in percent lean among treatments. Fasted pigs had higher longissmus dorsi (LD) ultimate pH (pHu), darker lean color, higher marbling scores, and increased water-holding capacity (WHC) (P \u3c 0.05) than non-fasted pigs. Length of transport had significant effects on GP, LD pHu, Semimembranosus (SM) pHu, L*, color score, and WHC (P \u3c 0.05). As transport time increased LD pHu increased and L * and cook loss decreased (P \u3c 0.05). Pigs that were transported for 8.0 h had lower (P \u3c 0.05) Warner-Bratzler Shear force (WBS) values than pigs transported for 0.5 h. Semimembranosus pHu, L*, color score and drip loss were the only traits where the fasting x transport interaction was significant (P \u3c 0.05). Fasting improved SM pHu, L *, color score and drip loss for pigs that were hauled 0.5 h, but when pigs were hauled for 2.5 h or 8.0 h fasting had little or no effect on these muscle quality traits. Both fasting and length of transport by themselves had positive effects on pork quality, but length of transport showed the greatest improvements in pork quality. When pigs were transported for 0.5 h, fasting for 48 h prior to harvest improved pork quality, but when pigs were transported 2.5 h or longer fasting did not improve pork quality. Fasting lowered GP and LD pHu in pigs from a genetic source that had high initial pork quality, while fasting had no effect on pigs from a genetic source with lower initial pork quality. Transport time lowered GP and increased LD pHu no matter which genetic source pigs were from