#17-090

Progress

Date Full Report Received

Date Abstract Report Received

Investigation

Institution:
Primary Investigator:

Marketing weight is an important economic variable that impacts the productivity and profitability of finishing pig production. Marketing weight has been increasing over the past decades driven by the dilution of fixed production cost over more weight per pig and the improvement of genetic selection of lean-type pigs. Along with it, pork carcass weights have increased by an average of 1.4 lb per year. While heavier market weights are associated with poorer feed efficiency, little data exists to understand how it influences other important production and economic factors. Little to no data are available to predict how heavier pigs (e.g. 320 lb. and above) are influenced by farm facilities (e.g. floor space per pig) or how meat quality or consumer acceptance is related to carcass size when pigs are harvested at body weights approaching 400 lb. Therefore, the primary objective of this study was to determine the space allowance needed to evaluate the carcass quality of pigs with increased live weights that might be expected in the next 50 years. To achieve this primary objective we had five specific goals: 1) compare k-value space allowances, 2) compare temperature decline of hams and loins, 3) compare fresh loin quality (muscle pH, color, marbling, firmness, and predicted tenderness) of loins, 4) determine how increased carcass size affects eating experience and purchasing preferences of consumers, and 5) compare muscle physiology, hypertrophy, and fiber types.

A total of 976 pigs were raised in a 160-d growth study. Pigs were fed 1 of 6 dietary treatments with 8 pens per treatment. The first four treatments reduced space allowance per pig via initial pen stocking density and had only one final marketing event. The fifth and sixth treatments consisted of different pig removal strategies. Pens of pigs were weighed and feed disappearance was measured on d 0, 13, 27, 41, 55, 69, 82, 93, 108, 122, 135, 147, and 160 to determine ADG, ADFI, and feed efficiency (F/G). When pigs were removed due to illness or death, pen gates were adjusted. Pigs were given ad libitum access to feed and water throughout the study. Diets were corn- and soybean meal-based and included 30 to 40% corn dried distillers grains with solubles until the final dietary phase. Diets were fed in 6 sequential phases from approximately 48 to 70, 70 to 120, 120 to 180, 180 to 230, 230 to 270, and 270 lb until the end of the study. The diets were formulated to meet or exceed NRC (2012) requirement estimates for finishing pigs and contained 1.18, 1.03, 0.88, 0.78, 0.76, and 0.77% standardized ileal digestible (SID) Lysine (Lys) in phases 1 through 6.

All pigs were raised and slaughtered in the Midwest US. Identity of the carcasses were maintained throughout the slaughter process to allow for carcass weight relationships with meat quality, consumer ratings, and fiber type characteristics to be determined. In total, 666 carcasses were evaluated.

The following data were collected from approximately all carcasses:
• Hot carcass weight
• Carcass composition- back fat and loin depth (via Fat-O-Meater)
• Boneless loin weight
• Subjective color, marbling, and firmness of boneless loins
• Instrumental color of the boneless loins
• Ultimate pH of the boneless loins

The following data were collected on approximately 33 % of all carcasses:
• Ham primal weight
• Instrumental color of the gluteus medius
• Ultimate pH of the gluteus medius
• Iodine Value
• Longissimus dorsi and semimembranosus muscle temperature decline
• Loin muscle slice shear force determination at 160 and 145 oC
• Purge and cook loss
• Aged chop quality measurements
o Subjective color, marbling, and firmness
o Instrumental color
o pH
• Proximate analysis
• Trained sensory panels for tenderness, juiciness, and flavor
• Consumer palatability ratings
• Consumer visual ratings

The following data were collected on approximately 50 carcasses:
• Fiber type determination
• Fiber type area percentage

Findings from the live phase are consistent with others that evaluate more traditional market weights where growth performance is reduced prior to pigs reaching their k-value, and align with recent models that predict the rate of change in growth performance as pigs are allowed more spacing during the finishing period. Similarly, it appears that pigs respond to removal of the heaviest pigs in the pen before market with the remaining pigs in the pen demonstrating compensatory gain after being provided with increased space. Additionally, results indicate that decreasing space allowance for heavy weight pigs reduced growth, intake, and final BW, although use of pig removals prior to final marketing may allow producers to maximize number of pigs marketed while balancing reduced growth performance generally accompanied with increased stocking density. Furthermore, growth continued to increase until approximately 340 lb, indicating a potential opportunity for swine producers to capture lean growth at much heavier weights than previously predicted.

Temperature decline of hams and loins were slower in heavier carcasses. It is not surprising that heavier carcasses produced heavier hams, and loins, as well as, more back fat and loin depth. Additionally, as carcass weight increased there was an increase in trained tenderness scores and decrease in slice shear force, indicating that as pigs get heavier, they become more tender. Water holding capacity also improved as carcasses got heavier, reducing purge and cook loss from chops.

Consumers rated chops from heavier carcasses as more tender. Additionally, they rated more chops from the heavy weight category as acceptable in terms of juiciness. The lowest percentage of chops rated as unsatisfactory were from the heavy weight group. However, weight group had no effect on acceptable flavor or overall like. Top loin chops from heavier carcasses also had improved tenderness compared to chops from lighter carcasses, similar to the results observed from the trained taste panel.

Weight of carcasses had no effect on fiber type or fiber type area percentage within the loin muscle.

From these results, the following conclusions can be made:
1) Decreasing space allowance for heavy weight pigs reduced growth, intake, and final BW, although use of pig removals prior to final marketing may allow producers to maximize number of pigs marketed while balancing reduced growth performance generally accompanied with increased stocking density. A pig removal strategy via multiple marketing events may provide producers a means to maximize stocking density while mediating reduced performance. There is a potential opportunity for swine producers to capture lean growth at much heavier weights.
2) Temperature decline of hams and loins is slowed as carcasses reach heavier weights.
3) As expected, increasing carcass weight will lead to heavier primal weights. Heavier pigs increase tenderness and water holding capacity of pork chops.
4) As hot carcass weights increase, there are no negative effects on loin quality or palatability characteristics. Tenderness was positively affected by increased weight; increasing the likelihood a consumer will have a satisfactory eating experience and thus encouraging repeat purchases.
5) Increases in carcass weight had no effect on muscle type percentage or area.