Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Master of Science in Animal Science (MS)

Degree Level

Graduate

Department

Animal Science

Advisor

Jason K. Apple

Committee Member

Charles Maxwell

Second Committee Member

Charles Rosenkrans

Third Committee Member

Michael Looper

Abstract

Barrows and gilts (n=210) were used to test the effects of crystalline amino acid (AA) supplementation of reduced crude protein (RCP) diets formulated on a net energy basis on quality characteristics of the LM from growing-finishing pigs. Pigs were blocked by weight, and pens (3 barrows and 3 gilts/pen) within each block were assigned randomly to either corn-soybean meal diets (C) or 1 of 3 RCP diets and added crystalline AA levels for the dietary treatments during each feeding phase. During the last 3-wk feeding phase, 10 ppm of ractopamine were included in all diets. At slaughter and after a 24-h rapid chilling period, a subsample of whole pork loins (3/pen) was collected during carcass fabrication and further processed into LM chops for quality data collection. A 2.5-cm-thick slice was removed from the anterior end of randomly selected fresh pork bellies (3 bellies/pen). Belly slices were further dissected into the outer s.c. (OSC) and middle s.c. (MSC) fat layers, as well as intermuscular fat (INT). Jowl, belly and LM samples were freeze-dried and analyzed for fatty acid composition. As CP decreased in swine diets, Japanese (P < 0.01), American (P = 0.032), and fat color scores decreased (linear, P = 0.017), whereas LM drip loss increased (linear, P = 0.015) with decreasing CP diets. Lightness (L*) value increased (P = 0.015) linearly with decreasing CP diets; yet, neither a* nor b* values were affected (P ≥ 0.414) by RCP treatments. Furthermore, marbling and firmness scores, cooking loss percentage, and shear force values were not (P ≥ 0.503) affected by dietary CP levels. Color was detrimentally affected by reducing dietary CP and adding crystalline AA in diets formulated on a net energy basis. There were no (P ≥ 0.132) dietary treatment × fat layer interactions; however, proportions of all SFA and all MUFA increased (linear, P ≤ 0.006), and proportions of all PUFA decreased (linear, P = 0.010), as CP was reduced in the diet. Also, belly fat IV decreased linearly (P < 0.001) with decreasing dietary CP. Total SFA were greatest (P < 0.05) in the INT, and SFA percentage was greater (P < 0.05) in the MSC than OSC. The OSC and MSC had greater (P < 0.05) proportions of all MUFA than INT, whereas OSC had greater (P < 0.05) proportions of PUFA than MSC and INT. The OSC had the greatest (P < 0.05) IV (74.0), and IV of the MSC was greater (P < 0.05) than that of the INT (70.0 vs. 68.1). Similarly, total PUFA percentages in the jowl and LM samples decreased (linear, P ≤ 0.0003), whereas MUFA percentages in the jowl and LM measured (linear, P ≤ 0.0062) with decreasing dietary CP. In particular, in swine diets oleic acid (18:1c9) increased (linear, P ≤ .0142) and linoleic acid (18:2n6) decreased in the LM and the jowl fat as CP was decreased. Similar to 18:2n6, linolenic acid (18:3n3) in the jowl fat and LM had decreased (linear, P ≤ .0001) 27% and 17.8% in the jowl fat and LM respectively, among RCP treatments. Results indicate that fatty acid composition differs greatly among the fat layers of fresh pork bellies, MUFA composition of pork belly fat was increased at the expense of PUFA by reducing dietary CP, suggesting enhanced de novo synthesis in pigs fed RCP diets supplemented with crystalline AA.

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