Changes in the histochemical properties and meat quality traits of porcine muscles during the growing-finishing period as affected by feed restriction, slaughter age or slaughter weight

¹ Agroscope Liebefeld-Posieux, Swiss Federal Research Station for Animal Production and Dairy Products (ALP), Posieux 1725, Switzerland
² Animal Science Department, University of Kentucky, Lexington 40546

^* To whom correspondence should be addressed. E-mail: giuseppe.bee{at}alp.admin.ch.

	Abstract

In this study the degree of contractile and metabolic development of myofibers in porcine LM, rectus femoris (RF), and dark and light portions of the semitendinosus (STD and STL, respectively) were determined and their impact on meat quality were compared both at the same age (but different BW; Trial 1) and at a given BW (but different age; Trial 2) after the growing and finishing period in 48 Swiss Large White barrows from 12 litters with ad libitum (A) or restricted (R, 80% of A) feed access. At 113 and 154 d of age, 6 barrows in treatment A (62.1 and 99.5 kg BW, respectively) and 6 siblings in treatment R (51.0 and 86.6 kg BW, respectively) were slaughtered (Trial 1). In Trial 2, a similar protocol was used except that barrows were slaughtered at either 61.3 (age: 104 or 119 d) or 101.3 kg BW (age: 145 or 167 d). Muscle fibers were stained and classified as slow-oxidative (SO), fast oxidative-glycolytic (FOG), and fast glycolytic (FG), and fiber area and distribution were determined. At both 113 and 154 d of age, R-barrows had smaller (P 0.04) SO fibers in the LM, STD, and STL, smaller (P < 0.01) FOG fibers in the STL, smaller (P = 0.03) FG fibers in the LM, and smaller (P 0.04) overall mean area in the LM, STD, and STL. In the STL and RF, R-barrows had fewer (P 0.06) FG and more (P 0.08) FOG fibers than A-barrows at 113 and 154 d of age. Except for smaller FOG fibers in the STD of R- compared with A-barrows slaughtered at the same BW, the myofiber size did not differ (P 0.11). However, the LM tended to have fewer (P = 0.06) SO and more (P < 0.01) FG fibers and the STD had more (P < 0.01) FOG fibers in R-barrows. Regardless whether R-barrows were slaughtered at the same age or the same BW as the A-barrows, shear force values and cooking losses were higher (P 0.08) in the STD and STL of R-barrows. These findings revealed that myofiber hypertrophy was impaired by feed restriction when compared at the same age but differences in myofiber size vanished when compared at the same BW. By contrast, restricted nutrient supply affected myofiber maturation depending on both the age and the BW but the impact differed between muscles. The absence of changes in myofiber type distribution among the younger/lighter and older/heavier barrows indicated that myofiber maturation was already completed in the younger/lighter barrows. Although changes in meat quality traits were affected by the feeding regimen they were not related to myofiber characteristics.

Key Words: Feed restriction, Maturation, Meat quality, Myofibers, Pigs

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