Effect of dietary zinc and ractopamine hydrochloride on pork chop muscle fiber type distribution, tenderness, and color characteristics1,2

Abstract

A total of 320 finishing pigs (PIC 327 × 1050; initially 98 kg) were used to determine the effects of adding Zn to diets containing ractopamine HCl (RAC) on muscle fiber type distribution, fresh chop color, and cooked meat characteristics. Dietary treatments were fed for approximately 35 d and consisted of a corn-soybean meal-based negative control (CON), a positive control diet with 10 mg/kg of RAC (RAC+), and the RAC+ diet plus 75, 150, or 225 mg/kg added Zn from either ZnO or Availa-Zn. Loins randomly selected from each treatment (n = 20) were evaluated using contrasts: CON vs. RAC+, interaction of Zn level × source, Zn level linear and quadratic polynomials, and Zn source. There were no Zn source effects or Zn source × level interactions throughout the study (P > 0.10). Pigs fed RAC+ had increased (P < 0.02) percentage type IIX and a tendency for increased (P = 0.10) percent type IIB muscle fibers. Increasing added Zn decreased (linear, P = 0.01) percentage type IIA and tended to increase (P = 0.09) IIX muscle fibers. On d 1, 2, 3, 4, and 5 of display, pork chops from pigs fed the RAC+ treatment had greater (P < 0.03) L* values compared to the CON. On d 0 and 3 of display, increasing added Zn tended to decrease (quadratic, P = 0.10) L* values and decreased (quadratic, P < 0.03) L* values on d 1, 2, 4, and 5. Pigs fed RAC+ had decreased (P < 0.05) a* values on d 1 and 4 of display and tended to have decreased (P < 0.10) a* values on d 0 and 2 compared to CON pork chops. Pork chops from the RAC+ treatment had a tendency for increased (P < 0.08) oxymyoglobin percentage compared to CON pork chops on d 1, 2, 4, and 5. On d 0, as dietary Zn increased in RAC+ diets, there was a decrease (linear, P < 0.01) in the formation of pork chop surface oxymyoglobin percentage. Metmyoglobin reducing ability (MRA) of pork chops on d 5 was decreased in the RAC+ group. Chops from pigs fed added Zn had increased (quadratic, P < 0.03) MRA on d 3 and 5 of the display period. There was a trend for increased (linear, P = 0.07) cooking loss with increasing Zn in RAC diets and treatments did not affect tenderness as measured by Warner-Bratzler shear force (P > 0.07). In conclusion, RAC+ diets produced chops that were lighter and less red but maintained a greater percentage of surface oxymyoglobin throughout a 5-d simulated retail display. Ractopamine reduced MRA at the end of the display period, but supplementing Zn to RAC diets restored MRA to near CON treatment levels at the end of the display period.

Effect of added zinc in diets with ractopamine hydrochloride on growth performance, carcass characteristics, and ileal mucosal inflammation mRNA expression of finishing pigs1,2

“…A 30-cm portion of the longissimus lumborum muscle (beginning at the 10th rib) from the left side of each pig was collected for immunohistochemical and fresh pork quality analysis. The results for the fresh pork quality analysis are reported in Paulk et al (2014).…”

Use of electromyography to detect muscle exhaustion in finishing barrows fed ractopamine HCl1

“…Studies reported RAC increased the rate of fatigue when pigs were roughly handled; however, these studies used indirect measures of blood metabolites as indicators (James et al, 2013;Peterson et al, 2015;Puls et al, 2015). Dietary RAC shifted muscle fiber type from oxidative to glycolytic metabolism (Paulk et al, 2014), but the impact of fiber shifts on fatigue remain unexplored.…”

“…Fibers that stained positive for both SC-71 and B-FF3 were labeled as type IIX fibers ( Fig. 1; Paulk et al, 2014). Cross-sectional area of muscle fibers was determined as the area within the dystrophin border.…”

“…The methods of Paulk et al (2014) were followed for fiber type immunohistochemistry with modifications. Cryosections were incubated in 5% horse serum and 0.2% TritonX-100 in PBS for 30 min to block all nonspecific binding sites.…”

Evaluating the impact of maternal vitamin D supplementation: I. Sow performance, serum vitamin metabolites, and neonatal muscle characteristics1,2

“…Then the cross sections were embedded in optimal cutting temperature tissue-embedding media (Fisher Scientific, Pittsburgh, PA), frozen by submersion in supercooled isopentane, and stored at −80°C until analysis. For each muscle sample, two 10-μm cryosections were collected on positively charged slides (MidSci), and muscle fibers were immunostained with antibodies validated by Town et al (2004) for the detection of primary and secondary muscle fibers and merged with the methods of Paulk et al (2014) to simultaneously identify muscle fiber cross-sectional area. Briefly, nonspecific antigen-binding sites were inhibited by incubating cryosections in 5% horse serum and 0.2% TritonX-100 (Fisher Scientific) in PBS for 30 min.…”