Department of Animal Sciences, University of Illinois, Urbana-Champaign, IL.
Choice Genetics, Des Moines, IA.
J Anim Sci. 2020 Sep 1;98(9). doi: 10.1093/jas/skaa275.
The objective was to determine the amount and variability of intramuscular fat (IMF) in a pork loin attributable to anatomical chop location, sex, and sire line. Pigs were sired by commercially available terminal Duroc boars selected for meat quality (MQ; n = 96) or lean growth (LG; n = 96) and equally split between barrows and gilts. After slaughter and fabrication, bone-in chops were removed from four locations of each left-side loin (A = 6th rib, B = 10th rib, C = last rib, and D = 4th lumbar vertebrae). An adjacent pair of chops from each location was collected and evaluated for visual color and marbling, subjective firmness, moisture and extractable lipid (IMF) (anterior chop), and Warner-Bratzler shear force (posterior chop). Data were analyzed using the MIXED procedure of SAS as a split-plot design. Homogeneity of variances was tested on raw data using Levene's test of the GLM procedure and found to be heterogeneous. Thus, a two-variance model was fit using the REPEATED statement of the MIXED procedure, grouped by pig. The mivque(0) option of the VARCOMP procedure was used to calculate the proportion of variability that each factor contributed to the total variance. Barrows (3.64%) produced chops with greater (P < 0.01) IMF content than gilts (3.20%), and barrows (2.14) had greater (P < 0.01) IMF variability than gilts (1.23). Chops from MQ pigs (4.02%) exhibited greater (P < 0.01) IMF content than LG (2.82%), and MQ (1.76) had greater IMF variability (P < 0.01) than LG pigs (0.97). Chops from locations A (3.80%) and D (3.77%) had greater IMF than B (3.34%; P < 0.01), and A, B, and D had greater IMF than C (2.77%; P < 0.01). Variances of IMF also differed (A = 1.44, B = 1.59, C = 1.05, and D = 2.18; P = 0.01) across chop locations. Of the variability in IMF, 33.0% was attributed to sire line, 10.16% to chop location, and 4.01% to sex, with 52.83% not accounted for by these three factors. Location A chops were the most (P < 0.01) tender (2.57 kg) and C chops the least (P < 0.01) tender (2.93 kg), while B and D chops were intermediate and not different from each other. No differences in variability (P = 0.40) of tenderness were observed among chop locations (A = 0.31, kg B = 0.24 kg, C = 0.24 kg, and D = 0.23 kg). These results demonstrated that variability in tenderness values did not reflect the variability of IMF. In conclusion, chop location, sex, and sire line all contribute to the amount and variability of pork loin marbling.
本研究旨在确定猪肉里脊中归因于解剖切块位置、性别和父本系的肌内脂肪（IMF）含量和变异性。猪由商业上可用的、经选择具有肉质（MQ）或瘦肉生长（LG）特性的终端杜洛克公猪配种，公猪和母猪的数量相等。屠宰和加工后，从每侧里脊的四个位置（A=第 6 肋骨、B=第 10 肋骨、C=最后一根肋骨和 D=第 4 腰椎）取出带骨的肉块。从每个位置的一对相邻肉块中采集和评估视觉颜色和大理石花纹、主观硬度、水分和可提取脂质（IMF）（前肉块）以及 Warner-Bratzler 剪切力（后肉块）。数据使用 SAS 的 MIXED 程序作为分割区组设计进行分析。使用 GLM 程序的 Levene 检验对原始数据进行方差齐性检验，发现方差不齐。因此，使用 MIXED 程序的 REPEATED 语句拟合了一个双方差模型，按猪分组。使用 VARCOMP 程序的 mivque(0)选项计算每个因素对总方差的贡献比例。公猪（3.64%）产生的肉块 IMF 含量高于母猪（3.20%）（P<0.01），公猪（2.14）的 IMF 变异性高于母猪（1.23）（P<0.01）。MQ 猪（4.02%）的 IMF 含量高于 LG 猪（2.82%）（P<0.01），MQ 猪（1.76）的 IMF 变异性高于 LG 猪（0.97）（P<0.01）。A 位置（3.80%）和 D 位置（3.77%）的 IMF 含量高于 B 位置（3.34%）（P<0.01），A、B 和 D 位置的 IMF 含量高于 C 位置（2.77%）（P<0.01）。IMF 的方差也在切块位置之间存在差异（A=1.44、B=1.59、C=1.05 和 D=2.18；P=0.01）。IMF 变异性的 33.0%归因于父本系，10.16%归因于切块位置，4.01%归因于性别，其余 52.83%无法用这三个因素来解释。A 位置的肉块最嫩（P<0.01）（2.57kg），C 位置的肉块最不嫩（P<0.01）（2.93kg），而 B 和 D 位置的肉块处于中间，彼此之间没有差异。在切块位置之间没有观察到嫩度变异性（P=0.40）的差异（A=0.31kg、B=0.24kg、C=0.24kg 和 D=0.23kg）。这些结果表明，嫩度值的变异性并不能反映 IMF 的变异性。总之，切块位置、性别和父本系都与猪肉里脊大理石花纹的含量和变异性有关。
