Meat quality traits in longissimus lumborum and gluteus medius muscles

This study analyzes quality traits of longissimus lumborum and gluteus medius in surgically castrated (SC) males, inmunocastrated (IC) males and IC female Iberian pigs reared in intensive conditions (n = 18/sex). Vaccination with Improvac® was applied at 18 and 26 weeks of age and slaughtering at 31 weeks. At such conditions, notable sex differences were found. Both muscles of IC males were less red (P < .01), longissimus had lower intramuscular fat (P < .01) and gluteus less Fe content (P < .01) than SC males and IC females. Loins from IC males also exhibited higher drip losses (2.7% at 24 h) than SC males (1.9%) and IC females (1.6%) (P < .001). Fatty acid composition of muscles differed among sexes, especially polyunsaturated fatty acids, which varied as follows: IC males > IC females > SC males in both muscles. It was concluded that meat quality traits differed between inmunocastrated and surgically castrated male Iberian pigs.


42
The surgical castration of male pigs is a habitual practice among producers with there is a growing public criticism regarding this practice (Prunier et al., 2006).  (Needham & Hoffman, 2015). 72 The Iberian pig is native from the Iberian Peninsula and has a long productive 73 cycle and a slow growing rate, characterized by a low capacity for protein deposition 74 and high-fat production, which is accentuated as animals go further in their productive 75 cycle (Nieto et al., 2012). Iberian meat products are especially appreciated due to their 76 high quality (Palma-Granados, Haro, Lara, Aguilera, Nieto & Seiquer, 2017a). Surgical 77 castration of males and females is a common practice in the production of Iberian pigs, 78 in which animals are slaughtered at 145 kg BW or more (Serrano,Valencia,Fuentetaja,79 Lázaro, & Mateos, 2009). Regarding meat quality, it has been observed that a better 80 product may be obtained from intact compared with castrated crossbred Iberian × Duroc

88
Since the performance of IC pigs seems to differ from SC, their nutrient 89 requirements could vary, and it has been proposed that inmunocastrated pigs may 90 require higher lysine levels than surgical castrates in order to improve the cutting yields until the end of the study, and they were provided ad libitum access to a commercial 123 diet (170 g CP, 1.1 g Lys and 13 MJ ME/kg) until they achieved 18 weeks of age and 124 approximately 40 kg BW. At this moment, entire male and females were vaccinated 125 against GnRH with Improvac® (Zoetis, Madrid, Spain) and all pigs were allocated into 126 one of 3 isoenergetic diets containing 160, 140 and 120 g CP and 14 MJ ME/kg DM in 127 a 3 × 3 factorial arrangement (n = 6 animals per treatment combination) in groups of 128 similar BW. Pigs were fed at 0.9 × ad libitum on a BW basis determined weekly and 129 with free access to water. From 40 kg BW until the end of the study feed intake was 130 individually monitored. Ad libitum feeding was determined according to the equations   Two muscles were selected for measuring meat quality traits: longissimus 144 lumborum, as a typical portion with high commercial value and gluteus medius, as one 145 of the valuable ham muscles (hereinafter referred to as longissimus and gluteus). 146 Evaluation of meat quality was followed based on reference methods (Font-i-Furnols, 147 Čandek-Potokar, Maltin & Prevolnik Povše, 2015).

148
The right half carcass was used for muscles measurements. Immediately after 149 slaughter, aliquots of longissimus and gluteus (≈ 5 g) were trimmed of connective and  Meat color measurements were performed instrumentally using a Minolta 169 colorimeter CR-400 (Konica Minolta Corp. Japan), in accordance with the CIE L*, a*, 170 b* colour system described by Honikel (1998). The colorimeter was previously 171 calibrated and the average of 3 random readings was used to measure L * (lightness, 172 from 0, dark, to 100, white), a* (redness) and b* (yellowness). Additionally, Chroma 173 (C*) and the hue angle (h°), defined as color intensity and saturation, respectively, were 174 obtained by using the following equations: C= (a* 2 + b* 2 ) 0.5 and h°= arctg b*/ a*.

175
Drip loss was determined following the method described by Honikel (1998).

176
Meat slices were weighed and placed within a container on a supporting mesh and 177 sealed; after storage periods of 24 and 48h at 4°C samples were weighed again to 178 determine drip loss. After freezing, samples were thawed for 24h at 4 °C in a mesh 179 within a plastic container tightly closed, to avoid contact between the defrosting water 180 and the sample; steaks were blotted dry and weighed to calculate thawing loss. To   The carrier gas (helium) flow rate was 1.2 mL/min with a split ratio of 50, and 1µl was The results were analyzed for each type of muscle (longissimus and gluteus) by a 246 analysis of variance (ANOVA) to study the effects of sex (SC males, IC males and IC 247 females), dietary protein content, replicate and their interactions. As no effect of 248 replicate and only minor effects of dietary protein content were found for the variables 249 evaluated (with no interactions), the data were re-analyzed using one-way ANOVA with 250 sex as the main factor. Data are presented as mean ± standard error for each sex. sex × muscle type was studied and, being not significant, was removed from the model.

265
Means were compared post-hoc by using the LSD test and differences were established 266 at P < 0.05.

267
The statistical calculations were carried out using STATGRAPHICS Centurion   The average slaughter weight was 103 ± 8, 109 ± 9, and 106 ± 11 kg for SC 278 males, IC males and IC females, respectively, with no differences among the 279 experimental groups (P = 0.172). Statistical correlations between the variables studied 280 are shown as supplementary material (Table S1 for longissimus and Table S2  drip loss, thawing loss and cooking loss is depicted in Figure 1. 288 It is known that the extent of pH fall p. m. due to glycolysis has a considerable 289 effect on several meat quality attributes in pigs, and a fast pH decline is associated with   The water holding capacity is known to influence sensory traits such as color, suggesting that reddish variation should be due to aspects other than iron oxidation. Nutritional composition of pork meat is strongly linked to quality and may be 358 affected by several factors such as breed, age, sex or feeding and production systems.

359
According with the results of the present assay, chemical composition of muscles 360 differed among SC males, IC males and IC females (Table 2). Both for longissimus and 361 gluteus muscles, the most different product was found in IC males, with higher moisture  (Table S1) and paler colors (lower a*, b* 377 and C* values, P < 0.05) in both muscles (Tables S1 and S2), confirming that meat  (Table S1).  (Tables S1 and S2). This correlation supports that high Fe content could be a risk factor The univariate analysis of the factors also allowed exploring differences between 484 longissimus and gluteus muscles. Strong differences (P < 0.001) were found for F2 485 (MUFA-SFA), F3 (a*, b*, C*) and F4 (redness, Fe, Zn, TBARS), and minor differences 486 (P < 0.05) for F7 (protein). However, factors influenced by IMF content and PUFA 487 composition (F1 and F5, respectively) and pH of the meat (F6) were similar for both 488 muscles. Differences observed between muscles might reflect the oxidative pattern of 489 the muscle fibers, characterized as oxidative (type Ι, red muscle) or glycolytic (type II, 490 white muscle), which is closely related to myoglobin concentration (Yu et al., 2017).

491
Thus, myoglobin affects quality traits such as color, but also, due to the different 492 oxidation state of Fe, may be related with the oxidative stability of the muscle (Muriel,493 Antequera & Ruiz, 2002). It is well known that the longissimus muscle belongs to 494 glycolytic muscle category, while gluteus is more oxidative. In accordance, due to    Table 1 673 Quality traits in longisimus lumborum and gluteus medius of surgically castrated (SC) males,