Effect of Gender on Growth Performance, Carcass Characteristics, Meat and Fat Composition of Pigs Slaughtered at 125 kg of Live Weight Destined to Teruel (Spain) Ham Production

Abstract

Duroc x (Landrace x Large White) barrows (n=60) and gilts (n=72), that consumed the same feed during the experimental period (25-125 kg of live weight) were used. The duration of experimental period was 130 and 143 days for barrows and gilts respectively. The average daily gain and average daily feed intake were significantly higher (P<0.05) in barrows than in gilts, but no significant differences between sexes were observed for the feed conversion efficiency. The gender had not significant influence on carcass weight, carcass yield, carcass inner length, ham length and perimeter, but fat thickness at the level of Gluteus medius muscle and the last rib were significantly higher (P<0.05) in barrows than in gilts. The number of thighs removed per pig in the slaughterhouse was significantly higher in gilts than in barrows. The intramuscular fat (IMF) percentage in Longissimus dorsi muscle was significantly higher in barrows than in gilts. The C14:0, C16:0, C16:1, C18:1 n-9, C20:1 and MUFA proportions were significantly higher (P<0.05) in barrows than in gilts, while C10:0, C18:2 n-6, n-6 and PUFA proportions were higher in gilts than in barrows. Positive relations among IMF and C16:0, C18:0, C18:1 n-9, SFA and MUFA fatty acids were observed, whereas negative relations among IMF and C18:2 n-6 and PUFA fatty acids were detected. These results indicate that meat and fat quality was slightly better in barrows than in gilts.

Keywords:

• pigs
• gender
• growth performance
• carcass
• meat
• fat composition

Introduction

Spain is the world leader in the production of dry-cured ham with a total production of 245,000 t in 2010 (AICE, 2010). Since 1997, the Denomination of Protected Origin (DPO) Teruel ham has been included in a list of special quality products by the European Union. Teruel ham production has increased considerably in recent years from 302,800 pieces in 2000 to 465,000 in 2010 (Consejo Regulador de la Denominación de Origen, 2011). The regulation of DPO Teruel ham establishes minimum levels of carcass weight (86 kg) and fat thickness over the Gluteus medius muscle (16 mm) in order to improve uniformity and quality of the end product. Some experiment have reported that barrows might be better than females for the ham industry (Latorre et al., 2003; Peinado et al., 2008). Although some studies have studied the effect of gender on performance and carcass quality of heavy pigs intended to Teruel ham (Latorre et al., 2008). However, to our knowledge there is not enough information available on the influence of gender on intramuscular fat (IMF) content and its fatty acid composition in Teruel pigs. IMF in pork has been reported to positively influence juiciness, tenderness and flavour (Wood, 1993) and fatty acids composition is important due to their effects on human health (Wood and Enser, 1997). Therefore, the aim of the experiment was to investigate the effect of gender on growth performance, meat composition and fatty acids profile of IMF from pigs slaughtered at 125 kg of body weight destined to Teruel ham production.

Materials and methods

All the experimental procedures used in this study were approved by the Ethics Committee of the Universidad Politécnica de Madrid and were in compliance with the Spanish guidelines for the care and use of animals in research (Boletín Oficial del Estado, 2005).

Animals, experimental design and diet

Crossbred barrows (n=60) and gilts (n=72) with 25.28 kg (SEM=0.92) of initial weight were used. All pigs were of same genetic type Duroc x (Landrace x Large White). Males were castrated at 5±2 days of age. On the experimental farm, pigs were randomly allotted to 22 groups, 10 of barrows and 12 of gilts, of similar initial weight. Each group included 6 animals. Pigs were housed in pens (3 m × 3 m) and had free access to pelleted barley-wheat-corn-soybean meal diet and water throughout the trial. The barrows and gilts consumed the same feed during all the experimental period. The duration of experimental period was 130 and 143 days for barrows and gilts respectively. The compositions of the unique diet in ingredients, major nutrients and fatty acids are shown in Table 1. Pigs were individually weighed at the beginning of trial and 16 hours before slaughter and feed consumption per pen was recorded every two weeks during experimental period. These data were used to calculate average daily gain (ADG), average daily feed intake (ADFI) and feed conversion efficiency (FCE).

Slaughter, measurements and analysis

Pigs were transported to a commercial slaughter plant where they were resting for 6 hours will full access water but not to feed. Then pigs were electrically stunned (225 to 380 V/0.5 A for 5 to 6 s), exsanguinated, scalded, stripped and eviscerated according to standard commercial procedures and split down the center of the vertebral column. Hot carcass weights were recorded and used to calculate carcass yield. At 45 min postmorten, carcass inner length (CIL) from the posterior edge of the symphysis pubis to the anterior edge of the first rib, ham length (HL) from the anterior edge of the symphysis pubis to the hock joint and ham perimeter (HP) at its widest were measured on the left side of each carcass using a flexible ruler with a precision of 1 mm (Latorre et al., 2009). In addition, on all the pigs 16 hours before slaughter, by means of a real-time ultrasound apparatus RTU (Kretz Technick Inc 600 V-.32, Sonovet, Austria) fat thickness measured at 6 cm from the dorsal mid-line from the skin at the level of last rib was taken (UF). Fat thickness at the level of Gluteus medius muscle (GM) and at the level of the last rib (LR) were measured by means a ruler with a precision of 1 mm. A piece of the Longissimus dorsi muscle at the level of the last rib was taken for the muscle and fatty acid analysis.

The estimation of diet metabolizable energy and fatty acid composition was carried out according to FEDNA (2010). AOAC (2000) procedures were used to analyse diet composition in dry matter (DM) crude protein, ether extract and ash and Longissimus dorsi muscle moisture and protein. The Longissimus dorsi IMF lipids were extracted by the procedure proposed by Folch et al. (1956). The lipidic extracts were methylated in the presence of sodium metoxide. Fatty acid samples were identified by gas chromatography as described elsewhere (López Bote et al., 1997) using a 6890 Hewlett-Packard gas chromatograph and 30 m x 0.32 mm x 0.25 m cross-linked polyethylene glycol capillary column. A temperature program of 170 to 245°C was used. The injector and detector were maintained at 250°C. The carrier gas (helium) flow rate was 3 mL/min.

Statistical analysis

The data were studied by means covariance analysis that included the gender as fixed effect and as covariates initial weight of the pigs (IW) for growth performance, and carcass weight (CW) for carcass characteristics and muscle composition. An additional covariance analysis with IMF percentage as covariate was carried out to study the fatty acid composition of Longissimus dorsi muscle. When any covariate was not significant (P>0.05) was removed in the corresponding statistical model. The experimental unit was a pig for all variables except for ADFI and FCE. For variables ADFI and FCE the experimental unit was a pen of six pigs. Moreover, to study the relationship between fat thickness (UF and GM), and IMF percentage and fatty acids proportion simple regression equations were calculated. Student’s t- test was used to compare intercepts and slopes of linear regression equations. All analysis were carried out by means the statistical packet SAS (1999).

Results and discussion

As expected, the ADG and ADFI were significantly higher (P<0.05) in barrows than in gilts, but no significant differences between sexes were observed for the FCE (Table 2). These results are in agreement with those found in other studies (Weatherup et al., 1998; Lebret et al., 2001; Augspurger et al., 2002; Latorre et al., 2003; 2004) in pigs except for the variable FCE. Most experiments have observed better FCE in gilts than in barrows, although, as in our experiment, Friesen et al. (1994), Cisneros et al. (1996) and Serrano et al. (2009), did not find differences between sexes for FCE when genetic lines more fatty were studied. A significant effect of covariate IW on the variables slaughter weight (SW), ADG and FCE was observed in the current experiment The effect of gender on carcass characteristics is provided in Table 3. The gender had not significant influence on the carcass variables CW, carcass yield (CY), CIL, HL and HP but GM, LR and UF were significantly higher (P<0.05) in barrows than in gilts. The number of hams removed per pig (HR/P) in the slaughterhouse was significantly higher in gilts than in barrows. It was due to that the removed carcasses percentage, as consequence of the fat lack, was 47.2% and 28.3% in gilts and barrows respectively. These values were higher than those found by Latorre et al. (2008; 2009). These authors observed that only from 20% to 24% of gilt carcasses and 0-10% barrow carcasses were removed. This may be due to that sire line of Duroc breed used in Latorre et al. (2008; 2009) trials was fatter than that utilized in the current experiment. Thus, Altarriba et al. (2005) showed that terminal sire line of Duroc breed had significant effect on fatness carcass. The covariate CW, introduced in the statistical model, had significant (P<0.05) effect on variables CIL, HL, HP, HR/P,GM, LR and UF. Latorre et al. (2004) found that the gilts had higher CY than barrows, but no significant differences were observed in other experiments (Latorre et al., 2003; 2008; Peinado et al., 2008; Serrano et al., 2009). Also Latorre et al. (2003; 2004) did not detect significant differences between barrows and gilts for the variables CIL and HL and, as in our study, barrows had higher GM and LR than gilts. However, in anterior works such authors found that HP was higher in barrows than in gilts, result that is not in accordance with that obtained in our experiment. It can be explained because the genetic types used by Latorre et al. (2003; 2004) were different that those used in the present study. It is interesting know the relationships between the variables GM and UF, in order to predict GM by means UF measures taken in the live animal before slaughter (ultrasound device), since the DPO Teruel ham establishes a minimum of 16 mm for fat thickness over the Gluteus medius muscle for that the carcass can be accepted to manufactured dry-cured ham. In the current experiment, the linear relation found between both variables was: GM=1.825+0.946 UF (R²=0.31, RSD=5.02, P<0.0001), which means that UF only accounted for 31% of the variation in GM. Therefore, UF is not a good predictor of GM.

The effect of gender on Longissimus dorsi muscle composition is shown in Table 4. The IMF percentage in Longissimus dorsi muscle was significantly higher in barrows than in gilts and moisture percentage higher in gilts than in barrows, whereas the gender had not significant influence on protein percentage. The variable CW affected significantly moisture and protein percentages, but had not effect on IMF percentage. The correlation coefficient between protein and moisture percentages and CW were low (r= -0.27 and r=0.23, respectively; P<0.01) and, as expected, between moisture and IMF percentages the correlation coefficient obtained was negative and significant (r=-0.71, P<0.0001). The higher IMF percentage observed in barrows is consistent with the backfat thickness data observed in this experiment. According to Barton-Gade (1987) the castration favours intramuscular fattenig of meat. Due to this, most experiments have reported higher IMF content in barrows than in gilts. Thus, Latorre et al. (2003) found greater IMF percentage in barrows than in gilts, although in this study the gender had not significant influence on moisture and protein percentages. Also Alonso et al. (2009) observed that barrows had more IMF percentage than gilts in Semimem - branosus muscle, and similar result was obtained in Longissimus dorsi muscle from Iberian pigs by Serrano et al. (2008, 2009). However, Mas et al. (2010) did not find significant differences in IMF between barrows and gilts in Pietrain sired pigs, which could be explained because Pietrain is a breed that has been very selected for lean production.

Fatty acid profile of IMF from Longissimus dorsi muscle is presented in Table 5. The C14:0, C16:0, C16:1, C18:1 n-9, C20:1 and Σ MUFA proportions were significantly higher (P<0.05) in barrows than in gilts, while C10:0, C18:2 n-6, Σ n-6 and Σ PUFA proportions were higher in gilts than in barrows. Piedrafita et al. (2001) found that gender affected the proportion of fatty acid, as gilts showed a higher proportion of C18:2 n-6 than barrows and barrows had a lower proportion of unsaturated fatty acid than gilts. Also Alonso et al. (2009) observed, in Semimembranosus muscle, that C18:2 n-6, Σ n-6 and Σ PUFA proportions were significantly higher (P<0.05) in gilts than in barrows, although C16:0, C18:1 n-9, Σ SFA and Σ MUFA proportions only were numerically higher (P>0.05) for barrows compared with gilts. According to Mas et al. (2010) Longissimus thoracis IMF from barrows had greater proportions of all SFA, particularly C14:0 and C16:0, compared with IMF from gilts, and the gender had not significant effect on C18:1 n-9, C18:2 n-6, Σ MUFA and Σ PUFA proportions. However, such authors observed higher C18:2 n-6 and Σ PUFA proportions in gilts Semimembranosus muscle subcutaneous fat compared to barrows. Latorre et al. (2009) and Serrano et al. (2009) reported that, in subcutaneous fat, C16:0, C18:0 and Σ SFA were higher and C18:2 anf Σ PUFA proportions were lower in barrows than in gilts, however no influence of gender on fatty acid profile of back fat was observed by Piasentier et al. (2009). Warnants et al. (1999) reported that barrows had higher percentages of SFA, C14:0 and C16:0, compared with gilts, with no differences in C18:1 n-9 and Σ MUFA between sexes. Also Nuernberg et al. (2005) observed that subcutaneous fat from gilts had lower Σ SFA and higher Σ PUFA proportions than barrows.

In the current experiment, IMF percentage had significant (P<0.05) effect on C10:0, C14:0, C16:0, C17:0, C18:0, C18:1 n-9, C18:2 n-6, C20:0, C20:1, C20:4 n-6, Σ n-6, Σ SFA, Σ MUFA and Σ PUFA proportions. When in the statistical model the IMF percentage was introduced as covariate the gender had not significant influence on most fatty acid proportions. Thus, under this statistical analysis the gender only had significant (P<0.05) effect on C14:0 and C16:1 proportions. The proportions observed in barrows and gilts were 1.26 and 1.20 (sem = 0.015) respectively for C14:0 and 3.55 and 3.29 (sem = 0.06) respectively for C16:1. These results indicate that the IMF percentage variable had a marked influence on fatty acid profile of Longissimus dorsi muscle, and that the differences observed between barrows and gilts are really due to differences of IMF percentages. The insaturation index C16:1/C16:0 was greater in barrows than in gilts but no differences were found for C18:1 n-9/C18:0 and Σ MUFA/Σ SFA indexes (Table 5). These results indicate that gender had no effect on the activity of delta-9-desaturase, enzyme responsible of the formation of C18:1 n-9 from C18:0. The n-6/n-3 ratio was significantly lower in barrows than in gilts, but in both genders n-6/n-3 values were very high. Nutritional recommendations for a healthy diet suggest that the ratio of Σ n-6 to Σ n-3 should be 4.0 or lower (Department of Health, 1994). An inadequate Σ n-6/Σ n-3 ratios have been high-lighted as risk factors in certain cancers and coronary heart diseases (Enser, 2001). Nevertheless, it is difficult to reduce n-6/n-3 ratio in fat from pigs due to the high content of C18:2 n-6 in the cereal-based diets usually given to swine which produce an undesirably high Σ n-6/Σ n-3 ratio (Wood et al., 2003). In order to quantify the relationships between major fatty acids proportions and IMF percentage simple regression equations were calculated (Table 6). Positive and significant relations between IMF and C16:0, C18:0, C18:1 n-9, Σ SFA and Σ MUFA fatty acids were observed, whereas negative and significant relations between IMF and C18:2 n-6 and Σ PUFA fatty acids were detected. The positive relation between C18:1 n-9 and IMF can be interesting for genetic selection in pig production, because an IMF increase implicates an increase of C18:1 n-9 and Σ MUFA contents and a reduction of C18:2, Σ n-6 and Σ PUFA proportions. The Σ PUFA content, may have important implications for meat quality characteristics, such as pork firmness (Apple et al., 2009), shelf-life (Morel et al., 2006) and flavour of meat (Wiseman et al., 2000) due to greater susceptibility of unsaturated fats to oxidation and the production of volatile compounds during cooking. The interaction between gender and IMF percentage for the major fatty acids was studied by means simple linear regression. Of such interactions only was significant (P<0.05) for C16:0 and Σ SFA fatty acids, and the equations found are shown in Table 7. According to equations in Table 7, as IMF increased the C16:0 and Σ SFA increased more intensively in barrows than in gilts.

Table 1. Composition and nutrient content of the experimental diet.

Ingredients, g/kg
Barley	330
Wheat	210
Corn	220
Soybean meal, 44% crude protein	190
Molasses beet	17
L-Lysine 50	5
Calcium carbonate	6
Dicalcium phosphate	12
Sodium chloride	5
Vitamin and mineral premix^°	5
Calculated nutrient composition^#
Metabolizable energy, kcal/kg	3070
Analyzed composition^§, g/kg
Dry matter	880.32
Crude protein, N x 6.25	155.62
Ether extract	21.71
Ash	57.40
Fatty acids^#, %
C16:0	2.51
C18:0	0.26
C18:1 n-9	3.37
C18:2 n-6	9.09
C18:3 n-3	0.65

°Provided the following (per kilogram of complete diet): retinyl acetate, 6000 U; cholecalciferol, 1200 mg; α-tocopheryl acetate, 12 U; thiamin, 0.2 mg; riboflavin, 2.5 mg; pyridoxine, 0.2 mg; niacin, 15 mg; cyanocobalamin, 15 g; pantothenic acid, 8 mg; menadione, 0.5 mg; choline, 350 mg; copper sulfate, 16 mg; ferrous sulfate, 75 mg; manganese oxide, 40 mg; zinc oxide, 110 mg; cobalt sulfate, 0.1 mg; sodium selenite, 0.3 mg; calcium iodate, 0.8 mg.

^#According to FEDNA (2010).

^§According to AOAC (2000).

Table 2. Effect of gender on growth performance on farm.

	Gender			P values
	Barrows	Gilts	SEM	Gender	Covariate
IW, kg	25.48	25.12	0.92	0.79	-
SW, kg	125.74	123.85	1.02	0.20	0.012
ADG, kg	0.781	0.698	0.013	0.0001	0.0001
ADFI, kg	2.19	2.06	0.020	0.0001	0.86
FCE, kg/kg	2.88	2.98	0.047	0.09	0.0001
FD, days	130	143	-	-	-

Number of observations: barrows, 60; gilts, 72. IW, initial weight; SW, slaughter weight; ADG, average daily gain; ADFI, average daily feed intake; FCE, feed conversion efficiency; FD, feeding days. The covariate was IW; therefore, WS, ADG, ADFI and FCE are leastsquare means.

Table 3. Effect of gender on carcass traits.

	Gender			P values
	Barrows	Gilts	SEM	Gender	Covariate
CW, kg	98.35	96.99	0.90	0.29	-
CY, %	78.22	78.30	0.29	0.85	-
CIL, cm	88.27	88.15	0.28	0.77	0.0001
HL, cm	49.64	49.76	0.20	0.69	0.0001
HP, cm	76.88	76.92	0.25	0.91	0.0001
HR/P	0.57	0.97	0.11	0.026	0.023
GM, mm	25.14	21.95	0.70	0.0018	0.019
LR, mm	31.26	28.94	0.51	0.002	0.0001
UF, mm	23.89	21.87	0.40	0.0005	0.002

Number of observations: barrows, 60; gilts, 72. CW, carcass weight; CY, carcass yield; CIL, carcass inner length; HL, ham length; HP, ham perimeter; HR/P, hams removed per pig; GM, fat thickness at level of the Gluteus medius muscle; LR, fat thickness at the level of the last rib; UF, ultrasounds fat thickness. The covariate was CW; therefore, CIL, HL, HP, HP/P, GM, LR and UF are least-square means.

Table 4. Effect of gender on Longissimus dorsi muscle composition.

	Gender			P values
	Barrows	Gilts	SEM	Gender	Covariate
Moisture, %	72.84	73.94	0.30	0.020	0.023
Protein, %	22.38	22.18	0.16	0.38	0.01
IMF, %	6.48	4.88	0.39	0.006	0.37

Number of observations: barrows, 60; gilts, 72. IMF, intramuscular fat. The covariate was the carcass weight; therefore, moisture and protein are least-square means.

Table 5. Fatty acid profile, in percentage of the total fatty acids, of the intramuscular fat from Longissimus dorsi muscle.

	Barrows	Gilts	SEM	P value
Fatty acid
C10:0	0.10	0.16	0.015	0.016
C12:0	0.076	0.073	0.0033	0.55
C14:0	1.27	1.19	0.018	0.0024
C15:1	0.017	0.027	0.0035	0.054
C16:0	23.10	22.56	0.15	0.019
C16:1^°	3.56	3.28	0.062	0.0028
C17:0	0.23	0.25	0.0089	0.12
C18:0	12.50	12.63	0.15	0.55
C18:1 n-9	45.42	44.13	0.43	0.043
C18:2 n-6	9.39	10.74	0.35	0.0095
C18:3 n-3	0.41	0.42	0.010	0.54
C18:4 n-3	0.052	0.056	0.0054	0.65
C20:0	0.17	0.16	0.0056	0.21
C20:1	0.76	0.70	0.016	0.034
C20:3 n-9	0.33	0.35	0.011	0.19
C20:4 n-6	2.29	2.73	0.17	0.078
Σ n-6	11.68	13.46	0.50	0.017
Σ n-3	0.46	0.47	0.012	0.48
Σ SFA	37.57	37.22	0.27	0.37
Σ MUFA	49.91	48.41	0.48	0.031
Σ PUFA	12.51	14.36	0.53	0.016
C16:1/C16:0	0.15	0.14	0.0026	0.032
C18:1 n-9/C18:0	3.67	3.52	0.066	0.15
Σ MUFA/Σ SFA	1.34	1.29	0.017	0.24
Σ n-6/Σ n-3	25.24	28.62	0.92	0.012

Number of observations: barrows, 60; gilts, 72.

°Sum of C16:1 n-9 and C16:1 n-7. SFA, saturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid.

Table 6. Relationships among major fatty acids proportions and intramuscular fat percentage in Longissimus dorsi muscle.

Regression equation	R^2	RSD	P value
C16:0 = 21.68+0.20 IMF	0.29	0.26	0.0001
C18:0 = 12.13+0.079 IMF	0.05	1.02	0.027
C18:1 n-9 = 38.10+4.09 ln IMF	0.43	2.10	0.0001
C18:2 n-6 = 16.39–3.92 ln IMF	0.60	1.49	0.0001
Σ SFA = 35.89+0.27 IMF	0.18	1.70	0.0001
Σ MUFA = 42.28+4.21ln IMF	0.38	2.45	0.0001
Σ PUFA = 22.63–5.69 ln IMF	0.58	2.30	0.0001

Number of pairs of values, 132. R², determination coefficient; RSD, residual standard deviation; P, probability; IMF, intramuscular fat; SFA, saturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid.

Table 7. Interaction between gender and intramuscular fat percentage for C16:0 and SFA fatty acids.

	Regression equation	Pairs of values, n	R^2	RSD	P
Barrows	C16:0 = 21.50^a+0.249^a IMF	60	0.41	0.88	0.0001
Gilts	C16:0 = 21.93^a+0.128^b IMF	72	0.12	0.99	0.015
Barrows	SFA = 35.20^a+0.370^a IMF	60	0.33	1.60	0.0001
Gilts	SFA = 36.40^a+0.168^b IMF	72	0.10	1.75	0.021

R², determination coefficient; RSD, residual standard deviation; P, probability; SFA, saturated fatty acid; IMF, intramuscular fat. For each fatty acid, intercepts and slopes with different superscripts are significantly different (P<0.05).

Conclusions

It is concluded that growth performance were better in barrows than in gilts in despite of higher fattening of barrows carcass. IMF percentage was higher in barrows than in gilts and as consequence the IMF from barrows had higher saturated and monounsaturated and lower polyunsaturated fatty acids proportions than that from gilts. It implicates that in this experiment fat quality was better in barrows than in gilts for ham industry.

Acknowledgments

This research was supported by Agri-Food Industry Association of Teruel (ATIA), Teruel, Spain, and by the National Institute of Agricultural and Food Technology Research (INIA), Spain, project PET-2007-08-C11-04 destined to improve the Teruel livestock.