Effect of replacing barley by increasing levels of olive cake in the diet of finishing pigs: Growth performances, digestibility, carcass, meat and fat quality

Animal Feed Science and Technology 197 (2014) 185–193

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Effect of replacing barley by increasing levels of olive cake in the diet of finishing pigs: Growth performances, digestibility, carcass, meat and fat quality M. Joven, E. Pintos, M.A. Latorre ∗ , J. Suárez-Belloch, J.A. Guada, M. Fondevila Instituto Universitario de Investigación en Ciencias Ambientales, Departamento de Producción Animal y Ciencia de los Alimentos, Universidad de Zaragoza, Miguel Servet 177, 50013 Zaragoza, Spain

a r t i c l e

i n f o

Article history: Received 10 March 2014 Received in revised form 20 August 2014 Accepted 21 August 2014 Keywords: Digestibility Fat Growth performances Olive cake Pigs

a b s t r a c t The effect of the solid by-product from the olive oil industry (olive cake) on digestibility, growth performances, and carcass, meat and fat characteristics was studied in sixty Duroc×(Landrace×Large White) gilts, of 69.5 ± 5.02 kg of body weight and 126 ± 3 days of age. Increasing levels of olive cake (0, 50, 100 and 150 g/kg of feed) were included in the diet by replacing the same proportion of barley. Five pens with three pigs per treatment were assayed, considering the pen as replicate. The trial lasted 35 days, and animals were slaughtered with 96.7 ± 7.45 kg of body weight. Daily feed intake increased (P=0.04) and daily gain tended to increase (P=0.06), both quadratically, with olive cake inclusion reaching the maximum values at 100 g olive cake/kg. The daily apparent digestible energy intake also increased quadratically (P=0.04) on increasing dietary olive cake content. The feed conversion ratio was not affected by diet. Also, the apparent organic matter digestibility tended to decrease quadratically (P=0.06) and energy digestibility decreased linearly (P<0.04) as the level of dietary olive cake level increased. The experimental treatment had scarce effects on carcass and meat characteristics; however, the inclusion of olive cake increased quadratically (P=0.04) carcass weight and decreased linearly (P=0.02) fat depth measured at Gluteus medius muscle. The experimental treatment did not modify the total polyunsaturated fatty acids proportion of subcutaneous fat but increasing levels of olive cake promoted a linear reduction (P=0.01) of total saturated fatty acid proportion and a linear increase (P=0.02) of total monounsaturated fatty acid percentage, especially that of C18:1 (P=0.01). We can conclude that olive cake might be included up to 100 g/kg in finishing pig diets improving some aspects of growth performances and carcass quality and also providing a healthier fatty acid profile in fat tissues. © 2014 Elsevier B.V. All rights reserved.

Abbreviations: ADFI, average daily feed intake; ADG, average daily gain; aNDFom, neutral detergent fibre; BW, body weight; CP, crude protein; ED, apparent gross energy digestibility; EE, ether extract; FCR, feed conversion ratio; IMF, intramuscular fat; MUFA, monounsaturated fatty acids; OMD, apparent organic matter digestibility; PUFA, polyunsaturated fatty acids; SFA, saturated fatty acids. ∗ Corresponding author. Tel.: +34 876554168; fax: +34 976761590. E-mail address: [email protected] (M.A. Latorre). http://dx.doi.org/10.1016/j.anifeedsci.2014.08.007 0377-8401/© 2014 Elsevier B.V. All rights reserved.

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Table 1 Analyzed chemical composition of the barley and olive cake used in the trial (g/kg, as fresh basis unless otherwise indicated).a Barley

Gross energy (MJ/kg) Dry matter Organic matter Crude protein Ether extract Neutral detergent fibre Acid detergent fibre Acid detergent lignin Fatty acids (g/kg of total fatty acids) C14:0 C16:0 C18:0 C18:1 C18:2 C18:3 a b

Olive cake Partially dried

Partially dried and pittedb

16.3 904 880 107 23.5 174 57.4 10.6

21.5 932 908 49.5 69.5 676 532 211

22.5 909 870 84.8 117 545 427 188

– – – – – –

– – – – – –

1.23 104 23.7 679 151 10.2

Analyzed in duplicate samples. Olive cake included in the experimental feeds.

1. Introduction The high prices of the main raw materials for animal feeding during last years has carried out an important increase of productive costs in farms. As a consequence, alternative ingredients have been evaluated but they must maintain optimum productive performances in animals and quality in the end product. In this context, some agro-industrial by-products such as olive cake, citrus pulp or grape marc, may be advantageously used. Spain is the greatest producer of olive oil with 2 million cultivated hectares of olive trees and a yearly mean production of 8 million tons of olives and 1.4 million tons of olive oil (Food and Agriculture Organization of the United Nations, 2012). The intensive growing and processing of olives produces large quantities of by-product (approximately 800 kg olive cake/Tm olives; Martín García et al., 2003) which is used in different ways. It can be pressed again for a second oil extraction whose economic value is lower than that obtained from the first extraction. Also, it is used as fuel for boilers. The chemical composition of olive cake varies widely depending on the olive variety, the proportion of its main components (skin, pulp and stone) and the extraction processing of oil (Alcaide and Nefzaoui, 1996). This by-product has been tested in sheep and lambs with a moderate success (Alcaide et al., 2003; Ben-Salem and Znaidi, 2008) because of the high proportion of residual fat. This should not be an inconvenient for porcine diets; however, the high lignin content from the stone limits its use in growing pigs. On the other hand, the proportion in monounsaturated fatty acids (MUFA), especially in oleic acid, could turn it an interesting dietary ingredient because it might modify the fatty acid profile of the pig fat tissues (Rhee et al., 1988; Mas et al., 2010). It has to be taken into account the increasing demand of modern society for healthy meat with less saturated fatty acids (SFA). The information in the literature about the use of olive cake in swine feeding is really scarce and mainly focused in traditional systems based on autochthonous pigs (Rupic´ et al., 1997; Hernández-Matamoros et al., 2011) fattened with different feeding and production systems to those used in improved pigs reared indoor. Therefore, the aim of this study was to investigate the effects of replacing barley by increasing levels of olive cake in the diet on growth performances, digestibility and carcass, meat and fat quality of finishing pigs. 2. Materials and methods 2.1. Experimental diets Fresh olive cake, as by-product of the first extraction of oil from olives (variety Empeltre), was taken from an olive-mill located in the North-Eastern of Spain (Cooperativa San Macario, Andorra, Teruel). Initially, it had high proportions of moisture (approximately 500 g/kg) and stone (rich in lignified fibre). Therefore, for the trial, it had to be partially dried (to 80–90 g moisture/kg) in an oven (at 55 ◦ C for 24 h), shredded using a mixer (50 rpm for 1 h) and sieved by a wire mesh (1.5 mm). Four experimental diets were formulated in base on increasing levels of olive cake (0, 50, 100 and 150 g/kg feed). The control diet (0 g/kg feed) contained barley and soybean meal as main ingredients and met or exceeded the nutrient levels ˜ recommended by Fundación Espanola Desarrollo Nutrición Animal (2013) for finishing pigs. The other diets were formulated by partial replacing barley with the same proportion of olive cake. All diets were formulated to be isoproteic although neutral detergent fibre (aNDFom) and ether extract (EE) increased with the dietary level of olive cake. The characterization of the chemical composition of olive cake and barley used in the trial is shown in Table 1. In additions, the ingredient composition ˜ Desarrollo Nutrición Animal, 2010) and analyzed nutrient composition of diets are and the estimated (Fundación Espanola presented in Table 2.

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Table 2 Composition and nutrient content of the experimental diets (g/kg, as fresh basis unless otherwise indicated). Olive cake (g/kg of diet)

Ingredient Barley Soybean meal (0.44 CP) Olive cake Sunflower oil l-Lysine (0.50) dl-Methionine (0.99) Sodium chloride Calcium carbonate Dicalcium phosphate Minerals, vitamins and additivesa Analyzed compositionb Gross energy (MJ/kg) Dry matter Organic matter Starch Crude protein Neutral detergent fibre Ether extract Fatty acids (g/kg of total fatty acids) C14:0 C16:0 C18:0 C18:1 C18:2 C18:3 Estimated analyses Acid detergent fibre Acid detergent lignin Lysine Calcium Available phosphorous

0

50

100

150

787 180 – 5.00 2.30 0.30 4.00 11.0 6.40 4.00

737 180 50 5.00 2.30 0.30 4.00 11.0 6.40 4.00

687 180 100 5.00 2.30 0.30 4.00 11.0 6.40 4.00

637 180 150 5.00 2.30 0.30 4.00 11.0 6.40 4.00

17.9 907 854 446 167 166 19.9

18.0 909 852 418 167 186 26.4

18.3 910 847 389 164 213 29.5

18.6 911 851 361 163 226 33.1

8.91 259 54.2 200 329 26.4

7.23 241 44.9 320 238 17.4

5.92 213 41.6 403 199 15.0

4.96 198 39.0 452 174 14.5

6.23 0.92 7.89 6.88 2.44

8.12 1.78 7.73 7.35 2.38

9.91 2.73 7.58 7.82 2.33

11.69 3.59 7.42 8.28 2.27

a Provided the following (per kg of complete diet): 6500 IU retinyl acetate; 2000 IU cholecalciferol; 6 IU all-rac-␣-tocopheryl acetate; 4 g menadione; 1.5 g thiamin; 16 g cyanocobalamin; 18 g niacin; panthotenic acid 9 g; 75 g sodium chloride; 110 g Zn; 16.6 g Mn; 99.9 g Fe; 12 g Cu; 0.48 g Co; 0.21 g Se; 0.99 g I; 499.8 FTU 4920 6-phytase and 10 IU E 4818 endo-1,4 ␤-xylanase. b Analyzed in duplicate samples.

Pigs received the experimental diets as meal, given ad libitum, and had free access to fresh water throughout the experiment which lasted 35 days. The feeds were sampled weekly and pooled for subsequent chemical analyses. 2.2. Animals and facilities All procedures using animals were carried out under a Project License approved by the Comisión Ética Asesora en Experimentación Animal from the University of Zaragoza, Spain. Care and use of animals were performed according to the Spanish Policy for Animal Protection 32/2007, which meets the European Union Directive 86/609 on the protection of animals used for experimental and other scientific purposes. A total of sixty Duroc×(Landrace×Large White) crossbred gilts, with 126 ± 3 days of age and weighing 69.5 ± 5.02 kg of body weight (BW) were chosen from a commercial farm (Turolense Ganadera SA, Teruel, Spain) and transported 130 km to the experimental facilities. Upon arrival, pigs were ear-tagged, distributed within each experimental treatment in five pens (blocks) of increasing BW in a randomized block design, resulting in five replicates of three gilts per treatment. Animals were housed in 100% slotted floor pens (2.0 m × 2.0 m) provided with a grow feeder and an automatic drinking device, in a temperature-controlled barn (20–22 ◦ C). The possible pathological incidences and deaths were daily controlled. 2.3. Growth performance and faeces sampling Individual BW and feed consumption per pen were weekly recorded from the arrival of gilts to the end of the trial, and the cumulative data recorded were used to calculate average daily gain (ADG) and average daily feed intake (ADFI) as the linear regression coefficient for each replicate. Feed conversion ratio (FCR) was also calculated from both parameters. From days 28 to 33 of the trial, chromium oxide as indigestible marker was added at 2 g/kg, and labelled feeds were sampled. On days 32 and 33 of the trial, representative faecal samples were collected from each pen between 9:00 and 10:00 am, dried (60 ◦ C, 72 h), ground to 1 mm and stored prior to chemical analysis for the determination of apparent organic

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matter and gross energy digestibility (OMD and ED, respectively). After 35 days of experiment, pigs were slaughtered for carcass and meat evaluation, as it will be described below.

2.4. Carcass measurements and meat and fat sampling The day before slaughter, animals (161 ± 3 days of age) were individually weighed (96.7 ± 7.45 kg) and transported 100 km to a commercial abattoir (Turolense Ganadera SA, Teruel, Spain), where they were kept in lairage for 8 h with full access to water but not feed. Gilts were stunned by exposure to CO2 (83% mean atmosphere concentration of gas; CO2 cycle of 90 s, with 60 s interval between discharges and sticking). After stunning, they were exsanguinated, scalded, dehaired, eviscerated and split down the midline according to standard commercial procedures. At the end of the slaughter line, hot carcass weight was individually recorded and used to calculate dressing percentage. At 45 min postmortem, carcass length from the posterior edge of the symphysis pubis to the anterior edge of the first rib, ham length from the anterior edge of the symphysis pubis to the hock joint, and ham perimeter at its widest were measured on the left side of each carcass using a flexible ruler with a precision of 0.5 cm. In addition, fat depth at 3rd to 4th last ribs and also at level of Gluteus medius muscle were measured by a ruler with a precision of 1 mm. The head was removed at the atlanto-occipital junction and carcasses were suspended in the air and refrigerated at 2 ◦ C (1 m/s airspeed; 90% relative humidity) for 12 h. Then, carcasses were processed, and hams, shoulders and loins were trimmed (removing part of the covering fat) to fit commercial requirements. Then they were individually weighed to calculate trimmed ham, shoulder and loin yields. After collection of these data, a section of 500 ± 25 g of loin (Longissimus thoracis muscle) was excised at the last rib level from each carcass. Also, a subcutaneous fat sample including fat layers, skin and lean was taken at the tail insertion in the coxal region. Meat and fat samples were placed in individual plastic bags and vacuum-packaged at −20 ◦ C until subsequent analyses.

2.5. Laboratory analyses Pooled samples of feeds, olive cake, barley and faeces were ground to a 1 mm mesh size with a Wiley mill to be analyzed in duplicate. In feeds, olive cake and barley samples, the dry matter was determined by oven drying at 105 ◦ C to constant weight (ref. 934.01), organic matter and total ash by muffle furnace (ref. 942.05), crude protein (CP) by the Kjeldahl method (ref. 976.05) and EE by Soxhlet analysis (ref. 2003.05) following the procedures of Association of Official Analytical Chemists (2005). Gross energy was determined by an isoperibolic bomb calorimeter (model 1356, Parr Instrument Company, Moline, IL, USA). In addition, the starch of feeds was analyzed by polarimetry after hydrolysis with ethanol and HCl (Commission of the European Communities, 1999). The aNDFom was assayed after treatment with heat stable amylase and expressed exclusive of residual ash, and this and the ash free acid detergent fibre and lignin were determined as described Van Soest et al. (1991) using an Ankom 220 Fiber Analyzer equipment (Ankom Technology, New York, USA). The chromium concentration in feeds and faecal samples were analyzed following the recommendations of Vega and Poppi (1997). Meat samples were evaluated for colour, chemical composition, water holding capacity and hardness. Briefly, the meat samples were thawed in vacuum-package bags for 24 h at 4 ◦ C, removed from packages, blotted dry for 20 min and weighed. Thawing loss was calculated with data from fresh and thawed weights. Loin colour was evaluated with a chromameter (CM 2002, Minolta Camera, Osaka, Japan) using objective measurements (Commission International de l’Eclairage, 1976). The average of three random readings was used to measure lightness (L*), redness (a*) and yellowness (b*). Additionally, chroma √ (c*) and hue angle (h*) were calculated as c* = (a*2 + b*2 ) and as h* = tan−1 (b*/a*)·57.29, respectively. Chroma is related to the quantity of pigments and high values represent a more vivid colour, and h* is the attribute of a colour perception related to the state of pigments (Wyszcecki and Stiles, 1982). Chemical composition of meat samples was analyzed for moisture by oven drying method, CP by using a Kjeldahl MT 2300 analyser (Höganäs, Switzerland) and intramuscular fat (IMF) by an ANKOM XT15 equipment (New York, USA) according to Boletín Oficial Estado (1979). Cooking loss was determined by the method described by Honikel (1998). Briefly, a loin slice (200 ± 20 g) was taken from each chop, weighed, placed in a plastic bag, and cooked to an internal temperature of 70 ◦ C in a 75 ◦ C water bath (Precisterm, J.P. Selecta S.A., Barcelona, Spain). Internal temperature was monitored during cooking with a handheld temperature probe (model HI 9063, Hanna Instruments, Woonsocket, RI). Cooked samples were allowed to cool at 15 ◦ C for 30 min, blotted dry, and weighed. Cooking loss was calculated with data from thawed and cooked weights. Samples were then cut in parallel to the long axis of the muscle fibres into rectangular cross-section slices of 10 mm × 10 mm and 30 mm length. Slices (6 per chop) were sheared perpendicularly to the fibre orientation, with a Warner-Bratzler device attached to an Instron Universal testing machine model 4301 (Massachusetts, USA). Lipids from subcutaneous fat samples were extracted in chloroform methanol, according to Bligh and Dyer (1959) and butylated hydroxytoluene was used as antioxidant. Fatty acid methyl esters were generated by trans-esterification of lipids extracts dissolved in n-hexane with KOH in methanol. Fatty acid methyl esters were collected in hexane for further analysis. The fatty acid composition was determined using a Hewlett-Packard 6890 II gas chromatograph with a capillary column SP2380 (100 m × 0.25 mm × 0.20 ␮m). Nitrogen was used as a gas carrier and the methyl esters were identified using retention times of Sigma chemical Co. standards. The lipids from feeds and olive cake samples were extracted and quantified by

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Table 3 Effect of increasing olive cake level in the diet of pigs on growth performance and apparent digestibility of organic matter and energy. Level of olive cake in diet (g/kg)

Initial body weight (kg) Final body weight (kg) Average gain (kg/day) Average feed intake (kg/day) Average apparent digestible energy intake (MJ/day) Feed conversion ratio Organic matter digestibility Gross energy digestibility

0

50

100

150

69.3 96.2 0.76 2.39y 33.6y 3.15 0.81 0.78x

69.4 97.0 0.78 2.55y 34.9y 3.27 0.80 0.76xy

69.6 98.7 0.84 2.78x 38.7x 3.30 0.79 0.76xy

69.5 94.9 0.72 2.515y 35.0y 3.53 0.78 0.75y

SEMa

Pb

0.367 1.158 0.077 0.029 1.081 0.151 0.009 0.009

NS NS Q0.06 Q0.04 Q0.04 NS Q0.06 L0.04

a

Standard error of the mean. There were 5 replicates (pens) per treatment with 3 pigs each. NS: not significant (P>0.10); L: linear; Q: quadratic. x,y: within a row, means without a common superscript letter differ (P<0.05). b

the method of Sukhija and Palmquist (1988). The proportions of total SFA, MUFA and polyunsaturated (PUFA) fatty acids were calculated from individual fatty acid percentages. 2.6. Statistical analysis Data were analyzed using Statistix 9.0 (Analytical Software 2008) by polynomial contrasts to evaluate linear, quadratic and cubic effects. The model included the diet as main effect and the initial BW as a block. The experimental unit was the pen (n = 5) with three gilts each. Statistical differences among mean values were assessed by the Tukey’s test. A P-value of ≤0.05 was considered as a significant difference between treatments and a P-value between 0.05 and 0.10 as a trend. 3. Results 3.1. Growth performances and nutrient digestibility No death was recorded during the trial. Although FCR was not affected (P>0.10), the ADFI increased (P=0.04) and the ADG also tended to increase (P=0.04) with the olive cake level in the diet (Table 3). In both cases, the evolution was quadratic, reaching the maximum values with the pigs given 100 g olive cake/kg and decreasing after, when 150 g olive cake/kg was fed. The daily apparent digestible energy intake also had a quadratic evolution (P=0.04) being higher with 100 g olive cake/kg than with the other diets. In addition, the OMD tended to decrease quadratically (P=0.06), especially between the control diet and 50 g olive cake/kg, and the ED decreased linearly (P=0.04) with the level of by-product in diet. The slaughter weight of pigs was not affected by the experimental treatment (P>0.10). 3.2. Carcass quality No differences due to the experimental treatment (P>0.10) were detected in carcass yield or ham length (Table 4). However, the carcasses from pigs fed 100 g olive cake/kg were heavier (P=0.04) and longer (P=0.01), and had wider hams Table 4 The effect of increasing olive cake level in diet on carcass characteristics of pigs. Level of olive cake in diet (g/kg)

Carcass weight (kg) Carcass yield (%) Carcass length (cm) Ham length (cm) Ham perimeter (cm) Backfat thickness 3rd to 4th last ribs (mm) Fat depth at m. gluteus medius (mm) Yield of main lean joints (% carcass) Hams Loins Shoulders Totalb a

Pb

0

50

100

150

74.6y 77.7 79.8y 36.8 70.9y 19.7 12.7x

74.4y 76.7 80.1y 36.7 72.9y 22.1 13.1x

77.9x 78.9 82.3x 36.8 74.1x 20.4 11.5xy

73.3y 77.3 79.5y 36.2 72.2y 18.7 10.0y

0.93 1.06 0.52 0.28 0.81 0.98 0.85

Q0.04 NS Q0.01 NS Q0.03 NS L0.02

28.5 7.96 15.9 52.3

28.6 8.09 15.9 52.6

28.0 8.05 15.5 51.5

28.2 8.16 16.0 52.3

0.40 0.13 0.28 0.67

NS NS NS NS

Standard error of the mean. There were 5 replicates (pens) per treatment with 3 pigs (carcasses) each. NS: not significant (P>0.10); L: linear; Q: quadratic. x,y: within a row, means without a common superscript letter differ (P<0.05). b

SEMa

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Table 5 The effect of increasing olive cake level in diet on fatty acid profile (g/kg) of subcutaneous fat of pigs. Level of olive cake in diet (g/kg)

C12:0 C14:0 C16:0 C16:1 C17:0 C17:1 C18:0 C18:1 C18:2 C18:3 C20:0 C20:1 C20:4 C20:5 Othersc SFAd MUFAe PUFAf a b c d e

0

50

100

150

0.78 11.9 218 19.4 4.60x 3.58x 125x 412y 156 9.92 1.76 6.76y 3.42 2.16 24.6 369x 447y 184

0.08 12.1 220 18.5 4.82x 3.58x 124x 413y 156 9.70 1.80 7.08xy 2.76 2.08 24.3 369x 447y 183

0.09 11.8 217 17.7 4.68x 3.44x 121xy 417xy 159 9.96 2.04 7.34xy 2.54 1.90 23.9 364xy 450xy 186

0.08 11.7 212 17.8 3.94y 2.98y 117y 424x 160 9.96 1.90 7.70x 3.12 2.28 24.2 353y 458x 190

SEMa

Pb

0.035 0.320 2.970 0.611 0.181 0.107 2.041 2.878 3.709 0.263 0.076 0.209 0.551 0.297 0.720 4.292 3.308 4.445

NS NS NS NS L0.02 Q0.02 L0.001 Q0.04 L0.01 L0.01 NS NS L0.07 L0.01 NS NS NS L0.01 L0.02 NS

Standard error of the mean. There were 5 replicates (pens) per treatment with 3 pigs (1 fat sample/pig) each. NS: not significant (P>0.10); L: linear; Q: quadratic. The sum of some minor fatty acids.  Saturated fatty acids.

  Monounsaturated fatty acids.

f Polyunsaturated fatty acids. x,y: within a row, means without a common superscript letter differ (P<0.05).

(P=0.03) than those from pigs fed the other diets. Fat depth at Gluteus medius muscle decreased linearly (P=0.02) as the olive cake inclusion increased. No effect of dietary treatment was observed on the proportion of main lean cuts (hams, shoulders and loins) in the carcass (P>0.10). 3.3. Meat and fat characteristics Chemical composition, water holding capacity and hardness were not modified by the experimental treatment (P>0.10; data not shown). However, lightness linearly decreased (P=0.02) and yellowness tended to linearly decrease (P=0.06) as olive cake increased in the diet. The by-product inclusion had a significant effect on fatty acid profile of subcutaneous fat (Table 5). The increase in the level of dietary olive cake promoted a linear reduction of SFA proportion (P=0.01) due to a quadratic reduction of C17:0 (P=0.02) and a linear decrease of C18:0 (P=0.01). Although C20:0 tended to increase (P=0.07), its contribution was minimal (on average 0.12% of total SFA). In addition, it was observed a linear increase in the MUFA percentage (P=0.02) because of linear increases (P=0.01) in C18:1 and C20:1, although the minority C17:1 (less than 0.08% of total MUFA) was decreased quadratically (P=0.04). The total PUFA proportion was not affected by dietary treatment (P>0.10). 4. Discussion 4.1. Chemical composition of olive cake The results of chemical composition analyses of olive cake show low CP and high EE and lignin contents, confirming previous works (Alburquerque et al., 2004; Alvarez-Rodríguez et al., 2009; Vargas-Bello-Pérez et al., 2013). A high variability in the composition of this by-product has been reported in the literature as it also happens with other by-products. Some reasons for it can be the different oil extraction method and olive varieties, the possibility of contaminations (i.e. with soil) or the posterior processing out such as drying or pitting. Thus, Alvarez-Rodríguez et al. (2009) evaluated the olive cake obtained in a two-phase system and found a similar composition to that reported here, except for a higher EE (265 vs. 117 g/kg), which was considered too high by the authors themselves. Alburquerque et al. (2004) analyzed a total of 20 samples of three campaigns (1997–2000) and found (on dry matter basis) 72 g CP/kg (ranged from 44 to 115 g/kg) and 121 g EE/kg (ranged from 77 to 194 g/kg). Alcaide et al. (2003) studied a high number of samples and detected wide ranges; 47–72.5 g CP/kg, 41–139 g EE/kg and 574–730 g aNDFom/kg (expressed on dry matter basis). Also, it has to be considered the high oleic content detected in the olive cake used in the present experiment (679 g/kg) although other authors have even found a higher proportion (758 g/kg; Vargas-Bello-Pérez et al., 2013). From all this, it can be deduced the importance of a high accuracy in the characterization of by-products prior to be used in the formulation of commercial feedstuffs.

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4.2. Growth performances and nutrient digestibility A quadratic effect of diet on ADFI was observed; the feed consumption increasing up to a maximum level reached with 100 g olive cake/kg. This could be related to the energy content of diet. The initial estimated metabolizable energy was 12.6, 12.2, 11.8 and 11.5 MJ/kg for diets containing 0, 50, 100 and 150 g olive cake/kg, respectively. To formulate the experimental ˜ Desarrollo Nutrición Animal (2010) for conventional ingrediets, we used the energy data provided by Fundación Espanola dients and the equation of Noblet et al. (2003) to estimate the energy content of olive cake. Cole et al. (1967) reported that, under ad libitum conditions, pigs try to keep a constant energy intake regulating the feed intake. However, the inclusion of 150 g olive cake/kg reduced ADFI and also the daily apparent digestible energy intake was decreased, compared with the 100 g/kg level, and it might be due to the refuse of feedstuff because of palatability problems or due to the high dietary fibre content which may cause satiety (Santomá, 1997). However, some authors have evaluated several fibrous ingredients in diets of growing pigs such as raygrass hay (Coffey et al., 1982), beet molasses (Longland and Low, 1988) or lupins (Brand et al., 1995), agreeing that the type of fibre has more influence on feed intake than the proportion of fibre. This would explain the good growth rate and feed consumption of pigs given diets containing 50 or 100 g olive cake/kg although the dietary ˜ aNDFom contents were higher than those recommended for growing pigs (Fundación Espanola Desarrollo Nutrición Animal, 2013). The ADG evolved quadratically in the same way than ADFI, with those pigs fed 100 g olive cake/kg reaching a 12% (83 g/day) higher growth rate than those fed the control diet and a 17% (126 g/day) higher rate than those fed 150 g olive cake/kg. The decreasing quadratic trend of OMD and the decreasing linear significance of ED as olive cake increased in the diet would be related to the dietary fibre level. In fact, an increase of 0.4 g aNDFom/kg per g of olive cake included in diet was observed. Our results confirm those reported by Le Gall et al. (2009) who detected significant quadratic decreases in OMD and ED when aNDFom increased from 131 to 344 g/kg in the feed of growing pigs. These depressive effects are caused firstly by the replacement of highly digestible nutrients such as CP or starch by partly undigestible cell wall materials (lignin, nonstarch polysaccharides) and secondly because the presence of dietary fibre influences the digestion and absorption processes along the gastrointestinal tract. From a productive point of view, the results obtained suggest that up to 100 g olive cake/kg can be included in commercial diets for growing pigs without impairing but even improving growth performance traits. 4.3. Carcass quality Although no effect of diet was observed on the slaughter weight (at the same age at slaughter), a quadratic increase of carcass weight was given reaching a maximum when 100 g olive cake/kg. Besides, those pigs fed this diet had longer carcasses and wider hams. Latorre et al. (2004) studied the relationship between pig slaughter weight and carcass size and observed an increase of carcass length and ham perimeter of 2 cm and 1.1 cm, respectively, per each increase of 10 kg BW. In general, shorter carcasses are commercially preferred because of their easier manipulation; however, Mediterranean consumers demand longer and thinner hams because those characteristics are currently associated to high quality hams. No influence of treatment was detected on carcass yield. Some authors (Baird et al., 1974; Coffey et al., 1982) have found a decrease in dressing percentage as dietary fibre level increased, whereas others (Donovan et al., 1993; Longland and Low, 1988) did not detect any effect. In a review, Santomá (1997) concluded that fibre stimulates the development of the gastrointestinal tract, which is removed during the slaughter, but the effect could depend on the length of the feeding period. The backfat thickness measured at Gluteus medius muscle decreased linearly as the dietary olive cake increased. This was unexpected considering the evolution observed in daily apparent digestible energy intake. In fact, several works have shown that the energy content of diet has a high impact on fatness in pigs (Suarez-Belloch et al., 2013) and poultry (Engel et al., 2001). In addition, Latorre et al. (2004) found a negative relationship between carcass fatness and yield of main lean cuts. In this regard, in the current trial, no effect was detected on fat depth at 3rd to 4th last ribs and also pigs from all treatments had similar proportion of hams, shoulders and loins. 4.4. Meat and fat characteristics The L* and b* values of loin decreased linearly as the dietary level of olive cake increased. The literature indicates that the IMF content can be also responsible, at least in part, for the tenderness (Barton-Gade, 1987) and for the yellowness (Latorre et al., 2008) of meat. However, in the current work, although the IMF proportion decreased and the hardness increased numerically with the level of olive cake, the effects were not significant. The loss of moisture neither was affected by the inclusion of the by-product in diet. Higher water holding capacity (lower moisture loss) have been related to higher pH values at 24 h postmortem which is associated to the lower glycogen reserve. However, in the present trial, it cannot be confirmed because pH could not be measured. One of the most expected results of the use of olive cake in pig diets was its effect on fatty acid profile of fat. However, Wood and Enser (1997) reported that major SFA and MUFA are synthesized and their concentrations are less influenced by diet than PUFA, which cannot be synthesized and therefore their tissue concentration responds rapidly to dietary changes. In the current work, the increase of dietary level of olive cake promoted a linear reduction of SFA proportion and a linear increase in the MUFA percentage. This agrees with the reports of Hernández-Matamoros et al. (2011), who found a higher

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concentration of MUFA and a lower of PUFA in IMF of Iberian pigs when olive cake was included in diet. The increase detected in MUFA in the fat tissue was mainly due to the high content in C18:1 in olive cake (679 g/kg). In a study of Rhee et al. (1988), high levels of high-oleic sunflower seed oil increased the concentration of oleic acid in muscle lipid from 42 to 53 g/100 g which improved sensory quality of meat in terms of tenderness, juiciness and flavor. The effect on flavor was presumably due to changes in the concentrations of flavor precursors developed during cooking. In the current trial, the PUFA proportion was not affected by the dietary treatment. Literature has demonstrated that diets rich in PUFA provide a high susceptibility to oxidation but our results were totally normal (Wood et al., 2008). 5. Conclusions The inclusion of moderate levels of olive cake (up to 100 g/kg) in diets for finishing pigs tended to improve the daily growth and decreased the carcass fat thickness. Although its effect was limited on meat characteristics, the use of dietary olive cake improved the fat composition by decreasing the total saturated fatty acids and increasing the total monounsaturated fatty acids, notably the proportion in oleic acid, which is also desirable from the point of view of consumer health. Conflict of interest statement The authors declare no conflicts of interest. Acknowledgements This work was funded through the CDTI Project IDI-20090836 (OTRI 2010/0397) of the Ministry of Science and Technology (Spanish Government), with participation of the Department of Industry and Innovation of the Government of Aragón and the European Social Fund. Jesús Suarez was granted by the University of Zaragoza. Thanks are also given to J. Artajona and B. 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