COBISS: 1.08 Agris category code: L51
THE ENERGY VALUE OF OLIVE OIL SOAP STOCKS FOR IBERIAN CROSSBRED PIGS
María Luz ROJAS-CANO Virginia RUIZ-GUERRERO Ana HARO , Luis LARA Rosa NIETO Jose Fernando AGUILERA 1 2
abstract
Twenty four Iberian x Duroc 50:50 barrows of 50 kg initial body weight (BW) were placed in individual pens and allotted to 4 dietary treatments in which olive oil soap stocks (OSS) replaced 0, 25, 50 and 75 g/kg of a basal diet based on barley, corn, soyabean meal and wheat middlings. The apparent digestibility of nutrients and the N balance were studied. In a second experiment, sixteen pigs in the finishing stage of growth were randomly allotted to two experimental diets containing 12.5 and 62.5 g of OSS/kg in replacement of the basal diet. Daily feed allowance was fixed at 0.90 x ad libitum intake, in two equal meals. The apparent digestibility of dry matter (DM), organic matter, crude protein (CP), crude fat (ether extract; EE) and gross energy (GE) was not altered by the level of OSS dietary inclusion, remaining at 0.793 ± 0.0078, 0.825 ± 0.0070, 0.767 ± 0.0131, 0.857 ± 0.0134 and 0.799 ± 0.0084, respectively. OSS contain 31.24 MJ ME/kg. No differences in N retention were found between the experimental diets, the average value being 23.2 ± 1.04 g N retained daily. The inclusion of OSS in the diet of the finishing pigs improved the average daily gain (924 ± 23.9 vs. 838 ± 23.9 g; P < 0.05), and showed a tendency to improve the feed conversion ratio (3.78 ± 0.125 vs. 4.11 ± 0.125; P = 0.077). However, Gain:ME intake (g/MJ) remained unchanged at 19.6 ± 0.40 on average.
Key words: olive oil soap stocks / energy value / Iberian pigs
1 introduction
Olive oil soap stocks (OSS), a by-product of the olive oil extraction industry, is a valuable source of oleic acid highly appreciated as a supplement in diets for fattening Iberian pigs reared on intensive feeding systems (González and Tejeda, 2007; González et al., 2012). Their use is limited by the content of unsaturated fatty acids (FA), due to the negative effect these FA may have on meat quality (FEDNA, 2003). Due to the high proportion of free FA, their digestibility tends to be comparatively lower than that of the oils they come from (Powles et al., 1995). Estimations of their energy value are currently made based on chemical parameters (free FA content, degree of unsaturation) by equations derived from studies carried out with other fat resources (Powles et al.,
1995). Furthermore, in spite of their extensive use, no systematic evaluation has been carried out on the effects of the use of OSS as ingredient of the feed mixture on feed efficiency, digestibility of nutrients and on protein accretion. The purpose of the present work was to determine the effects of the inclusion of OSS in the diet on growth performance, nutrient digestibility and N utilization of crossbred growing Iberian pigs.
2 materials and methods
A digestibility and balance trial was performed in Iberian (IB) x Duroc (DU) 50:50 barrows of app. 50 kg body weight (BW). The pigs were individually housed in 2 m2 pens located in an environmentally controlled room
1	Department of Physiology and Biochemistry of Animal Nutrition, Animal Nutrition Institute (INAN), Estación Experimental del Zaidín (CSIC), Camino del Jueves s/n, 18100 Armilla, Granada, Spain
2	Corresponding author, e-mail: jose.aguilera@eez.csic.es
at 20 ± 2 °C and randomly assigned to 4 homogeneous groups of 6 or 7 pigs each. Each group was offered one experimental diet. Four diets were prepared by replacing 0, 25, 50 and 75 g/kg of a basal diet, based on barley grain, corn grain, soyabean meal and wheat middlings (analysed composition (g/kg): CP, 145; acid detergent fibre, 52.4; total ash, 68.3. GE, 16.17 MJ/kg) with OSS to provide 4 different dietary fat contents [EE: 20.8, 46.2, 56.2 and 86.6 g/kg]. The amino acid (AA) pattern of the dietary protein followed the ideal protein concept (BSAS, 2003). The analysed composition of OSS was (g/kg): DM, 971; EE, 966; total N, 0.63; total ash, 1.34; GE, 38.77 MJ/ kg. Main fatty acid relative profile in the crude fat fraction was (%): C16:0, 13.3; C18:0, 3.39; C18:1 cis 9, 67.4; C18:1 cis 11, 2.04; C18:2 n6 (cis 9, cis 12), 9.99; C18:3 n3 a, 0.911. The SFA/USFA ratio was 0.22. Iodine and saponification indexes were 85 and 190, respectively. The feed mixtures were offered as pellets at 0.90 x ad libitum intake (estimated as described by Nieto et al., 2001), in 2 equal daily meals. Feed refusals were daily collected, dried and weighed to calculate actual feed intakes.
A feeding experiment was performed at the finishing stage of growth. Sixteen pigs were randomly allotted to two homogeneous groups of eight pigs each. Two experimental diets were prepared containing 12.5 and 62.5 g of OSS/kg in replacement of the basal diet. The daily feed allowance was fixed at 0.90 x ad libitum intake, given in two equal meals.
The experimental protocol was reviewed and ap-
proved by the Bioethical Committee of the Spanish National Research Council (CSIC).
Average daily feed intake, BW gain, feed efficiency, total tract apparent digestibility (TTAD) of DM, organic matter (OM), crude protein (CP), crude fat (ether extract, EE) and gross energy (GE), and the N balance were measured. The digestibility trial was initiated when the pigs attained 52.9 ± 0.58 kg BW after a period of 7 days on the restricted feed allowance. Total collection of faeces and urine was performed daily for 5 days. Aliquots were kept at -20 °C until analyses. Urine was collected into 50 ml 4 M-H2SO4. The feeding experiment began when the pigs weighed 90.2 ± 0.93 kg BW. The pigs were individually housed in 5 m2 pens located in a room at 19.0 ± 1.5 °C.
The following analytical procedures were carried out according to AOAC (2003): DM content of diets, OSS and freeze-dried faeces (#934.01); ether extract and total ash of diets, OSS and freeze-dried faeces (#920.39 and #942.05), and total N in diets, OSS and urine, by the Kjeldahl procedure (#984.13). In freeze-dried faeces total N was determined according to the Dumas' method, by total combustion in TruSpec CN equipment (Leco Corporation, USA). Gross energy (GE) of diets, OSS and freeze-dried samples of faeces and urine was measured in an isoperibolic bomb calorimeter (Parr Instrument Co., Moline, IL). The FA content of OSS were extracted and quantified according to Sukhija and Palmquist (1988). Pentadecanoic acid (C15:0; Sigma-Aldrich, Madrid, Spain) was used as internal standard. Fatty acid
Table 1: The effects of increasing proportions of olive soap stocks (OSS) in the diet on nutrient digestibility and N balance of IB x DU 50: 50 growing pigs
Experimental diet
OSS, g/kg	0	25	50	75		P-value	
Basal diet : OSS, g/g	1000 : 0	975 : 25	950 : 50	925 : 75	SEM	Linear	Quadratic
Coefficients of TTAD							
Dry matter	0.791	0.799	0.785	0.797	0.0039	NS	NS
Organic matter	0.825	0.831	0.817	0.826	0.0035	NS	NS
Crude protein	0.773	0.774	0.760	0.760	0.0065	NS	NS
Ether extract	0.865	0.859	0.857	0.846	0.0067	NS	NS
Gross energy (GE)	0.803	0.803	0.791	0.800	0.0042	NS	NS
ME/GE	0.772	0.780	0.768	0.779	0.0042	NS	NS
ME/DE	0.971	0.971	0.971	0.975	0.0011	NS	NS
N balance							
Retained N, g/day	24.8	23.6	22.7	21.8	1.04	NS	NS
Retained N/N intake	0.412	0.412	0.402	0.394	0.018	NS	NS
Retained N/N apparently absorbed	0.540	0.536	0.527	0.518	0.024	NS	NS
TTAD - total tract apparent digestibility 86 Acta agriculturae Slovenica, Supplement 4 - 2013
methyl esters were identified by gas chromatography as described elsewhere (López-Bote et al., 1997).
Orthogonal polynomial contrasts were used to determine linear and quadratic effects of dietary proportion of OSS on digestibility and N balance variables. The StatGraphics software Centurion XV, version 15.2.06, StatPoint Inc was used. The pig was the experimental unit for all the variables studied. Experimental data were also analysed by a one-way ANOVA. Statistical significance was assessed by the Tukey test, and the level of significance was established at 5%.
3	RESULTS
The coefficients of TTAD of DM, OM, CP, EE and GE were not altered by the level of OSS inclusion in the diet (Table 1). Also, the coefficient of metabolizability of GE and the ME:DE ratio remained unchanged The energy density of the diets increased linearly (P < 0.001) from 14.56 to 15.82 MJ of digestible energy (DE)/kg DM and from 13.99 to 15.42 MJ of ME/kg DM on increasing the proportion of OSS in the diet. The ME content of the experimental diets, corrected for N retention equal to zero: MEn = 0, increased linearly from 13.67 to 15.14 MJ/kg DM with increasing proportions of OSS in the diet (P < 0.001). The energy value of OSS, estimated from the linear regression relating the proportion (g/ kg) in which OSS replaces basal diet and the dietary ME content (kJ/g), was 31.24 MJ ME/kg. No differences in N retention were found between treatments. The average level of N retention was 23.2 ± 1.04 g/d, corresponding to average efficiencies of utilization of total N (retained N/N intake) and N apparently absorbed (retained N/ap-parent digestible N) of 0.405 ± 0.018 and 0.530 ± 0.024, respectively.
In the feeding experiment performed in the finishing stage of growth, average daily gain improved (924 ± 23.9 vs. 838 ± 23.9 g; P < 0.05), and feed conversion showed a tendency to improve (3.78 ± 0.125 vs. 4.11 ± 0.125; P = 0.077). in pigs fed the diet containing the highest dietary proportion of OSS. However, the ratio Gain:ME intake (g/MJ) remained unchanged at 19.6 ± 0.40 on average.
4	discussion
In the production of the crossbred IB pig, the incorporation of OSS to the feed mixture as provider of oleic acid is usually practiced to enhance the presence of this FA in animal tissues, thereby upgrading meat quality (González et al., 2012). The present experiment was de-
signed to cover the range of usual levels of incorporation of OSS in the diet for fattening and finishing pigs to validate the practical application of the experimental observations. Growth performance improved in finishing pigs fed the diet containing 62.5 g OSS/kg compared to those fed 12.5 g OSS/kg. Atteh and Leeson (1985) studied the effects of supplementing the diets of weaner pigs with 0, 5 or 10% acidulated soapstock for a period of 6 wk. No significant effect of the dietary soapstock level on feed intake and on the apparent digestibility of protein and fat was found, although there was a decrease (P < 0.05) in average daily gain when dietary soapstock level increased to 10%. Feed:gain ratio was not influenced by diet.
The conversion factor ME/ED = 0.97 determined in the present study, allows us to estimate the DE content of OSS as 33.13 MJ/kg DM (32.14 MJ ME/0.97), practically equal to the value of 33.07 (7.900 Mcal x 4.184) MJ DE/kg DM tabulated by FEDNA (2003). We have not observed any significant negative effect of OSS incorporation on TTAD of nutrients and energy or on N balance. Our results differ from those of Woerfel (1981), who observed decrease in DM, CP, and digestibility of certain AA following the addition of soybean oil soap stock to the diet. Also, Bruce et al. (2006) found in growing pigs a quadratic decrease in the apparent ileal digestibility of DM, CP and 5 AA (Ile, Phe, Trp, Gly, and Ser) when increasing concentrations of soybean oil soap stocks were included in semi-purified diets containing soybean meal.
In conclusion, the inclusion of olive oil soap stocks in the diet of fattening crossbred Iberian pigs up to 75 g/ kg did not affect the apparent digestibility of nutrients or body protein accretion. Olive oil soap stocks contained 32.14 kJ ME/g DM. In finishing pigs, OSS dietary inclusion improved average daily gain and tended to improve feed conversion.
5	acknowledgments
This study was financed by NANTA S.A. (Tres Cantos, Madrid, Spain).
6	references
AOAC 2003. Official Methods of Analysis, 17th ed. Association of Official Analytical Chemists, AOAC International, Gaithersburg, MD Atteh J.O., Leeson S. 1985. Effects of dietary soapstock on performance, nutrient digestibility and bone mineralization in weaner pigs fed two levels of calcium. Canadian Journal of Animal Science, 65: 945-952 Whittemore C.T., Close W.H., Hazzledine M.J. (2002). The need for nutrient requirement standards for pigs. A report
of the British Society of Animal Science nutritional Standards Working Group: pigs. Pig News and Information, 23, 3: 67N-74N
Bruce K.J., Karr-Lilienthal L.K., Zinn K.E., Pope L.L., Mahan D.C., Fastinger N.D., Watts M., Utterback P.L., Parsons C.M., Castaneda E.O., Ellis M., Fahey Jr. G.C. 2006. Evaluation of the inclusion of soybean oil and soybean processing by-products to soybean meal on nutrient composition and digestibility in swine and poultry. Journal of Animal Science, 84: 1403-1414 FEDNA 2003. Tablas FEDNA de composición y valor nutritivo de alimentos para la fabricación de piensos compuestos. Fundación Española para el Desarrollo de la Nutrición Animal, Madrid, Spain González E., Tejeda J.F. 2007. Effects of dietary incorporation of different antioxidant extracts and free-range rearing on fatty acid composition and lipid oxidation of Iberian pig meat. Animal, 1: 1060-1067 González E., Hernández-Matamoros A., Tejeda J.F. 2012. Two by-products of the olive oil extraction industry as oleic acid supplement source for Iberian pigs: effect on the meat's
chemical composition and induced lipoperoxidation. Journal of the Science of Food and Agriculture, 92: 2543-2551 López-Bote C., Rey A., Ruiz J., Isabel B., Sanz Arias R. 1997. Effect of feeding diets high in monounsaturated fatty acids and a-tocopheryl acetate to rabbits on resulting carcass fatty acid profile and lipid oxidation. Animal Science, 64: 177-186
Nieto R., Lara L., García M.A., Gómez F., Zaldive M., Cruz M., Pariente J.M., Moreno A., Aguilera J.F. 2001. Evaluación de un sistema integrado de alimentación en el cerdo ibérico. Análisis del consumo de alimentos e índices productivos. Sólo Cerdo Ibérico, 6: 57-59 Powles J., Wiseman J., Cole D.J.A., Jagger S. 1995. Prediction of the apparent digestible energy value of fats given to pigs. Animal Science, 61: 149-154 Sukhija P.S., Palmquist D.L. 1988. Rapid method for determination of total fatty acid content and composition of feedstuff's and feces. Journal of Agricultural and Food Chemistry, 36: 1202-1206
Woerfel J.B. 1981. Processing and utilization of by-products from soy oil processing. Journal of the American Oil Chemists' Society, 58: 188-191