Carcass traits, meat yield and fatty acid composition of adipose tissues and Supraspinatus muscle in goats fed blend of canola oil and palm oil

The study was conducted following the guidelines of research policy of the Universiti Putra Malaysia on animal welfare and ethics.

Twenty four Boer bucks (4–5 months old, 20.54 ± 0.47 kg body weight) were used in the study. Each animal was individually housed in wooden slatted floor pens (1.20 m × 0.80 m × 0.70 m) equipped with feeding and drinking facilities. The animals were randomly assigned to dietary treatments containing on dry matter basis 0, 4 or 8 % BCPO and fed for 100 d following two weeks of adaptation. All diets were formulated to meet the nutritional requirements of growing goats based on NRC [19] recommendations and animals were fed twice daily with ad libitum access to clean water. The proximate composition of the diets was determined following the method of AOAC [20] while acid detergent fibre (ADF) and neutral detergent fibre (NDF) were determined following the method of Van Soest et al. [21]. The ingredients and chemical composition of dietary treatments are presented in Table 1 while the fatty acid (FA) composition of the diets is presented in Table 2.

The animals were fasted for 12 h with free access to water, weighed and slaughtered in a commercial abattoir according to the Halal procedure as outlined in MS1500:2009 [22]. After slaughter, the head, fore- and hind limbs were removed at the atlanto-occipital, carpal and tarsal joints respectively. The animals were skinned while suspended by their achilles tendon and later eviscerated. Carcass and non-carcass components were weighed. Subcutaneous fat was sampled from inguinal region, omental fat was sampled near its free part close to the rumen (omentum majus), perirenal fat was sampled near the kidney on its great curve (between the renal fascia and renal capsule), and mesentery fat was sampled between the ileum and jejunum while pelvic fat was sampled at the left pelvic region. The Supraprinatus muscle was sampled from the right forelimb. The weight of gut fill was estimated by subtracting the weight of empty gut from the weight of full gut. Empty body weight was estimated as the difference between the slaughter weight and weight of gut fill. Dressing percentage (based on full live body weight and empty body weight) was estimated as described by Kadim et al. [23]. Dressed carcasses were weighed (hot carcass weight) within 45 min postmortem, chilled at 4 °C for 24 h and reweighed (cold carcass weight). Chilling loss was estimated as the difference between hot and cold carcass weight expressed as percentage. Carcasses were split along the midline into right and left halves. The right half was separated into neck, shoulder, breast flank, loin and leg cuts. Each cut was separated into lean, fat and bone. Longissimus muscle area (rib eye area) was measured between the 12th and 13th ribs using tracing paper and estimated using two-dimension polygons area calculator software as described by Branscome and Jesseman [24]. Carcass linear measurements were determined as outlined by Fisher and De Boer [25] and Laville et al. [26]. These measurements were used to estimate carcass compactness (cold carcass weight/internal carcass length), shoulder compactness (shoulder weight/length of shoulder) and leg compactness (leg weight/leg length) as described by Carrasco et al. [27]. Saleable meat yield (SMY) was estimated as SMY% = (100 – fat %) × (meat:bone)/ ((meat:bone) + 1) as outlined by Purchas [28].

The color coordinates of adipose tissues were measured with a ColorFlex spectrophotometer (Hunter Lab Reston, VA, USA) based on the International Commission on Illumination (CIE) Lab-values (also known as L*, a*, b*) with D65 illuminant and 10° standard observer. The device was calibrated against black and white reference tiles prior to use. The moisture content of the adipose tissue was measured in accordance to the method of AOAC [20].

Total carotenoid in feed and adipose tissues was determined in accordance to the method described by Okonkwo [29]. One gram of each sample was homogenized with 5 mL acetone. The content was stirred for 30 min and two 2.5 mL aliquot of acetone was used to rinse the flask and re-extract the residue. The extracts were pooled and 1 mL of deionized water was added. The mixture was transferred into 5 mL n-hexane and centrifuged at 3000 g for 10 min. The absorbance of the hexane layer was read at 450 nm using spectrophotometer (Secomam, Domont, France). Total carotenoid content was estimated by the following formula

The total lipids in feed and tissue samples was extracted in chloroform:methanol (2:1, v/v) mixture following the method of Folch et al. [30] modified by Rajion et al. [31]. The fatty acids were transmethylated into their fatty acid methyl esters (FAME) using 0.66 N KOH in methanol and 14 % methanolic boron trifluoride (BF₃) in accordance with the method of AOAC [20]. Heneicosanoic acid was used as the internal standard. The FAME was separated in a gas chromatograph (Agilent 7890A) equipped with a flame ionization detector (FID) and a splitless injector. The column used was fused silica capillary (Supelco SP-2560, 100 m, 0.25 mm ID, 0.20 mm film thickness). High purity nitrogen was used as the carrier gas at 40 mL/min. Compressed air and high purity hydrogen were used for the FID in the chromatograph. To facilitate optimal separation, the oven temperature was set at 100 °C, for 2 min and warmed to 170 °C at 10 °C/min, held for 2 min, warmed to 230 °C at 5 °C/min, and then held for 20 min. Identification of sample fatty acids was done by comparing the relative retention times of FAME peaks from samples with those of standards. The indices of Δ 9 desaturase enzyme activities (ID16 and ID18) and elongase enzyme activity in tissues were estimated as described by Malau-Aduli et al. [32] as follows: ID16 = 100(C16:1)/(C16:0 + C16:1), ID18 = 100(C18:1)/C18:0 + C18:1) and Elongation index = 100[(C18:0 + C18:1 n-9)/(C18:0 + C18:1n-9 + C16:0 + C16:1)].

The experiment followed a completely randomized design. Data obtained for all parameters were subjected to the generalized linear model (GLM) procedure of SAS [33]. Slaughter weight was used as a covariate. However, the covariate analysis was not significant. Orthogonal contrasts (linear and quadratic effects) were tested with coefficients estimated based on the level of dietary oil.

The ingredients and chemical composition of the experimental diets are shown in Table 1 while the fatty acid composition is shown in Table 2. In each treatment, oil palm fronds (OPF) accounted for 50 % of the total ration. The OPF is obtained from oil palm (Elaeis guinensis) tree and constitute one of the main by-products of the oil palm industry in Malaysia [34]. The OPF is made up of three main components namely the petioles, leaflets and rachis. The petiole is the main structure of the OPF and accounts for about 70 % of the dry matter (DM) of OPF. The proximate analysis of OPF used in the current study showed that it contained on DM basis: 4.6 % crude protein, 2 % ether extract, 39 % crude fiber, 78.5 % NDF, 56.4 % ADF, 3.2 % ash, and 5.7 MJ/kg metabolizable energy. As a percentage of total FA, the OPF contained 31.3 % C16:0, 5.4 % C16:1, 4.4 % C18:0, 20.9 % C18:1n-9, 16 % C18:2n-6, 17 % C18:3n-3 and 5 % other FA. The concentrate portion of the diets consisted of various ingredients which were adjusted to make the experimental diets isocaloric and isonitrogenous since the addition of graded level of BCPO would increase the energy content of the diet. This was done to prevent confounding experimental results that could accompany changing the protein and energy status of the diets. Thus, responses by animals can be attributed to the addition of BCPO to the diets. In addition, the varied ingredients (corn, soybean meal, palm kernel cake and rice bran) are not fat sources and thus contributed 1.74 and 1.67 % FA to the total FA in the 4 and 8 % BCPO diets respectively. Hence, the FA composition of such ingredients would not be a confounding factor in the current trial. Similar experimental design (control diet vs. oil based diets) which necessitates altering the composition of other dietary ingredients was used in goats [35], sheep [36, 37] and cattle [1, 2, 5, 38, 39]. The chemical composition of the experimental diets met the minimum requirements for growing goats recommended by NRC [19]. As expected, the total FA in the supplemented diets was greater than the control diet. Notably, addition of BCPO increased the concentration (g/kg DM) of C16:0, C18:1n-9, C18:3n-3 and C18:2n-6 but lowered the n6/n3 ratio.

The carcass traits of goats fed varying levels of BCPO are presented in Table 3. Dietary BCPO did not affect (P > 0.05) live, empty body and carcass weights, dressing percentage and meat yield in goats. Similarly, the rib eye area and other carcass linear measurements (Table 3), non-carcass components (Table 4) and proportion, weight and tissue composition of primal cuts (Table 5) were unaffected (P > 0.05). The back fat thickness, intramuscular fat (Table 3) of supraspinatus muscle, and the weights of perirenal, omental, mesentery and pelvic adipose depots (Table 4) were not influenced (P > 0.05) by diets. The carotenoid and moisture contents and color coordinates of all adipose tissues (Table 6) were similar (P > 0.05) across dietary treatments.

The FA composition of Supraspinatus (SS) muscle from goats fed varying level of BCPO is shown in Table 7. Regardless of the diet, the most abundant FA in SS was C18:1n-9 followed by C16:0 and C18:0 in that order. The proportion of C16:0 and C16:1n-7 decreased (P < 0.05) while that of C18:1n-9, C18:1 trans-11, CLA cis-9 trans-11, C18:3n-3 and C20:5n-3n increased (P < 0.05) as the level of BCPO increased in diet. The proportion of C18:0, C18:2n-6 and C20:4n-6 was not influenced (P > 0.05) by diet. The total saturated fatty acids (SFA), the n-6/n-3 ratio and ID 16 decreased (P < 0.05) while the total monounsaturated fatty acids (MUFA), PUFA/SFA ratio, ID 18 and elongation index increased (P < 0.05) with increase in the level of BCPO in diet.

The FA composition of omental, perirenal, mesentery and subcutaneous adipose tissues from goats fed graded levels of BCPO is shown in Tables 8, 9, 10and 11 respectively. The major fatty acids in all examined adipose tissues were C16:0, C18:0 and C18:1n-9.

In the omental depot, the proportion of C14:0, C16:1n-7 and C18:1 trans-11 decreased (P < 0.05) as the level of BCPO increased in diet. Goats fed 4 and 8 % BCPO had similar (P > 0.05) proportion of cis-9 trans-11 CLA which was greater (P < 0.05) than those fed the control diet. The proportion of C18:3n-3 was greater (P < 0.05) in goats fed 4 % BCPO compared with those fed 0 and 8 % BCPO. The proportion of C20:5n-3 increased (P < 0.05) while the n-6/n-3 decreased (P < 0.05) with increasing level of BCPO in diet. Proportions of C16:0, C18:0, C18:2n-6, C20:4n-6, trans-10 cis-12 CLA, C22:5n-3 and C22:6n-3, total FA, sums and ratios of FA and the estimated elongase and desaturase indices were not affected (P > 0.05) by diet.

In the perirenal depot, the proportion of C14:0, C16:1n-7, C18:0 and total SFA decreased (P < 0.05) as the level of BCPO increased in diet. The proportion of C18:1n-9 and CLA cis-9 trans-11, total MUFA and UFA:SFA increased (P < 0.05) with increasing level of BCPO in diet. The control goats had higher (P < 0.05) ID 16 compared to those fed 4 and 8 % BCPO. The ID 18 increased linearly (P < 0.05) as the level of BCPO increased in diet. No significant (P > 0.05) changes were observed for total FA, proportion of C16:0, C18:2n-6, C18:3n-3, C20:4n-6, C22:5n-3, C22:6n-3 and trans-10 cis-12 CLA and the estimated elongase activity across the treatments.

In the mesentery depot, the proportion of C14:0 decreased (P < 0.05) as the level of BCPO increased in diet. The proportion of C18:1n-9 in goats fed 8 % BCPO was significantly higher (P < 0.05) compared with those fed 0 and 4 % BCPO. Goats fed 4 and 8 % BCPO had greater (P < 0.05) proportion of C20:5n-3 than the control goats. No significant differences (P > 0.05) were observed between diets with respect to the proportions of C16:0, C16:1n-7, C18:0, C18:2n-6, C20:4n-6, C18:3n-3, C22:5n-3, C22:6n-3, C18:1 trans-11, cis-9 trans-11 CLA and trans-10 cis-12 CLA and total FA. Similarly, estimated elongase and desaturase indices were not affected (P > 0.05) by diet.

In the subcutaneous depot, dietary BCPO was not a significant source of variation (P > 0.05) influencing the proportions of all FA, sums and ratios of FA and the estimated elongase and desaturase indices. However, the proportions of C14:0 and C16:1n-7 tended (P = 0.07) to decrease while that of C22:5n-3 tended (P = 0.07) to increase with increase in the level of BCPO in diet.

Dietary BCPO had no effect on live, empty and carcass weights, carcass linear measurements, and meat yield in goats. This finding could be due to the similarity in the slaughter weight across dietary treatments. Slaughter weight is one of the major determinants of carcass weight and meat yield in ruminants [23, 37]. The similarity in slaughter weight was likely due to the similar nutrient composition of diets fed to the goats. This finding is consistent with the similarity in the feed efficiency and average daily gain observed in a companion feeding trial [18]. As found in the current study, dietary sunflower oil (2.5 %) compared with the control diet did not affect the dressing percentage and carcass measurements in goats [3]. Similarly, Bock et al. [10] observed that 3.5 % tallow or soybean soap stock versus control diet did not affect dressing percentage in steers. Also, goats fed 4.5 % soybean oil or sunflower oil had similar carcass traits as those fed control diet [35]. In contrast, decreased dressing percentage and hot carcass weight were observed in steers fed 4 % soybean oil [40] and 4 and 8 % animal-vegetable oil blends [39] while carcass yield increased in steers fed 3.5 % soybean oil, tallow or yellow grease versus steers fed control diet [2] and Nellore steers fed soybean and linseed oils or their calcium salts compared to those fed control diet [1]. The dressing percentage (based on empty body weight) of the goats ranged from 53.55 to 54.56 %. These values are similar to those reported by Marinova et al. [3] and Kadim et al. [23].

The similarity in the back fat thickness, intramuscular fat and the weights of adipose tissues across dietary treatments suggests that dietary supplementation of BCPO did not alter the deposition and distribution of fat in the adipose tissues of goats. This finding could be attributed to the similar metabolizable energy content of the diets. Feed energy supplied in excess of the basal requirement can increase fat deposition in animals [41]. The major substrate for de novo fatty acid synthesis in tissues is glucose [42]. Thus, diets capable of promoting glucose supply to the tissues might increase fat deposition. Propionate is a gluconeogenic precursor and thus could increase supply of glucose to the tissues [42, 43]. Erstwhile companion studies have shown that supplementation of BCPO did not affect in vitro [17] and in vivo [18] ruminal molar concentration of propionate. These observations lend credence to the similar fat deposition across the treatments. The current observation contrasts past studies [2, 39] wherein oil supplementation increased back fat thickness and weight of adipose tissues. In line with the current findings, dietary palm oil or its calcium soap compared with the basal diet did not affect the weights of omental and perirenal fat in lambs [37]. Marinova et al. [3] observed that dietary supplementation of 2.5 % sunflower oil did not affect the weight of perirenal fat, sweetbread and caul but increased intramuscular fat in lambs. The discrepancies between the current findings and the earlier reports could be due to differences in the amounts and fatty acid composition of the dietary lipids used.

The similarity in the weights of adipose tissues across dietary treatments corroborates the similarity in the moisture content of adipose tissues which suggests that supplementation of BCPO in diet did not play a significant role in the maturation of adipose cells. High proportion of water in adipose tissues signifies a less mature tissue [41]. Bas et al. [6] observed that the moisture content of omental and perirenal adipose tissue of goats raised indoors with concentrate (high fat diet) was lower than those raised outdoors with concentrate and grass or with only Argan pulp (low fat diet) suggesting that high fat diets may increase hyperplasia and hypertrophy of adipose cells.

Dietary BCPO had no effect on color coordinates especially yellowness and the concentration of total carotenoid in adipose tissues in goats. This observation is unexpected given the increase in dietary fat and carotenoid contents of the diet as the level of BCPO increased, and the 100 d feeding duration employed in this study. Diet and feeding duration are some of the important factors influencing the yellowness of adipose tissues in ruminants [44]. The absorption and deposition of carotenoid in various tissues in ferrets was positively correlated with dietary fat [45]. However, mammals differ in their ability to absorb carotenoids [46]. For example, humans can accumulate carotenes and xanthophylls in their adipose tissues without discrimination, cattle and horses can accumulate only carotenes while goats and sheep accumulate neither carotenes nor xanthophylls [46]. In addition, Mora et al. [47] reported that goats have higher levels of jejunal and duodenal 15, 15’dioxygenase activities than cattle when fed dietary beta-carotene which may explain the lower pigmentation of adipose tissue in goats compared with cattle. The 15, 15’dioxygenase is the enzyme responsible for the conversion of beta-carotene to retinal [47].

The management strategies employed in the current study were successful in ensuring similar carcass weight, carcass fatness and total fatty acids in all the tissues examined. Thus, the observed FA composition in the examined tissues was not confounded by carcass fatness.

Regardless of the diet, the most abundant FA in SS was C18:1n-9 and its concentration was influenced by diet. This observation is in tandem with previous studies in goats [35], sheep [36] and cattle [38] in which C18:1n-9 was identified as the most abundant FA in muscle following dietary oil supplementation. The increase in C18:1n-9 in response to BCPO could be due to the increase in dietary C18:1n-9 and/or increase in the Δ 9 desaturase enzyme activities (ID 18) necessary for the de novo conversion of C18:0 to C18:1n-9. This observation is consistent with those observed in a companion in vitro study where the ruminal concentration of C18:1n-9 after 24 h incubation increased as the level of BCPO increased in the substrate [17]. As found in the current study, supplementation of 3.3 % canola oil, canolamide or canola oil-canolamide mix oil increased the concentration of C18:1n-9 in bovine milk [5]. Conversely, 3 % dietary canola oil compared with 3 % palm oil did not affect the concentration of C18:1n-9 in longissimus lumborum muscle from goats [48].

Dietary supplementation of BCPO depressed the concentration of C16:0 and C16:1n-7 in SS muscle. These observations concur with those of Loor et al. [5] and Ferlay et al. [49]. Depression of medium chain FA in response to dietary unsaturated fats could be due to the inhibition of the activities of lipogenic enzymes required for the synthesis of medium chain FA or the preferential incorporation of long chain FA from diet and/or adipose tissues [4, 5, 49, 50]. This lends credence to the significant decrease in the Δ 9 desaturase activity (ID 16) which coincides with the linear decrease in the concentration of C16:0 and C16:1 as BCPO increased in diet. Palmitic acid (C16:0) can be converted to C16:1n-7 by Δ 9 desaturase [51].

The concentration of C18:1 trans-11 Vaccenic and CLA cis-9 trans-11 in SS increased as BCPO increased in diet. This observation could be due to the increase in the dietary concentration of unsaturated fatty acids. Both C18:1 trans-11 Vaccenic and CLA cis-9 trans-11 are intermediate products of ruminal biohydrogenation of unsaturated FA [4, 13, 14]. Feeding unsaturated FA causes incomplete biohydrogenation of unsaturated FA accompanied with biohydrogenation intermediates [13, 14]. In addition, it has been established that Δ 9 desaturation of C18:1 trans-11 Vaccenic in adipose tissue could yield CLA cis-9 trans-11 [4, 16, 17]. In line with the current observation, supplementation of 3.3 % canola oil, canolamide or canola oil-canolamide mix (Loor et al. [5] and 1 kg/day canola oil [50] increased the concentration of C18:1 trans-11 Vaccenic and CLA cis-9 trans-11 in bovine milk compared with the control diet.

The proportion of C18:0, C18:2n-6 and C20:4n-6 in SS was not influenced by diet. In contrast, the concentration of C18:3n-3 and C20:5n-3 increased linearly in response to dietary BCPO. Similarly, Karami et al. [48] found that 3 % canola oil compared with 3 % palm oil did not affect the concentration of C18:0, C18:2n-6 and C20:4n-6 but enhanced the concentration C18:3n-3 in longissimus lumborum muscle from goats. However, the authors did not observe increment in the concentration of long chain n-3 FA. The linear increase in the proportion of C18:3n-3 in goats fed 4 and 8 % BCPO relative to those fed control diet could be responsible for the increase in the proportion of C20:5n-3 in their muscles since the FA is a metabolite of C18:3n-3 [4] suggesting in vivo elongation and desaturation. This coincides with the linear increase in the elongation index in response to supplementation of BCPO. This observation is consistent with those of Gjerlaug-Enger et al. [52] who observed that dietary rapeseed products enhanced the concentration of C18:3n-3, C20:5n-3 and C22:5n-3 in longissimus dorsi muscle of pork compared with the control diet.

The linear increase in total n-3 PUFA was accompanied by a linear decrease in n6/n3 ratio as the level of BCPO increased in the diet. The n6/n3 ratio for the 4 and 8 % BCPO was within the range of the recommended value (<4) for healthy diet [53]. Dietary BCPO enhanced the total MUFA and decreased the total SFA in SS muscle. Diet had no effect on the total PUFA and total FA. The PUFA/SFA ratio increased with increase in dietary BCPO. This could be attributed to the decrease in the SFA in BCPO based diets. Regardless of diet, the PUFA/SFA ratio of SS was within the range of the recommended value (>0.4) [53].

The major fatty acids in all adipose tissues were C16:0, C18:0 and C18:1n-9. This observation is in line with those of Bas et al. [6] and Castro et al. [37]. The decrease in the proportion of C14:0 and C16:1n-7 in the perirenal and omental fats from goats fed 4 and 8 % BCPO relative to the control goats could be due to the reduction in the mRNA abundance and activity of lipogenic enzymes required for synthesis of medium chain FA [4]. The decrease in the proportion of C16:1n-7 coincides with the linear decrease in the Δ 9 desaturase activity (ID 16) as BCPO increased in the diets. Dietary BCPO deceased the proportion of C18:0 and total SFA and enhanced the concentration of C18:1n-9, CLA cis-9 trans-11 and total MUFA in perirenal fat. In omental fat, dietary BCPO increased the concentration of CLA cis-9 trans-11, C20:5n-3 and total PUFA. In the mesentery fat, goats fed 8 % BCPO had higher C18:1n-9 and Δ 9 desaturase activity (ID 18) compared to other diets. Also, BCPO caused a linear increase in the proportion of C20:5n-3. The current observation is consistent with those of Stanford et al. [54] who observed that increasing the level of canola screening in diets reduced the concentration of C14:0, C16:0, C16:1n-7, C18:0 and total SFA and enhanced that of C18:1n-9, C18:3n-3, total MUFA and PUFA in perirenal adipose tissue in lambs. In contrast, dietary rapeseed oil, linseed oil or hydrogenated rapeseed oil did not alter the fatty acid composition of perirenal adipose tissues in lambs [55].

Contrary to the findings in perirenal, mesentery and omental adipose tissues, dietary BCPO did not affect the FA composition of subcutaneous adipose tissue. This finding concurs with those of Potkański et al. [55] who observed that dietary rapeseed oil did not alter the FA composition of subcutaneous adipose tissues in lambs. Similarly, dietary fish oil did not alter the FA composition of subcutaneous adipose tissue in lambs [56]. Contrary to the present findings, earlier trials have reported significant alterations in the FA composition of subcutaneous adipose tissue when oils high in unsaturated FA were fed to sheep [57] and goats [35]. The inconsistencies observed in the FA composition of adipose tissues in response to dietary BCPO reflect variation in FA metabolism in the adipose tissues.