Effect of carbohydrate source and roasted of canola seed rich of oleic acid on performance, meat fatty acid profile and quality characteristics in fattening lambs

Red meat is one of the best dietary sources of fat and protein for humans. The fatty acid composition of meat has long been studied, but still receives a lot of attention in research because of its implications for human health. Besides a lower total fat intake, human nutritionists are recommending a higher intake of polyunsaturated fatty acids, and especially of n-3 fatty acids at the expense of n-6 fatty acids. Numerous animal feeding trials have been carried out using different species and breeds aiming at bringing the polyunsaturated fatty acid/saturated fatty acid (P/S) ratio of meat closer to the recommended value (>0.7), as well as for the n-6/n-3 ratio (<5). Sugar beet pulp (SBP) contains 70% carbohydrates mainly as neutral detergent soluble fiber, which has high water-binding capacity and a slow fermentation rate in rumen compared to the barley grain. Replacing barley with SBP may overcome digestive disorders such as acidosis problem and lead to the utilization of dietary energy towards animal growth, carcass gain, and muscle intramuscular fat deposition. On the other hand, feeds containing fats and oils are being used in animal diets to increase energy density and to manipulate intramuscular fat content and fatty acid composition of the meat. Canola seed contains approximately 40 to 43 % oil in which oleic acid, linoleic acid, and α-linolenic acid contribute to 61, 20 and 10%, respectively. High fat content of canola seed makes it an attractive feedstuff to improve energy density of diets for finishing lambs grown in dry regions, where pasture availability is low. To our knowledge, information containing the effects of SBP as a slow fermentable carbohydrate source with an inclusion of roasted canola seed on growth performance and meat quality characteristics of fattening lambs is not investigated. The objective of this study was to evaluate the effects SBP with or without RCS in a high concentrate diet on performance and muscle composition of Arabian fattening lambs. This experiment was approved by the Animal Care and Ethics Committee of Ramin University of Livestock Research. In this study, twenty-four Arabian male lambs, 4 months old, (23.7±2.5 kg; mean initial BW±SD) were kept in individualcages (1.4×1.2 m). The fattening period was 99 d including 14 d as adaptation period. At the start of the adaptation period, all the animals were treated for external and internal parasites and vaccinated against enterotoxaemia. The animals were randomly assigned to one of the four dietary treatments included 1) starch, 2) starch with roasted canol seeds, 3) Neutral detergent soluble fiber and 4) Neutral detergent soluble fiber with roasted canola seed. The diets were offered to animals to meet the requirements of growth rate at 250 g/day according to National Research Council (NRC, 2007). Lambs were weighed weekly throughout the experimental period prior to the morning feeding. Feed conversion ratio was calculated as the ratio between average daily intake and average daily gain. Average daily gain was calculated for each sheep from regression analysis of live weight vs. time from day 1 to 99 of each treatment. At the end of the trial, all the animals were slaughtered according to Halal method. Samples from Longissimus dorsi (LD) between 5th and 6th ribs trimmed of all external subcutaneous fat were collected. These were used to determine moisture, crude protein, fat, and ash contents of meat according to Association of Official Analytical Chemistry (AOAC, 2006). Lightness (L*), rednes (a*), and yellowness (b*) of meat samples were measured using a Minolta CR-300 colorimeter in the CIE L*a*b*. Hue angle (H*) was calculated as tan−1 (b*/a*) × (180/π) and Chroma (C*) as (a*2+b*2)1/2. The colorimeter was set for using the illuminant A and 10° standard observers. About 50 g of the LD muscle between 6th to 9th ribs were taken for determination of fatty acid profiles. Muscle lipids were extracted as described by Folch et al. (1957), using dichloromethane and methanol (2:1 vol/vol), instead of chloroform and methanol (2:1 vol/vol), and were methylated according to Metcalfe and Schmitz (1961). The transmethylated samples were analyzed by a gas chromatograph with a flame ionization detector and a capillary column measuring 100 m in length × 0.25 mm i.e., with a thickness of 0.20 mm. Helium was used as the carrier gas at a flow rate of 1 mL/min. Also, tridecanoic acid (C13:0) was used as internal standard. The initial temperature of the oven was 70 °C and was increased by 10 °C/min to 175 °C, where it was maintained for 25 min. The temperature was then increased by 7 °C/min to 220 °C, where it was maintained for 10 min, followed by another increase by 10 °C/min to 230 °C, where it remained for 4 min. The temperature of the injector was 280 °C, and the temperature of the detector was 300 °C. Identification of the fatty acids was carried out by comparison of the retention times with standards of fatty acids from butter, and the percentage of fatty acids was obtained by means of Chromquest 5.5 software. Performance data were analyzed completely random design with repeated measurement PROC MIXED and compound symmetry model. Meat Characteristics data were as a completely randomized design with a 2×2 factorial arrangement using PROC GLM in SAS software. Partial replacement of starch with soluble fiber significantly increased performance concentration of capric, c17:0 anteiso and behenic acid and significantly reduced lauric, heptadecanoic, oleic, linoleic and polyunsaturated fatty acids of longissimus dorsi (P<0.05). Addition of roasted canola seed to diets increased performance (average 288 g vs. 262 g) and reduced the concentration of isopalmitic and behenic acid and significantly increased concentration of Lauric, Myristic, Anteiso-pentadecanoic, Pentadecenoic, Palmitic, Palmitoleic, Stearic, Vaccenic, Conjugated linoleic, Oleic, α-Linolenic, γ-Linolenic, Gondoic, Docosatetraenoic, h-γ-Linolenic, Arachidonic, Eicosapentaenoic, Nervonic, Docosapentaenoic, Docosahexaenoic acids and the total concentration of unsaturated fatty acids with one or polyunsaturated fatty acid pattern longissimus dorsi (p<0.05). Canola seed addition significantly increased n-6/n-3 and p/s ratio (P<0.05). Replacement of starch with soluble fiber significantly decreased and fat addition significantly increased meat cholesterol concentratin (P<0.05). The results showed that the use of canola seeds by changing the indicators of unsaturated fatty acids, omega-6 to omega-3 ratios reform and polyunsaturated fatty acids to saturated fatty acids
can improve the quality and quantity of meat.