Effects of feeding omega-3 fatty acids and vitamin E on the chemical composition and microbial population of broiler meat

[摘要] ENGLISH ABSTRACT:Lipids remain one of the most important nutrients required by broilers. The growing awareness that some Westernsocieties have too high a dietary ratio of n-6/n-3 polyunsaturated fatty acids is of direct relevance to broiler nutrition andlipid metabolism. Meaningful quantities of n-3 polyunsaturates have been incorporated into major poultry tissues, so thatthe production of broiler meat with high n-3 polyunsaturates becomes advantageous for the broiler industry as they areperceived as having a 'healthier' lipid profile. Unfortunately, such broiler meat is rather susceptible to oxidativedeterioration, and oxidation often determines shelf life of poultry meat products. The addition of a-tocopherol (vitamin E)to broiler diets is an effective means of improving the oxidative stability of broiler meat. Elevated a-tocopherol levels inbroiler feeds increase tissue concentrations thereof resulting in improved stability of membranal structures which may beexpected to increase the oxidative stability of broiler meat and meat products.Three investigations were done at Mariendahl Poultry Research Station in Stellenbosch. The broilers were kept in 1 x 0.4x 0.5 m cages in a broiler rearing house. All the trials started with day-old chicks, except experiment 1 where 3-week oldbroilers were used. At the end of trials 2 and 3 the 6-week old broilers were slaughtered and the carcasses prepared forchemical analysis.Experiment 1: Metabolisabie energy of Canola acid oil and Famarol acid oil for broiler chickens.In trials with 21-day-old male broilers the true metabolisabie energy value, corrected for nitrogen retention (TMEn) wasdetermined by the balance method for Canala acid oil (CAO) and Famarol acid oil (FAO). The trials were duplicated, eachtime using different samples of the two oils from the same source (experiment 1 and 2). Each of the two oils were blendedin two ratios with a basal diet to form the test diets, viz. 100% Basal; 96% Basal: 4% Oil; 92% Basal: 8% Oil. Inexperiment 3, 50 % bran was added to the maize to form the basal diet. The balance trials lasted for 3 days after anadaptation period of 4 days. The TMEn values determined by regression for the broilers of CAO did not differ significantly(P>0.05) between experiments 1 and 2. However, the value for experiment 3 was significantly (P<0.05) higher than thosefor experiments 1 and 2. The TMEn values of FAO also did not differ significantly (P>0.05) between experiments 1 and 2,although the value for experiment 3 was significantly higher than that of experiment 1. The addition of 50 % bran to thebasal diet in experiment 3 could have stimulated the digestive breakdown process and hence increase the secretion ofdigestive enzymes. This could lead to an increase in the utilisation of the test lipid and therefore an increase in the TMEnvalue. The TMEn values of CAO differed significantly (P<0.05) from those of FAO for all three the experiments (exp.1:30.6 ± 0.399 MJ/kg for CAO vs. 25.9 ± 0.441 MJ/kg for FAO; expo 2: 31.0 ± 0.633 MJ/kg for CAO vs. 26.1 ± 0.668 MJ/kgfor FAO: expo 3: 32.1 ± 0.867 MJ/kg for CAO vs. 27.1 MJ/kg for FAO).Experiment 2:of broilers.The dietary effects of various combinations of Canala acid oil (CAO, a high level of C18:3n-3 and MUFA) and FamarolEffects of various dietary n-6/n-3 fatty acid ratios on the perfonnance and body compositionacid oil (FAO, a high level of 18:2n-6 and SFA) on tissue fatty acid composition were studied in broiler carcasses andabdominal fat pads. From day-old to six weeks, chicks were fed one of six diets containing 100% FAO, 80% FAO-20%CAO, 60% FAO-40% CAO, 40% FAO-60% CAO, 20% FAO-80% CAO, 100% CAO. There were no statistical differences(P>0.05) in average daily gain (1.71 ± 0.059 g) or feed conversion ratios (1.97 ± 0.051) among dietary groups. Nostatistical differences (P>0.05) were found in the chemical proximate composition of the carcasses for the moisture (66.20± 0.112 %), protein (17.63 ± 0.484 %), lipid (15.92 ± 1.507 %) and ash (0.95 ± 0.115 %) content among dietary groups.No statistical differences (P>0.05) were found in the chemical proximate composition of the abdominal fat pads for themoisture (28.77 ± 0.112 %), protein (3.03 ± 0.484 %), lipid (63.32 ± 9.789 %) and ash (0.45 ± 0.135 %) content amongdietary groups. With the increase in dietary CAO levels, the percentages of C18:2n-6 and C20:4n-6 in the carcassesdecreased respectively with 1.78 % from 20.88 % and 0.35 % from 1.05 %, whilst C18:3n-3 and longer chain n-3 fattyacids such as C20:5n-3 and C22:6n-3 increased respectively with 2.25 % from 1 %, 0.1 % from 0.1 % and 0.67 % from0.2 %. The same tendency was seen in the abdominal fat pads where C18:2n-6 and C20:4n-6 decreased respectivelywith 1.55 % from 20.75 % and 0.98 % from 1.2 % with an increase in dietary CAO, whilst C18:3n-3, C20:5n-3 andC22:6n-3 increased respectively with 2.13 % from 1.15 %, 0.45 % from 0.03 % and 0.95 % from 0.05 %. The n-3/n-6 ratioin the carcasses and abdominal fat pads increased respectively with 0.16 % from 0.06 % and 0.19 % from 0.06 % with anincrease in dietary CAO. These results clearly indicate that dietary CAO enriched with a-linolenic acid lower saturatedfatty acids respectively in broiler carcasses and abdominal fat pads with 4.88 % from 31.6 % and 10.63% from 31.1 %,whilst increasing monounsaturated fatty acids with 3.87 % from 44.95 % and 7.25 % from 46.7 % respectively andpolyunsaturated fatty acids with 1.02 % from 23.45 % and 2.38 % from 23.2 % respectively.Experiment 3: Effect of dietary vitamin E on the performance of broilers and oxidative stability, colour,microbiological stability, fatty acid composition and pH of broiler meat during refrigerated and frozen storage.Experiment 1 was carried out with 220 one-day-old broiler chicks to evaluate the effect of eleven concentrations of vitaminE (0, 20, 40, 60, 80, 100, 120, 140, 160, 180 and 200 mg a-tocopheryl acetate 1 kg diet) on their production performanceand the oxidative stability of their frozen broiler carcasses. The diets with vitamin E levels 0 to 100 mg were fed fromday-old to 42 days of age while the diets with vitamin E levels 120 to 200 mg were fed from 21 to 42 days of age. Theoxidative stability, evaluated by thiobarbituric acid reactive substances (TBARS) values, was determined after 30, 90, 120and 150 days of storage at -20°C. There were no statistical differences (P>0.05) in average daily gain (1.85 ± 0.111 g) orfeed conversion ratios (2.29 ± 0.397) among dietary groups. TBARS values increased significantly (P<0.05) withincreasing time of storage (basal diet: day 30 = 1.71 ± 0.51; day 150 = 4.89 ± 0.51), but decreased significantly (P<0.05)with increasing vitamin E levels (day 150: basal = 4.89 ± 0.51; 100 mg / kg = 1.09 ± 0.27). Experiment 2 was carried outwith day-old broiler chicks to evaluate the effect of five concentrations of vitamin E (0, 40, 80, 120 and 160 mg atocopherylacetate / diet) on their performance and the oxidative stability of their refrigerated carcasses. The experimentaldiets were fed from day-old to 42 days of age. The oxidative stability, evaluated by TBARS values, colour deteriorationand microbiological stability were determined after 0, 4, 8, 10 and 12 days of storage at 4°C. Fatty acid analysis was doneon the samples of days 0 and 12. There were no statistical differences (P>0.05) in average daily gain (1.88 ± 0.117 g) orfeed conversion ratios (2.37 ± 0.467) among dietary groups. TBARS values increased significantly (P<0.05) withincreasing time of storage, but decreased significantly (P<0.05) with increasing vitamin E levels. There were no statisticaldifferences (P>0.05) in colour measurements for L* (44.97 ± 0.662), a* (5.23 ± 0.315) or b* (12.76 ± 0.321) valuesbetween treatments. Microbiological counts increased significantly (P<0.05) over time with vitamin E concentrationshowing no effect. There were no statistical differences (P>0.05) for any of the fatty acid groups measured (SFA: Day 0 =26.1 ± 1.13%, Day 12 = 26.1 ± 1.17%; MUFA: Day 0 = 41.4 ± 1.46%, Day 12 = 40.2 ± 2.28%; PUFA: Day 0 = 32.4 ± 1.95%, Day 12 = 33.8 ± 2.52%) among dietary groups. Similarly, none of the fatty acids showed statistical significant(P>0.05) concentration changes over time. There were no statistical differences (P>0.05) in pH (6.01 ± 0.206) amongdietary groups.

[发布机构] Stellenbosch University