脂肪和L-肉碱对大口黑鲈饲料中蛋白质的节约作用

本试验旨在探讨脂肪和L-肉碱对大口黑鲈饲料中蛋白质的节约作用.采用3 × 2(蛋白质脂肪比×L-肉碱)完全随机设计,配制了不同蛋白质脂肪比(39.9%/7.4%、30.3%/13.9%和21.5%/19.5%)和L-肉碱水平(0和1 g/kg饲料)的6种等能饲料.选取平均初重为(3.27±0.21)g的大口黑鲈幼鱼270尾,随机分为6组(每组3个重复,每个重复15尾),随机饲喂1种饲料,试验期6周.结果表明:随着饲料中脂肪水平从7.4%升高到19.5%(蛋白质水平从39.9%下降到21.5%),鲈鱼的增重率从685%显著降低到176%(P<0.05),饲料效率从1.15增加到2.33(P<0.05),且投喂蛋白质脂肪比为21.5%/19.5%饲料的鲈鱼的肥满度显著低于投喂蛋白质脂肪比为39.9%/7.4%和30.3%/13.9%饲料的鲈鱼(P<0.05).投喂蛋白质脂肪比为21.5%/19.5%饲料的鲈鱼体水分含量显著低于投喂蛋白质脂肪比为39.9%/7.4%的饲料(P<0.05),且随着饲料中脂肪水平从7.4%升高到19.5%(蛋白质水平从39.9%下降到21.5%).全鱼脂肪含量从5.6%显著升高到11.5%(P<0.05),全鱼粗蛋白质含量从15.6%显著下降到10.4%(P<0.05).鱼体肝脏和肌肉中脂肪含量以及肝体指数在投喂蛋白质脂肪比为21.5%/19.5%饲料时达到最高值.此外,随着饲料中脂肪水平从7.4%升高到19.5%(蛋白质水平从39.9%下降到21.5%),淋巴细胞百分比由38.30%升高到48.41%(P<0.05),粒细胞百分比由51.75%下降到42.14%(P<0.05).由此得出,以节约蛋白质为目的的过量添加脂肪会导致鱼体生长速度降低,甚至引起脂肪肝的发生和机体免疫系统的应激反应.此外,饲料中添加1 g/kg的L-肉碱并不能提高大口黑鲈的生长性能,但蛋白质脂肪比和L-肉碱对淋巴细胞百分比和粒细胞百分比存在互作作用,并在饲喂添加1 g/kg L-肉碱的蛋白质脂肪比为21.5%/19.5%的饲料时达到峰值.

Protein Sparing Effect of Lipid and L-carnitine in Diets for Largemouth Bass (Micropterus salmoides)

A 3×2 (protein/lipid ratio× L-carnitine) factorial experiment was conducted to evaluate the protein sparing effect of lipid and L-carnitine in diets for largemouth bass, Micropterus salmoides. Two hundred and seventy fingerlings with aver-age body weight of (3. 27 ± 0. 21) g were randomly divided into six groups with 3 replicates each and fifteen fingerlings per replicate. Six isocaloric experimental diets were formulated with three protein/lipid ratios (39. 9%/7. 4% , 30. 3%/13. 9% and 21. 5%/19. 5%) crossing two L-carnitine levels (0 and 1 g/kg), and were fed to the fingerlings for six weeks. The results showed as follows: weight gain rate was 686% when fish were fed the 39. 9%/7. 4% (protein/lipid) diet but was reduced to 176% when fish were fed the 21. 5%/19. 5% diet (P<0. 05). Condition factor of fish fed 21. 5%/19. 5% (protein/lipid) diet was significantly lower than that of fish fed 39. 9%/7. 4% (protein/lipid) and 30. 3%/13. 9% (protein/lipid) diets (P<0. 05). FCR was increased significantly from 1.15 to 2. 33 when the dietary lipid level was increased from 7. 4% to 19. 5% (protein level was decreased from 39. 9% to 21. 5%) (P<0. 05). Body moisture content was lower in the fish fed 21. 5%/19. 5% than that in the fish fed 39. 9%/7. 4% diet (P<0. 05). When the dietary lipid level increased from 7. 4% to 19. 5% (protein level decreased from 39. 9% to 21. 5%) , the body crude lipid content increased from 5. 6% to 11. 5% while body crude protein content decreased from 15. 6% to 10. 4% (P<0. 05). The liver lipid, muscle lipid and hepatosomatic index reached the highest values when fish were fed 21. 5%/19. 5% (protein/lipid) diet. The percentage of lymphocytes was significantly increased from 38. 30% to 48. 41% (P<0. 05), and the percentage of granulocytes was significantly decreased from 51. 75% to 42.14% (P<0. 05) when dietary lipid level was increased from 7. 4% to 19. 5% (protein level was decreased from 39. 9% to 21. 5%). It was concluded that more dietary lipid addition with the aim to spare dietary protein slowed the growth of largemouth bass, and led to a fatty liver and immune suppression. Moreover, though the addition of 1 g/kg L-carnitine in diet had no effect on all the parameters tested relevant to fish growth performance, an interactive effect of dietary protein/lipid ratio with L-carnitine was observed in the percentages of granulocytes and lymphocytes with the peak values found in the fish fed 21. 5%/19. 5% (protein/lipid) and 0.1% L-carnitine diet.