| Sixty male Tan lambs(21±1.23 kg body weight)fed a finishing diet(concentrate-to-forage [C: F]ratio: 35:65 or 55:45)and daily supplementation of chromium methionine(Cr-Met)(0,0.75,or 1.50 g/d)were used in a completely randomized design with a 2×3 factorial arrangement of treatments.According to the results of the growth experiment,meat quality and fatty acid composition of body tissue,the optimum concentrate level and Cr-Met addition dosage were determined.According to the results of ruminal fermentation,fatty acid composition,bacteria abundance and gene expression related to tissue conjugated linoleic acid(CLA)synthesis in Tan lambs,the regulatory mechanism of dietary concentrate level and Cr-Met supplementation on CLA synthesis were investigated.(1)The effects of dietary concentrate level(35:65 C:F or 55:45 C:F)and Cr-Met supplementation(0,0.75,or 1.50 g/d)on growth performance and meat quality of Tan lambs showed that lambs the from HC group had higher average daily gain and leg proportion(P<0.05),but no significant effects were found on abdominal fat deposition(P>0.05).Cr-Met supplementation had no significant effect on the average daily gain of Tan lambs(P>0.05).The proportion of rack and loin in lambs from the HC group increased linearly(P<0.05)with increasing Cr-Met supplementation.In summary,the 55:45 C:F diet can shorten the fattening time of Tan lambs,and Cr-Met supplementation in a high-concentrate diet could improve the economic benefits of carcass cuts.(2)The effects of dietary concentrate level(35:65 C:F or 55:45 C:F)and Cr-Met supplementation(0,0.75,or 1.50 g/d)on the fatty acid composition in body tissues of Tan lambs.The results showed that high-concentrate diet did not significantly decrease(P>0.05)the c9t11 CLA contents in subcutaneous fat and longissimus dorsi muscle of Tan lambs.Cr-Met supplementation at 0.75 g/day increased the c9t11 CLA content in longissimus dorsi muscle of Tan lambs in both the low-concentrate diet and highconcentrate diet(P<0.05).The atherogenic index(AI)and thrombogenic index(TI)in liver,subcutaneous fat and longissimus dorsi muscle of Tan lambs decreased significantly in turn(P<0.05).In summary,CrMet supplementation at 0.75 g/day had a significant effect on c9t11 CLA in longissimus dorsi muscle,and the longissimus dorsi muscle had the highest unsaturation of fatty acids.(3)The effects of dietary concentrate level(35:65 C:F or 55:45 C:F)and Cr-Met supplementation(0.75 g/d)on ruminal biohydrogenation in Tan lambs were studied.The results showed that the highconcentrate diet significantly decreased the DNA abundance of Butyrivibrio fibrisolvens vaccenic acid subgroup,the concentrations of trans C18:1 and c9t11 CLA(P<0.05),but the content of C18:0 had a slight increase(P>0.05).Compared with the high-concentrate diet group without Cr-Met supplementation,the contents of trans C18:1,t11 C18:1 and c9t11 CLA in the rumen showed an increasing trend in the highconcentrate diet group with 0.75 g/d Cr-Met(P>0.05),but the content of C18:0 had a slight decrease(P>0.05).In summary,the 55:45 C: F diet promoted the ruminal biohydrogenation of unsaturated fatty acids.Cr-Met supplementation inhibited the terminal step of ruminal biohydrogenation,causing the accumulation of t11 C18:1 in the rumen.(4)The effects of dietary concentrate level(35:65 C:F or 55:45 C:F)and Cr-Met supplementation(0.75 g/d)on the expression of genes related to CLA synthesis in Tan lambs.The results showed that the regulation of dietary concentrate level and Cr-Met supplementation on conjugated linoleic acid synthesisrelated genes in tissues were affected by tissue differences.The changes of c9t11 CLA content in tissues were not always consistent with the changes of SCD m RNA expression,the expression of fatty acids transporter genes LPL and FABP3 could play an important role in c9t1 CLA synthesis.In conclusion,the 55:45 C:F diet could be used as a basic diet to produce the meat containing rich c9t11 CLA.Cr-Met supplementation at 0.75 g/day could increase the c9t11 CLA content in the longissimus dorsi muscle of lambs fed low-and high-concentrate diets.Cr-Met could inhibit the terminal reduction reaction of ruminal biohydrogenation and regulate the expression of fatty acid uptake and transport genes and further affect the c9t11 CLA synthesis in tissues. |
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