Effects Of Yeast Cultures Addition To Diets On Meat Quality Of Yaks And Its Mechanism

Nowadays people are paying more and more attention to the quality of animal-origin foods,as a feed additive the application of yeast culture in animal feeding has received extensive attention from scholars at home and abroad.Previous studies on the effect of yeast culture on ruminant diet showed that YC could improve ruminant performance,rumen environment and meat quality.The purpose of this study was to explore the effects of YC addition on yak performance,meat quality,muscle fatty acid composition,volatile flavor components,rumen environment and expression of lipid metabolism related genes.In order to study more deeply the mechanism of YC affecting the quality of yak meat,this is important for the quality and safety of animal products.Thirty Jinchuan male yaks with similar age and body weight of about 227±57 kg were randomly divided into three treatment groups with 10 yaks in each group.0%,0.4% and 0.8% YC were extra added to the TMR,respectively.Using artificial TMR method,feed twice a day,official feeding period of 100 days.At the end of the feeding experiment,six yaks were selected for slaughter test in each treatment group.The longissimus,rumen fluid and rumen epithelial tissue samples were collected from each yak.The longissimus muscle was used to determine meat quality,fatty acid composition,volatile flavor substances and expression of lipid metabolism related genes;determination of microbial diversity in rumen fluid by 16 s rRNA;at the same time,the composition of volatile fatty acids in rumen was determined with reference to the method of national standard;rumen epithelial tissue sample for measuring nipple height and width,determination of rumen stratum corneum thickness by HE staining.The results were showed as below:(1)The dry matter intake of the yak in the 0.4% and 0.8% YC addition groups was significantly lower than that in the control group(P<0.05),but there was no significant difference in ADG and F/G among the three groups(P>0.05);compared with the control group,the net meat percentage of the YC groups increased by 2.77% and 8.13%,and the slaughter rate increased by 2.07% and 6.45%,respectively,but had no difference between treatment groups(P>0.05);there was no significant difference in apparent digestibility of DM,CP,NDF and ADF among the three groups(P>0.05).(2)Compared with the control group,the IMF content and meat yellowness of yak in 0.8% addition group were significantly increased(P<0.05);there was no significant difference between the SFA and UFA content in the muscle of YC addition group and the control group(P>0.05),the contents of stearic acid(18:0)and arachidic acid(20:0)in the 0.8% YC addition group were 18.16% and 0.13%,respectively,which were significantly lower than the control group(P<0.05),trans-oleic acid(C18:1n9t)was detected only in the control group,the content of palmitoleic acid(16:1)in 0.8% addition group was 4.99%,which was significantly higher than the other two groups(P<0.05);among the volatile flavor compounds,(e)-2-octenal,decan-al and pentadecanal were detected only in the meat of yaks with 0.8% addition group,tetradehyde and octadecanal were detected only in Yak muscle of YC addition group,(e)-2-nonenal was detected only in the control group,the content of 2-ethylfuran in yak meat of 0.8% YC addition group was 1.19%,which was also significantly higher than that of the other two groups(P < 0.05).(3)Compared with the control group,the ACE,Chao I and Shannon index of rumen microorganisms in the 0.4% and 0.8% addition groups were significantly increased(P<0.05);compared with the control group,the proportion of bacteroides and sclerenchyma in the rumen increased in the 0.8% addition group,but there was no significant difference among the three groups(P>0.05)the proportion of rikenellaceae_RC9_gutgroup in the 0.4% and 0.8% addition groups was higher than that in the control group,10.76% and 10.37% respectively.(4)The acetic acid content in the rumen of the 0.8% YC addition group was significantly higher than that of the control group(P<0.05),the ratio of acetic acid/propionic acid in the 0.4% YC group was 4.33,which was significantly higher than that in the control group.(P<0.05).the height of the anterior and posterior cecum papillae in the rumen of Yaks in the control group and the 0.8% addition group were 8.42 mm and 8.68 mm,respectively,which were significantly higher than those in the 0.4% addition group(P<0.05),the thickness of the cuticle of the anterior and dorsal cecum in the 0.8% group was 12.67 ?m,which was significantly higher than that in the other two groups(P<0.05).(5)Compared with the other two groups,the expression level of Fatty Acid Synthase(FAS)gene in muscle increased significantly in the 0.4% YC addition group(P<0.05);the expression level of cardiac fatty acid binding protein(H-FABP)gene was the highest in 0.8% addition group(P<0.05).(6)Compared with the control group,the economic benefit of the yak in the 0.8% YC addition group increased,and the average profit per head increased by 25.17%.In conclusion,under this experimental condition,addition 0.8% YC to TMR can improve the performance of yak and improve the quality of yak meat.This change may be related to YC improving rumen microbial flora and promoting the expression of genes related to lipid metabolism.