| In present, yak cultivation mainly still adopt the traditional farming system, which causes low growth performance, long maketing cycle, and poor meat quality. Barn feeding in cold season and staggering the slaughter period is the key solution to these problem. This study was conducted to investigate the effects of dietary energy concentration on performance, serum indexes, rumen fermentation, carcass traits, and intramuscular fat metabolism in finishing yaks fed indoors through two experiments. This experiment may provide basic datas and experimental basis for the efficient yak cultivation.Experiment 1 Effects of dietary energy concentration on performance and rumen fermentation in finishing yaks fed indoorsThirty 3-year-old male yaks with an average body weight of (114.57±21.56 kg) were randomly allocated to one of three dietary treatments, inculding low energy group, middle energy group and high energy group, with 5 replicates per group and 2 yaks per replicate. Acording to Chinese feeding standard of beef cattle (2004) recommended nutrient requirements of finishing beef cattle, the ration of middle energy group was designed according to the nutrient requirements of 150 kg finishing beef cattle with average daily gain (ADG) of 500 g. Yaks were fed indoors with different combined net energy (Nemf) concentration diet,3.72 MJ/kg (82%, low energy group),4.52 MJ/kg (100%, middle energy group) and 5.32 MJ/kg (118%, high energy group), respectively. Yaks were submitted to 30 days of adaptation to experimental installations and rations and the formal experiment last 120 days. At the end of the trial, six yaks from each treatment according to the body weight were slaughtered and rumen fluid was sampled for rumen fermentation parameters and microbes determination. The results showed as following:(1) With the increase of dietary energy concentration, the ADG increased significantly (P<0.05) and the ADG of three groups is 286.92,446.75,770.42 g/d, respectively, while F/G decreased significantly (P<0.05). There were no significant differences in ADFI among groups (P>0.05).(2) Height, body length, chest girth and chest depth increased significantly with dietary energy concentration increased (P<0.05).(3) Increasing dietary energy concentration resulted in a significant improvement of serum GLU and TG content (P<0.05), but a significant decrease of UN and NEFA content (P<0.05). The TC, HDL-C, LDL-C and ALP content of low energy group was significantly higher than the other two groups (P<0.05). The ALB content of high energy group was significantly higher than the other two groups (P<0.05). No significant influence of dietary energy concentration was detected on TP, GLB, LDH content and A/G (P>0.05).(4) Improving dietary energy concentration significantly improved serum IGF-1 content (P<0.05). The Ins content of high energy group was significantly higher than low energy group (P<0.05). The leptin concent of high energy group was significantly higher than the other two groups (T<0.05).(5) As dietary energy concentration enhanced, NH3-N content, acetic acid content and the ration of acetic acid to propionic acid were decreased significantly (P<0.05), while MCP, propionic acid and TVFA were increased significantly (P<0.05). Dietary energy concentration had no significantly effect on pH and butyrate acid content (P>0.05).(6) Improving dietary energy concentration significantly increased the population of rumen protozoa, starch degrading bacteria (S. bovis, P. ruminicola and R. amylophilus) (P<0.05), significantly decreased the population of fungi, fibrolytic bacteria (R. albus and B. fibrisolven) (P<0.05).(7) Combined net energy requirement of Chinese feeding standard of beef cattle (2004) was low for finishing yaks fed indoors in cold season to develop growth potential.Experiment 2 Effects of dietary energy concentration on carcass traits and intramuscular fat metabolism in finishing yaks fed indoorsSlaughter trail was similar with experiment 1, yaks were slaughtered and sampled, the results showed as following:(1) The before slaughter liveweight, carcass weight, dressing percentage, meat percentage, back fat thickness and loin muscle area all increased significantly by improving dietary energy concentration (P<0.05).(2) The carcass chest depth, carcass depth, hind leg around, hind leg wide, waist meat thick, and rid meat thick of high energy group were siginificantly higher than the other two groups (P<0.05). Carcass length and hind leg length of high energy group were siginificantly higher than low energy group (P<0.05). Thigh meat thick increased siginificantly with dieatry energy concentration increased (P<0.05).(3)The ribeye, high rib, outsid flat, everound, topside and kunckle weight of HE group were significantly higher than low energy group and middle energy group (P<0.05), while there was no significant difference between low energy group and middle energy group (P>0.05). With dietary energy concentration increased, striplion, brisket, shank and shoulder chops weight increased significantly (P<0.05), while tenderlion and chuck tender weight showed no significant difference among groups (P>0.05).(4) Increasing dietary energy concentration resulted in a significant improvement of IMF content (P<0.05) but a significant decrease of cooking loss, driage, shearing force and moisture content (P<0.05), while no significant influence of dietary energy concentration was detected on pH45min, pH24h and color parameters (P>0.05).(5) with increasing energy concentration of the diets, the proportions of C 18:2, C20:4 and PUFA increased significantly (P<0.05), while the proportions of C 16:0 and SFA decreased significantly (P<0.05).(6) Increasing dietary energy concentration significantly upregulated mRNA levels of lipogenic gene (FAS, ACC, SERBP-1, SCD, PPARy) and fatty acid transport gene (H-FABP, LPL) (P<0.05). downregulated mRNA levels of lipolytic gene (HSL, CPT-1)(P<0.05).In conclusion, improving dietary energy concentration promoted rumen protozoa and starch degrading bacteria growth, inhibited fungi and fibrolytic bacteria growth, improved NH3-N utilization. MCP synthsis and VFAs concentration, promoted propionate fermentation and glucose, lipid and nitrogen metabolism, improved energy utilization efficiency, thus enhanced profermance. Improving dietary energy concentration improved carcass traits and prime cuts production, up-regulatd intramuscular lipogenic gene expression and fatty acid transport gene expression, promoted intramuscular fat accumulation, increased PUFA content and improved meat quality. Combined net energy requirement of Chinese feeding standard of beef cattle (2004) was low for finishing yaks fed indoors in cold season to develop growth potential. |
