Enzyme is a green feed additive.It plays an irreplaceable role in animal feed digestion process,preventing diseases,regulating metabolic balance of animal,improving feed nutrient degradability,protecting ecological environment and promoting animal health.With the development of mechanism and production process to the depth,and with the application effect more significant,the fields of enzyme applications are becoming larger and larger.The paper on the mechanism of enzyme action in ruminant animals,and the effect of the application of the new method of enzyme identified were reviewed to provide a reference for the enzyme in ruminant research and applications.

The experiment was conducted to study the effect of different additions of canola rapeseed on the activity of digestive enzymes in jejunum and cecal chyme and the relationship among the activities of each enzyme.A total of 18 healthy castrated yaks with the same age,gender and body condition were randomly divided into 3 groups and fed with rapeseed for 21.75%(H),10%(M)and 0%(L)of the concentrate feed,six treatments were repeated for each treatment group,and each repeat was fed alone.The results showed that:(1)There was no significant effect of different rapeseed additions on the activi-ties of amylase(AMS),lipase(LPS)and cellulase(CLS)in jejunum(P>0.05).The trypsin(TRS)activity in H group was significantly higher 51.30%,45.08% than that in M group and L group.(2)The activities of AMS and CLS in H group were significantly higher than those in M and L groups(P<0.05).The AMS activity in H group was higher 75.26% and 72.22% than that of M group and L group,CLS activity was higher 68.73% and 52.48% than that in M group and L group.(3)There was a significant positive correlation between AMS and CLS activities in the digestive enzyme activity of jejunum chyme (P <0.01);and there was a significant positive correlation between AMS,LPS,TRS and CLS in the digestive enzyme activity of cecal chyme(P<0.01).

This study was conducted to investigate the effects of dietary iodide content on rumen fermentation of yaks in vitro.Potassium iodide was used as additive and diet for yaks was used as a substrate for in vitro ru-men fermentation.Iodine content in substrate was designed as 0.1, 0.3, 0.5, 0.7 and 0.9 mg/kg, respectively. The fermentation lasted for 48 h.Gas production, rumen fermentation characteristic parameters and digestive enzyme activities were measured after fermentation.The results showed as follows:when the content of iodine in substrate was 0.3 mg/kg, the concentrations of microbial protein ( MCP) , acetic acid ( C2) , propionic acid ( C3) , butyric acid ( C4) , isovaleric acid ( i-C5) , valeric acid ( C5) and total volatile fatty acid ( TVFA) , as well as the activities of amylase ( AMS) , lipase ( LPS) and trypsin ( TYS) in fermentation fluid reached the highest, which were 3.694 g/L, 56.286 mmol/L, 28.906 mmol/L, 9.507 mmol/L, 1.552 mmol/L, 0.919 mmol/L, 97.769 mmol/L, 1.567 U/mL, 0.453 U/mL, 60.787 U/mL, respectively; when the con-tent of iodine in substrate was 0.5 mg/kg, dry matter digestibility ( DMD) reached the highest, as 69.39% , which was significantly higher than other treatments ( P<0.05); when the content of iodine in substrate was 0.7 mg/kg, cellulose ( CLS) activity in fermentation fluid reached the highest, which was 79.956 U/mL, and C2/C3 in fermentation fluid reached the lowest, which was 1.636.Based on the various indexes, under in vitro conditions, when the content of iodine in substrate was 0.3 to 0.7 mg/kg, in vitro ruminal fermentation of yaks is at high level.

In order to compensate for the problem of insufficient support for monitoring of the nutrient value of pasture in the Qinghai-Tibet Plateau,we examined the dynamic nutritional value of grassland pasture under grazing conditions in the Qinghai-Tibet Plateau.During the period September 2015 to August 2016,we selected typical Tibetan herdsmen and grazing pastures to track yak grazing,and simulated the collection of edible for-age for sampling.The nutrient composition and total energy of the pasture were analyzed,and the dry matter digestibility of pasture was determined using a two-step in vitro method.The following results were obtained. 1)The contents of crude protein,ether extract,acid detergent fiber,ash,calcium,and phosphorus were 3.68%~19.21%,0.86%~2.74%,9.65%~43.83%,44.70%~76.23%,5.40%~9.62%,2.13%~5.12%,and 0.027%~0.190%,respectively,and the contents of CP and ash in May were significantly higher than those in other months (P <0.01).2)The digestibility of pasture was 42.72%~72.47%,which was significantly higher than that of other months (P <0.01 ).3)Total energy (GE),digestive energy (DE),and metabolic energy (ME)were 17.76 ~ 19.67,7.81 ~ 13.26,and 6.40 ~ 10.87 MJ ·kg-1 ,respectively.There was no significant difference in the GE of forage in different months (P >0.05),although it was the highest in June,followed by November.DE and ME were significantly higher in May than in other months (P <0.05),and the lowest in December,followed by April and June.In conclusion,the natural forage of Haiyan County,Qinghai Province in May and June is of good quality,whereas in October to March,the nutritional value of forage is low.There-fore,in view of the different types of seasonal grassland grazing throughout the year,it is recommended that pastoralists and farmers use natural grassland to supplement feed for breeding yaks in October to March.In the future,we will conduct follow-up monitoring of forage grass,and determine the fine feeding of grazing yak.

This study aimed to explore the nutritional status of yaks in Haiyan county, the main yak grazing ar?ea in Qinghai province, to provided scientific basis for the formulation of targeted supplement measures. The natural forage yield, and dry matter intake, body weight and serum biochemical indicators of grazing yaks in Haiyan county, Qinghai province were determined in September 2015 to August 2016, and the correlation be?tween average daily gain and serum biochemical indictors was analyzed. The results showed as follows: edible grass yield of natural pasture was higher in July than in other months; dry matter intake of grazing yaks was significantly higher in spring than in autumn and winter, and autumn was significantly lower than other seasons (P<0.05); average daily gain was negatively increased in January, February, March, October, November and December, after April, it was increased gradually, and June and July were significantly higher than other months ( P<0.05); serum glucose ( GLU) was significantly higher in July than in other months except June and October ( P<0. 05);serum alkaline phosphatase ( ALP) activity and urea nitrogen ( UN) content were lower in February and March than in other months;the correlation results showed that average daily gain had significant positive correlation with serum UN content ( P<0.05) . In conclusion, natural forage in October to March of the next year in Haiyan county, Qinghai province is undersupply, average daily gain of yaks is nega?tively increased, and is gradually increased after April, so it is suggested that under the condition of rotation grazing, feeding mode of natural forage combined with feed supplementation can be applied in October to March of the next year.