| Acertain level of NDF is needed to maintain the normal pH value of Rumen in the diet of dairy cows.Although roughage is the main source of NDF,it usually inhibits the dry matter intake(DMI)of dairy cows.It has been suggested that the main reason why NDF can maintain normal rumen pH is not that it stimulates saliva secretion,but that it reduces the average rumen fermentation rate of OM.According to this assumption,low-quality roughage such as wheat straw can also be used to reduce the average fermentation speed of OM,and its inhibition to DMI can be overcome by reducing the particle size,such as crushing.The purpose of this study is to test this hypothesis.45 healthy,disease-free mid-lactating Holstein cows were selected on a commercial dairy farm and randomly divided into three groups of 15 heads each.The basic diet is the mid-lactation diet used in the dairy farm,and the alfalfa hay in the basic diet is replaced with grass powder particles made of fresh dry wheat straw in equal proportions.The experimental treatments were: control group(group I,0% replacement),20% replacement group(group II,20%replacement),and 40% replacement group(group III,40% replacement).The test was conducted for a total of 10 weeks,including a pre-test period of 2 weeks and a full test period of 8 weeks,the result is as follows:(1)The replacement of alfalfa hay by wheat straw powder particles significantly increased the DMI of dairy cows(P < 0.01).The average daily DMI of each cow in Groups II and III was increased by 0.41kg/d and 1.62kg/d compared with the control group The feed intake also increased significantly due to the increase in DMI.The dietary DM and apparent digestibility of each nutrient were not significantly different between groups(P > 0.05).(2)The test treatment had no significant effect on the output of 4% standard milk,milk protein,milk fat,lactose,milk fat,lactose,milk urea nitrogen,and total solid content(P >0.05),wheat straw powder particle replacement has a tendency to reduce milk protein content(P < 0.1).(3)The test treatment had no significant effect on the rumen pH and total VFAs and the concentrations of acetic acid,propionic acid,butyric acid,isobutyric acid,valeric acid,isovaleric acid and n-hexanoic acid(P > 0.05).(4)Wheat straw particle replacement increased dietary nitrogen intake and urinary nitrogen elimination(P < 0.01),but there was no significant difference between milk nitrogen secretion and fecal nitrogen excretion(P > 0.05).(5)The differences between prolactin,insulin,IGF-1,growth hormone and glucagon were very significant(P < 0.01).The difference between AST and total protein groups was significant(P < 0.05).The urea nitrogen in groups II and III was significantly higher than that in group I(P < 0.01).The blood glucose in group ? was higher than that in groups II and III(P < 0.01).There were no significant differences between the ALT,albumin,and triglyceride groups(P > 0.05).(6)Compared with control group,? group,? per head after removing the daily feed raw milk sales revenue increased by 0.35 yuan and 1.54 yuan respectively.The results of this study generally support the speculation that fresh dried wheat straw powder can be used as a source of NDF for lactating dairy cows,as application technology promotion,the support of larger and more systematic test results is still needed. |
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