| A certain level of roughage is needed in dairy cow diets to prevent rumen acidosis.The general explanation for the mechanism is that roughage stimulates saliva secretion to neutralize rumen fermentation to produce acid.The ability of roughage to stimulate saliva secretion is related to particle size.The concept of dietary physical effective fiber(pe NDF)is the product of the dietary NDF content and the dietary physical effective factor(average particle size).Under the guidance of this theory,high-yield dairy cow rations need to use high-quality roughage,and should have a larger particle size.In recent years,some studies have shown that the level and particle size of dietary roughage have limited effects on saliva secretion.The main mechanism of roughage for preventing rumen acidosis is to reduce the average rumen fermentation rate of the diet.This is to overcome the effect of roughage on DMI of dairy cows by reducing the particle size.It is possible to improve the feeding effect of low-and medium-quality roughage.The theoretical hypothesis of this subject is: low and medium-quality roughage has a slow rumen fermentation rate,which can appropriately increase the level of dietary concentrate,and its disadvantage of suppressing the DMI effect of dairy cows can be overcome by reducing the particle size.According to theoretical assumptions,the subject selected 60 healthy Holstein lactating cows with 2～3 litters,average milk production of 29.2±0.47 kg/d,body weight of 641±24kg,and lactation days of 129±18 days,and randomly divided them into three groups,each with 20 head.Test cows were fed equal-energy protein rations and fed with different types of hay.The amount of hay fed per test cow,the control group is 3.5 kg/d imported alfalfa hay,the test group is 1.75 kg/d alfalfa + 0.5 kg/d wheat straw powder,and the test group is 1 kg/d wheat straw.Powder particles.The test site is Shandong Hi-Speed Biological Engineering Co.,Ltd.The test period is October to December.The entire test is 10 weeks,including a 2-week pre-test and an 8-week positive test.The test results are as follows:(1)Compared with the control group,there was no significant difference in the nutrient intake of the test group(P>0.05);the DM,NDF,and ADF intake of the test group were significantly reduced(P<0.05).There was no significant difference in the intake of protein and organic matter(P>0.05).The above results show that: crushing wheat straw can alleviate its inhibitory effect on DMI,but a higher feed rate(1 kg/d)still significantly inhibits DMI in dairy cows.(2)The test treatment had no significant effect on milk production,milk protein,milk fat,lactose output,milk protein,lactose,and total solid content(P>0.05),but significantly increased the milk fat rate.The milk volume has a decreasing trend(P=0.06).Compared with the control group,the 4% standard milk yield of the test group was significantly increased(P<0.05);the milk urea nitrogen content of the test group was significantly increased(P<0.05).The above results indicate that higher wheat straw meal feeding rate(1 kg/d)has a tendency to reduce milk production of dairy cows,which is related to the decrease of DMI and endocrine changes.In addition,there are obvious differences in blood biochemical and hormone indicators,and detailed mechanisms are necessary for in-depth research.(3)The test treatment had no significant effect on the PH value of rumen juice,butyric acid,propionic acid,isobutyric acid,valeric acid and n-hexanoic acid(P>0.05),but significantly increased the total VFA,acetic acid,ethylene-propylene ratio,isobutyric acid,isobutyric acid and valeric acid(P<0.01).The above results indicate that the rumen p H value is not significantly reduced until the wheat straw powder dosage reaches 1 kg/d,which supports the view that the rumen p H value is controlled mainly by reducing the fermentation rate of the diet. |
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