| With the improvement of living levels,there is a growing demand for dairy products.In order to improve economic efficiency and maintain high milk yield of dairy cows,farmers usually increase the proportion of concentration in the basic diet to meet the energy needs of dairy cows.This high-precision raw material contains carbohydrates that are easily fermented and repeatedly fermented in the rumen of dairy cows for a long time.It produces a large amount of volatile fatty acids(VFA),causing the rumen pH to fall below normal for a long time to damage the rumen microflora,which in turn causes subacute ruminal acidosis(SARA).A large number of studies have shown that adding yeast to the diet can not only provide necessary nutrients for cows,but also improve the rumen environment.And it also alleviated SARA to a certain extent.Glycerol can be used as a raw sugar precursor to alleviate the disease caused by negative energy balance in dairy cows and it can also be used in animal feed.Selenium is an important trace element,which has the function of improving immunity,improving reproductive performance and enhancing the body’s antioxidant ability.It can also scavenge free radicals and alleviate oxidative stress in dairy cows.There had been many studies on adding glycerol,selenium or yeast to dairy cow diets alone.However,there were few reports on the combination of glycerol,selenium and yeast applied to dairy cow,especially to cows suffering from subacute rumen acidosis.The high-yield glycerol yeast and selenium-enriched yeast isolated by our laboratory were mixed and cultured together to get a glycerol-producing and selenium enriched yeast product,which contained lots of organic selenium and glycerol obtained by fermentation under appropriate conditions.The glycerol content and stability of the glycerol-producing and selenium-enriched yeast product were determined at first.Subsequently,the Holstein cows were used as experimental animals,and the effects of dietary supplementation of glycerol-producing and selenium-enriched yeast product on rumen metabolism,milk quality and antioxidant capacity in dairy cows were investigated to provide data support for futher aplication of glycerol-producing and selenium-enriched yeast product in dairy cows.Experiment I Detecting the glycerol concentration and the stability of glycerol-producing and selenium-enriched yeast productIn this experiment,the concentration of glycerol in glycerol-producing and selenium-enriched yeast product was determined by periodate oxidation method.The product was stored in clean plastic buckets at room temperature(25℃).The glycerol concentration and yeast count were determined every 15 d to evaluate the stability of glycerol-producing and selenium-enriched yeast product.The results showed that the glycerol concentration of glycerol-producing and selenium-enriched yeast product was 109.41 g·L-1 and the number of live yeast was 7.9×108 CFU·mL-1.When the product was kept 60 d,the glycerol concentration was 107.15 g · L-1 and the number of live yeast was 5.5×105 CFU·mL-1.When the product was kept 75 d,the glycerol concentration was 106.19 g · L-1 and the number of live yeast was 3.2×103 CFU·mL·-1.It can be seen that the product can be stored at room temperature for at least two months and it remains a good stability.Experiment II Effects of glycerol-producing and selenium-enriched yeast product on the rumen metabolic indexes in dairy cow with SARAThis study aimed to evaluate the effects of adding glycerol-producing and selenium-enriched yeast product to basic diet on the rumen fluid pH and other rumen metabolic indicators in dairy Holstein cows.In this experiment,using a 2×2 repeat crossover test design,four rumen-cannulated lactating Holstein cows were randomly assigned to no-yeast group(ie,a control group)and yeast group(ie,a treatment group),2 cows in each group.The cows in the control group were fed a basic diet.Each cow in the treatment group ate the diet added 1 L of glycerol-producing and selenium-enriched yeast product(containing yeast selenium 5 mg,glycerol 109.41 g,live yeast 7.9× 108 CFU·mL-1)per day during lunch.The experiment was completed in 2 periods,each period consisting of 12-day-long preliminary experiment period and 3-day-long sampling period.Blood samples were collected before noon feeding on 13 d,14 d,15 d,and the rumen fluid samples were collected at 0 h,2 h,4 h and 6 h after noon feeding respectively.The results showed that compared with the pH=5.52 of rumen fluid at 4 h after feeding in the control group,the pH of the rumen fluid in the treatment group was 5.62,which significantly increased(P<0.05).And the cows in treatment group had higher rumen average pH(P=0.07).The ratio of propionic acid:TVFA in rumen fluid of dairy cows in treatment group was 25.41%,which significantly higher than that in the control group(P<0.05).However,the acetate:propionate ratio was 2.43,which was significantly lower than that in the control group(P<0.05).In addition,the concentration of microbial protein in rumen fluid of the treatment group was 1.25 mg · mL-1,which was significantly higher than that in the control group(P<0.05).And the concentration of NH3-N(P=0.08)in rumen fluid of the treatment group had a increasing trend while LPS(P=0.07)had a decreasing trend.However,the concentration change of lactic acid in the rumen fluid and the concentration changes of lactic acid,LPS and pH in the blood were insignificant.This experiment showed that dietary supplementation of glycerol-producing and selenium-enriched yeast product can alleviate the SARA in dairy cow to a certain extent by increasing pH and the proportion of propionic acid in rumen fluid and decreasing the ratio of acetate:propionate.Experiment III Effects of glycerol-producing and selenium-enriched yeast product on antioxidant capacity and milk quality of dairy cow with SARAThis study aimed to evaluate the effects of adding glycerol-producing and selenium-enriched yeast product to diet on antioxidant capacity and milk quality of dairy cow.Twenty dairy Holstein cows were randomly divided into two groups,as similar as possible with respect to expected parity,lactation and body condition score.The control group received a basal diet.The treatment group received a basic diet added 1 L of glycerol-producing and selenium-enriched yeast product(containing yeast selenium 5 mg,glycerol 109.41 g,live yeast 7.9×109 CFU·mL-1)per day per cow.This experiment included a 3-day-long pre-feeding period,the formal experiment time was 21d.DMI was measured and recorded daily for each cow throughout the experimental period.Blood samples and milk samples were collected for analysis on 0 d,7 d,14 d,21 d.The results showed that the activity of serum GSH-Px and the concentration of serum GLU and TP were respectively 178.9U·mL-1,64.55 mmol· L-1 and 71.22g·L-1,which were all significantly higher than those in the control group(P<0.05).And there was a slight increase in serum total antioxidant capacity(P=0.09)in treatment group.In addition,the milk fat percentage of treatment group was 3.37%,which was significantly higher than that of the control group(P<0.05).The percentage of milk protein was 3.15%,which increased(P=0.06)slighter than that of the control group.And the number of somatic cells decreased slightly(P=0.07)when compared with the control group.However,there were no changes in milk yield and other milk ingredients between two groups.This experiment showed that dietary supplementation of glycerol-producing and selenium-enriched yeast product can improve the antioxidant capacity and milk quality of dairy cow with SARA to a certain extent. |
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