Optimization Of Solid State Fermentation Conditions Of Aging Corn And Its Feeding Effect On Lactating Cows

The continued use of conventional corn as animal feed will lead to significant increases in production costs for livestock and poultry farming as corn prices rise.Aging corn(AC)is a product of deterioration of quality and physical and chemical properties of corn after long-term storage.Although the conventional nutrient content of AC is similar to that of conventional corn,its low digestibility and high fatty acid value limit its widespread use in animal production.Direct use of AC as feed material without treatment can reduce the performance and antioxidant capacity of animals.Solid state fermentation is an effective method to improve feed quality,which can improve nutrient digestibility and nutritional value.Based on the above background,this study proposed to use solid-state fermentation technology to improve the quality of AC.Through the collaborative fermentation of acid protease and Lactobacillus rhamnosus,response surface optimization method was adopted to gradually optimize the fermentation conditions of AC,and further fermented aging corn(FAC)feed lactating cows to mitigate the possible adverse effects of AC.This study is of great significance to improve the utilization rate of feed resources,reduce the cost of production and promote the development of dairy farming.Experiment 1:Optimization of aging corn solid state fermentation conditionsThe situ starch degradation of fermented aging corn was taken as the response value.Firstly,the effects of aging corn moisture content,inoculation size,enzyme dosage,fermentation temperature and fermentation time on the response value were studied through single factor experiment,so as to provide the optimal level of factors for the subsequent optimization.The Plackett-Burman experimental design was then used to study the primary and secondary effects between multiple factors,the results showed that the response values were significantly affected by moisture content,inoculation size and enzyme dosage(P<0.05),and the interaction effect should be considered in the subsequent optimization,while the optimum values of fermentation temperature and fermentation time were set according to the single factor test results.The level of the central test point of the response surface was determined by the steepest ascent experiments.Finally,the Box and Behnken experimental design were used to study the interaction between the influencing factors,and the optimal fermentation conditions were analyzed:moisture 41.44%,inoculation size 7.04×10~8CFU/g,enzyme dosage 0.51%,temperature 36℃,time 20 d.Under these conditions,the predicted degradation rate of starch of FAC was 63.04%.Fermentation was performed 3 times according to the above fermentation conditions,the rumen degradation rates of starch obtained were 62.75%,63.15%and 63.54%,respectively,which were close to the predicted values.Experiment 2:Improvement effect of solid state fermentation on aging corn qualityThe chemical composition and antioxidant capacity of aging corn before and after fermentation were measured and compared according to the optimized solid-state fermentation conditions.The results showed that fermentation decreased the contents of neutral detergent fiber,acid detergent fiber,soluble carbohydrate,prolamin,p H value and fatty acid value(P<0.05),but increased the starch content(P<0.05);fermentation increased the DPPH radical scavenging ability,hydroxyl radical scavenging ability and reducing ability of AC(P<0.05).Experiment 3:Study on feeding effect of dairy cows in lactation periodSix healthy third-parity Holstein cows with similar BW(614±39.4 kg),DIM(146±21.5 d),and milk yield(33.7±2.26 kg/d;all mean±standard deviation)were used in a replicated 3×3Latin square design with 3 periods of 21 d.These cows were fed three different diets:(1)basal diet without replacement of conventional corn(CC group);(2)replacement of conventional corn with aging corn in basal diet(AC group);and(3)replacement of conventional corn with fermented aging corn in basal diet(FAC group).For each period,the initial 14 d were used for diet adaptation,then blood and ruminal fluid were collected on d 15,16,and 17,as well as feed,milk,and feces were collected on d 19,20,and 21.The results showed that compared with CC and AC groups,the FAC treatment increased the production of milk(34.0,33.7,and 35.2 kg/d for CC,AC,and FAC group,respectively),energy corrected milk,4%milk fat corrected milk,lactose and milk protein(P<0.05),but decreased the SCS(P<0.05).Plasma catalase activity in AC group was lower than CC group and FAC group(P<0.05),and malondialdehyde concentration was the highest among the three groups(P<0.05).Compared with CC and AC groups,the FAC treatment decreased the plasma triglyceride,malondialdehyde concentration and rumen p H(P<0.05),but increased the plasma immunoglobulin G concentration,starch digestibility and rumen total volatile fatty acid concentration(P<0.05).The molar proportion of acetate was higher on AC than FAC(P<0.05).The relative abundance of Succinivibrionaceae＿UCG＿002 in the rumen was higher on AC than CC and FAC(P<0.05).Compared with CC and AC groups,the FAC treatment decreased the relative abundance of Succinivibrionaceae,but increased the relative abundance of Prevotella(P<0.05)and Ruminococcus(P<0.05).The relative abundance of Prevotellaceae was higher on FAC than CC(P=0.05),but the relative abundance of Succinivibrionaceae＿UCG＿001 was lower on FAC than CC(P<0.05).In addition,the Simpson index was lower on FAC than CC and AC(P<0.05),and the Shannon index was higher on FAC than AC(P=0.05).This study drew the following conclusions:(1)The optimal solid-state fermentation conditions for aging corn:moisture 41.44%,inoculation size 7.04×10~8CFU/g,enzyme dosage 0.51%,temperature 36℃,time 20 d.(2)Solid state fermentation improved the nutritional value and in vitro antioxidant capacity of aging corn.(3)Feeding aging corn decreased the antioxidant capacity of dairy cows,while feeding fermented aging corn increased the lactation performance,antioxidant capacity,immune capacity and starch digestibility of dairy cows.In conclusion,solid state fermentation improves the availability of aging corn by improving its quality,and it is feasible for fermented aging corn to be used as a substitute for conventional corn in the production of dairy cows.