Using biological additives to improve dietary nutrient conservation and utilization by lactating dairy cows.

摘要

Four experiments were conducted to evaluate the effect of adding biological additives to the diet or feeds of lactating dairy cows on their performance or the quality of the feeds or diets. The objective of Experiment 1 was to determine the effect of dietary addition of a fibrolytic enzyme preparation containing cellulase, xylanase and esterase activities on the performance of dairy cows fed low or high-concentrate diets. Enzyme application did not affect milk yield or intake of DM, but increased digestibility of DM, CP, NDF, and ADF, and increased the efficiency of milk production. Increasing the concentrate level reduced ruminal pH but increased intakes of DM and CP, digestibility of DM (DMD) and CP, and milk yield and milk protein yield. Cows fed LCE instead of HC had less DMI, similar milk yield and greater efficiency of milk production. Enzyme application did not affect ruminal pH or ruminal degradation of the diets. However, increasing the level of concentrate supplementation decreased the pH, increased the immediately soluble dietary fraction, and tended to decrease the potentially degradable fraction.;Experiment 2 was designed to determine if the enzyme used in Experiment 1 primarily exerted its hydrolytic effect prior to ingestion or within the rumen. A second objective was to determine if the enzyme was more effective on specific components of the diet. Substrates were incubated in a buffer or a buffer-enzyme solution in triplicate for up to 24 h and chemical composition and DM disappearance were measured. Application of the enzyme reduced concentrations of NDF and hemicellulose, and increased water-soluble carbohydrate (WSC) concentration and DM disappearance. Incubation of enzyme-treated substrates in RF resulted in greater DMD than incubation in W except for AH, which had similar DMD in both media. Enzyme addition increased DMD and NDFD in W by 10 and 84% respectively, but had no effect on DMD and NDFD in RF; suggesting that preingestive effects of the enzyme were greater than ruminal effects. Enzyme effects on NDF, WSC, and hemicellulose concentration or DMD and NDFD in W or RF did not depend on the substrate. Therefore, this study provided no evidence that the enzyme preferentially hydrolyzed specific substrates and it suggested that preingestive effects of the enzyme were greater than ruminal effects under the conditions of the study.;Experiment 3 determined the effect of bacterial inoculants on the fermentation and quality of corn silages. Four replicates of each treatment were weighed into polyethylene bags within 20-L mini silos, which were stored for 575 d at ambient temperature (25°C) in a covered barn. After silos were opened, aerobic stability, chemical composition, and yeast and mold counts were determined. The DNA from treated and untreated silages was isolated using a lysozyme/sodium dodecyl sulfate lysis and phenol/chloroform extraction method. The DNA was used as a template for a conventional PCR with primers designed on the 16S rRNA gene to detect the presence of L. buchneri in silage samples. The WSC concentrations of all silages were reduced during the fermentation. However, B500 had the greatest residual WSC concentration, suggesting that plant sugars were less extensively fermented by the bacteria in this inoculant compared to those in other treatments. Dry matter loss was lower in BUC silages compared with Control and B2 silages. The PCR analysis confirmed the presence of similar populations of L. buchneri in all treatments, perhaps explaining why aerobic stability was high in all silages. The inoculants had differing effects on the fermentation of the silages with BUC producing the most desirable fermentation and least DM losses.;Experiment 4 determined the effect of applying three different bacterial inoculants to corn silage on the performance of lactating dairy cows. Chemical composition and yeast and mold counts of silages did not differ among treatments. Treatment with BUC improved silage aerobic stability by 200% and numerically resulted in the least losses compared with other treatments. Inoculant treatment did not affect DMI or digestibility of DM or CP. However, cows fed B2 had lower NDF and ADF digestibility than cows fed the control diet. Consequently, cows fed B2 had lower digestible NDF and ADF intake than cows fed the control diet. Nevertheless, milk yield, milk composition, and feed efficiency were not affected by treatment. Therefore, the inoculants did not affect the performance of the cows, but application of L. buchneri improved the aerobic stability of corn silage.;These experiments indicate that fibrolytic enzyme application can improve nutrient digestion and efficiency of milk production by lactating dairy cows. Application of the bacterial inoculants improved the fermentation of silages in one study and improved aerobic stability in another study, but feeding inoculated silages did not affect the performance of lactating dairy cows. (Abstract shortened by UMI.)