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United States Department of Agriculture

Agricultural Research Service

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Location: Dairy Forage Research

2008 Annual Report

1a. Objectives (from AD-416)
1) Identify and measure plant chemical and physical characteristics and dietary interactions that may alter nutrient digestibility and excretion by lactating dairy cattle. 2) Determine the effects of level of intake and digestion kinetics on diet component digestibility with current industry-representative lactating cows. 3) Measure the impact of fermentative digestion on nutrient utilization, quantify the transformations of nutrients into end-products of fermentation, and use molecular techniques to characterize and quantify changes in populations of ruminal bacterial species as affected by diet and animal. 4) Develop an integrated system for evaluating forage genotypes and validate the usefulness of in vitro, in situ, and small ruminant digestibility in assessing the utilization of nutrients by lactating dairy cows representing current levels of production.

1b. Approach (from AD-416)
1) The effects of PPO-modified plants, silage inoculants and lauric acid on protein utilization will be studied. Digestibility of corn silage with altered lignin/phenolic characteristics and alfalfa with down-regulated COMT and CCOMT to modify lignin will be evaluated with lambs and lactating cows. 2) Intake and digestibility from lactating cow trials will be compiled and digestibility of dry matter, fiber and soluble organic matter will be regressed on intake. Digestion kinetics will be measured on ration ingredients from trials. 3) In vitro fermentations using mixed ruminal microbes will be used to measure changes in digestion kinetics and microbial populations associated with direct-fed microbials, monensin, non-fiber carbohydrate sources, forage species and pH. 4) In vitro, lamb and lactating cow digestibilities will be compared to develop an integrated system for evaluating new forage genotypes.

3. Progress Report
Holstein cows were fed 4 diets that provided 0, 223, 407 or 549 g lauric acid/day to study the effects of feeding lauric acid, a fatty acid that suppresses protozoal numbers in the rumen. Lauric acid feeding resulted in a stepwise reduction in protozoal numbers in the rumen, with the highest level reducing protozoa by 64%. Feed intake was depressed at all levels of lauric acid (by 24% at the highest level). Production of milk/milk components was also lower at most levels of lauric acid. Results indicate protozoa in the rumen may impair feed utilization, but substantial reduction in feed intake resulting from feeding lauric acid makes this an impractical means for suppressing rumen protozoa. The rumen-sampling portion of the study with lactating cows to evaluate the interaction of NFC source & relative protein degradability on a corn silage-based diet was completed. Based on these results, the production portion of the study that will require more cows will be performed later this year. Seed of sfe corn mutants & comparison inbred lines has been planted at the U.S. Dairy Forage Research Center to be harvested as silage in the fall of 2008 for a dairy cow production trial & for lamb digestibility trials in FY09. Analysis of the first year grazing results have been completed & the second year of the trial is in progress to evaluate the chemical & physical factors that affect intake & digestibility of grasses during grazing. Tissue samples from 79 cull cows have been collected & submitted for histopathological evaluation. A historical database of cow intakes & digestibilities from the USDA-ARS Beltsville Energy Metabolism Unit was used to evaluate the effects of intake on digestibility of lactating cows. Efforts are underway to merge this data with treatment mean intakes & digestibilities from published reports. Compilation of in-house data is behind schedule & this effort will continue through the next project year. Fermentations to assess the effects of direct-fed microbials have been completed & samples analyzed, see project 3655-31000-022-01T for details. Alfalfa & corn silages were made with several inoculants to identify factors potentially affecting animal performance. Changes in microbial populations under milk-fat depressing conditions are reported in 3655-21000-046-3T. Digestibility studies by lambs of two genetically modified alfalfas and corresponding nulls (forage only diets) have been completed for 1st, 2nd, and 3rd harvests. Results of digestion trials for 1st harvests indicate that alfalfas with reduced lignin from down-regulation of two enzymes in the lignin biosynthesis pathway have improved digestibility compared to nulls. Digestion trials using young lambs with intakes in excess 3.3% of body weight per day fed total mixed rations containing reduced-lignin alfalfas were completed. Preliminary analysis suggests that digestion coefficients of these diets by lambs were similar to those of lactating cows feed corresponding diets during a collaborator’s digestion trials. These research activities are related to improving the conversion of forage to milk production in support of the NP101 Action Plan, Component 2.

4. Accomplishments
1. Established that population sizes of individual bacterial species in the rumens of cows varies during daily feeding cycles. Despite common notions that the population sizes of individual bacterial species vary in response to feeding, there are no systematic data on how these populations vary over the course of the daily feeding cycle, or across several feeding cycles. Genetic probes were used to determine that rumen bacterial community composition varied substantially among different cows maintained on the same diet, but within each cow this composition typically reset itself by the end of each feeding cycle. The bacterial community associated with feed particles was more stable than the unattached, free-floating bacterial community. These results provide baseline data on bacterial community structure necessary to assess the effects of feed additives on rumen microbial populations. This accomplishment addresses research components described under NP101 Food Animal Production, Problem Statement 2C: Improving Efficiency of Nutrient Utilization and Conversion to Animal Products.

2. Cow diets and management impact nutrient losses from dairy farms. We conducted two integrated feed-manure management trials and a survey of dairy feed practices and to examine relationships between dairy diets, milk production, manure nutrient excretions and environmental risks. On Wisconsin dairy farms, approximately 20-35% of feed crude protein (CP) and phosphorus (P) is secreted into milk and the remaining is excreted in manure. The amount and form of N and P excreted in manure, and manure N and P losses to the environment were highly influenced by what was fed to dairy cows, and other management practices. For example, feeding dietary CP above recommended levels increased excretions of N in manure, especially of N in urine and also subsequent ammonia N loss from barns and field after manure land application. Unnecessary dietary P supplements dramatically increased total and water-soluble P concentrations in manure, and also runoff P from soil surfaces after manure application. On Wisconsin dairy farms, the use of total mixed rations, balancing rations at least four times per year, and milking thrice daily results in highest milk yields and levels of feed N and P transformed into milk. Dietary options and practices are available that satisfy the nutritional requirements of high-producing dairy cows, and also produce manure less susceptible to environmental loss. This accomplishment addresses research components described under NP101 Food Animal Production, Problem Statement 2C: Improving Efficiency of Nutrient Utilization and Conversion to Animal Products.

Review Publications
Ferreira, G., Mertens, D.R. 2007. Measuring detergent fibre and insoluble protein in corn silage using crucibles or filter bags. Animal Feed Science And Technology. 133(3-4):335-340.

Filya, I., Muck, R.E., Contreras-Govea, F.B. 2007. Inoculant effects on alfalfa silage: fermentation products and nutritive value. Journal of Dairy Science. 90(11):5108-5114.

Muck, R.E., Filya, I., Contreras-Govea, F.B. 2007. Inoculant effects on alfalfa silage: in vitro gas and volatile fatty acid production. Journal of Dairy Science. 90(11):5115-5125.

Weimer, P.J., Stevenson, D.M., Mertens, D.R., Thomas, E.E. 2008. Effect of monensin feeding and withdrawal on populations of individual bacterial species in the rumen of lactating dairy cows fed high-starch rations. Applied Microbiology and Biotechnology. 80(1):135-145.

Last Modified: 05/25/2017
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