1a. Objectives (from AD-416):
Objective 1: Maximize N use efficiency and animal performance by determining the optimal levels and qualities of dietary protein appropriate for differing base forages in dairy cattle diets, and determining the influence of polyphenol (o-quinones, tannins) or other feed additives on feed N use efficiency. • Sub-objective 1.A. Investigate the factors affecting optimal levels of protein in diets based on different forage types. • Sub-objective 1.B. Determine the influence of dietary polyphenols on efficiency of nitrogen use for milk production. Objective 2: Assess the relationships of ruminal microbial community profile or animal genotype, with animal factors including feed efficiency and lactation performance in dairy cattle. • Sub-objective 2.A. Evaluate the relationship between rumen microbial profile and animal performance. • Sub-objective 2.B. Evaluate relationships among lifetime health and production history and animal genome. Objective 3: Determine how the interactions among dietary components influence product formation by ruminal microbes and implications for effects on digesta passage from the rumen, in order to optimize meeting animal nutrient requirements and enhancing animal performance. • Sub-objective 3.A. Determine the quantitative effects of nonfiber carbohydrates and protein on in vitro fermentation kinetics and substrate-to-fermentation end-product conversions. • Sub-objective 3.B. Investigate the effects of interactions among dietary components on lactating dairy cattle. • Sub-objective 3.C. Evaluate the influence of dietary components and characteristics on amounts, proportions, and passage of ruminal liquid digesta.
1b. Approach (from AD-416):
Sub-objectives 1.A and 1.B: Latin square feeding studies with lactating dairy cows will be performed to test the effects of: 1) different combinations of dietary forage and supplemental protein sources, and 2) the interaction of dietary tannins and crude protein level of the diet as they influence milk production and efficiency of nitrogen use for milk production. Omasal sampling will be performed using triple markers in order to quantify differences among dietary treatments in flow of amino acids (AA) from the rumen (~metabolizable AA supply to the animal). Effects of tannin and protein levels on nitrogen volatilization will also be evaluated using manure samples from this study. Sub-objective 2.A: Studies will explore the relationship of ruminal microflora profile and milk fat depression (MFD) in lactating dairy cows. 1) Cultures of Megasphaera eldenii strains isolated and enriched from cows displaying or not displaying MFD will be used to determine if they differentially metabolize linoleic acid to produce biohydrogenated fatty acids implicated in MFD. 2) Ruminal inocula collected from lactating dairy cows displaying or not displaying MFD on diets designed to induce MFD. M. elsdenii will be quantified in the archived ruminal samples, and ARISA will be used to identify samples containing unidentified bacterium AL383 which has been shown to be negatively correlated with M. elsdenii. The intent is to identify AL383, isolate it, and assess its interactions with M. elsdenii. Sub-objective 2.B: The impact of interactions of cow genome, lactation performance, and accrual of disease events over multiple lactations will be investigated using records of 4000 genotyped cows. Phenotypic data will be used to establish heritability of phenotypes, and adjust phenotypic data for effects of age on increased risk of decreased performance/increased treated disease events. Phenotypic and genotypic data will then be subject to a genome-wide association analysis. Sub-objective 3.A: In vitro fermentations will be used to investigate relationships among nonfiber carbohydrate sources and level and type of protein supply as they alter the profile, amount, and rate of fermentation product formation by ruminal microbes. Batch culture fermentations of less than 8 hours with multiple destructive sampling times will be used to define patterns of substrate disappearance and microbial product appearance. Sub-objective 3.B: The impact of the protein x carbohydrate interactions described in 3.A combined with influence of changing rates of liquid passage and forage sources will be investigated in studies with lactating cows. Latin square studies with 2 x 2 factorial arrangements of dietary protein solubility and a salt concentration will be performed with repeated ruminal sampling to describe rumen function, omasal sampling to determine AA flow from the rumen, and lactation performance measurements. Sub-objective 3.C: A series of in vivo studies with lactating cows will be conducted to explore the effects of dietary components (salts, soluble protein) on ruminal digesta liquid and dry matter (DM) proportions, total digesta weight, liquid passage rate, and water intake.
3. Progress Report:
Six strains of Megasphaera elsdenii were isolated from cows that were not milkfat-depressed. To test the hypothesis that the ruminal bacterium M. elsdenii can elicit milkfat depression in some dairy cows, three cows were dosed with 3-liter cultures of this bacterial species, and compared to three cows dosed with a blank culture medium. Ruminal samples were taken to test for persistence of the inoculated strain, and milk samples were collected to determine milkfat status of the dosed and undosed cows. In a separate experiment, cows grouped on the basis of high- and low-feed efficiency (HE and LE, respectively, based on energy-corrected milk per unit dry matter intake) displayed differences in the species composition of the ruminal bacterial community. HE cows had a core set of species present in all cows within the group, while LE cows lacked a core set of species present in all members but not present in HE cows. Bacteria in the genera Sharpea and Shuttleworthia were more abundant in the HE cohort, while Desulfovibrio and Oscillospira were found in higher abundance in the LE cohort. Farmers of participating herds have been contacted. Data on lactation performance, incidence of treatment events, definitions of treatment events, and genomic data are being collected. Glucose and corn starch type by nitrogen level experiments have been completed. It was found that ruminal organic acid concentration is not a valid measure to evaluate the impact of experimental treatments on the progress of ruminal fermentation in vivo. This is because the volume of liquid in the rumens of cows is not similar, having ranges of 34 to 48 kilograms of liquid within each study. To use concentrations directly, for more than a description of ambient conditions in the rumen, the values must be based on the same liquid amount. Other experiments are being developed that are suitable for use, addressing possible alternative methods and the core question of what factors affect liquid flux in the rumen.
1. Improved starch assay in widespread commercial use to evaluate feed quality. Feed analyses are essential to determining the nutritional value of a feed relative to meeting an animal’s nutrient requirements, as well as for setting the commercial values of feeds. ARS researchers in Madison, Wisconsin, modified and transferred to industry an improved method that more accurately and easily measures the starch content of feeds. In a 12-month period, that assay was used by three commercial feed analysis laboratories to analyze a total of 282,537 samples with a total market value of $369,232. The method has also been widely adopted by commercial and research laboratories. The starch assay is currently the focus of an Association of Analytical Chemists collaborative study to determine its suitability as an official method for regulatory purposes, including feed nutritional labeling. The improved method gives the agricultural community a more reliable way to evaluate the nutritional and economic value of feeds.
2. Bacterial communities in the rumen differ in high-efficiency versus low-efficiency cows. Milk production in cows is influenced by a number of factors, including diet, host genetics, and the bacterial communities in the rumen. Rumen bacteria are directly responsible for the production of volatile fatty acids (VFA) that are used by the cow as precursors for milkfat synthesis. ARS researchers in Madison, Wisconsin, in collaboration with University of Wisconsin scientists, characterized the total ruminal bacterial community and VFA profiles in eight Holstein dairy cows. These cows were separated into high- and low-production efficiency groups, and both rumen solids and liquids were analyzed for total bacterial community structure. The researchers identified significant differences in bacterial community composition between high- and low-efficiency groups and between the solid and liquid fractions. They also identified a core set of bacterial species shared among all high-efficiency cows, but no core set was found among all low-efficiency animals. Chemical profiles between high- and low-efficiency groups were similar, but propionic acid concentration was significantly higher in low-efficiency cows, and succinic acid was significantly higher in high-efficiency cows. These data showed that there is a specific ruminal bacterial community associated with feed efficiency in dairy cows, but these differences cannot be detected by simple chemical analysis of rumen contents.
3. A measurement commonly used by researchers to evaluate rumen fermentation is not reliable. Organic acids are an important energy source to the animal, and they are produced when rumen microbes ferment feeds. Since the 1940’s, researchers in ruminant nutrition have used the concentration of organic acids in rumen fluid as an indicator of the effect of experimental treatments for enhancing or reducing fermentation of feed in the rumen. However, recent findings by ARS researchers at Madison, Wisconsin show that this approach can give misleading interpretations regarding the impact of treatments. The reason is that for measurements to be valid for evaluating treatment effects, they need to be on the same basis. For concentrations, that means that they would need to be found in similar amounts of liquid in the rumen. In fact, the amounts of liquid in the rumen were shown to vary by up to 106 pounds, or 176%, between the lowest and highest amounts within studies with lactating cows. Because of this finding, new approaches will need to be found to evaluate the impact of treatments on the progress of ruminal feed fermentation, and conclusions drawn from past studies will need to be reconsidered.
Hymes Fecht, U.C., Broderick, G.A., Muck, R.E., Grabber, J.H. 2013. Replacing alfalfa or red clover silage with birdsfoot trefoil silage in total mixed rations increases production of lactating dairy cows. Journal of Dairy Science. 96(1):460-469.