Location:2009 Annual Report
1a. Objectives (from AD-416)
The overall objectives of the research project are to apply modern genomic tools to the identification and characterization of genetic pathways, physiological mechanisms, and microbial-host interactions that modulate nutrient uptake, partitioning, and loss in cattle. The specific objectives include development of resources for identification of selectable markers of nutrient efficiency, identification and characterization of genetic pathways and/or genomic regions influencing critical regulatory pathways of nutrient efficiency and transport, and development of intervention strategies to enhance nutrient uptake and partitioning in cattle.
1b. Approach (from AD-416)
To identify and characterize factors affecting nutrient use efficiency in cattle, resources will be developed including a phenotypic database of dairy efficiency and corresponding DNA and tissue collections, methods for live animal intestinal tissue collection suitable for gene expression studies, and sub-populations of dairy cattle to investigate inflammation and nutrient use interactions. Novel DNA sequencing technology will also be evaluated for its utility in characterizing changes in rumen microbial populations during rumen development. Transcript profiling techniques including microarray and quantitative real-time PCR will be used to establish molecular markers of proliferation, development and differentiation of the bovine gastrointestinal tract, and to identify metabolic and hormone pathways controlling nutrient metabolism in the ruminant gastrointestinal tract. Finally, two dietary strategies that potentially affect the rumen microbial population and production efficiency will be studied for their effects on nutrient use efficiency in cattle.
3. Progress Report
Multiple experiments were conducted during FY 2009 to address the three overall project objectives and FY 2009 National Program Components related to development of genome-enabling resources, identifying critical genes and their interactions, reducing animal stress as it relates to nutrient use efficiency, and improving overall efficiency of nutrient use. Details of these experiments are provided below under "Accomplishments." In addition, several studies were conducted examining various aspects of nutrient use efficiency in cattle. Gene expression analysis was completed for a study in dairy calves to characterize gene pathways involved in rumen development and growth. In addition, metagenomic analysis of the rumen microbial community dynamics and shifts in their functional profiles in these animals was initiated. The first survey of expression of genes affecting absorptive capacity of the gut during different stages of growth, pregnancy and lactation of dairy cattle was completed. Tissue sections from these animals were also evaluated for expression of proteins to corroborate gene expression findings and to characterize cellular and tissue localization of these proteins in the digestive tract of cattle. Further, metabolic flux within two gastrointestinal cell types of cattle was studied to improve understanding of how nutrient supply to the gut can influence amino acid use by cattle. Laboratory analyses of samples collected from two animal studies examining forage versus concentrate feeding and dietary effects on amino acid use by the gut of cattle were also completed. A preliminary evaluation of the relationship between variation in a gene involved in inflammation (TNF-alpha) and physiological response to bacterial infection of the mammary gland was completed in Holstein heifers. In addition, genotypes for this genetic variant were determined for 72 dairy cows, which will be correlated with their milk production and health records. Knowledge gained from these studies will help to identify factors that modulate nutrient availability, uptake, partitioning, and loss in dairy cattle. A better understanding of these processes will assist in the development of intervention strategies to maximize nutrient utilization, and ultimately reduce impacts of cattle production on the environment.
1. Expanded database to identify markers of feed efficiency in dairy cattle and estimated heritability of the residual feed intake trait. Measures of feed intake and feed efficiency in dairy cattle are extremely limited and are needed for future genetic improvement in our dairy herds. A fully automated system to continuously monitor daily feed intake of individual lactating dairy cows with minimal impact on feeding behavior, which was implemented in July 2007, was continued in FY 2009. To date, over 143 cows have been evaluated during the first 90 days of their lactation and heritability of the residual feed intake trait (a measure of feed efficiency) was estimated at 0.10, a level similar to other traits in dairy cattle such as somatic cell count and persistency of lactation. In addition, DNA samples from these animals were archived for future genetic analysis to develop genetic markers of feed efficiency.
2. Completed characterization of gut microbes in cattle using metagenomics tools to understand rumen microbial dynamics in response to fatty acids. Changes in the rumen microbial community can have profound effects on the health and ability of the cow to sufficiently and efficiently digest feed. Novel next-generation sequencing technologies were applied to characterize and quantify members of the rumen microbial ecosystem of cattle in response to a dietary fatty acid (propionate) treatment. The work demonstrated that propionate altered microbial populations and enzyme activities in the rumen, resulting in higher nitrogen retention and utilization efficiency. These findings explain mechanisms and identify means of improving nutrient utilization in cattle.
3. Evaluated a dietary intervention for reducing detrimental effects of inflammation in cattle. The normal inflammatory response of cattle to infection can have detrimental effects on function of critical proteins in the body. The damage is due to the production of reactive nitrogen and reactive oxygen free radicals generated during inflammation. To identify means to minimize these damaging effects, two forms of Vitamin E (alpha-enriched tocopherol versus gamma-delta tocopherol) were evaluated in cattle for their ability to minimize protein damage in the liver. The generated data constituted the first quantitative measurement of gamma-delta tocopherol in cattle as a result of oral treatment and revealed that the feeding of gamma-delta tocopherol was superior to that of alpha tocopherol in reducing the amount of nitrated protein generated during inflammation. The results also provided the basis for further experiments which will assess the utility of gamma-delta tocopherol as a treatment for health stabilization during the stressful times of calving and weaning.
4. Identified mechanisms of growth regulation in important cellular models of cattle using novel molecular approaches. Knowledge of mechanisms that regulate tissue growth and cellular repair from infection are needed to develop means to improve nutrient use efficiency in cattle. A study of molecular and cellular effects of a specific fatty acid, butyrate, was conducted in two cell types of cattle. Novel molecular methods known as ChIP-seq, which couple chromatin immunoprecipitation with high-throughput next-generation sequencing, were established in the laboratory to complete these studies. Results of this work will help to determine how nutritional management can affect important biological processes ranging from regulation of gene expression and growth, to wound repair and recovery from enteric infection. Management of these processes is critical to improve feed efficiency and attain profitable animal production.
5. Identified genes mediating immune response of bovine cells to bacterial cell components. Lipopolysaccharide is a major component of the outer membrane of Gram-negative bacteria such as Escherichia coli and induces a strong response from normal animal immune systems. Despite extensive investigation over the past 20 years regarding the biological effects of this bacterial component, the cellular and molecular mechanisms of action are still not completely understood. Gene networks in immune cells of cattle in response to lipopolysaccharide stimulation were evaluated and GLG1/E-selectin was identified as a key component in the early response of cells. Results of this work provide potential targets for reducing inflammation in cattle and minimizing nutrient losses to non-productive biological pathways.
6. Identified a critical signaling module that functions as a potential negative feedback mediator of growth hormone. Growth hormone treatment is a potential tool for managing the energy-demanding processes that challenge an animal's response to infection. There is little knowledge of the signal transduction pathways involved in growth hormone interaction with the inflammatory response. A cell line derived from cattle kidney cells was used to investigate the critical control points underlying growth hormone response and signaling pathways in these cells using a functional proteomic approach. Results identified the major paths or targets of growth hormone action and identified a critical biological complex (AKT/PKB-eNOS) as a negative feedback mediator of growth hormone actions.
Connor, E.E., Siferd, S., Elsasser, T.H., Clover, C.M., Van Tassell, C.P., Sonstegard, T.S., Fernandes, V., Capuco, A.V. 2008. Effects of increased milking frequency on gene expression in the bovine mammary gland. Biomed Central (BMC) Genomics. 9:362.