Brief Summary of Minutes of Annual Meeting

The need as indicated by stakeholders. Over 55% of the calcium, 17% of the protein, and 15% of the energy in the US diet are supplied by dairy products; thus, the US consumer is a major stakeholder for the NC-1009 committee. Consumers want dairy products that are safe and inexpensive, but increasingly they also want an environmentally friendly dairy industry that promotes animal well-being. Recently, attention has been given to bioactive molecules in milk (in addition to Calcium) such as conjugated linoleic acids. Yet at its core the NC 1009 committee functions to do basic and applied research on the feeding and nutritional biology of dairy cattle. Major stakeholders include other scientists, practicing nutritionists, veterinarians, and farmers. The needs of these stakeholders have been addressed by the Food Animal Integrated Research group in the FAIR 2002 document. The goals of FAIR 2002 are to strengthen global competitiveness, enhance human nutrition, protect animal health, improve food safety and public health, ensure environmental quality, and promote animal well-being. Because feed inputs are a major determinant of milk yield, cow health, feed efficiency, profitability, and waste output, the work of the NC-1009 committee is critical for most of these goals. The concentration of dairy animals into larger units is an established and continuing trend. This concentration makes some waste management issues more prominent but also more manageable.

The importance of our work. Natural resources are used efficiently when milk production per unit feed and per cow is high. To efficiently produce milk, a cow must have a well-developed mammary gland and be able to supply the gland with the nutrients it needs. Nutrition in the first year of life affects mammary gland development, and nutrition around the time of calving and throughout lactation has a major effect on the health, productivity, and efficiency of cows. Feeding for optimal nutrient intake requires not only the provision of the necessary nutrients for milk production but also consideration to the effects of diet on mammary capacity and on appetite, health, and metabolic regulation of the cow. Because feed costs account for half of all costs on a dairy farm, nutrition also significantly impacts farm expenses. The NC-1009 committee considers all of these factors for optimal feeding. For example, if we could maintain current milk production while feeding diets with 4 percentage units less total protein, we would decrease N losses to the environment in the US by 470,000 metric tons per year and save US dairy farmers $1 billion per year in feed costs. This type of progress only can be made if we take an integrated approach, with the use of mechanistic bio-mathematical models that accurately describe metabolism and production of cows.

Integration of results. This committee has a proven track record of making significant impacts in our knowledge dairy cattle nutrition and metabolism and in the way that dairy cattle are fed and managed nationwide. We use the same approach that has proven effective in the past: that is to challenge and refine our models of dairy nutrition and metabolism. Computer-based, mechanistic, and quantitative metabolic models are useful in two ways: first, they help us determine critical needs in research and second they enable practical improvements in dairy cow feeding. Critical research needs are determined by using existing data from NC-1009 members or conducting new experiments to test model predictions of physiological responses to experimental diets. Examples of such responses include, rumen pH, microbial growth and function; alterations in gene expression and hormonal release of organs such as the adipose tissue; and alterations in milk fatty acid compositions. By challenging our working models in this way, we identify shortcomings that then become the basis for developing new testable hypotheses for further experimentation. Results from new experiments are incorporated into the models, and they are challenged again for further refinement. Thus, we continue to build our models so they are more mechanistic, quantitative, and accurate. These qualities enable us to improve practical feeding recommendations for dairy cattle in a variety of environmental and feeding conditions.

Need for Cooperative Work. Important and complex problems require coordinated effort of many personnel. Considerable progress has been made in dairy nutrition, but practical problems remain and no single research group has the skills and resources needed to solve them alone. Only through cooperation can State Experiment Stations address the complex interactions among feed supply, nutrient use, genetic capability, and milk composition. Our committee is comprised of dairy scientists with a broad base of specialties that encompass feed analysis, feeding management, ruminal microbial metabolism, intestinal digestion, physiology and metabolism of splanchnic, adipose, muscle, and mammary tissues, endocrine regulation, molecular and cellular biology, and mathematical modeling. Furthermore, in testing and refining nutrition models for the whole country, we must consider the variation in forages and environment that exist among regions. Thus, we have scientists from every dairy region in the country. In addition, the explosion of new information in genomics, gene expression, gene array work, metabolomics and proteomics requires that we integrate this knowledge into our understanding of metabolic efficiency. Cooperation among stations is required to deal with this information and to solve problems, and will have a national impact in understanding the complex interrelationships of nutrient digestion and metabolism in lactating dairy cows and to apply this knowledge.

Impacts on Science and Other Impacts. This project exemplifies the proven effectiveness of the cooperative regional approach. As detailed in the "Related Current and Previous Work" section below, results of this cooperative effort have become benchmarks of scientific progress and have led to practical feeding recommendations used worldwide. Project Leaders for the NC-185 regional project have received numerous awards for research, both basic and practical, from the American Dairy Science Association, the American Society of Animal Sciences, and industry groups. Most of the Project Leaders are in continuous demand as speakers for scientific and industry conferences in nutrition. The impact on basic and practical nutrition from Project Leaders has been profound in the areas of starch and protein chemistry and nutrition, feed processing, nutrient metabolism, and lactation biology. This group provided a major contribution to the 2001 version of the National Research Councils (NRC's) Nutrient Requirements of Dairy Cattle. Four of the 10 scientists on the NRC panel were from the NC-185 committee, and a significant portion of the data used in the latest edition came from NC-1009 committee members. In 2005, the group presented a symposium at ADSA/FASS on regulation of nutrient use in dairy cattle (references are in bibliography). Thus, this committee has had a major impact on improving the biological, economical, and environmental efficiency of the US dairy industry.

Summary of progress:

One overriding goal in feeding cattle is to find the optimal combination of chemical and physical properties of feeds that provides the proper amount and balance of absorbed nutrients to match the ability given by the genotype of the cow or herd. This is a major challenge because of the tremendous variety of feedstuffs available, their complexity of interactions among feed particles, nutrients and organisms in the rumen, genetic variance within and among herds, and the rapidly changing nutrient requirements of a cow around the time of parturition. The amount and profile of absorbed nutrients in dairy cattle are a function of rumen fermentation and intestinal digestion. Feed particles and microbes that escape the rumen can be digested in the small intestine to produce amino acids, monosaccharides, and lipids for absorption.

The chemical and physical properties of feeds determine the availability of nutrients critical to the production of milk and milk components in a variety of ways. For example, the chemical composition (including total protein, nonprotein nitrogen, amino acid balance, organic acids, lipids, fiber, and non-fiber carbohydrate) dictates directly the availability of nutrients to support rumen microbial growth and the absorbed nutrients available to the animal to support milk synthesis. The physical properties of feeds, either inherent in the plant structure or altered by various processing methods, alters degradability in the rumen, and thus determines the proportion of feed fermented and used for rumen microbial growth and the proportion that passes to the small intestine. The cow is a fully integrated system in which one, even minor, change in nutrient input may lead to a variety of downstream events that alters function at the animal level. Since the last revision, we now understand more fully that this also includes changes in gene expression, and endocrine responses that were unknown or just discovered 5 years ago (IGF-1, leptin and ghrelin from the adipose tissue, for example).

Dietary carbohydrate fractions differ in the profiles of glucogenic and lipogenic metabolites they yield from ruminal and intestinal digestion. The amount and types of carbohydrates also impact rumen pH, which, in turn, alters fermentation and can alter the yield of nutrients, even amino acids, for absorption. Thus the various carbohydrate fractions have differential effects on the yield and composition of milk. Recent improvements in methods will allow more accurate prediction of optimal amounts and ruminal availability of non-fiber carbohydrates for efficient production of milk and milk components. More importantly, because of the integrative modeling approach of this committee, we have a quantitative knowledge of the maximal percentage contribution of these fractions to overall yield and efficiency on different diets, and can move on to further work.

The amount and balance of absorbed amino acids also helps determine milk yield, not only milk protein synthesis. This availability of amino acids, in turn, is a function of the amount of feed protein which passes undegraded through the rumen and the amount of ruminally synthesized microbial protein that reaches the small intestine. Because microbial protein has a better amino acid profile than many feed proteins, this remains an important area of study. Microbial protein yield is also a function of the amount and type of organic matter fermented. Thus, microbial protein yield varies by source of carbohydrate and protein, and rate of fermentation. This is a classic example of the need for an integrated approach to dairy cattle nutrition-we must continue to design experiments across state lines that allow a full scope of study of the key variables. We need to continue to build a comprehensive model that explicitly includes these types of interactions.

Synthesis of milk and milk components is a function of both the synthetic potential of the mammary gland and the supply of metabolites to the mammary gland. Supply of metabolites comes from dietary components, some of which are modified in other tissues, and from mobilization of body lipids and amino acids. There is an interaction between metabolism of body tissues, the supply of dietary nutrients and the milk production potential of the cow (as well as other animals) which has been recognized for quite some time which provide an extreme range of response of animals to even the same diet. While many dairy scientists have been slow to recognize the importance of these interactions, several stations in this project have been studying these interactions across a range of diets, genetic potentials, and stages of lactation (AL, CA, IA, IN, KS, MI, PA,WA and more recently, OH, MD, VA, VT, ). Data has been used to refine our feeding recommendations on a wide variety of feedstuffs.

New concepts on the interactions of nutrition and gene expression is exemplified with work just two stations: IN, at which new information on molecular control of expression of the enzymes that control gluconeogenesis in the liver are showing specific differences between the cow and other animals. At WA, work with supplemental chromium, a nutrient known to be required for many years, a positive feed intake and milk production response was obtained with supplemental chromium, along with a reduction in lipolysis and an increase in lipogenesis in adipose tissue, removing the negative effects of fatty acid mobilization on feed intake in early lactation.

Many nutritionists have now recognized that we cannot do relevant nutritional research with integrating this work with genetics and gene expression. Many nutrients are now known to affect gene expression in several organs, which then alters the animal response to the diet or further changes in the diet. Newer additions to the committee (VT, MD, OH) as well as adapting previous members (IN, MI, AL, WA) have begun serious efforts in identifying genetic responses to diet and to lactation. This work falls presently into the basic aspect-providing hard data to other scientists and advanced professionals on the key interactions of genetics and diet. This holds future promise in even more efficient feeding management and breeding programs.

Major advancements have occurred in our knowledge of the interaction of metabolism and the endocrine system. Studies at AL, IN, and MI, in collaboration with other NC-1009 members, have illustrated the role of nutrition in the IGF-I system of dairy cattle. Studies at IA have illustrated the role of glucagon in lipid metabolism and shown its potential benefit as a treatment for fatty liver. Work has been done on the role of leptin, which is known to alter feed intake, yet a clear understanding of the physiological role of leptin in lactation has been elusive.

If we are to improve the accuracy and precision of predicting nutrient use, we must continue to improve mechanistic, dynamic models of metabolism. The newer Dairy Nutrient Requirements book (NRC, 2001) was based in large part on data from this committee. In the 5 years since its publication, it has gained great respect in the industry. However, the process of revision of this document, and the model within it, also pointed out many of the shortcomings in our current knowledge base. The new version is limited especially in predicting dietary nutrient interactions, which consequently hamper our ability to predict rumen microbial metabolism and microbial protein yield and therefore responses to rumen-undegraded protein, carbohydrate, and fat supplements. Other significant limitations are the ability to predict short term versus long-term nutritional responses and changes in body fat and protein use. More mechanistic modeling of the metabolism of the lactating dairy cow will allow for evaluation of these interactions.

The most comprehensive mechanistic and dynamic model of metabolism in the dairy cow is called 'Molly', developed at CA with inputs from most NC-185 members. Members of this project also have been instrumental in developing the new NRC model (NRC, 2001), which serves as the standard for dairy ration formulation and evaluation in the US. These different computer nutrition programs are currently in use for predicting nutrient requirements and productivity of lactating dairy cows. While all of these systems are soundly based on available data, all have weaknesses in the areas defined by Objectives 1 and 2. The rate of degradation of feedstuffs, the effect of various dietary carbohydrates on rumen fermentation and microbial protein synthesis, and quantitative data on metabolic interchanges among nutrients and body tissues limit the accuracy of these systems. New collaborative efforts by the NC-1009 project are needed to remove these inaccuracies.

Molly is limited in its ability to describe the rapid changes in nutrient use that occur in early lactation and in predicting physiological responses to high feed intakes or diets with atypical amino acid, fiber, or starch contents. This is not surprising, given the paucity of these types of data when the model was originally constructed in the 1970 and 1980s. The modeling work done spurred new research into getting those data. Work done by a newer member of the committee (OH) was used to challenge Molly for its description of energy use in the viscera. Visceral metabolism can account for the majority of maintenance requirements and can be highly variable. Errors in the model reflected a lack of knowledge of visceral metabolism in early and mid lactation. Using data generated we challenged and improved the descriptions of energy use in the model, further increasing its utility in research and application (McNamara, 2005, 2006).

Quantitative data are still needed on the supply of milk component precursors available under different metabolic and nutritional conditions, such as early lactation. Data also are needed on the metabolic interconversions of nutrients, such as the use of amino acids for gluconeogenesis and thus milk lactose synthesis, and the partitioning of body fat and fat derived from the diet or lipogenesis for milk fat synthesis. These data will enable further refinement of current nutrition recommendations and aid in interpretation of feeding experiments.

Other Specific accomplishments:

Reductions in feeding levels for ruminally degradable protein would reduce nitrogen losses in manure and improve animal efficiency. As ammonia emissions from manure are driven by the amount of urinary N deposited in manure, such changes would lead to reduced ammonia emissions from animal and manure storage facilities. Improved knowledge of the mechanisms that regulate milk protein synthesis will allow development of models that better predict the requirements for milk protein synthesis. This in turn will allow more refined estimates of N requirements and reduced safety margins in feeding systems. Such an outcome will also work to reduce ammonia emissions from animal and manures storage facilities. Phosphorus availability in the digestive tract is an important determinant of the amount that must be fed and the amount that is lost in feces. Model development has helped identify key aspects of P digestion that warrant further examination and must be considered in requirement models to achieve greater reductions in P feeding levels.(VA)

This research evaluates the relationships between milk urea nitrogen, plasma urea nitrogen and urine urea nitrogen. Milk urea N can be a used to predict UUN excretion and may be extended to estimate NH3 emissions from dairy cattle manure because there is a strong relationship between UUN excretion and NH3 emissions. The information from this research can also be used to test metabolic models for urine urea excretion. (CA)

Greater use of flax in the nutrition of dairy cattle can supplement lactation diets with not only protein and energy, but compliment the growing interest in designer foods with milk enriched with omega-3 and omega-6 from such grains as flax seed. Furthermore, preliminary evidence suggests that dairy cow fed flax also have improved reproductive health with improved pregnancy rates. It has been estimated that if dairy cow pregnancy rates could be increased, an estimated cost savings to the dairy enterprise of $8.73 per cow per year could be realized for every percentage unit gained. (ND)