A 100-Year Review: From ascorbic acid to zinc-Mineral and vitamin nutrition of dairy cows.

Mineral and vitamin nutrition of dairy cows was studied before the first volume of the Journal of Dairy Science was published and is still actively researched today. The initial studies on mineral nutrition of dairy cows were simple balance experiments (although the methods available at the time for measuring minerals were anything but simple). Output of Ca and P in feces, urine, and milk was subtracted from intake of Ca and P, and if values were negative it was often assumed that cows were lacking in the particular mineral. As analytical methods improved, more minerals were found to be required by dairy cows, and blood and tissue concentrations became primary response variables. Those measures often were poorly related to cow health, leading to the use of disease prevalence and immune function as a measure of mineral adequacy. As data were generated, mineral requirements became more accurate and included more sources of variation. In addition to milk yield and body weight inputs, bioavailability coefficients of minerals from different sources are used to formulate diets that can meet the needs of the cow without excessive excretion of minerals in manure, which negatively affects the environment. Milk, or more accurately the lack of milk in human diets, was central to the discovery of vitamins, but research into vitamin nutrition of cows developed slowly. For many decades bioassays were the only available method for measuring vitamin concentrations, which greatly limited research. The history of vitamin nutrition mirrors that of mineral nutrition. Among the first experiments conducted on vitamin nutrition of cows were those examining the factors affecting vitamin concentrations of milk. This was followed by determining the amount of vitamins needed to prevent deficiency diseases, which evolved into research to determine the amount of vitamins required to promote overall good health. The majority of research was conducted on vitamins A, D, and E because these vitamins have a dietary requirement, and clinical and marginal deficiencies became common as diets for cows changed from pasture and full exposure to the sun to stored forage and limited sun exposure. As researchers learned new functions of fat-soluble vitamins, requirements generally increased over time. Diets generally contain substantial amounts of B vitamins, and rumen bacteria can synthesize large quantities of many B vitamins; hence, research on water-soluble vitamins lagged behind. We now know that supplementation of specific water-soluble vitamins can enhance cow health and increase milk production in certain situations. Additional research is needed to define specific requirements for many water-soluble vitamins. Both mineral and vitamin research is hampered by the lack of sensitive biomarkers of status, but advanced molecular techniques may provide measures that respond to altered supply of minerals and vitamins and that are related to health or productive responses of the cow. The overall importance of proper mineral and vitamin nutrition is known, but as we discover new and more diverse functions, better supplementation strategies should lead to even better cow health and higher production.

A 100-Year Review: Fat feeding of dairy cows.

Over 100 years, the Journal of Dairy Science has recorded incredible changes in the utilization of fat for dairy cattle. Fat has progressed from nothing more than a contaminant in some protein supplements to a valuable high-energy substitute for cereal grains, a valuable energy source in its own right, and a modifier of cellular metabolism that is under active investigation in the 21st century. Milestones in the use of fats for dairy cattle from 1917 to 2017 result from the combined efforts of noted scientists and industry personnel worldwide, with much of the research published in Journal of Dairy Science. We are humbled to have been asked to contribute to this historical collection of significant developments in fat research over the past 100 years. Our goal is not to detail all the work published as each development moved forward; rather, it is to point out when publication marked a significant change in thinking regarding use of fat supplements. This approach forced omission of critically important names and publications in many journals as ideas moved forward. However, we hope that a description of the major changes in fat feeding during the past 100 years will stimulate reflection on progress in fat research and encourage further perusal of details of significant events.

A 100-Year Review: Protein and amino acid nutrition in dairy cows.

Considerable progress has been made in understanding the protein and amino acid (AA) nutrition of dairy cows. The chemistry of feed crude protein (CP) appears to be well understood, as is the mechanism of ruminal protein degradation by rumen bacteria and protozoa. It has been shown that ammonia released from AA degradation in the rumen is used for bacterial protein formation and that urea can be a useful N supplement when lower protein diets are fed. It is now well documented that adequate rumen ammonia levels must be maintained for maximal synthesis of microbial protein and that a deficiency of rumen-degradable protein can decrease microbial protein synthesis, fiber digestibility, and feed intake. Rumen-synthesized microbial protein accounts for most of the CP flowing to the small intestine and is considered a high-quality protein for dairy cows because of apparent high digestibility and good AA composition. Much attention has been given to evaluating different methods to quantify ruminal protein degradation and escape and for measuring ruminal outflows of microbial protein and rumen-undegraded feed protein. The methods and accompanying results are used to determine the nutritional value of protein supplements and to develop nutritional models and evaluate their predictive ability. Lysine, methionine, and histidine have been identified most often as the most-limiting amino acids, with rumen-protected forms of lysine and methionine available for ration supplementation. Guidelines for protein feeding have evolved from simple feeding standards for dietary CP to more complex nutrition models that are designed to predict supplies and requirements for rumen ammonia and peptides and intestinally absorbable AA. The industry awaits more robust and mechanistic models for predicting supplies and requirements of rumen-available N and absorbed AA. Such models will be useful in allowing for feeding lower protein diets and increased efficiency of microbial protein synthesis.

Endogenous Synthesis of Amino Acids Limits Growth, Lactation, and Reproduction in Animals.

Amino acids (AAs) are building blocks of protein. Eight AAs (Ala, Asn, Asp, Glu, Gln, Gly, Pro, and Ser) are formed by all animals, whereas de novo synthesis of Arg occurs in a species-specific manner in most mammals (e.g., humans, pigs, and rats). Synthesizable AAs were traditionally classified as nutritionally nonessential for animals, because they were thought to be formed in sufficient amounts. However, this assumption is not supported by evidence showing that 1) rats grow slowly when their diets do not contain Arg, Glu, or Gln despite adequate provision of all other proteinogenous AAs; 2) pigs cannot achieve maximum growth, lactation, or reproduction performance when fed corn- and soybean meal-based diets meeting National Research Council-recommended requirements of protein and AAs without supplemental Arg, Glu, Gln, Gly, or Pro; 3) chickens exhibit increases in lean tissue gain and feed efficiency when their diets are supplemented with Glu, Gln, Gly, and Pro; 4) lactating cows cannot obtain maximum milk protein production without a postruminal supply of Gln or Pro; 5) fish cannot achieve maximum growth when diets do not contain Gln or Pro; and 6) men fail to sustain spermatogenesis when fed an Arg-deficient diet. Quantitative analysis of nitrogen metabolism showed that AA synthesis in animals is constrained by both precursor availability and enzyme activity. Taken together, these findings support the conclusion that the endogenous synthesis of AAs limits growth, lactation, and reproduction in animals. This new knowledge can guide the optimization of human nutrition for improving health and well-being.

Evaluation of the impact of dietary petroselinic acid on the growth performance, fatty acid composition, and efficacy of long chain-polyunsaturated fatty acid biosynthesis of farmed Nile tilapia.

The present study aimed to investigate the potential role of dietary petroselinic acid (PSA) in enhancing the n-3 long-chain polyunsaturated fatty acid (LC-PUFA) content in fish tissues. Three isolipidic casein-based diets were formulated to comprise graded levels of PSA (0, 10, or 20% of total fatty acid) with the incremented inclusion of coriander seed oil. Fish growth and nutrient digestibility were not significantly (P > 0.05) influenced by dietary PSA level. In general, dietary PSA affected the fatty acid composition of tilapia tissues and whole-body, which reflected dietary fatty acid ratios. Dietary PSA significantly (P < 0.05) increased ß-oxidation, particularly on α-linolenic acid (18:3n-3) and linoleic acid (18:2n-6). This study provided evidence that PSA, a pseudoproduct mimicking the structure of 18:3n-6, did reduce Δ-6 desaturation on 18:2n-6 but, contrary to popular speculation, did not stimulate more Δ-6 desaturase activity on 18:3n-3. The overall Δ-6 desaturase enzyme activity may be suppressed at high dietary levels of PSA. Nevertheless, the n-3 and n-6 LC-PUFA biosynthesis was not significantly inhibited by dietary PSA, indicating that the bioconversion efficiency is not modulated only by Δ-6 desaturase. The deposition of n-3 LC-PUFA in liver and fillet lipids was higher in fish fed PSA-supplemented diets.