After an informative synthesis on the history of animal nutrition, this article discusses current and future trends in ruminant nutrition, with a special focus on net energy, metabolisable protein, and novel nutrients.
Nutrition, as an applied discipline, always goes hand in hand with theoretical developments. As new concepts are discovered, they are evaluated for application; the feasible ones remain and the rest are rejected.
Concisely, nutrition is about:
In addition to the requirements for macronutrients, micronutrients and their relevance for animals were also studied.
Since then, the science of nutrition is advancing rapidly, helped by the development of new analytical technologies.
Later in this article, we will discuss some of the current technologies helping us to improve nutritional management. It is necessary to remember that, although the knowledge on feed analysis and nutritional requirements was limited in those days, there was always the need of defining the nutritional value of feed, as well as to make recommendations on how to feed animals of different categories.
The first known system was deviced by Albert Thaer (1752 – 1828), who defined the nutritional values of feed in relation to a standard sample of hay.
Already in 1864, Henneberg & Stohmann developed the Wendee system for feed analysis, comprising crude fibre, crude protein, nitrogen-free extract and ether extract. In the same year, Wolff defined “Digestible nutrients”, precursor of the TDN system (Fig. 1). This system appeared in the book “Cattle Feeding Manual”, published by Armsby en 1880. In 1898, the TDN system appears in the boook “Feeds and Feeding” by Henry, and it continues being used today.
Figure 1. The Total Digestible Nutrients (TDN) system
Kellner, in 1905, defined the concept of cotton equivalent, precursor of the net energy systems used in Scandinavia and France at present.
Blaxter, in 1962, introduced the Energy requirements by factorial method, i.e. separating them in different functions such as maintenance, physical activity, lactation, growth, etc.
The concept of factorial requirements became popular with the first publication of “Recommended Nutrient Allowances for Beef Cattle” (Fig. 2), released by the US National Research Council (NRC) in 1945. Such publication has been revised 8 times, in 1950, 1958, 1963, 1970, 1976, 1984, 1996 (and 2000), and 2016. Each edition, reviews the scientific the latest literature on beef cattle nutrition, for all the life stages and diverse production systems, introducing new concepts, data and equations.
In the 1970’s edition, the nutritional requirements of ruminal microorganisms were included. In 1984, the edition included the California Net Energy System, published by Bill Garrett and Glen Lofgreen in 1968. After 52 years, this system is still being widely used around the world.
In the sixth revision (1984), important changes were made to the calculations of requirements for energy and degradable protein in the rumen, as well as the concept of bypass protein.
The 1996 and 2000 revision (the 7th one) already included more complex, mechanistic models.
The eighth revision (2016) of “Nutrient Requirements of Beef Cattle” added several sections, including:
There was also an update of the chapters from the 7th edition, with a substantial effort to provide the reader with improved predictive equations to model the supply of nutrients and metabolism.
The tendency in all the formulation systems based on “Nutrient Requirements of Beef Cattle” is to express the protein requirements of the animal, as well as feed valorisation, based on the quantity of available amino acids in the small intestine, known as Metabolisable Protein (MP). This concept has important theoretical validity since it reflects the utilisation of the protein in the diet.
Figure 3. Simplified summary of nitrogen utilisation in dairy cows and other ruminants (Source: Satter and Roffler, 1975).
It is important to mention that the theoretical concept of metabolisable protein actually has a practical application. To estimate the MP value of any diet, it is necessary to add the quantities of digestible protein reaching the intestine from endogenous and exogenous sources (Figs. 3 and 4).
The estimation of those quantities depends on the knowledge about the efficiency of synthesis of microbial protein. At the same time, this efficiency depends on the supply of fermentable carbohydrates and lipids in the diet, as well as on the fermentation rates and passage through the rumen, among other factors.
Figure 4. Nitrogen fractions in ruminant diets and degradation rates (Source: Feeds and Feeding 2015. Animal Production Department, FCV, UNCPBA).
These factors are almost impossible to quantify under the best experimental conditions, with fistulated and cannulated animals, without considering the conditions in which the animals are in practice; the extrapolation of experimental conditions to the field is not easy.
It is evident that, currently, the concept of nutrient has expanded to include the bio-active components. In this category, we can include:
Figure 5. Effect of the supplementation with essential oils on the number of ruminal protozoa (Source: Khiaosa-ard et al., 2013, J. Anim. Sci. 2013.91:1819–1830).
Figure 6. Structure of tanins (Source: Huang et al. (2017)
Figure 7. In vivo and in vitro effect of tanins on methane production in relation with digestible organic matter (Source: Jayanegara et al. ,2012, J. Anim. Physiol. Anim. Nutr. 96:365–375)
These new bioactive components are already fully considered by the scientific community. However, since their effects are complex and variable, further research is needed to better understand their mechanisms of action and to predict their efficacy with reasonable confidence.
This article was originally published in nutriNews Spain, with the title “Tendencias actuales y futuras de nutrición en rumiantes”.
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