Ruminants amino acid requirements

Animal organisms generally require effective assistance of intestinal flora, as in ruminants, to assimilate inorganic nitrogen into body protein. This accounts for the human needs of a daily requirement of 70-80 grams of protein, However, over half of the protein-constituent amino adds can be derived from other amino acids by their own enzymic reactions. Thus, amino acids are classified as essential or nonessential. Amino acid requirements vary with the physiological state of the animal, age. and possibly with the nature of the intestinal flora. 

For satisfying amino acid requirements of ruminants, experts developed a procedure, as a result of which the degradation of administered synthetic amino acids takes place in the small- and large intestines and not in the rumen. On the basis of microcapsule coating, the method of dimethionine coating was elaborated, and a plant with several tons of capacity has been established. Daily administration of only a few grams of protected methionine raised milk production by 1.2-1.51/day. 

In addition to a general requirement for protein, non-ruminant animals have a specific dietary requirement for the ten or so essential (or indispensable) amino acids. Over the past 30 years many experiments have been conducted to determine the quantitative requirements for essential amino acids, and protein requirements have now been supplemented (or even replaced) by requirements for some or all of these amino acids. Requirements may also be stated in terms of ideal protein (protein containing essential amino acids in exactly the proportions required by the animal) or standardised deal digestible amino acids , as explained in Chapter 13. 

Meeting the requirements of non-ruminants for a balanced supply of essential amino acids requires the use of expensive protein sources, such as fishmeal, or high levels of less well-balanced protein sources such as soya bean meal (see Chapter 13). Economics dictate that the latter option is usually taken, and, in order to meet the requirements for the limiting amino acid, an excess of total protein has to be supplied. This is deaminated and the nitrogen is excreted both processes require energy, and such protein oversupply is wasteful in terms of both protein and energy metabolism. In addition, the excreted nitrogen may be a source of pollution in the environment. 

Not all animals obtain the essential amino acids from plants. Some (the ruminants) can by-pass the main route by direct assimilation of the amino acids produced by symbiotic bacteria in the gut. These bacteria can break down cellulose, the main structural carbohydrate of plants, and can also synthesise all the amino acids, required for their growth and development, from a simple fixed-nitrogen source. The ruminant obtains its more complex nitrogen requirements by digestion of dead bacteria. (Goats, for example, can survive on a diet of hay and ammonia.) This may appear to be a somewhat one-sided symbiosis, with the bacteria carrying out all the important functions but, in return, the bacteria obtain from the animal a copious supply of carbohydrate and are maintained in a favourable environment with respect to temperature and medium composition. 

Binding of the substrate urea to a nickel ion in urease is an integral part of the mechanism in the hydrolysis reaction (Nielsen 1984). Both ruminants and monogastric animals require urease for the decomposition of urea into ammonia, which is needed for the microbial synthesis of ammonia that, in turn, is necessary for amino acid and protein synthesis. This process also takes place in the appendix of monogastric animals and some species of ruminants (roe deer). 

A system for the quantitative nutrition of ruminant animals should embody the processes described, which requires that factors such as degradabUity, efficiency of nitrogen captme, microbial protein yield, digestibihty of microbial protein, digestibihty of dietary imdegraded protein and the trae biological value of the absorbed nitrogen or its essential amino acid content be quantified. 

Different feeding standards adopt different approaches to estimate energy and protein requirements for growth. Protein requirements for pigs and poultry are generally more detailed than those of ruminants and horses because they include estimates of requirements for specific amino acids. 

This is so because non-ruminant animals require a dietary source of homocysteine, which is normally provided in the form of methionine. ibiimals metabolize these sulfur amino acids eventually to inorganic sulfate. Plants complete the cycle of sulfur by reductive assimilation of inorganic sulfate to methionine (and cysteine) (Siegel, 1975), and are thus the ultimate source of methionine in most animal diets. 

To optimize milk protein production, requirements must be accurately determined and matched with dietary supply. Through microbial digestion in the reticulo-rumen, ruminants have a capacity to utilize forages that are indigestible in non-ruminants. Dietary proteins are degraded in the rumen and used in microbial protein synthesis, which modifies dietary supply of protein both quantitatively and qualitatively making predictions of the amount and profile of amino acids (AA) absorbed from the small intestine difficult. 

The lower value for feed MP can be expected, since bacterial MP is associated with increased supply of other nutrients (energy), whereas feed MP provides only absorbed amino acids that may also have poorer profile compared with bacterial MP. The transfer efficiency of infused casein was clearly higher than that of feed MP in production trials (0.29 vs. 0.10 and 0.14). Higher efficiency can be expected for post-ruminally infused casein than for feed MP due to its better AA profile. In the North American dataset, the low coefficient can partly be due to overfeeding of MP, but in the North European dataset the diets supplied on average 93% of MP requirement calculated according to NRC (2001) and the cows should be responsive to increased MP supply. 

---